Mars might have formed in the asteroid belt, study finds

While they are relatively close to each other, astronomically speaking, Earth and Mars are quite different in terms of chemical composition – a fact which a new study claims could be explained if the Red Planet had originally formed in a completely different part of the solar system.

The study, which is currently available online and will appear in the June 15 edition of Earth and Planetary Science Letters, suggests that Mars originally formed within the asteroid belt, and later migrated to its current location between the asteroid belt and the sun, explained Seeker.

That would explain why the elements on the Red Planet have different atomic masses than those on Earth, said lead study author Ramon Brasser, an associate professor from the Tokyo Institute of Technology’s Earth-Life Science Institute. But how did it migrate to its current position?

Brasser explained that the cause is likely the interaction between Mars and planetesimals (small objects) in the asteroid belt. Since the planet is more massive than the asteroids and other bodies surrounding it, he said, “it tends to lose energy” when interacting with them. Those interactions, he said, cause the planetesimals to be passed to Jupiter, then ejected from the solar system.

Kevin Walsh, a planetary scientist at the Southwest Research Institute in Boulder, Colorado who was not a member of Brasser’s team, told Science News that the newly-published study is part of a re-analysis of the origins of the solar system, and that since scientists have learned that “planets move around, possibly a lot,” they “may not have formed where we see them today.”

Analysis of Venus’ isotopes needed to confirm the theory

Scientists had long believed that the solar system formed when a cloud of gas and dust became gravitationally compressed, possibly by a passing star, explained Seeker. Over time, particles of dust and gas accumulated and formed the sun and the planets, they said. However, many experts now believe that the planets may have migrated at some point during this process.

One theory of planetary formation, known as the Grand Tack model, suggests that Mars ended up being smaller than the Earth because of Jupiter, which migrated towards the sun until it made it to Mars’ current orbit, and was then pulled back to the outer solar system by Saturn. In such a scenario, Jupiter’s journey to the sun caused material to accumulate and form Venus and Earth. The leftover material, the researchers said, formed Mercury and Mars.

However, while running Grand Tack simulations as part of their new study, Brasser’s team found that in about one out of every 50 scenarios, Mars actually formed in the asteroid belt, not close to the Earth’s current orbit, said Science News. Then it was pulled towards the sun by Jupiter during the gas giant’s migration – a voyage which also diverted material away from the Red Planet, thus resulting in its relatively small mass.

“Bulk elemental and isotopic data for Martian meteorites demonstrate that key aspects of Mars’ composition are markedly different from that of Earth,” the study authors wrote. “This suggests that Mars formed outside of the terrestrial feeding zone during primary accretion. It is, therefore, probable that Mars always remained significantly farther from the Sun than Earth.”

Their “potential dynamical pathway” of Mars formation would help explain the “strict age and compositional constraints, as well as mass differences” between the Red Planet and other inner worlds in the solar system, they added. Confirming this theory, the researchers explained, would require an analysis of Venus’ elements and isotopes, which according to their theory should be similar to those found on Earth.


Image credit: NASA JPL