It's one of the major mysteries of the inner solar system: How did Mars - a tiny world only a tenth the mass of Earth - capture its cluster of orbit-sharing Trojan asteroids? Trojans are asteroids that co-orbit either ahead of a planet, at the L 4 Lagrangian point, or behind it at the L 5 point.
Mars has never had an easy time as a planet, constantly getting bombarded with asteroids throughout its history as its atmosphere was stripped away to nearly nothing. A study published in Nature Astronomy today further highlights Mars's struggles by highlighting an enormous and violent impact in the Red Planet's recent past.
That last theory is perhaps the most interesting, because it means that future Mars astronomers may not even need to step foot on the planet to study its history. They could just swing by the Trojans, shave off a few pieces, and fly them back to Earth's laboratories.
Researchers at the Weizmann Institute of Science in Rehovot and the Côte d'Azur Observatory in France are proposing a new and unique origin for Mars Trojan asteroids, which travel along the planet's orbital path around the Sun, and are not quite like those that populate the asteroid belt between Mars and Jupiter.
Mars has an asteroid entourage, with nine so-called Trojans trailing in its wake. Now it seems these travelling companions all had the same violent beginning: as the innards of a mini-planet, eviscerated in a violent collision. Some remnants may even have been incorporated into the material that became Mars.
Trojan asteroids are a fascinating thing. Whereas the most widely known are those that orbit Jupiter (around its L4 and L5 Lagrange Points), Venus, Earth, Mars, Uranus and Neptune have populations of these asteroids as well.
The Trojan asteroids that follow Mars in its orbit might have come from the planet itself, blown off in an ancient impact rather than being late arrivals, a new study suggests. Several planets in Earth's solar system have Trojan asteroids - bodies that run ahead of or behind the planet.