For decades, planetary scientists have always wanted to fully understand the process of planet formation, and what is responsible for the various sizes of each planet in our Kuiper Belt; they think they have the answers now.
Using complex modeling techniques, scientists from Southwest Research Institute have been able to provide reasons why Mars is much smaller than Earth, and the fundamental processes that go into work in planet formations. Their findings have been published in the Proceedings of the National Academy of Sciences.
"This numerical simulation actually reproduces the structure of the inner solar system, with Earth, Venus, and a smaller Mars," said Hal Levison, an Institute scientist at the SwRI Planetary Science Directorate.
The scientists already know that Mars has only 10% of Earth’s mass. But their model showed that planets form when objects collect together and then assimilate through accretion – a process whereby rocks join with rocks to form mountains, and mountains join with other mountains to form larger city-sized objects.
"Understanding why Mars is smaller than expected has been a major problem that has frustrated our modeling efforts for several decades," said Levison. "Here, we have a solution that arises directly from the planet formation process itself."
The modeling calculations were done by Levison and co-authors Katherine Kretke, Kevin Walsh and Bill Bottke, all of them SwRI's Planetary Science Directorates. The team theorized that the process of Viscously Stirred Pebble Accretion (VSPA) is at the bottom of planet growth, where dust grows to become pebbles which in turn gravitate together and then collapse to form asteroid-sized objects.
"This means that very few pebbles collide with objects near the current location of Mars. That provides a natural explanation for why it is so small," said Kretke.
"Similarly, even fewer hit objects in the asteroid belt, keeping its net mass small as well. The only place that growth was efficient was near the current location of Earth and Venus."
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The model used for this understanding determines the history of the asteroid belt, and Bottke noted that "this presents the planetary science community with a testable prediction between this model and previous models that can be explored using data from meteorites, remote sensing, and spacecraft missions."