A family of asteroids that share the orbit of Mars may be pieces of the planet itself thrown into space after an impact, a study has revealed. And they may represent an alluring target for unmanned or even manned missions.
The trojan asteroids of Mars are those that either trail or sit in front of the planet in its orbit, similar to the Jupiter trojans. Their origin has been a bit of a mystery, however, with some proposing they came from the asteroid belt and others saying they came directly from other impacts.
This paper, led by David Polishook from the Massachusetts Institute of Technology and published in Nature Astronomy, supports the latter theory.
They looked at seven of the nine trojan asteroids that belong to a cluster called Eureka, named after the largest asteroid in that group, 5261 Eureka. This cluster was thought to have formed about 1 billion years ago, although the rocks themselves may have originated from the dawn of the Solar System.
In their paper, the team suggest that this cluster may be impact debris from the Martian mantle. This is based on an olivine-rich composition, which is rare on asteroids but common in the largest impact basins on Mars. Meteorites known to come from Mars are also known to have a similar composition.
“Using numerical simulations, we show that the Mars Trojans are more likely to be impact ejecta from Mars than captured olivine-rich asteroids transported from the main [asteroid] belt,” the team writes.
Exactly what sort of impact this would have been isn’t clear. But they note it may have been similar to the giant impact that caused the huge depression covering most of the northern hemisphere of Mars, known as the Borealis basin. The object that caused this basin is estimated to have been 1,600 to 2,700 kilometers (990 to 1,680 miles) across.
The only problem is how this impact material would have got into a trojan orbit, trailing or leading the planet. The researchers propose this may be the result of “jumps” in the orbit of Mars, caused by the gravitational pull of other planets during its formation.
Perhaps the most exciting aspect of the research, if confirmed, is that these asteroids represent a much more simple destination to visit than Mars itself. So if we wanted to return a sample of Mars to Earth, we could visit one of these trojan asteroids, rather than landing on the planet. A mission to Jupiter's trojans, called Lucy, is currently in the works.