Did we find the stolen twin of our Moon?
A close observation of a trojan asteroid called (101429) 1998 VF31, trailing in the gravitational wake of Mars, raises some interesting questions about its origin. Could this be the stolen twin of our Moon?
A trojan is a small celestial body, mostly asteroids that share the orbit of a larger celestial body. They remain in a stable orbit approximately 60 degrees either ahead or behind the main body.
Most trojan asteroids we know share Jupiter’s orbit, but Earth and Mars have them too. The trojan (101429) 1998 VF31 appears to be unique among all the ones trailing Mars’ orbit. All other trojans of the red planet, called the L5 Martian trojans, belong to what is known as the Eureka family. They are believed to have come loose from their parent space rock.
Using a spectrograph called X-SHOOTER on the European Southern Observatory’s 8-m Very Large Telescope (VLT) in Chile, astronomers from the Armagh Observatory and Planetarium (AOP) in Northern Ireland observed how sunlight reflects off 101429 and other L5 trojans in the Eureka family.
The spectral signature didn’t match its kin in the Eureka family, but it closely matched our Moon’s. The researchers say that this trojan possibly represents a relic fragment of the Moon’s original solid crust. The findings are reported in Icarus.
According to AOP astrochemist Galin Borisov, “The spectrum of this particular asteroid seems to be almost a dead-ringer for parts of the Moon where there is exposed bedrock such as crater interiors and mountains.”
If this is true, then it raises the next question, how did the Moon’s long-lost twin end up as a trojan bound together with Mars?
In the early Solar system, the space between the newly-formed planets was full of debris, and collisions were common. A shard from such collision on Moon could have reached Mars’s orbit and trapped in its Trojan clouds.
Another theory suggests 101429 to be a fragment of Mars ended up looking like our Moon due to weathering by solar radiation.
Further observations with a more powerful spectrograph or even a visit by a future spacecraft might shed more light on its origins.
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