Sunday, October 19, 2014

New simulations explain why Mars is so small

Press release IAG/2014-02, Embargoed until 2014 February 20 at 13:00 UT

Press-release example by Viviana Peña Márquez, student of Divulgação em Astronomia at IAG/USP

Astronomers present model to help solve Mars’ size mystery 

Existent planet formation theories have successfully explained why there are jovian and terrestrial planets in our solar system, but have failed to justify why the Red Planet is so small. According to most models, Mars should be as big as Venus and Earth, but the planet is only a tenth of its neighbours  Through new simulations, an international team led by Brazilian astronomer André Izidoro, shed light on the mystery of why Mars failed to grow similar in size.

Previous simulations of planet formation, with a solar nebula that varies smoothly with distance from the Sun, produce a body with approximately the size of our own planet Earth in the orbit of Mars, i.e. 1.5 AU* from the Sun. A puzzling matter since the four rocky planets are composed by the same planetary embryos.

Following studies showed that a planet with the size of Mars could have formed in its orbit if the solar nebula was nonuniform, with a belt containing more material near today’s Earth, followed by a belt with less material in the region where the Red Planet is today.

Contrast between “Grand Tack” model (B) and Izidoro’s model (A). (c) Science

Up to now, the most valid theory to explain such unusual distribution is called the “Grand Tack” model, that assumes the inward and then outward migration of Jupiter. These unlikely events in the early Solar System could have created favorable conditions for the formation of a planet such as Mars.

Looking for a better alternative to the “Grand Tack” model, Izidoro and his team assumed that material flowed toward the Sun moving at different speeds at different distances from the star, generating a depletion of material somewhere between 1 AU and 3 AU. A gap that could explain Mars’ size. “This deficit in local mass may be common in protoplanetary disks. However, the location and characteristics of this region can be very sensitive to the properties of each model. In our case, Mars formation around 1.5 AU is also due to the gravitational effects exerted by Jupiter and Saturn,” explains Izidoro. 

Othon Winter, researcher of the UNESP Orbital Dynamics and Planetology Group, concludes: “The model is quite complete because, besides giving an explanation to the mystery of the size of the Red Planet, it also maintains and manages to generate the other terrestrial planets in their current orbits and masses.”

This research was presented in the paper “Terrestrial planet formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars”, by André Izidoro et al. to appear in the Astrophysical Journal Letters (February 2014).

The team is composed of André Izidoro (Universidade Estadual Paulista, Brazil [UNESP] - University of Nice-Sofia, France), Nader Haghighipour (University of Hawaii-Manoa, USA), Othon Winter (UNESP), and Masayoshi Tsuchida (UNESP). 


Research Paper


* One astronomical unit (AU) is the distance from the Earth to the Sun.

André Izidoro
University of Nice-Sophia, Nice, France.
Phone: xx x xxxx xxxx
E-mail: xxxxxxx@xxxxx.xxxx.xx

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