Rebecca Martin of the University of Colorado at boulder and Mario Livio of the Institute for space telescope in Baltimore have developed a rather extravagant theory, suggesting that for the formation of life on Earth in the Solar system must be the asteroid belt, according to where it is now. Otherwise you would not! This leads to the following conclusion: the search for extraterrestrial life should be to focus on those systems that are close to the "snow line" has its own asteroid belt.

If gas giants migrate inside the snow line, the zone is destroyed (above), if not migrate at all, on the contrary, does not lose asteroids, becoming too tight. (Illustration : NASA, ESA, STScI / A. Feild.)

This is how scientists argue. Observations ekzoplanety systems show that the so-called warm dust, which is, apparently, the result of the collisions of asteroids, concentrated in the areas close to "snow line". This can be explained by the fact, that it formed giant planets, light elements which could not condense on the surface of a heavenly body, whether it closer to the Sun. The enormous gravity of such giants, according to scientists, excludes formation of planet earth from asteroid belt: planetesimals in this case simply cannot regroup, because from the centre of gravity of the asteroid belt them pulls a gas giant in our Jupiter). However, despite the universality of the scenario of forming the asteroid belt, and his fate for more than 95% of the time does not coincide with a share our belt. The fact that 96% of the studied planetary systems (501 from 520) gas giants removed from its sun at a distance less than the distance to "snow line". Formed for her, due to gravitational resonance they gradually migrated inside her, rasshiryaya asteroids of the belt and dramatically reducing their concentration within the "snow line".

Here we come to a very difficult moment hypothesis. According to Americans, the asteroids are not just necessary for the formation of life on planets. Even if life arises without them, its development to complex forms hardly possible. Why? First, the late heavy bombardment, apparently, has brought to the surface a lot of water from areas "snow line". And without water, the origin of life is difficult. Secondly, systematic falling asteroids of the zone should "update personnel", eliminating the dominant species at the top of the food pyramid, and letting their little brothers to try his luck in the new liberated ecological niche. In General, everything that doesn't kill the biosphere of the Earth completely, makes it stronger, etc.

Opinion unusual. And it's not just that a lot of water even in the earth's mantle. The very hypothesis that regular mini-Apocalypse necessary for formation of complex life forms, not fully proven in actual biological environment and requires serious examination. In some past age number of species, apparently, was not less than ours, which suggests a good level of development of complex life without asteroid intervention... it is Not clear that it should be borne in mind by "snow line". According to the concept of weak young Sun, the asteroid belt at the dawn of the Solar system, at least in part was on the inside "snow line", and now the situation has changed significantly.

Finally (and this is a question №1 on the theory that "life will flourish only where it regularly beat asteroids"), as the authors, the fact that only 4% of systems of gas giants are outside the "snow line" (as we do), "definitely can be a consequence of the effect of selective observations". Indeed, the current methods of the search for exoplanets are able to cope with the gas giants, as close to the lights - that is, as a rule, located deep inside "snow line". If the giants, as in the Sun, are located abroad, to find them until it is practically unreal. So how can you be sure that only 4% ekzoplanety systems there Jupiter beyond the snow line", preventing develop complex life within it?

The theory will soon appear in the journal Monthly Notices of the Royal Astronomical Society, and with its Preprint available here.

Prepared according to NASA.