If Mars is so small it might be Jupiter’s fault

From the left: Venus, Earth, Mars. A comparison of their sizes (image NASA)
From the left: Venus, Earth, Mars. A comparison of their sizes (image NASA)

The size of Mars is an issue that’s been puzzling astronomers for a long time: according to scientific theories on the formation of our solar system the red planet should be similar to the Earth and Venus in terms of size and mass, maybe even bigger. In fact in Mars orbit the amount of matter at the dawn of the solar system had to be even a little higher than the matter that formed the two neighboring planets.

Scientists now have access to much more data than once and thanks to the access to a computing power that was unthinkable a few years ago they can create extremely sophisticated simulations of even complex systems such as a solar system in formation.

In recent days the journal Nature has published a new study by an international team led by Dr. Kevin Walsh of the Southwest Research Institute┬«, with the participation of scientists Alessandro Morbidelli, Sean N. Raymond, David P. O’Brien and Avi M. Mandell that could shed light on the mystery of the mass of Mars.

Today Jupiter has an average distance from the sun about five times greater than Earth. According to the simulation created by the team led by Dr. Kevin Walsh however Jupiter was born at a distance a little closer, about three and a half times the distance of Earth. At that time there was a considerable amount of gas around the Sun and the proto-Jupiter was drawn closer to it until it ended more or less in today’s Mars orbit. The proto-Saturn got closer to the Sun as well binding to Jupiter in terms of gravity.

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Inevitably Jupiter formed also absorbing a lot of gas in the area where it arrived. Over time the gravity bond of Jupiter and Saturn, together with those of the outer planets brought the two biggest planets away from the Sun reaching the current positions.

According to this research Mars formed only after Jupiter move away but obviously the remaining material was relatively limited and this would explain the reduced mass of the red planet.

The movements of Jupiter and Saturn also led to the creation of the asteroid belt and the simulation carried out has led not only to have rocky asteroids formed from debris left by the passage of the two planets but also of objects made mostly of ice which came from the edge of the solar system and got diverted by the Jupiter’s gravity. The simulation therefore explains why in the asteroid belt there are actually two different types of objects.

This type of planetary dynamics also explains why in some of the solar systems observed in the last years there are planets of the type called “hot Jupiter”, gas giants very close to their stars, even more than Mercury to the Sun, so they have very high temperatures.

Clearly the results of this research need to be tested because science advances keeping on studying even topics that seem well known. If the simulation created by the team led by Dr. Kevin Walsh were to be confirmed it will mean that really Mars has a mass about one tenth fo the Earth, insufficient to retain an atmosphere, because of Jupiter. Talk about having cosmic bad luck…

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