On May 10th, 2018 we learned about

Evidence related to the early days of our solar system found in an out-of-place asteroid

Found: Lost asteroid, spotted in the Kuiper belt, past Pluto

No collar or leash, but answers to the name 2004 EW95, and spots of  ferric oxides and phyllosilicates seem to be from asteroid belt near Mars. Please contact the Astrophysics Research Centre at the Queen’s University Belfast, UK if it’s yours.

Identifying an errant asteroid

Obviously, nobody is likely to respond to the above, because among other factors, nobody knew this asteroid was missing. When astronomers found the carbon-rich rock in the darkness of the Kuiper belt, they weren’t even sure of what they were seeing, as very little light can really be reflected off an 186-mile-long object 2,788,674,218 miles from the Sun. Still, it a wider range of light than its neighboring pieces of ice and rock, which is why researchers started to suspect that it wasn’t originally from that part of the solar system.

Most asteroids in the Kuiper belt are rather dull to look at. They don’t offer much variation in the frequencies of light they reflect off their surfaces. 2004 EW95, on the other hand, reflected light spectra consistent with  ferric oxides and phyllosilicates, minerals that would have originated closer to the Sun when our solar system was forming. Subsequent observations and careful analysis eventually confirmed this composition, strongly indicating that 2004 EW95 had been formed in the asteroid belt, not the Kuiper belt.

Launched by planets on the loose

This then raises the question of how this particular asteroid would have ended up so far from home, although that’s a question astronomers are happy to answer. Multiple models of the formation of our solar system include a period of time when the gas giant planets, like Saturn and Jupiter, were not in stable orbits around the Sun. The extreme mass and therefore gravity of these planets would have shoved and smashed smaller objects around them, possibly even clearing the inner solar system of many of the asteroids that were once closer to the Sun. If these models were true, it would be likely that some objects would have been launched by the gas giants’ gravity into deeper space. So the likely relocation of 2004 EW95 in the Kuiper belt is the first direct evidence to support these models.

Since Jupiter, Saturn and Uranus now have more stable orbits, 2004 EW95 probably won’t get pulled back to the asteroid belt any time soon. However, it may not be too lonely (do asteroids get lonely?) as astronomers have spotted other rocks that probably immigrated to the Kuiper belt before. However, the size, distance and darkness make confirming an asteroid’s composition difficult, which is why 2004 EW95 is the first time we’ve been able to more thoroughly vet what one of these lost rocks was made of.

Source: Exiled asteroid discovered in outer reaches of solar system, EurekAlert!

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