Europa (moon)

Last updated

Europa's trailing hemisphere in approximate natural color. The prominent crater in the lower right is Pwyll and the darker regions are areas where Europa's primarily water ice surface has a higher mineral content. Imaged on 7 September 1996 by Galileo spacecraft.
Discovered by Galileo Galilei
Simon Marius
Discovery date8 January 1610 [1]
Pronunciation /jʊˈrpə/ [2]
Named after
Ευρώπη Eyrōpē
Jupiter II
Adjectives Europan /jʊˈrpən/ [3] [4]
Orbital characteristics [5]
Epoch 8 January 2004
Periapsis 664862 km [lower-alpha 1]
Apoapsis 676938 km [lower-alpha 2]
Mean orbit radius
670900 km [6]
Eccentricity 0.009 [6]
3.551181 d [6]
Average orbital speed
13743.36 m/s [7]
Inclination 0.470° (to Jupiter's equator)
1.791° (to the ecliptic) [6]
Satellite of Jupiter
Group Galilean moon
Physical characteristics
Mean radius
1560.8±0.5 km (0.245 Earths) [8]
3.09×107 km2 (0.061 Earths) [lower-alpha 3]
Volume 1.593×1010 km3 (0.015 Earths) [lower-alpha 4]
Mass (4.799844±0.000013)×1022 kg (0.008 Earths) [8]
Mean density
3.013±0.005 g/cm3 (0.546 Earths) [8]
1.314  m/s2 (0.134 g) [lower-alpha 5]
0.346±0.005 [9] (estimate)
2.025 km/s [lower-alpha 6]
Synchronous [10]
0.1° [11]
Albedo 0.67 ± 0.03 [8]
Surface temp. minmeanmax
Surface50 K [12] 102 K (−171 °C)125 K
5.29 (opposition) [8]
Surface pressure
0.1 µPa (10−12 bar) [13]

    Europa /jʊˈrpə/ ( Loudspeaker.svg listen ), or Jupiter II, is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa was discovered in 1610 by Galileo Galilei [1] and was named after Europa, the Phoenician mother of King Minos of Crete and lover of Zeus (the Greek equivalent of the Roman god Jupiter).


    Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and has a water-ice crust [14] and probably an iron–nickel core. It has a very thin atmosphere, composed primarily of oxygen. Its surface is striated by cracks and streaks, but craters are relatively few. In addition to Earth-bound telescope observations, Europa has been examined by a succession of space-probe flybys, the first occurring in the early 1970s.

    Europa has the smoothest surface of any known solid object in the Solar System. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath the surface, which could conceivably harbor extraterrestrial life. [15] The predominant model suggests that heat from tidal flexing causes the ocean to remain liquid and drives ice movement similar to plate tectonics, absorbing chemicals from the surface into the ocean below. [16] [17] Sea salt from a subsurface ocean may be coating some geological features on Europa, suggesting that the ocean is interacting with the sea floor. This may be important in determining whether Europa could be habitable. [18] In addition, the Hubble Space Telescope detected water vapor plumes similar to those observed on Saturn's moon Enceladus, which are thought to be caused by erupting cryogeysers. [19] In May 2018, astronomers provided supporting evidence of water plume activity on Europa, based on an updated analysis of data obtained from the Galileo space probe, which orbited Jupiter from 1995 to 2003. Such plume activity could help researchers in a search for life from the subsurface Europan ocean without having to land on the moon. [20] [21] [22] [23]

    The Galileo mission, launched in 1989, provides the bulk of current data on Europa. No spacecraft has yet landed on Europa, although there have been several proposed exploration missions. The European Space Agency's Jupiter Icy Moon Explorer (JUICE) is a mission to Ganymede that is due to launch in 2022 and will include two flybys of Europa. [24] NASA's planned Europa Clipper should be launched in 2024. [25]

    Discovery and naming

    Europa, along with Jupiter's three other large moons, Io, Ganymede, and Callisto, was discovered by Galileo Galilei on 8 January 1610, [1] and possibly independently by Simon Marius. The first reported observation of Io and Europa was made by Galileo on 7 January 1610 using a 20×-magnification refracting telescope at the University of Padua. However, in that observation, Galileo could not separate Io and Europa due to the low magnification of his telescope, so that the two were recorded as a single point of light. The following day, 8 January 1610 (used as the discovery date for Europa by the IAU), Io and Europa were seen for the first time as separate bodies during Galileo's observations of the Jupiter system. [1]

    Europa is the namesake of Europa, daughter of the king of Tyre, a Phoenician noblewoman in Greek mythology. Like all the Galilean satellites, Europa is named after a lover of Zeus, the Greek counterpart of Jupiter. Europa was courted by Zeus and became the queen of Crete. [26] The naming scheme was suggested by Simon Marius, [27] who attributed the proposal to Johannes Kepler: [27] [28]

    ... Inprimis autem celebrantur tres fœminæ Virgines, quarum furtivo amore Iupiter captus & positus est... Europa Agenoris filia... à me vocatur... Secundus Europa... [Io,] Europa, Ganimedes puer, atque Calisto, lascivo nimium perplacuere Jovi.

    ... First, three young women who were captured by Jupiter for secret love shall be honoured, [including] Europa, the daughter of Agenor... The second [moon] is called by me Europa... Io, Europa, the boy Ganymede, and Callisto greatly pleased lustful Jupiter. [29]

    The names fell out of favor for a considerable time and were not revived in general use until the mid-20th century. [30] In much of the earlier astronomical literature, Europa is simply referred to by its Roman numeral designation as Jupiter II (a system also introduced by Galileo) or as the "second satellite of Jupiter". In 1892, the discovery of Amalthea, whose orbit lay closer to Jupiter than those of the Galilean moons, pushed Europa to the third position. The Voyager probes discovered three more inner satellites in 1979, so Europa is now counted as Jupiter's sixth satellite, though it is still referred to as Jupiter II. [30] The adjectival form has stabilized as Europan. [4] [31]

    Orbit and rotation

    Animation of the Laplace resonance of Io, Europa and Ganymede (conjunctions are highlighted by color changes) Galilean moon Laplace resonance animation 2.gif
    Animation of the Laplace resonance of Io, Europa and Ganymede (conjunctions are highlighted by color changes)

    Europa orbits Jupiter in just over three and a half days, with an orbital radius of about 670,900 km. With an orbital eccentricity of only 0.009, the orbit itself is nearly circular, and the orbital inclination relative to Jupiter's equatorial plane is small, at 0.470°. [32] Like its fellow Galilean satellites, Europa is tidally locked to Jupiter, with one hemisphere of Europa constantly facing Jupiter. Because of this, there is a sub-Jovian point on Europa's surface, from which Jupiter would appear to hang directly overhead. Europa's prime meridian is a line passing through this point. [33] Research suggests that the tidal locking may not be full, as a non-synchronous rotation has been proposed: Europa spins faster than it orbits, or at least did so in the past. This suggests an asymmetry in internal mass distribution and that a layer of subsurface liquid separates the icy crust from the rocky interior. [10]

    The slight eccentricity of Europa's orbit, maintained by the gravitational disturbances from the other Galileans, causes Europa's sub-Jovian point to oscillate around a mean position. As Europa comes slightly nearer to Jupiter, Jupiter's gravitational attraction increases, causing Europa to elongate towards and away from it. As Europa moves slightly away from Jupiter, Jupiter's gravitational force decreases, causing Europa to relax back into a more spherical shape, and creating tides in its ocean. The orbital eccentricity of Europa is continuously pumped by its mean-motion resonance with Io. [34] Thus, the tidal flexing kneads Europa's interior and gives it a source of heat, possibly allowing its ocean to stay liquid while driving subsurface geological processes. [16] [34] The ultimate source of this energy is Jupiter's rotation, which is tapped by Io through the tides it raises on Jupiter and is transferred to Europa and Ganymede by the orbital resonance. [34] [35]

    Analysis of the unique cracks lining Europa yielded evidence that it likely spun around a tilted axis at some point in time. If correct, this would explain many of Europa's features. Europa's immense network of crisscrossing cracks serves as a record of the stresses caused by massive tides in its global ocean. Europa's tilt could influence calculations of how much of its history is recorded in its frozen shell, how much heat is generated by tides in its ocean, and even how long the ocean has been liquid. Its ice layer must stretch to accommodate these changes. When there is too much stress, it cracks. A tilt in Europa's axis could suggest that its cracks may be much more recent than previously thought. The reason for this is that the direction of the spin pole may change by as much as a few degrees per day, completing one precession period over several months. A tilt could also affect the estimates of the age of Europa's ocean. Tidal forces are thought to generate the heat that keeps Europa's ocean liquid, and a tilt in the spin axis would cause more heat to be generated by tidal forces. Such additional heat would have allowed the ocean to remain liquid for a longer time. However, it has not yet been determined when this hypothesized shift in the spin axis might have occurred. [36]

    Physical characteristics

    Size comparison of Europa (lower left) with the Moon (top left) and Earth (right) Europa, Earth & Moon size comparison.jpg
    Size comparison of Europa (lower left) with the Moon (top left) and Earth (right)

    Europa is slightly smaller than the Moon. At just over 3,100 kilometres (1,900 mi) in diameter, it is the sixth-largest moon and fifteenth-largest object in the Solar System. Though by a wide margin the least massive of the Galilean satellites, it is nonetheless more massive than all known moons in the Solar System smaller than itself combined. [37] Its bulk density suggests that it is similar in composition to the terrestrial planets, being primarily composed of silicate rock. [38]

    Internal structure

    It is estimated that Europa has an outer layer of water around 100 km (62 mi) thick; a part frozen as its crust, and a part as a liquid ocean underneath the ice. Recent magnetic-field data from the Galileo orbiter showed that Europa has an induced magnetic field through interaction with Jupiter's, which suggests the presence of a subsurface conductive layer. [39] This layer is likely to be a salty liquid-water ocean. Portions of the crust are estimated to have undergone a rotation of nearly 80°, nearly flipping over (see true polar wander), which would be unlikely if the ice were solidly attached to the mantle. [40] Europa probably contains a metallic iron core. [41] [42]

    Surface features

    Approximate natural color (left) and enhanced color (right) Galileo view of leading hemisphere PIA01295 Europa Global Views in Natural and Enhanced Colors.jpg
    Approximate natural color (left) and enhanced color (right) Galileo view of leading hemisphere

    Europa is the smoothest known object in the Solar System, lacking large-scale features such as mountains and craters. [43] However, according to one study, Europa's equator may be covered in icy spikes called penitentes, which may be up to 15 meters high, due to direct overhead sunlight on the equator, causing the ice to sublime, forming vertical cracks. [44] [45] [46] Although the imaging available from the Galileo orbiter does not have the resolution needed to confirm this, radar and thermal data are consistent with this interpretation. [46] The prominent markings crisscrossing Europa appear to be mainly albedo features that emphasize low topography. There are few craters on Europa, because its surface is tectonically too active and therefore young. [47] [48] Europa's icy crust has an albedo (light reflectivity) of 0.64, one of the highest of all moons. [32] [48] This indicates a young and active surface: based on estimates of the frequency of cometary bombardment that Europa experiences, the surface is about 20 to 180 million years old. [49] There is currently no full scientific consensus among the sometimes contradictory explanations for the surface features of Europa. [50]

    The radiation level at the surface of Europa is equivalent to a dose of about 5400  mSv (540 rem) per day, [51] an amount of radiation that would cause severe illness or death in human beings exposed for a single Earth-day (24 hours). [52] The duration of a Europan day is approximately 3.5 times that of a day on Earth, resulting in 3.5 times bigger radiation exposure. [53]


    Realistic-color Galileo mosaic of Europa's anti-Jovian hemisphere showing numerous lineae PIA19048 realistic color Europa mosaic edited.jpg
    Realistic-color Galileo mosaic of Europa's anti-Jovian hemisphere showing numerous lineae
    Enhanced-color view showing the intricate pattern of linear fractures on Europa's surface PIA20028 - Europa's varied surface features (rotated).jpg
    Enhanced-color view showing the intricate pattern of linear fractures on Europa's surface

    Europa's most striking surface features are a series of dark streaks crisscrossing the entire globe, called lineae (English: lines). Close examination shows that the edges of Europa's crust on either side of the cracks have moved relative to each other. The larger bands are more than 20 km (12 mi) across, often with dark, diffuse outer edges, regular striations, and a central band of lighter material. [54] The most likely hypothesis is that the lineae on Europa were produced by a series of eruptions of warm ice as the Europan crust spread open to expose warmer layers beneath. [55] The effect would have been similar to that seen in Earth's oceanic ridges. These various fractures are thought to have been caused in large part by the tidal flexing exerted by Jupiter. Because Europa is tidally locked to Jupiter, and therefore always maintains approximately the same orientation towards Jupiter, the stress patterns should form a distinctive and predictable pattern. However, only the youngest of Europa's fractures conform to the predicted pattern; other fractures appear to occur at increasingly different orientations the older they are. This could be explained if Europa's surface rotates slightly faster than its interior, an effect that is possible due to the subsurface ocean mechanically decoupling Europa's surface from its rocky mantle and the effects of Jupiter's gravity tugging on Europa's outer ice crust. [56] Comparisons of Voyager and Galileo spacecraft photos serve to put an upper limit on this hypothetical slippage. A full revolution of the outer rigid shell relative to the interior of Europa takes at least 12,000 years. [57] Studies of Voyager and Galileo images have revealed evidence of subduction on Europa's surface, suggesting that, just as the cracks are analogous to ocean ridges, [58] [59] so plates of icy crust analogous to tectonic plates on Earth are recycled into the molten interior. This evidence of both crustal spreading at bands [58] and convergence at other sites [59] suggests that Europa may have active plate tectonics, similar to Earth. [17] However, the physics driving these plate tectonics are not likely to resemble those driving terrestrial plate tectonics, as the forces resisting potential Earth-like plate motions in Europa's crust are significantly stronger than the forces that could drive them. [60]

    Chaos and lenticulae

    PIA01092 - Evidence of Internal Activity on Europa.jpg
    Europa chaotic terrain.jpg
    Left: surface features indicative of tidal flexing: lineae, lenticulae and the Conamara Chaos region (close-up, right) where craggy, 250 m high peaks and smooth plates are jumbled together

    Other features present on Europa are circular and elliptical lenticulae (Latin for "freckles"). Many are domes, some are pits and some are smooth, dark spots. Others have a jumbled or rough texture. The dome tops look like pieces of the older plains around them, suggesting that the domes formed when the plains were pushed up from below. [61]

    One hypothesis states that these lenticulae were formed by diapirs of warm ice rising up through the colder ice of the outer crust, much like magma chambers in Earth's crust. [61] The smooth, dark spots could be formed by meltwater released when the warm ice breaks through the surface. The rough, jumbled lenticulae (called regions of "chaos"; for example, Conamara Chaos) would then be formed from many small fragments of crust, embedded in hummocky, dark material, appearing like icebergs in a frozen sea. [62]

    An alternative hypothesis suggest that lenticulae are actually small areas of chaos and that the claimed pits, spots and domes are artefacts resulting from over-interpretation of early, low-resolution Galileo images. The implication is that the ice is too thin to support the convective diapir model of feature formation. [63] [64]

    In November 2011, a team of researchers from the University of Texas at Austin and elsewhere presented evidence in the journal Nature suggesting that many "chaos terrain" features on Europa sit atop vast lakes of liquid water. [65] [66] These lakes would be entirely encased in Europa's icy outer shell and distinct from a liquid ocean thought to exist farther down beneath the ice shell. Full confirmation of the lakes' existence will require a space mission designed to probe the ice shell either physically or indirectly, for example, using radar. [66]

    Work published by researchers from Williams College suggests that chaos terrain may represent sites where impacting comets penetrated through the ice crust and into an underlying ocean. [67] [68]

    Subsurface ocean

    Two possible models of Europa EuropaInterior1.jpg
    Two possible models of Europa
    Europa - internal structure
(artwork; 25 May 2021) PIA24477-Europa-Internal-Illustration-20210525.jpg
    Europa - internal structure
    (artwork; 25 May 2021)

    Scientists' consensus is that a layer of liquid water exists beneath Europa's surface, and that heat from tidal flexing allows the subsurface ocean to remain liquid. [16] [69] Europa's surface temperature averages about 110  K (−160  °C ; −260  °F ) at the equator and only 50 K (−220 °C; −370 °F) at the poles, keeping Europa's icy crust as hard as granite. [12] The first hints of a subsurface ocean came from theoretical considerations of tidal heating (a consequence of Europa's slightly eccentric orbit and orbital resonance with the other Galilean moons). Galileo imaging team members argue for the existence of a subsurface ocean from analysis of Voyager and Galileo images. [69] The most dramatic example is "chaos terrain", a common feature on Europa's surface that some interpret as a region where the subsurface ocean has melted through the icy crust. This interpretation is controversial. Most geologists who have studied Europa favor what is commonly called the "thick ice" model, in which the ocean has rarely, if ever, directly interacted with the present surface. [70] The best evidence for the thick-ice model is a study of Europa's large craters. The largest impact structures are surrounded by concentric rings and appear to be filled with relatively flat, fresh ice; based on this and on the calculated amount of heat generated by Europan tides, it is estimated that the outer crust of solid ice is approximately 10–30 km (6–19 mi) thick, [71] including a ductile "warm ice" layer, which could mean that the liquid ocean underneath may be about 100 km (60 mi) deep. [72] This leads to a volume of Europa's oceans of 3 × 1018 m3, between two or three times the volume of Earth's oceans. [73] [74]

    The thin-ice model suggests that Europa's ice shell may be only a few kilometers thick. However, most planetary scientists conclude that this model considers only those topmost layers of Europa's crust that behave elastically when affected by Jupiter's tides.[ citation needed ] One example is flexure analysis, in which Europa's crust is modeled as a plane or sphere weighted and flexed by a heavy load. Models such as this suggest the outer elastic portion of the ice crust could be as thin as 200 metres (660 ft). If the ice shell of Europa is really only a few kilometers thick, this "thin ice" model would mean that regular contact of the liquid interior with the surface could occur through open ridges, causing the formation of areas of chaotic terrain. [75] Large impacts going fully through the ice crust would also be a way that the subsurface ocean could be exposed. [67] [68]


    Closeup views of Europa obtained on 26 September 1998; images clockwise from upper left show locations from north to south as indicated at lower left. Europa PIA2387x - Chaos Transition, Crisscrossing Bands & Chaos Near Agenor Linea.jpg
    Closeup views of Europa obtained on 26 September 1998; images clockwise from upper left show locations from north to south as indicated at lower left.

    The Galileo orbiter found that Europa has a weak magnetic moment, which is induced by the varying part of the Jovian magnetic field. The field strength at the magnetic equator (about 120 nT) created by this magnetic moment is about one-sixth the strength of Ganymede's field and six times the value of Callisto's. [76] The existence of the induced moment requires a layer of a highly electrically conductive material in Europa's interior. The most plausible candidate for this role is a large subsurface ocean of liquid saltwater. [41]

    Since the Voyager spacecraft flew past Europa in 1979, scientists have worked to understand the composition of the reddish-brown material that coats fractures and other geologically youthful features on Europa's surface. [77] Spectrographic evidence suggests that the dark, reddish streaks and features on Europa's surface may be rich in salts such as magnesium sulfate, deposited by evaporating water that emerged from within. [78] Sulfuric acid hydrate is another possible explanation for the contaminant observed spectroscopically. [79] In either case, because these materials are colorless or white when pure, some other material must also be present to account for the reddish color, and sulfur compounds are suspected. [80]

    Another hypothesis for the colored regions is that they are composed of abiotic organic compounds collectively called tholins. [81] [82] [83] The morphology of Europa's impact craters and ridges is suggestive of fluidized material welling up from the fractures where pyrolysis and radiolysis take place. In order to generate colored tholins on Europa there must be a source of materials (carbon, nitrogen, and water) and a source of energy to make the reactions occur. Impurities in the water ice crust of Europa are presumed both to emerge from the interior as cryovolcanic events that resurface the body, and to accumulate from space as interplanetary dust. [81] Tholins bring important astrobiological implications, as they may play a role in prebiotic chemistry and abiogenesis. [84] [85] [86]

    The presence of sodium chloride in the internal ocean has been suggested by a 450 nm absorption feature, characteristic of irradiated NaCl crystals, that has been spotted in HST observations of the chaos regions, presumed to be areas of recent subsurface upwelling. [87]

    Sources of heat

    Tidal heating occurs through the tidal friction and tidal flexing processes caused by tidal acceleration: orbital and rotational energy are dissipated as heat in the core of the moon, the internal ocean, and the ice crust. [88]

    Tidal friction

    Ocean tides are converted to heat by frictional losses in the oceans and their interaction with the solid bottom and with the top ice crust. In late 2008, it was suggested Jupiter may keep Europa's oceans warm by generating large planetary tidal waves on Europa because of its small but non-zero obliquity. This generates so-called Rossby waves that travel quite slowly, at just a few kilometers per day, but can generate significant kinetic energy. For the current axial tilt estimate of 0.1 degree, the resonance from Rossby waves would contain 7.3×1018 J of kinetic energy, which is two thousand times larger than that of the flow excited by the dominant tidal forces. [89] [90] Dissipation of this energy could be the principal heat source of Europa's ocean. [89] [90]

    Tidal flexing

    Tidal flexing kneads Europa's interior and ice shell, which becomes a source of heat. [91] Depending on the amount of tilt, the heat generated by the ocean flow could be 100 to thousands of times greater than the heat generated by the flexing of Europa's rocky core in response to gravitational pull from Jupiter and the other moons circling that planet. [92] Europa's seafloor could be heated by the moon's constant flexing, driving hydrothermal activity similar to undersea volcanoes in Earth's oceans. [88]

    Experiments and ice modeling published in 2016, indicate that tidal flexing dissipation can generate one order of magnitude more heat in Europa's ice than scientists had previously assumed. [93] [94] Their results indicate that most of the heat generated by the ice actually comes from the ice's crystalline structure (lattice) as a result of deformation, and not friction between the ice grains. [93] [94] The greater the deformation of the ice sheet, the more heat is generated.

    Radioactive decay

    In addition to tidal heating, the interior of Europa could also be heated by the decay of radioactive material (radiogenic heating) within the rocky mantle. [88] [95] But the models and values observed are one hundred times higher than those that could be produced by radiogenic heating alone, [96] thus implying that tidal heating has a leading role in Europa. [97]


    Water plumes on Europa detected by the Galileo space probe PIA21922-EuropaPlumesDetectedByGalileoSpacecraft-ArtistConcept-20180514.jpg
    Water plumes on Europa detected by the Galileo space probe
    Photo composite of suspected water plumes on Europa Photo composite of suspected water plumes on Europa.jpg
    Photo composite of suspected water plumes on Europa

    The Hubble Space Telescope acquired an image of Europa in 2012 that was interpreted to be a plume of water vapour erupting from near its south pole. [100] [99] The image suggests the plume may be 200 km (120 mi) high, or more than 20 times the height of Mt. Everest. [19] [101] [102] It has been suggested that if they exist, they are episodic [103] and likely to appear when Europa is at its farthest point from Jupiter, in agreement with tidal force modeling predictions. [104] Additional imaging evidence from the Hubble Space Telescope was presented in September 2016. [105] [106]

    In May 2018, astronomers provided supporting evidence of water plume activity on Europa, based on an updated critical analysis of data obtained from the Galileo space probe, which orbited Jupiter between 1995 and 2003. Galileo flew by Europa in 1997 within 206 km (128 mi) of the moon's surface and the researchers suggest it may have flown through a water plume. [20] [21] [22] [23] Such plume activity could help researchers in a search for life from the subsurface Europan ocean without having to land on the moon. [20]

    The tidal forces are about 1,000 times stronger than the Moon's effect on Earth. The only other moon in the Solar System exhibiting water vapor plumes is Enceladus. [19] The estimated eruption rate at Europa is about 7000 kg/s [104] compared to about 200 kg/s for the plumes of Enceladus. [107] [108] If confirmed, it would open the possibility of a flyby through the plume and obtain a sample to analyze in situ without having to use a lander and drill through kilometres of ice. [105] [109] [110]

    In November 2020, a study was published in the peer-reviewed scientific journal Geophysical Research Letters suggesting that the plumes may originate from water within the crust of Europa as opposed to its subsurface ocean. The study's model, using images from the Galileo space probe, proposed that a combination of freezing and pressurization may result in at least some of the cryovolcanism activity. The pressure generated by migrating briny water pockets would thus, eventually, burst through the crust thereby creating these plumes. In a press release from NASA's Jet Propulsion Laboratory referencing the study, these suggested sources for Europa's plumes would potentially be less hospitable to life. This is due to a lack of substantial energy for organisms to thrive off of, unlike proposed hydrothermal vents on the subsurface ocean floor. [111] [112]


    Observations with the Goddard High Resolution Spectrograph of the Hubble Space Telescope, first described in 1995, revealed that Europa has a thin atmosphere composed mostly of molecular oxygen (O2), [113] [114] and some water vapor. [115] [116] [117] The surface pressure of Europa's atmosphere is 0.1  μPa, or 10−12 times that of the Earth. [13] In 1997, the Galileo spacecraft confirmed the presence of a tenuous ionosphere (an upper-atmospheric layer of charged particles) around Europa created by solar radiation and energetic particles from Jupiter's magnetosphere, [118] [119] providing evidence of an atmosphere.

    Magnetic field around Europa. The red line shows a trajectory of the Galileo spacecraft during a typical flyby (E4 or E14). Europa field.png
    Magnetic field around Europa. The red line shows a trajectory of the Galileo spacecraft during a typical flyby (E4 or E14).

    Unlike the oxygen in Earth's atmosphere, Europa's is not of biological origin. The surface-bounded atmosphere forms through radiolysis, the dissociation of molecules through radiation. [120] Solar ultraviolet radiation and charged particles (ions and electrons) from the Jovian magnetospheric environment collide with Europa's icy surface, splitting water into oxygen and hydrogen constituents. These chemical components are then adsorbed and "sputtered" into the atmosphere. The same radiation also creates collisional ejections of these products from the surface, and the balance of these two processes forms an atmosphere. [121] Molecular oxygen is the densest component of the atmosphere because it has a long lifetime; after returning to the surface, it does not stick (freeze) like a water or hydrogen peroxide molecule but rather desorbs from the surface and starts another ballistic arc. Molecular hydrogen never reaches the surface, as it is light enough to escape Europa's surface gravity. [122] [123]

    Observations of the surface have revealed that some of the molecular oxygen produced by radiolysis is not ejected from the surface. Because the surface may interact with the subsurface ocean (considering the geological discussion above), this molecular oxygen may make its way to the ocean, where it could aid in biological processes. [124] One estimate suggests that, given the turnover rate inferred from the apparent ~0.5 Gyr maximum age of Europa's surface ice, subduction of radiolytically generated oxidizing species might well lead to oceanic free oxygen concentrations that are comparable to those in terrestrial deep oceans. [125]

    The molecular hydrogen that escapes Europa's gravity, along with atomic and molecular oxygen, forms a gas torus in the vicinity of Europa's orbit around Jupiter. This "neutral cloud" has been detected by both the Cassini and Galileo spacecraft, and has a greater content (number of atoms and molecules) than the neutral cloud surrounding Jupiter's inner moon Io. Models predict that almost every atom or molecule in Europa's torus is eventually ionized, thus providing a source to Jupiter's magnetospheric plasma. [126]


    Pioneer 10 - p102b.jpg
    In 1973 Pioneer 10 made the first closeup images of Europa – however the probe was too far away to obtain more detailed images
    Europa - July 9 1979 (18267960842).jpg
    Europa seen in detail in 1979 by Voyager 2

    Exploration of Europa began with the Jupiter flybys of Pioneer 10 and 11 in 1973 and 1974 respectively. The first closeup photos were of low resolution compared to later missions. The two Voyager probes traveled through the Jovian system in 1979, providing more-detailed images of Europa's icy surface. The images caused many scientists to speculate about the possibility of a liquid ocean underneath. Starting in 1995, the Galileo space probe orbited Jupiter for eight years, until 2003, and provided the most detailed examination of the Galilean moons to date. It included the "Galileo Europa Mission" and "Galileo Millennium Mission", with numerous close flybys of Europa. [127] In 2007, New Horizons imaged Europa, as it flew by the Jovian system while on its way to Pluto. [128]

    Future missions

    Conjectures regarding extraterrestrial life have ensured a high profile for Europa and have led to steady lobbying for future missions. [129] [130] The aims of these missions have ranged from examining Europa's chemical composition to searching for extraterrestrial life in its hypothesized subsurface oceans. [131] [132] Robotic missions to Europa need to endure the high-radiation environment around Jupiter. [130] Because it is deeply embedded within Jupiter's magnetosphere, Europa receives about 5.40 Sv of radiation per day. [133]

    In 2011, a Europa mission was recommended by the U.S. Planetary Science Decadal Survey. [134] In response, NASA commissioned Europa lander concept studies in 2011, along with concepts for a Europa flyby (Europa Clipper), and a Europa orbiter. [135] [136] The orbiter element option concentrates on the "ocean" science, while the multiple-flyby element (Clipper) concentrates on the chemistry and energy science. On 13 January 2014, the House Appropriations Committee announced a new bipartisan bill that includes $80 million funding to continue the Europa mission concept studies. [137] [138]

    Old proposals

    JIMO Europa Lander Mission.jpg
    Left: artist's concept of the cryobot and its deployed "hydrobot" submersible. Right: Europa Lander Mission concept, NASA 2005. [145]

    In the early 2000s, Jupiter Europa Orbiter led by NASA and the Jupiter Ganymede Orbiter led by the ESA were proposed together as an Outer Planet Flagship Mission to Jupiter's icy moons called Europa Jupiter System Mission, with a planned launch in 2020. [146] In 2009 it was given priority over Titan Saturn System Mission . [147] At that time, there was competition from other proposals. [148] Japan proposed Jupiter Magnetospheric Orbiter .

    Jovian Europa Orbiter was an ESA Cosmic Vision concept study from 2007. Another concept was Ice Clipper, [149] which would have used an impactor similar to the Deep Impact mission—it would make a controlled crash into the surface of Europa, generating a plume of debris that would then be collected by a small spacecraft flying through the plume. [149] [150]

    Jupiter Icy Moons Orbiter (JIMO) was a partially developed fission-powered spacecraft with ion thrusters that was cancelled in 2006. [130] [151] It was part of Project Prometheus. [151] The Europa Lander Mission proposed a small nuclear-powered Europa lander for JIMO. [152] It would travel with the orbiter, which would also function as a communication relay to Earth. [152]

    Europa Orbiter – Its objective would be to characterize the extent of the ocean and its relation to the deeper interior. Instrument payload could include a radio subsystem, laser altimeter, magnetometer, Langmuir probe, and a mapping camera. [153] [154] The Europa Orbiter received a go-ahead in 1999 but was canceled in 2002. This orbiter featured a special ice-penetrating radar that would allow it to scan below the surface. [43]

    More ambitious ideas have been put forward including an impactor in combination with a thermal drill to search for biosignatures that might be frozen in the shallow subsurface. [155] [156]

    Another proposal put forward in 2001 calls for a large nuclear-powered "melt probe" (cryobot) that would melt through the ice until it reached an ocean below. [130] [157] Once it reached the water, it would deploy an autonomous underwater vehicle (hydrobot) that would gather information and send it back to Earth. [158] Both the cryobot and the hydrobot would have to undergo some form of extreme sterilization to prevent detection of Earth organisms instead of native life and to prevent contamination of the subsurface ocean. [159] This suggested approach has not yet reached a formal conceptual planning stage. [160]

    Habitability potential

    A black smoker in the Atlantic Ocean. Driven by geothermal energy, this and other types of hydrothermal vents create chemical disequilibria that can provide energy sources for life. Blacksmoker in Atlantic Ocean.jpg
    A black smoker in the Atlantic Ocean. Driven by geothermal energy, this and other types of hydrothermal vents create chemical disequilibria that can provide energy sources for life.

    So far, there is no evidence that life exists on Europa, but Europa has emerged as one of the most likely locations in the Solar System for potential habitability. [125] [161] Life could exist in its under-ice ocean, perhaps in an environment similar to Earth's deep-ocean hydrothermal vents. [131] [162] Even if Europa lacks volcanic hydrothermal activity, a 2016 NASA study found that Earth-like levels of hydrogen and oxygen could be produced through processes related to serpentinization and ice-derived oxidants, which do not directly involve volcanism. [163] In 2015, scientists announced that salt from a subsurface ocean may likely be coating some geological features on Europa, suggesting that the ocean is interacting with the seafloor. This may be important in determining if Europa could be habitable. [18] [164] The likely presence of liquid water in contact with Europa's rocky mantle has spurred calls to send a probe there. [165]

    Europa - possible effect of radiation on biosignature chemicals PIA22479-Europa-JupiterMoon-ArtistConcept-20180723.jpg
    Europa – possible effect of radiation on biosignature chemicals

    The energy provided by tidal forces drives active geological processes within Europa's interior, just as they do to a far more obvious degree on its sister moon Io. Although Europa, like the Earth, may possess an internal energy source from radioactive decay, the energy generated by tidal flexing would be several orders of magnitude greater than any radiological source. [166] Life on Europa could exist clustered around hydrothermal vents on the ocean floor, or below the ocean floor, where endoliths are known to inhabit on Earth. Alternatively, it could exist clinging to the lower surface of Europa's ice layer, much like algae and bacteria in Earth's polar regions, or float freely in Europa's ocean. [167] If Europa's ocean is too cold, biological processes similar to those known on Earth could not take place. If it is too salty, only extreme halophiles could survive in that environment. [167] In 2010, a model proposed by Richard Greenberg of the University of Arizona proposed that irradiation of ice on Europa's surface could saturate its crust with oxygen and peroxide, which could then be transported by tectonic processes into the interior ocean. Such a process could render Europa's ocean as oxygenated as our own within just 12 million years, allowing the existence of complex, multicellular lifeforms. [168]

    Evidence suggests the existence of lakes of liquid water entirely encased in Europa's icy outer shell and distinct from a liquid ocean thought to exist farther down beneath the ice shell. [65] [66] If confirmed, the lakes could be yet another potential habitat for life. Evidence suggests that hydrogen peroxide is abundant across much of the surface of Europa. [169] Because hydrogen peroxide decays into oxygen and water when combined with liquid water, the authors argue that it could be an important energy supply for simple life forms.

    Clay-like minerals (specifically, phyllosilicates), often associated with organic matter on Earth, have been detected on the icy crust of Europa. [170] The presence of the minerals may have been the result of a collision with an asteroid or comet. [170] Some scientists have speculated that life on Earth could have been blasted into space by asteroid collisions and arrived on the moons of Jupiter in a process called lithopanspermia. [171]

    See also


    1. Periapsis is derived from the semimajor axis (a) and eccentricity (e): a(1  e).
    2. Apoapsis is derived from the semimajor axis (a) and eccentricity (e): a(1 + e).
    3. Surface area derived from the radius (r): 4πr 2.
    4. Volume derived from the radius (r): 4/3πr 3.
    5. Surface gravity derived from the mass (m), the gravitational constant (G) and the radius (r): Gm/r2.
    6. Escape velocity derived from the mass (m), the gravitational constant (G) and the radius (r): .

    Related Research Articles

    Galilean moons Four largest moons of Jupiter

    The Galilean moons are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter in March 1610. They were the first objects found to orbit a planet other than the Earth.

    <i>Galileo</i> project Unmanned NASA spacecraft which studied the planet Jupiter and its moons

    Galileo was an American robotic space program that studied the planet Jupiter and its moons, as well as several other Solar System bodies. Named after the Italian astronomer Galileo Galilei, the Galileo spacecraft consisted of an orbiter and an entry probe. It was delivered into Earth orbit on October 18, 1989 by Space ShuttleAtlantis on the STS-34 mission, and arrived at Jupiter on December 7, 1995, after gravitational assist flybys of Venus and Earth, and became the first spacecraft to orbit Jupiter. It launched the first probe into Jupiter, directly measuring its atmosphere. Despite suffering major antenna problems, Galileo achieved the first asteroid flyby, of 951 Gaspra, and discovered the first asteroid moon, Dactyl, around 243 Ida. In 1994, Galileo observed Comet Shoemaker–Levy 9's collision with Jupiter.

    Callisto (moon) Second largest Galilean moon of Jupiter and third largest in the solar system

    Callisto, or Jupiter IV, is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System that may not be properly differentiated. Callisto was discovered in 1610 by Galileo Galilei. At 4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1883000 km. It is not in an orbital resonance like the three other Galilean satellites—Io, Europa, and Ganymede—and is thus not appreciably tidally heated. Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward. Because of this, there is a sub-Jovian point on Callisto's surface, from which Jupiter would appear to hang directly overhead. It is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt.

    Triton (moon) Largest moon of Neptune

    Triton is the largest natural satellite of the planet Neptune, and was the first Neptunian moon to be discovered, on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, an orbit in the direction opposite to its planet's rotation. Because of its retrograde orbit and composition similar to Pluto, Triton is thought to have been a dwarf planet, captured from the Kuiper belt.

    Ganymede (moon) Largest moon of Jupiter and in the Solar System

    Ganymede, a satellite of Jupiter, is the largest and most massive of the Solar System's moons. The ninth-largest object of the Solar System, it is the largest without a substantial atmosphere. It has a diameter of 5,268 km (3,273 mi), making it 26% larger than the planet Mercury by volume, although it is only 45% as massive. Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field. Outward from Jupiter, it is the seventh satellite and the third of the Galilean moons, the first group of objects discovered orbiting another planet. Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.

    Enceladus Natural satellite (moon) orbiting Saturn

    Enceladus is the sixth-largest moon of Saturn. It is about 500 kilometers (310 mi) in diameter, about a tenth of that of Saturn's largest moon, Titan. Enceladus is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon only reaches −198 °C (−324 °F), far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide range of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrains.

    Io (moon) Innermost of the four Galilean moons of Jupiter

    Io, or Jupiter I, is the innermost and third-largest of the four Galilean moons of the planet Jupiter. Slightly larger than the Moon, Io is the fourth-largest moon in the Solar System, has the highest density of any moon, and has the lowest amount of water of any known astronomical object in the Solar System. It was discovered in 1610 by Galileo Galilei and was named after the mythological character Io, a priestess of Hera who became one of Zeus's lovers.

    Cryovolcano Type of volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock

    A cryovolcano is a type of volcano that erupts volatiles such as water, ammonia or methane into an extreme environment at or below their freezing point, essentially reenacting the typical sort of lava volcanism seen on Earth with liquid and frozen volatiles acting as geological allegories to molten and solid rock respectively. Collectively referred to as cryomagma, cryolava or ice-volcanic melt, these substances are usually liquids and can form plumes, but can also be in vapour form. After the eruption, cryomagma is expected to condense to a solid form when exposed to the very low surrounding temperature. Cryovolcanoes may potentially form on icy moons and other objects with abundant water past the Solar System's snow line. A number of features have been identified as possible cryovolcanoes on Pluto, Titan and Ceres, and a subset of domes on Europa may have cryovolcanic origins. In addition, although they are not known to form volcanoes, ice geysers have been observed on Enceladus and potentially Triton.

    Colonization of Europa Proposed concepts for the human colonization of Europa

    Europa, the fourth-largest moon of Jupiter, is a subject in both science fiction and scientific speculation for future human colonization. Europa's geophysical features, including a possible subglacial water ocean, make it a possibility that human life could be sustained on or beneath the surface.

    Ceres (dwarf planet) Largest asteroid and also a dwarf planet

    Ceres is the largest object in the asteroid belt between the orbits of Mars and Jupiter. Ceres was the first asteroid discovered, on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily. Originally considered a planet, it was reclassified as an asteroid in the 1850s after the discovery of dozens of other objects in similar orbits. In 2006, it was reclassified again as a dwarf planet – the only one always inside Neptune's orbit – because, at 940 km (580 mi) in diameter, it is the only asteroid large enough for its gravity to make it plastic and to maintain it as a spheroid. In January 2014, emissions of water vapor were detected around Ceres, creating a tenuous, transient atmosphere known as an exosphere. This was unexpected because asteroids typically do not emit vapor, a hallmark of comets.

    The exploration of Jupiter has been conducted via close observations by automated spacecraft. It began with the arrival of Pioneer 10 into the Jovian system in 1973, and, as of 2016, has continued with eight further spacecraft missions. All of these missions were undertaken by the National Aeronautics and Space Administration (NASA), and all but two were flybys taking detailed observations without landing or entering orbit. These probes make Jupiter the most visited of the Solar System's outer planets as all missions to the outer Solar System have used Jupiter flybys. On 5 July 2016, spacecraft Juno arrived and entered the planet's orbit—the second craft ever to do so. Sending a craft to Jupiter is difficult, mostly due to large fuel requirements and the effects of the planet's harsh radiation environment.

    Ocean world A planetary body that includes a significant amount of water or other liquid

    An ocean world, ocean planet, water world, aquaplanet, or panthalassic planet is a type of terrestrial planet that contains a substantial amount of water as hydrosphere on its surface or as a subsurface ocean. The term ocean world is also used sometimes for astronomical bodies with an ocean composed of a different fluid or thalassogen, such as lava, ammonia or hydrocarbons like on Titan's surface.

    Extraterrestrial liquid water is water in its liquid state that naturally occurs outside Earth. It is a subject of wide interest because it is recognized as one of the key prerequisites for life as we know it and thus surmised as essential for extraterrestrial life.

    Volcanism on Io Volcanism of Io, a moon of Jupiter

    Volcanism on Io, a moon of Jupiter, is represented by the presence of volcanoes, volcanic pits and lava flows on the moon's surface. Its volcanic activity was discovered in 1979 by Voyager 1 imaging scientist Linda Morabito. Observations of Io by passing spacecraft and Earth-based astronomers have revealed more than 150 active volcanoes. Up to 400 such volcanoes are predicted to exist based on these observations. Io's volcanism makes the satellite one of only four known currently volcanically active worlds in the Solar System.

    Habitability of natural satellites Measure of the potential of natural satellites to have environments hospitable to life

    The habitability of natural satellites is a measure of the potential of natural satellites to have environments hospitable to life. Habitable environments do not necessarily harbor life. Natural satellite habitability is an emerging field which is considered important to astrobiology for several reasons, foremost being that natural satellites are predicted to greatly outnumber planets and it is hypothesized that habitability factors are likely to be similar to those of planets. There are, however, key environmental differences which have a bearing on moons as potential sites for extraterrestrial life.

    Exploration of Io Overview of the exploration of Io, Jupiters innermost Galilean and third-largest moon

    The exploration of Io, Jupiter's innermost Galilean and third-largest moon, began with its discovery in 1610 and continues today with Earth-based observations and visits by spacecraft to the Jupiter system. Italian astronomer Galileo Galilei was the first to record an observation of Io on January 8, 1610, though Simon Marius may have also observed Io at around the same time. During the 17th century, observations of Io and the other Galilean satellites helped with the measurement of longitude by map makers and surveyors, with validation of Kepler's Third Law of planetary motion, and with measurement of the speed of light. Based on ephemerides produced by astronomer Giovanni Cassini and others, Pierre-Simon Laplace created a mathematical theory to explain the resonant orbits of three of Jupiter's moons, Io, Europa, and Ganymede. This resonance was later found to have a profound effect on the geologies of these moons. Improved telescope technology in the late 19th and 20th centuries allowed astronomers to resolve large-scale surface features on Io as well as to estimate its diameter and mass.

    Europa Clipper Planned multiple-flyby study of Europa

    Europa Clipper is an interplanetary mission in development by NASA comprising an orbiter. Planned for launch in October 2024, the spacecraft is being developed to study the Galilean moon Europa through a series of flybys while in orbit around Jupiter.

    Planetary oceanography also called exo-oceanography is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry and planetary geology, it only began after the discovery of underground oceans in Saturn's Titan and Jupiter's Europa. This field remains speculative until further missions reach the oceans beneath the rock or ice layer of the moons. There are many theories about oceans or even ocean worlds of celestial bodies in the Solar System, from oceans made of diamond in Neptune to a gigantic ocean of liquid hydrogen that may exist underneath Jupiter's surface.

    This article is intended to provide an overview of various aspects of the tectonics on icy moons.


    1. 1 2 3 4 Blue, Jennifer (9 November 2009). "Planet and Satellite Names and Discoverers". USGS. Archived from the original on 25 August 2009. Retrieved 14 January 2010.
    2. "Europa". Lexico UK Dictionary. Oxford University Press.
      "Europa". Merriam-Webster Dictionary .
    3. G.G. Schaber (1982) "Geology of Europa", in David Morrison, ed., Satellites of Jupiter, vol. 3, International Astronomical Union, p 556 ff.
    4. 1 2 Greenberg (2005) Europa: the ocean moon
    5. "JPL HORIZONS solar system data and ephemeris computation service". Solar System Dynamics. NASA, Jet Propulsion Laboratory. Archived from the original on 7 October 2012. Retrieved 10 August 2007.
    6. 1 2 3 4 "Overview of Europa Facts". NASA. Archived from the original on 26 March 2014. Retrieved 27 December 2007.
    7. "By the Numbers | Europa". NASA Solar System Exploration. Archived from the original on 6 May 2021. Retrieved 6 May 2021.
    8. 1 2 3 4 5 Yeomans, Donald K. (13 July 2006). "Planetary Satellite Physical Parameters". JPL Solar System Dynamics. Archived from the original on 14 August 2009. Retrieved 5 November 2007.
    9. Showman, A. P.; Malhotra, R. (1 October 1999). "The Galilean Satellites". Science. 286 (5437): 77–84. doi:10.1126/science.286.5437.77. PMID   10506564. S2CID   9492520.
    10. 1 2 Geissler, P. E.; Greenberg, R.; Hoppa, G.; Helfenstein, P.; McEwen, A.; Pappalardo, R.; Tufts, R.; Ockert-Bell, M.; Sullivan, R.; Greeley, R.; Belton, M. J. S.; Denk, T.; Clark, B. E.; Burns, J.; Veverka, J. (1998). "Evidence for non-synchronous rotation of Europa". Nature . 391 (6665): 368–70. Bibcode:1998Natur.391..368G. doi:10.1038/34869. PMID   9450751. S2CID   4426840.
    11. Bills, Bruce G. (2005). "Free and forced obliquities of the Galilean satellites of Jupiter". Icarus. 175 (1): 233–247. Bibcode:2005Icar..175..233B. doi:10.1016/j.icarus.2004.10.028. Archived from the original on 27 July 2020. Retrieved 29 June 2019.
    12. 1 2 McFadden, Lucy-Ann; Weissman, Paul; Johnson, Torrence (2007). The Encyclopedia of the Solar System. Elsevier. p.  432. ISBN   978-0-12-226805-2.
    13. 1 2 McGrath (2009). "Atmosphere of Europa". In Pappalardo, Robert T.; McKinnon, William B.; Khurana, Krishan K. (eds.). Europa. University of Arizona Press. ISBN   978-0-8165-2844-8.
    14. Chang, Kenneth (12 March 2015). "Suddenly, It Seems, Water Is Everywhere in Solar System". The New York Times . Archived from the original on 9 May 2020. Retrieved 13 March 2015.
    15. Tritt, Charles S. (2002). "Possibility of Life on Europa". Milwaukee School of Engineering. Archived from the original on 9 June 2007. Retrieved 10 August 2007.
    16. 1 2 3 "Tidal Heating". Archived from the original on 29 March 2006.
    17. 1 2 Dyches, Preston; Brown, Dwayne; Buckley, Michael (8 September 2014). "Scientists Find Evidence of 'Diving' Tectonic Plates on Europa". NASA . Archived from the original on 4 April 2019. Retrieved 8 September 2014.
    18. 1 2 Dyches, Preston; Brown, Dwayne (12 May 2015). "NASA Research Reveals Europa's Mystery Dark Material Could Be Sea Salt". NASA . Archived from the original on 15 May 2015. Retrieved 12 May 2015.
    19. 1 2 3 Cook, Jia-Rui C.; Gutro, Rob; Brown, Dwayne; Harrington, J. D.; Fohn, Joe (12 December 2013). "Hubble Sees Evidence of Water Vapor at Jupiter Moon". NASA. Archived from the original on 15 December 2013. Retrieved 12 December 2013.
    20. 1 2 3 4 Jia, Xianzhe; Kivelson, Margaret G.; Khurana, Krishan K.; Kurth, William S. (14 May 2018). "Evidence of a plume on Europa from Galileo magnetic and plasma wave signatures". Nature Astronomy . 2 (6): 459–464. Bibcode:2018NatAs...2..459J. doi:10.1038/s41550-018-0450-z. S2CID   134370392.
    21. 1 2 McCartney, Gretchen; Brown, Dwayne; Wendel, JoAnna (14 May 2018). "Old Data Reveal New Evidence of Europa Plumes". Jet Propulsion Laboratory . Archived from the original on 17 June 2019. Retrieved 14 May 2018.
    22. 1 2 3 Chang, Kenneth (14 May 2018). "NASA Finds Signs of Plumes From Europa, Jupiter's Ocean Moon". The New York Times . Archived from the original on 14 May 2018. Retrieved 14 May 2018.
    23. 1 2 3 Wall, Mike (14 May 2018). "This May Be the Best Evidence Yet of a Water Plume on Jupiter's Moon Europa". . Archived from the original on 14 May 2018. Retrieved 14 May 2018.
    24. 1 2 Amos, Jonathan (2 May 2012). "Esa selects 1bn-euro Juice probe to Jupiter". BBC News Online . Archived from the original on 11 May 2020. Retrieved 2 May 2012.
    25. Borenstein, Seth (4 March 2014). "NASA plots daring flight to Jupiter's watery moon". Associated Press. Archived from the original on 5 March 2014. Retrieved 5 March 2014.
    26. Arnett, Bill (October 2005). "Europa". Nine Planets. Archived from the original on 28 March 2014. Retrieved 27 April 2014.
    27. 1 2 Marius, S.; (1614) Mundus Iovialis anno M.DC.IX Detectus Ope Perspicilli Belgici Archived 25 August 2011 at WebCite , where he attributes the suggestion Archived 1 November 2019 at the Wayback Machine to Johannes Kepler
    28. "Simon Marius (January 20, 1573 – December 26, 1624)". Students for the Exploration and Development of Space. University of Arizona. Archived from the original on 13 July 2007. Retrieved 9 August 2007.
    29. Marius, SImon (1614). Mundus Iovialis: anno MDCIX detectus ope perspicilli Belgici, hoc est, quatuor Jovialium planetarum, cum theoria, tum tabulæ. Nuremberg: Sumptibus & Typis Iohannis Lauri. p. B2, recto and verso (images 35 and 36), with erratum on last page (image 78). Archived from the original on 2 July 2020. Retrieved 30 June 2020.
    30. 1 2 Marazzini, Claudio (2005). "I nomi dei satelliti di Giove: da Galileo a Simon Marius" [The names of Jupiter's satellites: from Galileo to Simon Marius]. Lettere Italiane (in Italian). 57 (3): 391–407. JSTOR   26267017.
    31. US National Research Council (2000) A Science Strategy for the Exploration of Europa
    32. 1 2 "Europa, a Continuing Story of Discovery". Project Galileo. NASA, Jet Propulsion Laboratory. Archived from the original on 5 January 1997. Retrieved 9 August 2007.
    33. "Planetographic Coordinates". Wolfram Research. 2010. Archived from the original on 1 March 2009. Retrieved 29 March 2010.
    34. 1 2 3 Showman, Adam P.; Malhotra, Renu (May 1997). "Tidal Evolution into the Laplace Resonance and the Resurfacing of Ganymede". Icarus. 127 (1): 93–111. Bibcode:1997Icar..127...93S. doi:10.1006/icar.1996.5669. S2CID   55790129.
    35. Moore, W. B. (2003). "Tidal heating and convection in Io". Journal of Geophysical Research. 108 (E8): 5096. Bibcode:2003JGRE..108.5096M. CiteSeerX . doi:10.1029/2002JE001943.
    36. Cook, Jia-Rui C. (18 September 2013) Long-stressed Europa Likely Off-kilter at One Time Archived 17 August 2014 at the Wayback Machine .
    37. Mass of Europa: 48×1021 kg. Mass of Triton plus all smaller moons: 39.5×1021 kg (see note g here)
    38. Kargel, Jeffrey S.; Kaye, Jonathan Z.; Head, James W.; Marion, Giles M.; Sassen, Roger; Crowley, James K.; Ballesteros, Olga Prieto; Grant, Steven A.; Hogenboom, David L. (November 2000). "Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life". Icarus. 148 (1): 226–265. Bibcode:2000Icar..148..226K. doi:10.1006/icar.2000.6471. Archived from the original on 31 July 2020. Retrieved 10 January 2020.
    39. Phillips, Cynthia B.; Pappalardo, Robert T. (20 May 2014). "Europa Clipper Mission Concept". Eos, Transactions American Geophysical Union. 95 (20): 165–167. Bibcode:2014EOSTr..95..165P. doi:10.1002/2014EO200002.
    40. Cowen, Ron (7 June 2008). "A Shifty Moon". Science News. Archived from the original on 23 March 2012. Retrieved 29 May 2008.
    41. 1 2 Kivelson, Margaret G.; Khurana, Krishan K.; Russell, Christopher T.; Volwerk, Martin; Walker, Raymond J.; Zimmer, Christophe (2000). "Galileo Magnetometer Measurements: A Stronger Case for a Subsurface Ocean at Europa". Science . 289 (5483): 1340–1343. Bibcode:2000Sci...289.1340K. doi:10.1126/science.289.5483.1340. PMID   10958778. S2CID   44381312.
    42. Bhatia, G.K.; Sahijpal, S. (2017). "Thermal evolution of trans-Neptunian objects, icy satellites, and minor icy planets in the early solar system". Meteoritics & Planetary Science. 52 (12): 2470–2490. Bibcode:2017M&PS...52.2470B. doi:10.1111/maps.12952.
    43. 1 2 "Europa: Another Water World?". Project Galileo: Moons and Rings of Jupiter. NASA, Jet Propulsion Laboratory. 2001. Archived from the original on 21 July 2011. Retrieved 9 August 2007.
    44. Rincon, Paul (20 March 2013). "Ice blades threaten Europa landing". BBC News. Archived from the original on 7 November 2018. Retrieved 21 June 2018.
    45. Europa may have towering ice spikes on its surface Archived 21 January 2021 at the Wayback Machine . Paul Scott Anderson, Earth and Sky. 20 October 2018.
    46. 1 2 Hobley, Daniel E. J.; Moore, Jeffrey M.; Howard, Alan D.; Umurhan, Orkan M. (8 October 2018). "Formation of metre-scale bladed roughness on Europa's surface by ablation of ice" (PDF). Nature Geoscience. 11 (12): 901–904. Bibcode:2018NatGe..11..901H. doi:10.1038/s41561-018-0235-0. S2CID   134294079. Archived (PDF) from the original on 31 July 2020. Retrieved 11 January 2020.
    47. Arnett, Bill (7 November 1996) Europa Archived 4 September 2011 at the Wayback Machine .
    48. 1 2 Hamilton, Calvin J. "Jupiter's Moon Europa". Archived from the original on 24 January 2012. Retrieved 27 February 2007.
    49. Schenk, Paul M.; Chapman, Clark R.; Zahnle, Kevin; and Moore, Jeffrey M. (2004) "Chapter 18: Ages and Interiors: the Cratering Record of the Galilean Satellites" Archived 24 December 2016 at the Wayback Machine , pp. 427 ff. in Bagenal, Fran; Dowling, Timothy E.; and McKinnon, William B., editors; Jupiter: The Planet, Satellites and Magnetosphere, Cambridge University Press, ISBN   0-521-81808-7.
    50. "High Tide on Europa". Astrobiology Magazine. 2007. Archived from the original on 29 September 2007. Retrieved 20 October 2007.
    51. Frederick A. Ringwald (29 February 2000). "SPS 1020 (Introduction to Space Sciences)". California State University, Fresno. Archived from the original on 25 July 2008. Retrieved 4 July 2009.
    52. The Effects of Nuclear Weapons, Revised ed., US DOD 1962, pp. 592–593
    53. "Europa: Facts about Jupiter's Moon, Europa • The Planets". The Planets. Archived from the original on 11 January 2021. Retrieved 9 January 2021.
    54. Geissler, P.E.; Greenberg, R.; Hoppa, G.; McEwen, A.; Tufts, R.; Phillips, C.; Clark, B.; Ockert-Bell, M.; Helfenstein, P.; Burns, J.; Veverka, J.; Sullivan, R.; Greeley, R.; Pappalardo, R.T.; Head, J.W.; Belton, M.J.S.; Denk, T. (September 1998). "Evolution of Lineaments on Europa: Clues from Galileo Multispectral Imaging Observations". Icarus. 135 (1): 107–126. Bibcode:1998Icar..135..107G. doi:10.1006/icar.1998.5980. S2CID   15375333.
    55. Figueredo, Patricio H.; Greeley, Ronald (February 2004). "Resurfacing history of Europa from pole-to-pole geological mapping". Icarus. 167 (2): 287–312. Bibcode:2004Icar..167..287F. doi:10.1016/j.icarus.2003.09.016.
    56. Hurford, T.A.; Sarid, A.R.; Greenberg, R. (January 2007). "Cycloidal cracks on Europa: Improved modeling and non-synchronous rotation implications". Icarus. 186 (1): 218–233. Bibcode:2007Icar..186..218H. doi:10.1016/j.icarus.2006.08.026.
    57. Kattenhorn, Simon A. (2002). "Nonsynchronous Rotation Evidence and Fracture History in the Bright Plains Region, Europa". Icarus. 157 (2): 490–506. Bibcode:2002Icar..157..490K. doi:10.1006/icar.2002.6825.
    58. 1 2 Schenk, Paul M.; McKinnon, William B. (May 1989). "Fault offsets and lateral crustal movement on Europa: Evidence for a mobile ice shell". Icarus. 79 (1): 75–100. Bibcode:1989Icar...79...75S. doi:10.1016/0019-1035(89)90109-7.
    59. 1 2 Kattenhorn, Simon A.; Prockter, Louise M. (7 September 2014). "Evidence for subduction in the ice shell of Europa". Nature Geoscience. 7 (10): 762–767. Bibcode:2014NatGe...7..762K. doi:10.1038/ngeo2245.
    60. Howell, Samuel M.; Pappalardo, Robert T. (1 April 2019). "Can Earth-like plate tectonics occur in ocean world ice shells?". Icarus. 322: 69–79. Bibcode:2019Icar..322...69H. doi:10.1016/j.icarus.2019.01.011. S2CID   127545679.
    61. 1 2 Sotin, Christophe; Head, James W.; Tobie, Gabriel (April 2002). "Europa: Tidal heating of upwelling thermal plumes and the origin of lenticulae and chaos melting" (PDF). Geophysical Research Letters. 29 (8): 74-1–74-4. Bibcode:2002GeoRL..29.1233S. doi:10.1029/2001GL013844. Archived (PDF) from the original on 31 July 2020. Retrieved 12 April 2020.
    62. Goodman, Jason C. (2004). "Hydrothermal plume dynamics on Europa: Implications for chaos formation". Journal of Geophysical Research. 109 (E3): E03008. Bibcode:2004JGRE..109.3008G. doi:10.1029/2003JE002073. hdl: 1912/3570 .
    63. O'Brien, David P.; Geissler, Paul; Greenberg, Richard (October 2000). "Tidal Heat in Europa: Ice Thickness and the Plausibility of Melt-Through". Bulletin of the American Astronomical Society. 30: 1066. Bibcode:2000DPS....32.3802O.
    64. Greenberg, Richard (2008). Unmasking Europa. Copernicus. Springer + Praxis Publishing. pp. 205–215, 236. ISBN   978-0-387-09676-6. Archived from the original on 22 January 2010. Retrieved 28 August 2017.
    65. 1 2 Schmidt, Britney; Blankenship, Don; Patterson, Wes; Schenk, Paul (24 November 2011). "Active formation of 'chaos terrain' over shallow subsurface water on Europa". Nature. 479 (7374): 502–505. Bibcode:2011Natur.479..502S. doi:10.1038/nature10608. PMID   22089135. S2CID   4405195.
    66. 1 2 3 Airhart, Marc (2011). "Scientists Find Evidence for "Great Lake" on Europa and Potential New Habitat for Life". Jackson School of Geosciences. Archived from the original on 18 December 2013. Retrieved 16 November 2011.
    67. 1 2 Cox, Rónadh; Bauer, Aaron W. (October 2015). "Impact breaching of Europa's ice: Constraints from numerical modeling: IMPACT BREACHING OF EUROPA'S ICE". Journal of Geophysical Research: Planets. 120 (10): 1708–1719. doi:10.1002/2015JE004877. Archived from the original on 1 October 2021. Retrieved 12 January 2021.
    68. 1 2 Cox, Rónadh; Ong, Lissa C. F.; Arakawa, Masahiko; Scheider, Kate C. (December 2008). "Impact penetration of Europa's ice crust as a mechanism for formation of chaos terrain". Meteoritics & Planetary Science. 43 (12): 2027–2048. Bibcode:2008M&PS...43.2027C. doi:10.1111/j.1945-5100.2008.tb00659.x. Archived from the original on 1 October 2021. Retrieved 12 January 2021.
    69. 1 2 Greenberg, Richard (2005). Europa: The Ocean Moon: Search for an Alien Biosphere. Springer Praxis Books. Springer + Praxis. pp. 7 ff. doi:10.1007/b138547. ISBN   978-3-540-27053-9.
    70. Greeley, Ronald; et al. (2004) "Chapter 15: Geology of Europa", pp. 329 ff. in Bagenal, Fran; Dowling, Timothy E.; and McKinnon, William B., editors; Jupiter: The Planet, Satellites and Magnetosphere, Cambridge University Press, ISBN   0-521-81808-7.
    71. Park, Ryan S.; Bills, Bruce; Buffington, Brent B. (July 2015). "Improved detection of tides at Europa with radiometric and optical tracking during flybys". Planetary and Space Science. 112: 10–14. Bibcode:2015P&SS..112...10P. doi:10.1016/j.pss.2015.04.005.
    72. Adamu, Zaina (1 October 2012). "Water near surface of a Jupiter moon only temporary". CNN News. Archived from the original on 5 October 2012. Retrieved 2 October 2012.
    73. Nemiroff, R.; Bonnell, J., eds. (24 May 2012). "All the Water on Europa". Astronomy Picture of the Day . NASA . Retrieved 8 March 2016.
    74. Williams, Matt (15 September 2015). "Jupiter's Moon Europa". Universe Today. Archived from the original on 10 March 2016. Retrieved 9 March 2016.
    75. Billings, Sandra E.; Kattenhorn, Simon A. (2005). "The great thickness debate: Ice shell thickness models for Europa and comparisons with estimates based on flexure at ridges". Icarus. 177 (2): 397–412. Bibcode:2005Icar..177..397B. doi:10.1016/j.icarus.2005.03.013.
    76. Zimmer, C (October 2000). "Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations". Icarus. 147 (2): 329–347. Bibcode:2000Icar..147..329Z. CiteSeerX . doi:10.1006/icar.2000.6456.
    77. "Europa Mission to Probe Magnetic Field and Chemistry". Jet Propulsion Laboratory. 27 May 2015. Archived from the original on 2 December 2020. Retrieved 29 May 2015.
    78. McCord, Thomas B.; Hansen, Gary B.; et al. (1998). "Salts on Europa's Surface Detected by Galileo's Near Infrared Mapping Spectrometer". Science. 280 (5367): 1242–1245. Bibcode:1998Sci...280.1242M. doi:10.1126/science.280.5367.1242. PMID   9596573.
    79. Carlson, R. W.; Anderson, M. S.; Mehlman, R.; Johnson, R. E. (2005). "Distribution of hydrate on Europa: Further evidence for sulfuric acid hydrate". Icarus. 177 (2): 461. Bibcode:2005Icar..177..461C. doi:10.1016/j.icarus.2005.03.026.
    80. Calvin, Wendy M.; Clark, Roger N.; Brown, Robert H.; Spencer, John R. (1995). "Spectra of the ice Galilean satellites from 0.2 to 5 µm: A compilation, new observations, and a recent summary". Journal of Geophysical Research. 100 (E9): 19, 041–19, 048. Bibcode:1995JGR...10019041C. doi:10.1029/94JE03349.
    81. 1 2 Borucki, Jerome G.; Khare, Bishun; Cruikshank, Dale P. (2002). "A new energy source for organic synthesis in Europa's surface ice". Journal of Geophysical Research: Planets. 107 (E11): 24–1–24–5. Bibcode:2002JGRE..107.5114B. doi:10.1029/2002JE001841.
    82. Whalen, Kelly; Lunine, Jonathan I.; Blaney, Diana L. (2017). MISE: A Search for Organics on Europa. American Astronomical Society Meeting Abstracts #229. 229. p. 138.04. Bibcode:2017AAS...22913804W.
    83. "Europa Mission to Probe Magnetic Field and Chemistry". Jet Propulsion Laboratory. 27 May 2015. Archived from the original on 2 December 2020. Retrieved 23 October 2017.
    84. Trainer, MG (2013). "Atmospheric Prebiotic Chemistry and Organic Hazes". Curr Org Chem. 17 (16): 1710–1723. doi:10.2174/13852728113179990078. PMC   3796891 . PMID   24143126.
    85. Coll, Patrice; Szopa, Cyril; Buch, Arnaud; Carrasco, Nathalie; Ramirez, Sandra I.; Quirico, Eric; Sternberg, Robert; Cabane, Michel; Navarro-Gonzalez, Rafael; Raulin, Francois; Israel, G.; Poch, O.; Brasse, C. (2010). Prebiotic chemistry on Titan ? The nature of Titan's aerosols and their potential evolution at the satellite surface. 38th Cospar Scientific Assembly. 38. p. 11. Bibcode:2010cosp...38..777C.
    86. Ruiz-Bermejo, Marta; Rivas, Luis A.; Palacín, Arantxa; Menor-Salván, César; Osuna-Esteban, Susana (16 December 2010). "Prebiotic Synthesis of Protobiopolymers Under Alkaline Ocean Conditions". Origins of Life and Evolution of Biospheres. 41 (4): 331–345. Bibcode:2011OLEB...41..331R. doi:10.1007/s11084-010-9232-z. PMID   21161385. S2CID   19283373.
    87. Trumbo, Samantha K.; Brown, Michael E.; Hand, Kevin P. (12 June 2019). "Sodium chloride on the surface of Europa". Science Advances. 5 (6): eaaw7123. Bibcode:2019SciA....5.7123T. doi:10.1126/sciadv.aaw7123. PMC   6561749 . PMID   31206026.
    88. 1 2 3 "Frequently Asked Questions about Europa". NASA. 2012. Archived from the original on 28 April 2016. Retrieved 18 April 2016.
    89. 1 2 Zyga, Lisa (12 December 2008). "Scientist Explains Why Jupiter's Moon Europa Could Have Energetic Liquid Oceans". Archived from the original on 17 February 2009. Retrieved 28 July 2009.
    90. 1 2 Tyler, Robert H. (11 December 2008). "Strong ocean tidal flow and heating on moons of the outer planets". Nature. 456 (7223): 770–772. Bibcode:2008Natur.456..770T. doi:10.1038/nature07571. PMID   19079055. S2CID   205215528.
    91. "Europa: Energy". NASA. 2012. Archived from the original on 28 April 2016. Retrieved 18 April 2016. Tidal flexing of the ice shell could create slightly warmer pockets of ice that rise slowly upward to the surface, carrying material from the ocean below.
    92. Tyler, Robert (15 December 2008). "Jupiter's Moon Europa Does The Wave To Generate Heat". University of Washington. Science Daily. Archived from the original on 14 May 2016. Retrieved 18 April 2016.
    93. 1 2 Stacey, Kevin (14 April 2016). "Europa's heaving ice might make more heat than scientists thought". Brown University. Archived from the original on 21 April 2016. Retrieved 18 April 2016.
    94. 1 2 McCarthy, Christine; Cooper, Reid F. (1 June 2016). "Tidal dissipation in creeping ice and the thermal evolution of Europa". Earth and Planetary Science Letters. 443: 185–194. Bibcode:2016E&PSL.443..185M. doi:10.1016/j.epsl.2016.03.006.
    95. Barr, Amy C.; Showman, Adam P. (2009). "Heat transfer in Europa's icy shell". In Pappalardo, Robert T.; McKinnon, William B.; Khurana, Krishan (eds.). Europa. University of Arizona Press. pp. 405–430. CiteSeerX . ISBN   978-0-8165-2844-8.
    96. Lowell, Robert P.; DuBosse, Myesha (9 March 2005). "Hydrothermal systems on Europa". Geophysical Research Letters. 32 (5): L05202. Bibcode:2005GeoRL..32.5202L. doi:10.1029/2005GL022375.
    97. Ruiz, Javier (October 2005). "The heat flow of Europa" (PDF). Icarus. 177 (2): 438–446. Bibcode:2005Icar..177..438R. doi:10.1016/j.icarus.2005.03.021.
    98. "Hubble discovers water vapour venting from Jupiter's moon Europa". ESA/Hubble Press Release. Archived from the original on 15 December 2013. Retrieved 16 December 2013.
    99. 1 2 "Photo composite of suspected water plumes on Europa". Archived from the original on 9 October 2016. Retrieved 6 October 2016.
    100. "Hubble discovers water vapour venting from Jupiter's moon Europa". Hubble Space Telescope/European Space Agency. 12 December 2013. Archived from the original on 16 April 2019. Retrieved 16 April 2019.
    101. Fletcher, Leigh (12 December 2013). "The Plumes of Europa". The Planetary Society. Archived from the original on 15 December 2013. Retrieved 17 December 2013.
    102. Choi, Charles Q. (12 December 2013). "Jupiter Moon Europa May Have Water Geysers Taller Than Everest". Archived from the original on 15 December 2013. Retrieved 17 December 2013.
    103. Dyches, Preston (30 July 2015). "Signs of Europa Plumes Remain Elusive in Search of Cassini Data". NASA. Archived from the original on 16 April 2016. Retrieved 18 April 2016.
    104. 1 2 Roth, L.; Saur, J.; Retherford, K. D.; Strobel, D. F.; Feldman, P. D.; McGrath, M. A.; Nimmo, F. (12 December 2013). "Transient Water Vapor at Europa's South Pole". Science. 343 (6167): 171–174. Bibcode:2014Sci...343..171R. doi:10.1126/science.1247051. PMID   24336567. S2CID   27428538.
    105. 1 2 Berger, Eric (26 September 2016). "Hubble finds additional evidence of water vapor plumes on Europa". NASA. ARS Technica. Archived from the original on 26 September 2016. Retrieved 26 September 2016.
    106. Amos, Jonathan (26 September 2016). "Europa moon 'spewing water jets'". BBC News. Archived from the original on 26 September 2016. Retrieved 26 September 2016.
    107. Hansen, C. J.; Esposito, L.; Stewart, A. I.; Colwell, J.; Hendrix, A.; Pryor, W.; Shemansky, D.; West, R. (10 March 2006). "Enceladus' Water Vapor Plume". Science. 311 (5766): 1422–1425. Bibcode:2006Sci...311.1422H. doi:10.1126/science.1121254. PMID   16527971. S2CID   2954801.
    108. Spencer, J. R.; Nimmo, F. (May 2013). "Enceladus: An Active Ice World in the Saturn System". Annual Review of Earth and Planetary Sciences . 41: 693. Bibcode:2013AREPS..41..693S. doi:10.1146/annurev-earth-050212-124025. S2CID   140646028.
    109. O'Neill, Ian (22 September 2016). "NASA: Activity Spied on Europa, But It's 'NOT Aliens'". Discovery News. Space. Archived from the original on 23 September 2016. Retrieved 23 September 2016.
    110. Huybrighs, Hans; Futaana, Yoshifumi; Barabash, Stas; Wieser, Martin; Wurz, Peter; Krupp, Norbert; Glassmeier, Karl-Heinz; Vermeersen, Bert (June 2017). "On the in-situ detectability of Europa's water vapour plumes from a flyby mission". Icarus. 289: 270–280. arXiv: 1704.00912 . Bibcode:2017Icar..289..270H. doi:10.1016/j.icarus.2016.10.026. S2CID   119470009.
    111. McCartney, Gretchen; Hautaluoma, Grey; Johnson, Alana; Tucker, Danielle (13 November 2020). "Potential Plumes on Europa Could Come From Water in the Crust". Jet Propulsion Laboratory . Archived from the original on 13 November 2020. Retrieved 13 November 2020.
    112. Steinbrügge, G.; Voigt, J. R. C.; Wolfenbarger, N. S.; Hamilton, C. W.; Soderlund, K. M.; Young D., D. A.; Blankenship, D.; Vance D., S. D.; Schroeder, M. (5 November 2020). "Brine Migration and Impact‐Induced Cryovolcanism on Europa". Geophysical Research Letters . 47 (21): {e2020GL090797}. Bibcode:2020GeoRL..4790797S. doi:10.1029/2020GL090797. S2CID   228890686.
    113. Hall, D. T.; Strobel, D. F.; Feldman, P. D.; McGrath, M. A.; Weaver, H. A. (1995). "Detection of an oxygen atmosphere on Jupiter's moon Europa". Nature. 373 (6516): 677–681. Bibcode:1995Natur.373..677H. doi:10.1038/373677a0. PMID   7854447. S2CID   4258306.
    114. Savage, Donald; Jones, Tammy; Villard, Ray (23 February 1995). "Hubble Finds Oxygen Atmosphere on Europa". Project Galileo. NASA, Jet Propulsion Laboratory. Archived from the original on 16 July 2016. Retrieved 17 August 2007.
    115. Water Vapor Was Just Found on Europa, More Evidence There's Liquid Water Beneath All that Ice. Archived 7 December 2019 at the Wayback Machine Evan Gough, Universe Today. 19 November 2019.
    116. NASA Scientists Confirm Water Vapor on Europa. Archived 20 November 2019 at the Wayback Machine Lonnie Shekhtman, NASA News. 18 November 2019.
    117. Paganini, L.; Villanueva, G. L.; Roth, L.; Mandell, A. M.; Hurford, T. A.; Retherford, K. D.; Mumma, M. J. (18 November 2019). "A measurement of water vapour amid a largely quiescent environment on Europa". Nature Astronomy. 4 (3): 266–272. Bibcode:2019NatAs.tmp..489P. doi:10.1038/s41550-019-0933-6. S2CID   210278335.
    118. Kliore, Arvydas J.; Hinson, D. P.; Flasar, F. Michael; Nagy, Andrew F.; Cravens, Thomas E. (July 1997). "The Ionosphere of Europa from Galileo Radio Occultations". Science . 277 (5324): 355–358. Bibcode:1997Sci...277..355K. doi:10.1126/science.277.5324.355. PMID   9219689.
    119. "Galileo Spacecraft Finds Europa has Atmosphere". Project Galileo. NASA, Jet Propulsion Laboratory. 1997. Archived from the original on 27 August 2009. Retrieved 10 August 2007.
    120. Johnson, Robert E.; Lanzerotti, Louis J.; Brown, Walter L. (1982). "Planetary applications of ion induced erosion of condensed-gas frosts". Nuclear Instruments and Methods in Physics Research. 198: 147. Bibcode:1982NucIM.198..147J. doi:10.1016/0167-5087(82)90066-7.
    121. Shematovich, Valery I.; Cooper, John F.; Johnson, Robert E. (April 2003). "Surface-bounded oxygen atmosphere of Europa". EGS – AGU – EUG Joint Assembly (Abstracts from the meeting held in Nice, France): 13094. Bibcode:2003EAEJA....13094S.
    122. Liang, Mao-Chang (2005). "Atmosphere of Callisto". Journal of Geophysical Research. 110 (E2): E02003. Bibcode:2005JGRE..110.2003L. doi:10.1029/2004JE002322. S2CID   8162816.
    123. Smyth, W. H.; Marconi, M. L. (2007). Processes Shaping Galilean Satellite Atmospheres from the Surface to the Magnetosphere. Workshop on Ices. 1357. p. 131. Bibcode:2007LPICo1357..131S.
    124. Chyba, C. F.; Hand, K. P. (2001). "PLANETARY SCIENCE: Enhanced: Life Without Photosynthesis". Science. 292 (5524): 2026–2027. doi:10.1126/science.1060081. PMID   11408649. S2CID   30589825.
    125. 1 2 Hand, Kevin P.; Carlson, Robert W.; Chyba, Christopher F. (December 2007). "Energy, Chemical Disequilibrium, and Geological Constraints on Europa". Astrobiology. 7 (6): 1006–1022. Bibcode:2007AsBio...7.1006H. CiteSeerX . doi:10.1089/ast.2007.0156. PMID   18163875.
    126. Smyth, William H.; Marconi, Max L. (2006). "Europa's atmosphere, gas tori, and magnetospheric implications". Icarus . 181 (2): 510. Bibcode:2006Icar..181..510S. doi:10.1016/j.icarus.2005.10.019.
    127. The Journey to Jupiter: Extended Tours – GEM and the Millennium Mission. Retrieved on 23 July 2013.
    128. "PIA09246: Europa". NASA photojournal. 2 April 2007. Archived from the original on 6 March 2016. Retrieved 9 March 2016.
    129. David, Leonard (7 February 2006). "Europa Mission: Lost In NASA Budget". Archived from the original on 24 December 2010. Retrieved 25 February 2007.
    130. 1 2 3 4 Friedman, Louis (14 December 2005). "Projects: Europa Mission Campaign; Campaign Update: 2007 Budget Proposal". The Planetary Society. Archived from the original on 11 August 2011.
    131. 1 2 Chandler, David L. (20 October 2002). "Thin ice opens lead for life on Europa". New Scientist. Archived from the original on 14 May 2008. Retrieved 27 August 2017.
    132. Muir, Hazel (22 May 2002) Europa has raw materials for life Archived 16 April 2008 at the Wayback Machine , New Scientist.
    133. Ringwald, Frederick A. (29 February 2000) SPS 1020 (Introduction to Space Sciences) Course Notes Archived 25 July 2008 at the Wayback Machine , California State University,
    134. Zabarenko, Deborah (7 March 2011). "Lean U.S. missions to Mars, Jupiter moon recommended". Reuters. Archived from the original on 7 September 2020. Retrieved 5 July 2021.
    135. "Europa Lander". NASA. Archived from the original on 16 January 2014. Retrieved 15 January 2014.
    136. March 2012 OPAG Meeting Archived 3 March 2016 at the Wayback Machine . Lunar and Planetary Institute, NASA. Retrieved on 23 July 2013.
    137. Khan, Amina (15 January 2014). "NASA gets some funding for Mars 2020 rover in federal spending bill". Los Angeles Times. Archived from the original on 21 April 2014. Retrieved 16 January 2014.
    138. Girardot, Frank C. (14 January 2014). "JPL's Mars 2020 rover benefits from spending bill". Pasadena Star-News. Archived from the original on 31 July 2017. Retrieved 15 January 2014.
    139. Selection of the L1 mission Archived 16 October 2015 at the Wayback Machine . ESA, 17 April 2012. (PDF). Retrieved on 23 July 2013.
    140. "JUICE – Science objectives". European Space Agency . 16 March 2012. Archived from the original on 8 June 2013. Retrieved 20 April 2012.
    141. Pappalardo, Robert; Cooke, Brian; Goldstein, Barry; Prockter, Louise; Senske, Dave; Magner, Tom (2013). "The Europa Clipper – OPAG Update" (PDF). JPL/APL. Archived (PDF) from the original on 25 January 2021. Retrieved 13 December 2013.
    142. "NASA's Europa Mission Begins with Selection of Science Instruments". NASA. 26 May 2015. Archived from the original on 5 July 2015. Retrieved 3 July 2015.
    143. Grush, Loren (8 October 2018). "Future spacecraft landing on Jupiter's moon Europa may have to navigate jagged blades of ice". The Verge. Archived from the original on 28 March 2019. Retrieved 16 April 2019.
    144. Guarino, Ben (8 October 2018). "Jagged ice spikes cover Jupiter's moon Europa, study suggests". The Washington Post. Archived from the original on 16 April 2019. Retrieved 15 April 2019.
    145. "Small RPS-Enabled Europa Lander Mission" (PDF). NASA–JPL. 13 February 2005. Archived from the original (PDF) on 8 October 2011.
    146. "NASA and ESA Prioritize Outer Planet Missions". NASA. 2009. Archived from the original on 10 August 2011. Retrieved 26 July 2009.
    147. Rincon, Paul (20 February 2009). "Jupiter in space agencies' sights". BBC News. Archived from the original on 21 February 2009. Retrieved 20 February 2009.
    148. "Cosmic Vision 2015–2025 Proposals". ESA. 21 July 2007. Archived from the original on 25 August 2011. Retrieved 20 February 2009.
    149. 1 2 McKay, C. P. (2002). "Planetary protection for a Europa surface sample return: The Ice Clipper mission". Advances in Space Research. 30 (6): 1601–1605. Bibcode:2002AdSpR..30.1601M. doi:10.1016/S0273-1177(02)00480-5. Archived from the original on 31 July 2020. Retrieved 29 June 2019.
    150. Goodman, Jason C. (9 September 1998) Re: Galileo at Europa Archived 24 January 2012 at WebCite , MadSci Network forums.
    151. 1 2 Berger, Brian; NASA 2006 Budget Presented: Hubble, Nuclear Initiative Suffer Archived 2 June 2009 at the Wayback Machine (7 February 2005)
    152. 1 2 Abelson & Shirley – Small RPS-Enabled Europa Lander Mission (2005). . (PDF). Retrieved on 23 July 2013.
    153. 2012 Europa Mission Studies Archived 3 June 2013 at the Wayback Machine . OPAG 29 March 2012 (PDF). Lunar and Planetary Institute, NASA. Retrieved on 23 July 2013.
    154. Europa Study Team (1 May 2012), "Europa Study 2012 Report" (PDF), Europa Orbiter Mission (PDF), JPL – NASA, archived from the original (PDF) on 2 February 2014, retrieved 17 January 2014
    155. Weiss, P.; Yung, K. L.; Kömle, N.; Ko, S. M.; Kaufmann, E.; Kargl, G. (2011). "Thermal drill sampling system onboard high-velocity impactors for exploring the subsurface of Europa". Advances in Space Research. 48 (4): 743. Bibcode:2011AdSpR..48..743W. doi:10.1016/j.asr.2010.01.015. hdl: 10397/12621 .
    156. Hsu, J. (15 April 2010). "Dual Drill Designed for Europa's Ice". Astrobiology Magazine. Archived from the original on 18 April 2010.
    157. Knight, Will (14 January 2002). "Ice-melting robot passes Arctic test". New Scientist. Archived from the original on 17 March 2008. Retrieved 27 August 2017.
    158. Bridges, Andrew (10 January 2000). "Latest Galileo Data Further Suggest Europa Has Liquid Ocean". Archived from the original on 8 February 2009.
    159. Preventing the Forward Contamination of Europa. National Academy of Sciences Space Studies Board. Washington (DC): National Academy Press. 2000. ISBN   978-0-309-57554-6. Archived from the original on 13 February 2008.
    160. Powell, Jesse; Powell, James; Maise, George; Paniagua, John (2005). "NEMO: A mission to search for and return to Earth possible life forms on Europa". Acta Astronautica. 57 (2–8): 579–593. Bibcode:2005AcAau..57..579P. doi:10.1016/j.actaastro.2005.04.003.
    161. Schulze‐Makuch, Dirk; Irwin, Louis N. (2001). "Alternative energy sources could support life on Europa". Eos, Transactions American Geophysical Union. 82 (13): 150. Bibcode:2001EOSTr..82..150S. doi:10.1029/EO082i013p00150 (inactive 31 October 2021). Archived from the original on 11 January 2020. Retrieved 11 January 2020.CS1 maint: DOI inactive as of October 2021 (link)
    162. Jones, Nicola (11 December 2001). "Bacterial explanation for Europa's rosy glow". New Scientist. Archived from the original on 27 February 2015. Retrieved 26 September 2016.
    163. "Europa's Ocean May Have An Earthlike Chemical Balance",, archived from the original on 18 May 2016, retrieved 18 May 2016
    164. Wall, Mike (9 June 2015). "NASA Aiming for Multiple Missions to Jupiter Moon Europa". Archived from the original on 11 June 2015. Retrieved 10 June 2015.
    165. Phillips, Cynthia (28 September 2006) Time for Europa Archived 25 November 2006 at the Wayback Machine ,
    166. Wilson, Colin P. (March 2007). Tidal Heating on Io and Europa and its Implications for Planetary Geophysics. Northeastern Section - 42nd Annual Meeting. Archived from the original on 5 September 2008. Retrieved 21 December 2007.
    167. 1 2 Marion, Giles M.; Fritsen, Christian H.; Eicken, Hajo; Payne, Meredith C. (2003). "The Search for Life on Europa: Limiting Environmental Factors, Potential Habitats, and Earth Analogues". Astrobiology. 3 (4): 785–811. Bibcode:2003AsBio...3..785M. doi:10.1089/153110703322736105. PMID   14987483. S2CID   23880085.
    168. Richard Greenberg (May 2010). "Transport Rates of Radiolytic Substances into Europa's Ocean: Implications for the Potential Origin and Maintenance of Life". Astrobiology. 10 (3): 275–283. Bibcode:2010AsBio..10..275G. doi:10.1089/ast.2009.0386. PMID   20446868.
    169. NASA – Mapping the Chemistry Needed for Life at Europa. Archived 8 April 2013 at the Wayback Machine . (4 April 2013). Retrieved on 23 July 2013.
    170. 1 2 Cook, Jia-Rui C. (11 December 2013). "Clay-Like Minerals Found on Icy Crust of Europa". NASA . Archived from the original on 30 January 2020. Retrieved 11 December 2013.
    171. Choi, Charles Q. (8 December 2013). "Life Could Have Hitched a Ride to Outer Planet Moons". Astrobiology Magazine. Astrobiology Web. Archived from the original on 12 December 2013. Retrieved 12 December 2013.

    Further reading