As we find more planetary systems elsewhere in the galaxy, something is confusing astronomers - why does our solar system appear so unique? Many other systems have ‘super-Earths’ and other planets in tight orbits close to their star, but ours does not. And now we might know why - because Jupiter acted like a ‘wrecking ball’ in the early solar system and knocked planets out of the solar system or into position. University of California scientists have presented a new theory for the solar system. They say early in its life, Jupiter swung through the inner planets (illustration of early solar system shown). This explains why there are no planets between Mercury and the sun. But it may also indicate our system is an 'oddball' in the galaxy . If this is true, it would suggest that the conditions that have allowed life on Earth to thrive are incredibly rare. The study published in Proceedings of the National Academy of Sciences helps explain why our solar system is so different from the hundreds of others discovered in recent years. ‘Now we can look at our own solar system in the context of all these other planetary systems, one of the most interesting features is the absence of planets inside the orbit of Mercury,’ said Professor Gregory Laughlin, of California University in Santa Cruz, who co-authored the study. ‘The standard issue planetary system in our galaxy seems to be a set of super-Earths with alarmingly short orbital periods. Our solar system is looking increasingly like an oddball.’ Aliens are real - not little green men visiting Earth as depicted in movies, but rather microbial life in our own solar system and intelligent life beyond. That’s according to two leading Search for Extraterrestrial Intelligence (Seti) researchers, who took part in a hearing at the House Committee on Science, Space, and Technology in Washington DC last August. During the talk dubbed ‘Astrobiology and the Search for Life in the Universe’ in May, the scientists laid out the evidence and reasoning for believing we are not alone. The speech was made by Dr Seth Shostak, Senior Astronomer at the Seti Institute in California, and Dr Dan Wethimer, Director of Seti Research. And, they added, with adequate support it is likely we will find alien life in some form or another within 20 years. Dr Wethimer said: ‘It would be bizarre if we are alone,’ he told the committee. ‘It would be a cramped mind that didn’t wonder what other life is out there.’ The new findings provide an explanation for this ‘gaping hole’ in our inner solar system between Mercury and the sun. But they also reveal certain characteristics of Earth and the other rocky planets, which would have formed later than the outer ones from a depleted supply of material. Namely, Jupiter may have helped Earth form in a habitable part of the solar system. And it also possibly played a part in Earth's size, ensuring it was not too big or small to host water and life. Computer models of the early solar system showed the migration of Jupiter may have shepherded small early planets - initiating a ‘collisional cascade’ in the inner solar system. Before this it’s plausible that rocky planets with deep atmospheres would have been forming close to the sun from a dense disk of gas and dust on their way to becoming typical ‘super-Earths’ like so many of the planets astronomers have found around other stars. As Jupiter moved inward, gravitational perturbations from the giant planet would have swept the inner planets and large space rocks into close-knit overlapping orbits - setting off a series of collisions that smashed all the planets into pieces. ‘It’s the same thing we worry about if satellites were to be destroyed in low-Earth orbit,’ said Professor Laughlin. ‘Their fragments would start smashing into other satellites and you’d risk a chain reaction of collisions. ‘Our work indicates that Jupiter would have created just such a collisional cascade in the inner solar system.’ As Jupiter (pictured from the Cassini spacecraft on 8 October 2000) moved inward in the early solar system, gravitational perturbations from the giant planet would have swept the inner planets and large space rocks into close-knit overlapping orbits - setting off a series of collisions that smashed all the planets into pieces . The study published in Proceedings of the National Academy of Sciences helps explain why our solar system is so different from the hundreds of others discovered in recent years. Notably, many other systems have super-Earths (illustration shown) - but our solar system has none . The resulting debris would then have spiraled into the sun under the influence of a strong ‘headwind’ from the dense gas still swirling around the sun. ‘The ingoing avalanche would have destroyed any newly-formed super-Earths by driving them into the sun,’ said Professor Laughlin. A second generation of inner planets would have formed later from the depleted material that was left behind, consistent with evidence that our solar system’s inner planets are younger than the outer planets. The resulting inner planets - Mercury, Venus, Earth and Mars - are also less massive and have much thinner atmospheres than would otherwise be expected. ‘One of the predictions of our theory is that truly Earth-like planets - with solid surfaces and modest atmospheric pressures - are rare,’ added Professor Laughlin. Ultimately, Jupiter's interaction with the inner solar system billions of years ago may have given rise to the solar system we know today (illustrated) - and also the conditions necessary for life on Earth, namely a habitable distance from the sun and a suitably-sized world . Planet hunters have detected well over a thousand exoplanets orbiting stars in our galaxy, including nearly 500 systems with multiple planets. What has emerged from these observations as the ‘typical’ planetary system is one consisting of a few planets with masses several times larger than the Earth’s - super-Earths - orbiting much closer to their host star than Mercury is to the sun. In systems with giant planets similar to Jupiter, they also tend to be much closer to their host stars than the giant planets in our solar system. The rocky inner planets of our solar system, with relatively low masses and thin atmospheres, may turn out to be fairly anomalous. According to Professor Laughlin, the formation of giant planets like Jupiter is somewhat rare, but when it occurs the giant planet usually migrates inward and ends up at an orbital distance similar to Earth’s. Only the formation of Saturn in our own solar system pulled Jupiter back out and allowed Mercury, Venus, Earth, and Mars to form. Therefore, another prediction of the paper is that systems with giant planets at orbital periods of more than about 100 days would be unlikely to host multiple close-in planets.
University of California has present a new theory for solar system . They say early in its life, Jupiter swung through the inner planets . This explains why there are no planets between Mercury and the sun . But it may also indicate our system is an 'oddball' in the galaxy . And it may mean conditions for life on Earth were extremely rare .