An asteroid trailing in Mars' gravitational wake has just been analyzed by a team of astronomers. Its spectral examination reveals a startling resemblance to the Moon, raising questions about the object's origins. Details of the study are published in the journal Icarus .
In astronomy, a Trojan is an object whose heliocentric orbit is in resonance of mean motion 1:1 with that of a planet, and which is located near the one of the two stable Lagrange points (L4 or L5) of the Sun-planet couple. Roughly imagine small asteroids positioned 60 degrees in front of and behind their planet.
Today there are 8,619 Trojans in the solar system, the vast majority of which (8,580 Trojans) frequent the environment of Jupiter. The rest is distributed among the other planets. Mars has less than ten of them.
That said, the objects that follow the red planet (placed behind, therefore) are called "Martian L5 Trojans". Until now, we thought all of them belonged to the "Eureka family", consisting of 5261 Eureka - the first discovered Martian Trojan - and a bunch of small fragments probably detached from this parent body. However, it seems that one of the asteroids – called (101429) 1998 VF31 – is different.
As part of a study, astronomers from the Armagh Observatory and Planetarium (Northern Ireland) examined these L5 Martian Trojans with the X-SHOOTER spectrograph, installed on Very Large Telescope (VLT), in Chile. The team looked specifically at how light from the Sun reflects off of these objects. It eventually emerged that asteroid 1998 VF31 displayed a spectral match with an object much closer to home:the Moon.
In other words, according to the researchers of this study, it is possible that this asteroid is a "fragment of the original solid crust of our satellite" . If so, how could this long-lost "twin" have ended up in the wake of the planet Mars? It is currently difficult to answer this question.
The astronomer Apostolos Christou, the main author of this work, nevertheless recalls that the first solar system was, several billion years ago, a place very different from 'today. “The space between the newly formed planets was filled with debris and collisions were commonplace” , he explains. “Large [planetsimal] asteroids were constantly hitting the Moon and other planets. A shard from such a collision could then have reached Martian orbit while the planet was still forming. .
It is also possible, the researcher suggests, that this Trojan was ultimately just a simple fragment of Mars which, through processes of alteration of solar radiation, ended up look like the moon. For now, the question remains open. Further observations with even more powerful spectrographs may be able to shed more light.
