Mars Might Have Abducted Our Moon's Twin

101429, you're old enough to know this... You're adopted!
Utku Kucukduner

The gravitational pull from large celestial bodies form a trail of smaller bodies behind it, this trail is called a gravitational wake. Now, observing a distant asteroid trailing behind the Red Planet with the latest technology, scientists have stumbled upon a surprising resemblance. A resemblance that raises questions about our trusty satellite.


The asteroid is called (101429) 1998 VF31, and it belongs to a group of trojan asteroids that share Mars' orbit. A trojan asteroid is a term typically reserved for asteroids co-orbiting Jupiter, but Neptune, Earth, and Mars have examples of this too. Their orbit lays either 60 degrees behind or in front of the body they follow.

101429 is especially intriguing among its group, L5 Martian Trojans per Science Alert. A new study led by Armagh Observatory and Planetarium in (AOP) investigates why.

How it was discovered

Utilizing a European Southern Observatory (ESO) spectrograph called X-SHOOTER, which is part of the Very Large Telescope (VLT) in Chile's Atacama Desert, the scientists measured and compared how sunlight reflects off 101429 and its family. Curious enough, L5 Trojans and 101429 are seemingly not related to each other, but that's not all. The adopted child had a spectral match closer to our home, our very own Moon.

Mars Might Have Abducted Our Moon's Twin
Source: AOP

AOP astrochemist Galin Borisov explains "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." 

The team is not sure as to its why. One possible explanation is that the L5 family originated from somewhere else far away while 101429 is in actuality a "relic fragment of the Moon's original solid crust". But if that's the case, how?

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How did we get here anyway?

Lead author Apostolos Christou from the AOP explains "The early Solar System was very different from the place we see today,"  and adds, "The space between the newly-formed planets was full of debris and collisions were commonplace. Large asteroids [planetesimals] were constantly hitting the Moon and the other planets. A shard from such a collision could have reached the orbit of Mars when the planet was still forming and was trapped in its Trojan clouds."

So, the space between these freshly formed planets was filled with debris, and collisions were common. The Moon and the other planets received an incessant beating from large asteroids. It's possible that the remnants of such a collision reached Mars' orbit in its formative phase and got a ride in its Trojan clouds.

While the idea is quite alluring, it's not the only explanation for 101429's history per scientists. It's also probable that the trojan is a fragment of Mars dislodged by a large asteroid. Or maybe, it's just a piece of asteroid that came to resemble the Moon after all the solar radiation it got.

The study is published in Icarus.

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