Mars may have been born in the asteroid belt


Mars and Earth have very different histories. A simple example: Earth is mostly covered with water, while Mars lost its water in the distant past. But scientists also know that the elements on Mars have different isotopes, or atomic masses, especially for chromium, titanium, and oxygen.

A new article published in the journal Letters of Earth and Planetary Sciences argues that these compositional differences are due to the fact that Mars formed in a different part of the solar system than where it is now. Instead of being between the sun and the asteroid belt, the article argues that Mars formed in the asteroid belt before migrating a little closer to the sun, where it is now. The migration occurred, according to the article, due to Mars’ gravitational interaction with planetesimals – small bodies such as asteroids – inside the belt.

“Since Mars is more massive than planetesimals, it tends to lose energy when it disperses these planetesimals because it transmits them to Jupiter, which then ejects them from the solar system,” Ramon Brasser, senior author and associate professor at Tokyo Institute of Technology’s Earth-Life Science Institute, wrote in an email.

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The dominant theory of solar system formation suggests that the sun and its planets formed after a cloud of gas and dust was compressed by gravity, possibly from a passing star. Over time, small particles of gas and dust have stuck together, forming the sun and modern planets.

There is still debate as to whether the planets migrated during this process. Previously, scientists had theorized that the rocky planets of Mercury, Venus, Earth, and Mars collect less gas than the gas giants of Jupiter, Uranus, Saturn, and Neptune because the rocky planets are closer to the sun. It was believed that the sun’s radiation blew most of the gas into the outer solar system. However, scientists have spotted several Jupiter-sized exoplanets very close to their host stars, which could involve a different formation process including migration.

In this case, the team tested their hypothesis about the formation of Mars by running simplified computer scenarios of the formation of terrestrial or rocky planets, and also examined samples from the Earth, Mars, the moon and Vesta. , which is an asteroid. . “We looked for analogues of Mars that accumulated matter in a part of the disk that the Earth did not, and we concluded that the only way to do that is to form Mars away from the Sun, in the belt. internal asteroid, ”Brasser wrote.

Based on previous work by Nicolas Dauphas and his colleagues at the University of Chicago, the simulations used by Brasser’s team began with planetary embryos under mars. Simulations suggest that Mars grew rapidly, then lost access to most materials, such as gas and dust, to develop within 5 to 10 million years of the formation of the solar system. It settled into its current orbit about 120 million years after the birth of the solar system, at which time its liquid surface hardened into a crust.

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Mars probably had liquid water flowing on its surface in the ancient past, but over time its atmosphere thinned and made it impossible for liquid water to exist on the surface. Brasser said, however, that the origins of Mars would not influence this process. While Mars formed in a colder environment (since the asteroid belt is further from the sun), it only stayed there for a few million years before migrating to its current location.

“As it only spent less than 100 million years beyond its current location, its atmospheric loss is dominated by the effects at its current location and by the brightening of the sun and the loss of its magnetic field,” Brew wrote.

He then plans to test his hypothesis using different models of the formation of terrestrial planets to see if they mimic the features of Mars better than the current model. Brasser added that Mars could be a “smoking gun” on how all of the rocky planets formed, so that’s one of the reasons he’s so interested in tackling the problem.

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