In modern times, numerous impact events on Mars have been detected. Although most have been inferred from the appearance of new impact craters on the planet, some have corresponded to marsquakes felt by the InSight lander. [1] To date, no impacting meteors have been directly observed as a fireball or discovered in space before impact.
As the best-explored planet in the Solar System (after Earth), Mars has been continuously explored by various spacecraft, landers, and rovers since 1997. The first probe to image Mars's surface in detail was Mariner 4 in 1965, and Mariner 9 became the first probe to orbit Mars in 1971. However, few early probes were able to image Mars in high enough resolution to detect new impact craters, which are typically less than 10 meters (33 ft) across. [2] Early probes reached resolutions of 790 meters (2,590 ft), while Mariner 9 was able to reach 98 meters (322 ft). [3] From 1976 to 1982, Viking 1 and Viking 2 imaged all of Mars at 150 meters (490 ft) resolution, with some areas imaged in up to 8 meters (26 ft) resolution. [4]
The Mars Global Surveyor , active from 1997 to 2006, was the first spacecraft able to image Mars in high enough resolution to detect new impacts, with a resolution of up to 1.5 meters (4.9 ft). The first detected impact, a 14.4-meter (47 ft)-diameter crater in southern Lucus Planum, happened between 27 January 2000, and 19 March 2001. [2] Since then, over 1,200 new impact craters have been found on Mars with 2001 Mars Odyssey , Mars Express , and Mars Reconnaissance Orbiter , over 1,100 of which were found by the last. [2]
Unlike on Earth, most impact craters on Mars come in clusters, caused by the meteor partially fragmenting before impact. [5] Due to Mars's tenuous atmosphere, with just 0.6% the surface pressure of Earth's, incoming meteors are much less prone to breaking up. [6] while a 10-meter (33 ft) asteroid falling over Earth is unlikely to reach the surface intact before being destroyed in a meteor air burst, [7] a 10-meter (33 ft) asteroid falling over Mars may leave a crater over 100 meters (330 ft) across, [8] or several smaller craters tens of meters across. [9]
There is significant observation bias in the locations of discovered impact craters: certain locations on Mars are of much more geological interest, and so are imaged more frequently and in detail than less notable ones. [5] Additionally, many new craters are first noticed by their 'blast zone' of ejecta, which can be 10-100 times the size of the crater itself. [5] However, only certain regions of Mars have subsurface material that can be ejected to create these features; in particular, the Tharsis rise, Olympus Mons, Elysium Mons, and Arabia Terra. As a result, very few impacts have been detected outside of these regions, despite impacts in theory happening randomly across the planet. [5]
Despite these biases, the existing observations of new Martian impacts suggest that asteroids of a given size impacting the planet are about 3 times more common than on Earth and the Moon, [10] with roughly 240 4-meter (13 ft) craters and one to seven 30-meter (98 ft) craters forming each year [11] (compared to the observed ~0.8). Larger impactors also seem to be more relatively frequent than on Earth or the Moon (i.e. the size-frequency distribution slope is shallower). [12] If this holds true for larger asteroid sizes, this suggests that Mars may be in a modern impact surge, [12] although atmospheric deceleration of small asteroids might explain the unexpectedly shallow slope, which would become more consistent with predictions for larger asteroids. [12]
The following is a list of detected impact events with a crater size of >15 meters, which excludes most meteoroid impacts (<1 meter asteroids). 10-15 meter craters discovered before 2010 are also included, before the rate of discovering such craters became dozens per year.
An asteroid is a minor planet—an object that is neither a true planet nor a comet—that orbits within the inner Solar System. They are rocky, metallic or icy bodies with no atmosphere. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter.
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's orbit, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets.
A meteoroid is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than meteoroids are classified as micrometeoroids or space dust. Most are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars.
An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effect. When large objects impact terrestrial planets such as the Earth, there can be significant physical and biospheric consequences, though atmospheres mitigate many surface impacts through atmospheric entry. Impact craters and structures are dominant landforms on many of the Solar System's solid objects and present the strongest empirical evidence for their frequency and scale.
3200 Phaethon, provisionally designated 1983 TB, is an active Apollo asteroid with an orbit that brings it closer to the Sun than any other named asteroid. For this reason, it was named after the Greek myth of Phaëthon, son of the sun god Helios. It is 5.8 km (3.6 mi) in diameter and is the parent body of the Geminids meteor shower of mid-December. With an observation arc of 35+ years, it has a very well determined orbit. The 2017 Earth approach distance of about 10 million km was known with an accuracy of ±700 m.
High Resolution Imaging Science Experiment is a camera on board the Mars Reconnaissance Orbiter which has been orbiting and studying Mars since 2006. The 65 kg (143 lb), US$40 million instrument was built under the direction of the University of Arizona's Lunar and Planetary Laboratory by Ball Aerospace & Technologies Corp. It consists of a 0.5 m (19.7 in) aperture reflecting telescope, the largest so far of any deep space mission, which allows it to take pictures of Mars with resolutions of 0.3 m/pixel, resolving objects below a meter across.
A marsquake is a quake which, much like an earthquake, would be a shaking of the surface or interior of the planet Mars as a result of the sudden release of energy in the planet's interior, such as the result of plate tectonics, which most quakes on Earth originate from, or possibly from hotspots such as Olympus Mons or the Tharsis Montes. The detection and analysis of marsquakes could be informative to probing the interior structure of Mars, as well as identifying whether any of Mars's many volcanoes continue to be volcanically active.
2007 WD5 is an Apollo asteroid some 50 m (160 ft) in diameter and a Mars-crosser asteroid first observed on 20 November 2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD5 caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on 30 January 2008. However, by 9 January 2008, additional observations allowed NASA's Near Earth Object Program (NEOP) to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact. 2007 WD5 most likely passed Mars at a distance of 6.5 Mars radii. Due to this relatively small distance and the uncertainty level of the prior observations, the gravitational effects of Mars on its trajectory are unknown and, according to Steven Chesley of NASA's Jet Propulsion Laboratory Near-Earth Object program, 2007 WD5 is currently considered 'lost' (see lost asteroids).
65803 Didymos is a sub-kilometer asteroid and binary system that is classified as a potentially hazardous asteroid and near-Earth object of the Apollo group. The asteroid was discovered in 1996 by the Spacewatch survey at Kitt Peak, and its small 160-meter minor-planet moon, named Dimorphos, was discovered in 2003. Due to its binary nature, the asteroid was then named Didymos, the Greek word for 'twin'.
2008 TC3 (Catalina Sky Survey temporary designation 8TA9D69) was an 80-tonne (80-long-ton; 90-short-ton), 4.1-meter (13 ft) diameter asteroid that entered Earth's atmosphere on October 7, 2008. It exploded at an estimated 37 kilometers (23 mi) above the Nubian Desert in Sudan. Some 600 meteorites, weighing a total of 10.5 kilograms (23.1 lb), were recovered; many of these belonged to a rare type known as ureilites, which contain, among other minerals, nanodiamonds.
(214869) 2007 PA8 is an asteroid and slow rotator, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 1.4 kilometers in diameter.
C/2013 A1 is an Oort cloud comet discovered on 3 January 2013 by Robert H. McNaught at Siding Spring Observatory using the 0.5-meter (20 in) Uppsala Southern Schmidt Telescope.
2014 AA was a small Apollo near-Earth asteroid roughly 2–4 meters in diameter that struck Earth on 2 January 2014. It was discovered on 1 January 2014 by Richard Kowalski at the Mount Lemmon Survey at an apparent magnitude of 19 using a 1.52-meter (60 in) reflecting telescope at Mount Lemmon Observatory. 2014 AA was only observed over a short observation arc of about 70 minutes, and entered Earth's atmosphere about 21 hours after discovery. Nonetheless, it remains one of only a few asteroids observed before impact.
2004 TN1 is a sub-kilometer near-Earth asteroid and potentially hazardous object of the Apollo group, approximately 180 meters (600 ft) in diameter. It was first observed by the Near-Earth Asteroid Tracking at Palomar Observatory on 5 October 2004. The asteroid has a notably low sub-lunar Earth-MOID of 0.38 LD. As of 2019, it has only been observed in Fall 2004.
2015 TB145 is a sub-kilometer asteroid, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 650 meters (2,000 feet) in diameter. It safely passed 1.27 lunar distances from Earth on 31 October 2015 at 17:01 UTC, and passed by Earth again in November 2018.
2013 TX68 is an Apollo asteroid and near-Earth object discovered on 6 October 2013 by the Catalina Sky Survey, during which it was near a close approach of 5.4 Lunar distances (LD) from the Earth. The asteroid only has a 10-day observation arc which makes long-term predictions of its position less certain. It was observed for three days as it approached Earth in the night sky starting with the sixth of October, 2013. Then it became unobservable by being between the Earth and the Sun, then not recovered due to its small size and dimness. Precovery images by Pan-STARRS from 29 September 2013 were announced on 11 February 2016 that extended the observation arc to 10 days. It was removed from the Sentry Risk Table on 11 February 2016, so there is no risk of impact from this object for the next hundred years or more. The asteroid was last observed on 9 October 2013.
2019 OK is a near-Earth asteroid noted for its sudden, surprise discovery on the day before its close flyby in 2019. The object's size is estimated at 57 to 130 metres across, the closest asteroid of such size discovered in 2019. It is uncommon for asteroids of this moderately large size to pass within 100,000 km (62,000 mi) of Earth.
Dimorphos is a natural satellite or moon of the near-Earth asteroid 65803 Didymos, with which it forms a binary system. The moon was discovered on 20 November 2003 by Petr Pravec in collaboration with other astronomers worldwide. Dimorphos has a diameter of 177 meters (581 ft) across its longest extent and it was the target of the Double Asteroid Redirection Test (DART), a NASA space mission that deliberately collided a spacecraft with the moon on 26 September 2022 to alter its orbit around Didymos. Before the impact by DART, Dimorphos had a shape of an oblate spheroid with a surface covered in boulders but virtually no craters. The moon is thought to have formed when Didymos shed its mass due to its rapid rotation, which formed an orbiting ring of debris that conglomerated into a low-density rubble pile that became Dimorphos today.
In modern times, numerous impact events on Jupiter have been observed, the most significant of which was the collision of Comet Shoemaker–Levy 9 in 1994. Jupiter is the most massive planet in the Solar System and thus has a vast sphere of gravitational influence, the region of space where an asteroid capture can take place under favorable conditions.
It was the first spacecraft to enter orbit around another world. ... [It] continues to orbit Mars to this day, sailing around the planet deaf and dumb in the cold darkness.
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