Why Mars is so much smaller than the Earth?

Southwest Research Institute (Southwest Research Institute, SwRI) astronomer Hal Levison et al., Through the establishment of a new computer simulation program of planet formation process, that the planet is via gravel (pebble) such a small celestial body has grown up . By such growth mode, these astronomers reconstructed the sun inside of the structure containing the Earth, Venus and Mars and other celestial bodies, could explain why Mars is so much smaller than the Earth; the same growth pattern, it can also be used to explain in Jupiter and Saturn Why such a gas giant planet formation speed so quick question.

Quality of Mars is only about one tenth of the earth only, why neighboring planets but the difference is so big about it, puzzled scientists for a long time the theory of the solar system. In the standard model of planet formation, similar to the size of the objects is through the so-called "accretion (accretion)" cumulative growth process, rock and other rock pile up into a mountain stage objects, hill and merged into the city level objects, then to Such push. However, since the typical accretion model can produce very close to the size of Earth and Venus, Naturally, Mars and Earth are almost the same should even be bigger than the Earth. In addition, these models also overestimate the total mass of the asteroid belt, it is clear that there must be some standard model needs to be improved.

Levison and others to improve the formation process start directly from the planet. Their simulation results show that: the accretion through the so-called "viscosity agitation gravel (Viscously Stirred Pebble Accretion, VSPA) growth model of the planet, the solar system's structure really seen naturally into today's appearance in VSPA. mode, dust directly into the gravel which grow only a few centimeters to 10 centimeters in diameter small bodies, the latter part of the gravel collapse due to gravity (gravitationally collapse) and gradually formed asteroid rating celestial Under appropriate conditions, these original asteroid can be efficiently annexation of residual gravel, with aerodynamic resistance (aerodynamic drag) will turn around and pulling these gravel original asteroid, and more about the closer and eventually landed on asteroids, the original asteroid was able By this process grew to row star objects. This process allows a few asteroids within a very short period of time to become planets.

However, this new simulation results also found that the original asteroid opportunity to gather gravel and grew up not all the same. For example: Ceres diameter of 1,000 kilometers, is the largest objects in the asteroid belt between Mars and Jupiter within; a celestial star Ceres, in the current growth rate of the Earth's orbit where the position is extremely fast, but if in the current orbit of Mars location outside due to aerodynamic drag is too weak, unable to capture and gravel leaving residual impact of low growth efficiency, which is why Mars is so much smaller than the Earth reason.

Similarly, the asteroid belt farther than Mars, less opportunity to capture the impact of residual gravel, so the total mass of the asteroid belt's only as good as the standard model predicts that much. Therefore, the numerical simulation of the asteroid belt deep historical involvement, previous simulations predict asteroid belt initially contained several times the mass of Earth material showed in this planet began to grow, and the new simulation from the thought that the asteroid belt So far not much quality start. Between the old and the new simulation, using a variety of ways meteor observation, telemetry and space missions, etc., you can verify its correctness and scientific prediction connection, which makes Levison, who was quite excited and proud.