Research Suggests Mars Formed in the Asteroid Belt

Earth and Mars are very different planets right now, but they’re both small, rocky planets in the inner solar system. However, a new study suggests Mars may also have different origins than Earth. Researchers from Tokyo Institute of Technology claim that analysis of Mars’ composition supports the idea that it was originally formed in the asteroid belt, and then migrated to the inner solar system. This could alter much of what we know about the early eons of our little corner of the cosmos.

The team, led by planetary scientist Ramon Brasser, began investigating this based on the fact that Mars has a different ratio of isotopes than Earth does; especially chromium, titanium, and oxygen. That could indicate it originated outside the inner solar system where it now resides.

From what we currently understand, the solar system formed as the disk of gas and dust around the young sun was compressed by gravity. Eventually, planets, asteroids, and comets developed. Scientists theorize that rocky planets exist closer to the sun because the solar wind blew most of the gas into the outer solar system where we see gas giants. It’s unclear if planets migrated through different orbits during that process, but evidence from exoplanets suggests it’s possible. There are plenty of “hot Jupiters” out there — gas giants that orbit close to their stars.

To evaluate Mars as a candidate for migration, the team first considered its make up. They compared analyses of Mars with those of Earth, the moon, and the asteroid Vesta. Mars, it seems, has a composition most similar to objects found in the asteroid belt between Jupiter and the current orbit of Mars.

That’s not enough to support the claim Mars migrated inward, so the physics of such a maneuver had to be considered. If Mars formed in the asteroid belt, it would have encountered many objects smaller than itself. Simulations indicate that Mars would have grown to its current size in five to 10 million years after the solar system formed. Interacting with the asteroids in the belt would have been a net loss of energy for Mars, and the simulations predict it would have slipped into a tighter orbit around the sun after about 100 million years. The rest of the planet’s history would have unfolded as we currently understand it — the sun grows more intense, Mars loses its atmosphere, and most of the surface water dries up.

The next step is to run more simulations to see if any of them can provide a better match for the properties of Mars we currently observe. If scientists settle on Martian migration as a fact, it could tell us a lot about how all rocky planets form.