The distant asteroid following Mars' gravitational trail has been observed in more detail than ever before, and the close-up reveals a surprising similarity that raises some interesting questions about the object's origin.
The asteroid in question, named (101429) 1998 VF31, is part of a group of Trojan asteroids orbiting Mars.
Trojans are celestial bodies that fall into gravitationally balanced regions of space near other planets 60 degrees in front of and behind the planet.
Most of the Trojan asteroids we know are in orbit around Jupiter, but other planets, including Mars and Earth, also have them.
What makes (101429) 1998 VF31 interesting is that among the closing Trojans of the Red Planet (the ones that follow Mars as it orbits the Sun), 1998 VF31 seems unique.
The rest of the group, called the L5 Martian Trojans, belongs to the so-called Eureka family, consisting of 5261 Eureka – the first Martian Trojan to be discovered – and a group of small fragments believed to have broken off from a larger cosmic rock.
However, 1998 VF31 is different, and in a new study by astronomers at the Armagh Observatory and Planetarium (AOP) in Northern Ireland, researchers wanted to find out why.
Image of Mars and Trojans; 1998 VF31- blue dot circled around L5. (AOP)
Using a spectrograph called X-SHOOTER at the European Southern Observatory's Very Large Telescope (VLT) in Chile, the team investigated how sunlight reflects off 1998 VF31 and its L5 cousins in the Eureka family. Only it looks like 1998 VF31 and the Eureka clan are not at all related, analysis shows that 1998 VF31 shows spectral coincidence for a satellite much closer to home.
“The spectrum of this particular asteroid seems almost accurate for those parts of the Moon where there are exposed bedrocks, such as craters and mountains,” explains AOP astrochemist Galin Borisov.
While we still cannot be sure why this is so, the researchers believe it plausible that the origin of this Martian Trojan began somewhere far from the Red Planet, and 1998 VF31 is a 'relict fragment of the original solid crust of the Moon'.
If so, how did the Moon's long-lost twin end up as a Trojan associated with Mars?
“The early solar system was very different from what we see today,” explains the study's lead author, astronomer AOP Apostolos Christou.
'The space between the newly formed planets was full of debris and collisions were common. Large asteroids [planetesimals] constantly hit the Moon and other planets. A debris from such a collision could reach Mars orbit when the planet was still forming and was captured by gravity. '
It's an interesting idea, but the researchers say it's not the only explanation for 1998 VF31's past. It is also possible, and perhaps more likely, that the asteroid is instead a fragment of Mars chipped off by a similar incident that collided with the Red Planet; or it may be an ordinary asteroid, which, due to the processes of weathering by solar radiation, has become similar to the moon.
The results are reported in Icarus.
