2008 EV5 started its existence as part of a much larger body in the asteroid belt, with a likely diameter greater than 100 kilometers.[13]2008 EV5's immediate history likely started when its parent body experienced a large cratering event or, more likely, a catastrophic disruption event that resulted in a highly fractured, shattered, or reaccumulated object (rubble pile). As a result, 2008 EV5 may have been produced as a reassembly of ejected fragments. The location of what is now 2008 EV5 within this parent body is unknown.[14]
Given the available modeling work and data, the most plausible source family candidates for 2008 EV5 are Eulalia, New Polana, and Erigone. This assumes that 2008 EV5's true albedo is considerably lower than 10%. If it does have a high albedo, a plausible source would be a population of high-albedo C-type asteroids in the inner asteroid belt. Second tier candidate families for the high-albedo case are Baptistina and Pallas.[14]
From here, the newly liberated 2008 EV5 began to change via the forces referred to as the Yarkovsky and YORP effects. The Yarkovsky effect describes a small force that affects orbital motion. It is caused by sunlight; when objects heat up in the Sun, they reradiate the energy away as heat, which in turn creates a tiny thrust. This recoil acceleration is much weaker than solar and planetary gravitational forces, but it can produce substantial orbital changes over timescales ranging from many millions to billions of years. The same physical phenomenon also creates a thermal torque that probably caused 2008 EV5 to take on a top-like appearance.[3][14][15]
Dynamical models indicate that 2008 EV5 migrated inward across the inner asteroid belt over long timescales (i.e. the order of ~0.01–1 Gyr) until it reached a planetary gravitational resonance that drove it into the near-Earth asteroid (NEA) population over a timescale of the order of ~1 Myr. From there, gravitational interactions with both the planets and resonances allowed it to reach its current orbit within a few Myr to a few tens of Myr.[14]
Close approaches
On 23 December 2008, 2008 EV5 made a close approach to Earth at a distance of 8.4 lunar distances (0.022 AU, 3.2 million km), its closest until 2169.[3] Its brightness peaked on 26 December about 13.2 magnitude.
2008 Path of 2008 EV5 close approach, with 3 day motion markers
2008 EV5 is an oblate spheroid (also described as "muffin-shaped"[17])
400 m (1,300 ft) in diameter. It rotates very slowly in a retrograde direction. There is a 150 m (490 ft) diameter concave feature, possibly an impact crater, or a relic feature from a previous episode of rapid rotation that caused the asteroid's shape to reconfigure.[3]
Visible and near-infrared spectroscopy show that 2008 EV5's composition is similar to that of carbonaceous chondrite meteorites.[12]
Proposed sample return mission
2008 EV5 was the preliminary baseline target of NASA's proposed sample-returnAsteroid Redirect Mission. Besides 2008 EV5, several other asteroids, including Itokawa and Bennu, were considered for this mission,[18][19] before its cancellation in 2017.
^Skiff, Brian A.; Bowell, Edward; Koehn, Bruce W.; Sanborn, Jason J.; McLelland, Kyle P.; Warner, Brian D. (July 2012). "Lowell Observatory Near-Earth Asteroid Photometric Survey (NEAPS) - 2008 May through 2008 December". The Minor Planet Bulletin. 39 (3): 111–130. Bibcode:2012MPBu...39..111S. ISSN1052-8091.
^Galad, Adrian; Vilagi, Jozef; Kornos, Leonard; Gajdos, Stefan (July 2009). "Relative Photometry of Nine Asteroids from Modra". The Minor Planet Bulletin. 36 (3): 116–118. Bibcode:2009MPBu...36..116G. ISSN1052-8091.
