A distant asteroid trailing within the gravitational wake of Mars has been observed in greater detail than ever before, and therefore the close-up reveals a surprising resemblance – one that raises some interesting questions about the object’s ancient origins.
The asteroid in question, called (101429) 1998 VF31, is a component of a bunch of trojan asteroids sharing the orbit of Mars.
Trojans are celestial bodies that constitute gravitationally balanced regions of space within the vicinity of other planets, located 60 degrees before and behind the world.
Most of the trojan asteroids we all know about share Jupiter’s orbit, but other planets have them too, including Mars and Earth too.
What makes (101429) 1998 VF31 (hereafter ‘101429’) interesting is that among the Red Planet’s trailing trojans (the ones that follow behind Mars because it orbits the Sun), 101429 appears to be unique.
Depiction of Mars and trojans; 101429 is the blue point circling L5. (AOP)
The rest of the group, called the L5 Martian Trojans, all belong to what’s called the Eureka family, consisting of 5261 Eureka – the primary Mars trojan discovered – and a bunch of small fragments believed to own come loose from their parent space rock.
101429 is different, though, and in an exceedingly new study led by astronomers from the Armagh Observatory and Planetarium (AOP) in European countries, researchers wanted to look at why.
Using a spectrograph called X-SHOOTER on the EU Southern Observatory’s 8-m Very Large Telescope (VLT) in Chile, the team examined how sunlight reflects off 101429 and its L5 kin within the Eureka family. Only, it’s like 101429 and also the Eureka clan aren’t kin in spite of everything, with the analysis revealing 101429 shows a spectral match for a satellite much closer to home.
“The spectrum of this particular asteroid seems to be almost a dead-ringer for parts of the Moon where there’s exposed bedrock like crater interiors and mountains,” explains AOP astrochemist Galin Borisov.
While we won’t make certain yet why that’s, the researchers say it’s plausible that this Martian trojan’s origins began somewhere far from Mars, with 101429 representing a “relic fragment of the Moon’s original solid crust”.
If that’s true, how did the Moon’s long-lost twin find yourself as a trojan bound along with Mars?
Spectral comparison of 101429 and the Moon’s surface. (AOP
“The early system was very different from the place we see today,” explains lead author of the study, AOP astronomer Apostolos Christou.
“The space between the newly-formed planets was filled with debris and collisions were commonplace. Large asteroids [planetesimals] were constantly hitting the Moon and therefore the other planets. A shard from such a collision could have reached the orbit of Mars when the earth was still forming and was trapped in its Trojan clouds.”
It’s a captivating idea, but the researchers say it is not the sole explanation for 101429’s past. it is also possible, and maybe more likely, that the trojan instead represents a fraction of Mars chipped off by an identical quite incident impacting the Red Planet; or it would just be a commonplace asteroid that, through the weathering processes of radiation, ended up looking a bit like the Moon.
Further observations with even more powerful spectrographs may be able to shed more light on this question of space parentage, as could a future spacecraft visit, the team says, “which could, on the way to the Trojans, obtain spectra at Mars or the Moon for direct comparison with the asteroid data”.