Social Sciences Brazil , Brasil, Friday, July 04 of 2014, 10:08

Astronomers develop new model to explain the formation of Mars

International study led by Brazilian researchers analyzes the density of the cloud that formed the Solar System to explain the size of the Red Planet

Elton Alisson/Agência FAPESP/DICYT Models of formation of the Solar System’s rocky planets developed in the past two decades have been successful in explaining the origin of Venus and Earth, which are similar in size, as well as that of Mercury, which has only 5% of the Earth’s mass.


High-resolution computer simulations, however, have still failed to explain how Mars formed and why the planet has only 10% of the Earth’s mass.


According to researchers, this is an intriguing question because the four planets are all products of similar planetary embryos – celestial bodies with sizes similar to the current planets – that merged over tens of millions of years ago.


An international team– made up of researchers from Brazil, the United States, Germany and France, and led by the Orbital Dynamics and Planetology Group of the São Paulo State University (Unesp), Guaratinguetá campus – recently performed a series of simulations, demonstrating that the size of Mars may be related to the density of the protosolar nebula – the cloud of gas and dust that gave rise to the Solar System – in the planet’s orbit.


Findings from the FAPESP-funded thematic project, “Orbital dynamics of minor bodies,” were described in an article published in February 2014 in The Astrophysical Journal from the American Astronomical Society.


The study was cited by John Chambers, researcher in the Department of Terrestrial Magnetism of the Carnegie Institution for Science, in the United States, in an article published in the May issue of the journal Science.


“Most simulations of terrestrial planet formation are unable to generate a Mars-sized body in its orbit, which is situated at a distance of 1.5 astronomical units [AU, equivalent to approximately 150 million kilometers] from the Sun,” Othon Cabo Winter, researcher in the Orbital Dynamics and Planetology Group and project coordinator, told Agência FAPESP.


“These models typically produce a Mars-like body in the orbit of Mars at approximately the mass of the Earth, much larger than its actual mass,” said the researcher, author of the article together with André Izidoro, who is currently a post-doc at the Observatoire de la Côte d'Azur (OLCD) in Nice, France.


Grand Tack


According to Winter, one of the models already proposed to try to explain the formation of Mars is what is known as “Grand Tack,” developed by researchers at the OLCD.


The model holds that during the formation of the Solar System, 4.5 billion years ago, the orbit of Jupiter, the giant planet closest to Mars, migrated from its current position at 5 AU from the sun closer to the orbit of the red planet, 2 AU from the sun.


As it approached Mars’ orbit, Jupiter may have crossed the asteroid belt and swept away most of the planetesimals (solid bodies made of cosmic dust and ice, similar to asteroids and comets) and planetary embryos found in the asteroid belt or near the red planet’s orbit, closer to the Sun.


As a result, according to the Grand Tack model, the mass of Mars and the asteroid belt were reduced and the planetesimal and planetary matter ultimately formed Earth and Venus.


Because of gravitational interactions with the solar nebula and Saturn, however, Jupiter would have returned to its current orbit. “This model is valid but quite questionable because it is unlikely that this really would have happened,” Winter said.


Alternative model


To develop an alternative model to the Grand Tack, the Brazilian researchers, in cooperation with colleagues at the OLCD, along with the Astrobiology Institute of the US National Aeronautics and Space Administration (NAI, NASA, USA) and the Institute of Astronomy and Astrophysics at the University of Tübingen, in Germany, conducted a series of simulations of the gas and dust flows within the protosolar nebula during its formation.


The simulations suggest that the matter flowed in the direction of the Sun, moving at different speeds, at varying distances from the star. In the region between 1 and 3 AU from the Sun, the protosolar nebula could have suffered a loss or reduction (depletion) of matter equivalent to between 50% and 75% of its density.


The model assumes that the loss of this volume of “planetary construction blocks” by the protosolar nebula in this region near Mars’ orbit would have caused a reduction of the final mass of Mars and the growth of the Earth and Venus.


“We’ve studied a number of parameters and concluded that if there were a 50% to 70% mass-depletion of the protosolar nebula in the region of between 1 and 3 AU, there is over a 50% chance that a planet with a similar mass on the current orbit of Mars, in addition to Earth, Venus and a few objects in the asteroid belt, would have been formed,” Winter said.


“The model is very complete because it addresses the formation of Mars and, in addition, maintains and is able to generate the other terrestrial planets at their mass and current orbit,” he went on to say.


Possible contributions


In Winter’s estimation, the new model closed a gap in the previous model of the formation of the Solar System, indicating that the profile of mass density of the protosolar cloud had not been uniform and had undergone depletions. “These data could have implications for studies that attempt to explain such things as the formation of the asteroid belt,” he said.


The model could also contribute to research studies in the area of astrobiology, a field of knowledge that constitutes the interface between astronomy, biology, chemistry, geology and atmospheric sciences, among other things, related to objects from Mars moving toward Earth, in addition to studies about extrasolar planets, he said.