Astronomers have analyzed an asteroid trailing in Mars' gravitational wake, uncovering a spectral profile remarkably similar to the Moon. This finding, detailed in the journal Icarus, challenges assumptions about its origins.
In astronomy, Trojans are small bodies sharing a planet's orbit in a stable 1:1 resonance, positioned near the L4 or L5 Lagrange points—roughly 60 degrees ahead of or behind the planet.
The solar system hosts 8,619 known Trojans, with 8,580 around Jupiter. Other planets have far fewer, and Mars counts fewer than ten.
Martian L5 Trojans trail behind the Red Planet. Previously, all were thought to belong to the Eureka family, named after 5261 Eureka, including fragments likely broken from this parent body. Yet, asteroid (101429) 1998 VF31 stands apart.
Researchers from Armagh Observatory and Planetarium in Northern Ireland used the X-SHOOTER spectrograph on the Very Large Telescope (VLT) in Chile to study these L5 Trojans. By examining sunlight reflected off these objects, they found 1998 VF31's spectrum closely matches the Moon.
The team suggests this asteroid could be "a fragment of the original solid crust of our satellite." If true, how did it reach Mars' orbit? Lead author Apostolos Christou notes the early solar system was chaotic: "The space between the newly formed planets was filled with debris and collisions were commonplace." A shard from such an impact might have been captured by Mars during its formation.
Alternatively, it could be a Martian fragment altered by solar radiation to resemble lunar material. Further observations with advanced spectrographs are needed to resolve this.
