Discovery | |
---|---|
Discovered by | Karl Ludwig Harding |
Discovery date | 1 September 1804 |
Designations | |
(3) Juno | |
Pronunciation | /ˈdʒuːnoʊ/ JOO-noh [1] |
Named after | Juno (Latin: Iūno) |
Main belt (Juno clump) | |
Adjectives | Junonian /dʒuːˈnoʊniən/ [2] |
Symbol | (historically astronomical, now astrological) |
Orbital characteristics [3] | |
Epoch 13 September 2023 (JD 2453300.5) | |
Aphelion | 3.35 AU (501 million km) |
Perihelion | 1.985 AU (297.0 million km) |
2.67 AU (399 million km) | |
Eccentricity | 0.2562 |
4.361 yr | |
Average orbital speed | 17.93 km/s |
37.02° | |
Inclination | 12.991° |
169.84° | |
2 April 2023 | |
247.74° | |
Earth MOID | 1.04 AU (156 million km) |
Proper orbital elements [4] | |
Proper semi-major axis | 2.6693661 AU |
Proper eccentricity | 0.2335060 |
Proper inclination | 13.2515192° |
Proper mean motion | 82.528181 deg / yr |
Proper orbital period | 4.36215 yr (1593.274 d) |
Precession of perihelion | 43.635655 arcsec / yr |
Precession of the ascending node | −61.222138 arcsec / yr |
Physical characteristics | |
Dimensions | (288 × 250 × 225) ± 5 km [5] (320 × 267 × 200) ± 6 km [6] |
254±2 km [5] 246.596±10.594 km [3] | |
Mass | (2.7±0.24)×1019 kg [5] (2.86±0.46)×1019 kg [7] [lower-alpha 1] |
Mean density | 3.15±0.28 g/cm3 [5] 3.20±0.56 g/cm3 [7] |
Equatorial surface gravity | 0.112 m/s2 (0.0114 g0) |
Equatorial escape velocity | 0.168 km/s |
7.21 hr [3] (0.3004 d) [8] | |
Equatorial rotation velocity | 31.75 m/s [lower-alpha 2] |
Pole ecliptic latitude | 27° ± 5° [9] |
Pole ecliptic longitude | 103° ± 5° [9] |
0.202 [5] 0.238 [3] [10] | |
Temperature | ~163 K max: 301 K (+28°C) [11] |
S [3] [12] | |
7.4 [13] [14] to 11.55 | |
5.33 [3] [10] | |
0.30" to 0.07" | |
Juno (minor-planet designation: 3 Juno) is a large asteroid in the asteroid belt. Juno was the third asteroid discovered, in 1804, by German astronomer Karl Harding. [15] It is one of the twenty largest asteroids and one of the two largest stony (S-type) asteroids, along with 15 Eunomia. It is estimated to contain 1% of the total mass of the asteroid belt. [16]
Juno was discovered on 1 September 1804, by Karl Ludwig Harding. [17] It was the third asteroid found, but was initially considered to be a planet; it was reclassified as an asteroid and minor planet during the 1850s. [18]
Juno is named after the mythological Juno, the highest Roman goddess. The adjectival form is Junonian (from Latin jūnōnius), with the historical final n of the name (still seen in the French form, Junon) reappearing, analogous to Pluto ~ Plutonian. [2] 'Juno' is the international name for the asteroid, subject to local variation: Italian Giunone, French Junon, Russian Юнона (Yunona), etc. [lower-alpha 3]
The old astronomical symbol of Juno, still used in astrology, is a scepter topped by a star, ⟨ ⟩. There were many graphic variants with a more elaborated scepter, such as , sometimes tilted at an angle to provide more room for decoration. The generic asteroid symbol of a disk with its discovery number, ⟨③⟩, was introduced in 1852 and quickly became the norm. [19] [20] The scepter symbol was resurrected for astrological use in 1973. [21]
Juno is one of the larger asteroids, perhaps tenth by size and containing approximately 1% the mass of the entire asteroid belt. [22] It is the second-most-massive S-type asteroid after 15 Eunomia. [6] Even so, Juno has only 3% the mass of Ceres. [6] The orbital period of Juno is 4.36578 years. [23]
Amongst S-type asteroids, Juno is unusually reflective, which may be indicative of distinct surface properties. This high albedo explains its relatively high apparent magnitude for a small object not near the inner edge of the asteroid belt. Juno can reach +7.5 at a favourable opposition, which is brighter than Neptune or Titan, and is the reason for it being discovered before the larger asteroids Hygiea, Europa, Davida, and Interamnia. At most oppositions, however, Juno only reaches a magnitude of around +8.7 [24] —only just visible with binoculars—and at smaller elongations a 3-inch (76 mm) telescope will be required to resolve it. [25] It is the main body in the Juno family.
Juno was originally considered a planet, along with 1 Ceres, 2 Pallas, and 4 Vesta. [26] In 1811, Schröter estimated Juno to be as large as 2290 km in diameter. [26] All four were reclassified as asteroids as additional asteroids were discovered. Juno's small size and irregular shape preclude it from being designated a dwarf planet.
Juno orbits at a slightly closer mean distance to the Sun than Ceres or Pallas. Its orbit is moderately inclined at around 12° to the ecliptic, but has an extreme eccentricity, greater than that of Pluto. This high eccentricity brings Juno closer to the Sun at perihelion than Vesta and further out at aphelion than Ceres. Juno had the most eccentric orbit of any known body until 33 Polyhymnia was discovered in 1854, and of asteroids over 200 km in diameter only 324 Bamberga has a more eccentric orbit. [27]
Juno rotates in a prograde direction with an axial tilt of approximately 50°. [9] The maximum temperature on the surface, directly facing the Sun, was measured at about 293 K on 2 October 2001. Taking into account the heliocentric distance at the time, this gives an estimated maximum temperature of 301 K (+28 °C) at perihelion. [11]
Spectroscopic studies of the Junonian surface permit the conclusion that Juno could be the progenitor of chondrites, a common type of stony meteorite composed of iron-bearing silicates such as olivine and pyroxene. [28] Infrared images reveal that Juno possesses an approximately 100 km-wide crater or ejecta feature, the result of a geologically young impact. [29] [30]
Based on MIDAS infrared data using the Hale Telescope, an average radius of 135.7±11 was reported in 2004. [31]
Juno was the first asteroid for which an occultation was observed. It passed in front of a dim star (SAO 112328) on 19 February 1958. Since then, several occultations by Juno have been observed, the most fruitful being the occultation of SAO 115946 on 11 December 1979, which was registered by 18 observers. [32] Juno occulted the magnitude 11.3 star PPMX 9823370 on 29 July 2013, [33] and 2UCAC 30446947 on 30 July 2013. [34]
Radio signals from spacecraft in orbit around Mars and on its surface have been used to estimate the mass of Juno from the tiny perturbations induced by it onto the motion of Mars. [35] Juno's orbit appears to have changed slightly around 1839, very likely due to perturbations from a passing asteroid, whose identity has not been determined. [36]
In 1996, Juno was imaged by the Hooker Telescope at Mount Wilson Observatory at visible and near-IR wavelengths, using adaptive optics. The images spanned a whole rotation period and revealed an irregular shape and a dark albedo feature, interpreted as a fresh impact site. [30]
Juno reaches opposition from the Sun every 15.5 months or so, with its minimum distance varying greatly depending on whether it is near perihelion or aphelion. Sequences of favorable oppositions occur every 10th opposition, i.e. just over every 13 years. The last favorable oppositions were on 1 December 2005, at a distance of 1.063 AU, magnitude 7.55, and on 17 November 2018, at a minimum distance of 1.036 AU, magnitude 7.45. [37] [38] The next favorable opposition will be 30 October 2031, at a distance of 1.044 AU, magnitude 7.42.
Vesta is one of the largest objects in the asteroid belt, with a mean diameter of 525 kilometres (326 mi). It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, the virgin goddess of home and hearth from Roman mythology.
Pallas is the third-largest asteroid in the Solar System by volume and mass. It is the second asteroid to have been discovered, after Ceres, and is likely a remnant protoplanet. Like Ceres, it is believed to have a mineral composition similar to carbonaceous chondrite meteorites, though significantly less hydrated than Ceres. It is 79% the mass of Vesta and 22% the mass of Ceres, constituting an estimated 7% of the mass of the asteroid belt. Its estimated volume is equivalent to a sphere 507 to 515 kilometers in diameter, 90–95% the volume of Vesta.
The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids or minor planets. The identified objects are of many sizes, but much smaller than planets, and, on average, are about one million kilometers apart. This asteroid belt is also called the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System.
9 Metis is one of the larger main-belt asteroids. It is composed of silicates and metallic nickel-iron, and may be the core remnant of a large asteroid that was destroyed by an ancient collision. Metis is estimated to contain just under half a percent of the total mass of the asteroid belt.
10 Hygiea is a major asteroid located in the main asteroid belt. With a mean diameter of between 425 and 440 km and a mass estimated to be 3% of the total mass of the belt, it is the fourth-largest asteroid in the Solar System by both volume and mass, and is the largest of the C-type asteroids in classifications that use G type for 1 Ceres. It is very close to spherical, apparently because it had re-accreted after the disruptive impact that produced the large Hygiean family of asteroids.
15 Eunomia is a very large asteroid in the middle asteroid belt. It is the largest of the stony (S-type) asteroids, with 3 Juno as a close second. It is quite a massive asteroid, in 6th to 8th place. It is the largest Eunomian asteroid, and is estimated to contain 1% of the mass of the asteroid belt.
63 Ausonia is a stony Vestian asteroid from the inner region of the asteroid belt, approximately 100 kilometers in diameter. It was discovered by Italian astronomer Annibale de Gasparis on 10 February 1861, from the Astronomical Observatory of Capodimonte, in Naples, Italy. The initial choice of name for the asteroid was "Italia", after Italy, but this was modified to Ausonia, an ancient classical name for the Italian region.
96 Aegle is a carbonaceous asteroid and the namesake of the Aegle family located in the outer regions of the asteroid belt, approximately 170 kilometers in diameter. It was discovered on 17 February 1868, by French astronomer Jérôme Coggia at the Marseille Observatory in southeastern France. The rare T-type asteroid has a rotation period of 13.8 hours and has been observed several times during occultation events. It was named after Aegle ("brightness"), one of the Hesperides from Greek mythology.
704 Interamnia is a large F-type asteroid. With a mean diameter of around 330 kilometres, it is the fifth-largest asteroid, after Ceres, Vesta, Pallas and Hygiea. Its mean distance from the Sun is 3.067 AU. It was discovered on 2 October 1910 by Vincenzo Cerulli, and named after the Latin name for Teramo, Italy, where Cerulli worked. Its mass is probably between fifth and tenth highest in the asteroid belt, with a mass estimated to be 1.2% of the mass of the entire asteroid belt. Observations by the Very Large Telescope's SPHERE imager in 2017–2019, combined with occultation results, indicate that the shape of Interamnia may be consistent with hydrostatic equilibrium for a body of its density with a rotational period of 7.6 hours. This suggests that Interamnia may have formed as an equilibrium body, and that impacts changed its rotational period after it fully solidified.
324 Bamberga is one of the largest asteroids in the asteroid belt. It was discovered by Johann Palisa on 25 February 1892 in Vienna. It is one of the top-20 largest asteroids in the asteroid belt. Apart from the near-Earth asteroid Eros, it was the last asteroid which is ever easily visible with binoculars to be discovered.
1743 Schmidt, provisional designation 4109 P-L, is a dark background asteroid from the inner regions of the asteroid belt, approximately 19 kilometers in diameter. It was discovered during the Palomar–Leiden survey on 24 September 1960, by astronomers Ingrid and Cornelis van Houten at Leiden, on photographic plates taken by Tom Gehrels at Palomar Observatory in California. The C-type asteroid has a rotation period of 17.5 hours. It was named for the optician Bernhard Schmidt.
921 Jovita is a dark background asteroid, approximately 58 kilometers in diameter, located in the outer regions of the asteroid belt. It was discovered on 4 September 1919, by astronomer Karl Reinmuth at the Heidelberg-Königstuhl State Observatory in southwest Germany. The carbonaceous C-type asteroid (Ch) has a rotation period of 15.6 hours and is likely spherical in shape. It was named "Jovita", a common German female name unrelated to the discoverer's contemporaries, that was taken from the almanac Lahrer Hinkender Bote.
956 Elisa is a Flora asteroid from the inner regions of the asteroid belt, approximately 10.5 kilometers in diameter. It was discovered on 8 August 1921, by German astronomer Karl Reinmuth at the Heidelberg Observatory. The V-type asteroid has a rotation period of 16.5 hours. It was named after Elisa Reinmuth, mother of the discoverer.
Ceres is a dwarf planet in the middle main asteroid belt between the orbits of Mars and Jupiter. It was the first known asteroid, discovered on 1 January 1801 by Giuseppe Piazzi at Palermo Astronomical Observatory in Sicily, and announced as a new planet. Ceres was later classified as an asteroid and then a dwarf planet, the only one not beyond Neptune's orbit.
1143 Odysseus, provisional designation 1930 BH, is a large Jupiter trojan located in the Greek camp of Jupiter's orbit. It was discovered on 28 January 1930, by German astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany, and later named after Odysseus, the legendary hero from Greek mythology. The dark D-type asteroid has a rotation period of 10.1 hours. With a diameter of approximately 125 kilometers, it is among the 10 largest Jovian trojans.
1030 Vitja, provisional designation 1924 RQ, is a dark background asteroid from the outer regions of the asteroid belt, approximately 60 kilometers in diameter. It was discovered on 25 May 1924, by Soviet–Russian astronomer Vladimir Albitsky at the Simeiz Observatory on the Crimean peninsula. The asteroid was named in honor of Viktor Zaslavskij (1925–1944), a relative of the discoverer.
1929 Kollaa, provisional designation 1939 BS, is a stony Vestian asteroid from the inner regions of the asteroid belt, approximately 7 kilometers in diameter. It was discovered by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland, on 20 January 1939. The asteroid was named after the Kollaa River in what is now Russia.
4383 Suruga, provisional designation 1989 XP, is a Vestian asteroid and binary system from the inner regions of the asteroid belt, approximately 6.5 kilometers in diameter. It was discovered on 1 December 1989, by Japanese astronomer Yoshiaki Oshima at Gekko Observatory, Japan. The asteroid was named after the former Japanese Suruga Province. Its synchronous minor-planet moon, S/2013 (4383) 1, measures approximately 1.33 kilometers and has a period of 16.386 hours.
6257 Thorvaldsen, provisional designation 4098 T-1, is a bright Vestian asteroid from the inner regions of the asteroid belt, approximately 4.3 kilometers in diameter. It was discovered during the Palomar–Leiden Trojan survey on 26 March 1971, by Ingrid and Cornelis van Houten at Leiden, and Tom Gehrels at Palomar Observatory in California. The asteroid was named for Danish sculptor Bertel Thorvaldsen.