Privileged Planet: comparing solar systems (Introduction)

by David Turell , Tuesday, February 02, 2016, 05:40 (3005 days ago) @ David Turell

Only six percent of ones seen are like ours and have gas giants like Jupiter:-http://www.forbes.com/sites/brucedorminey/2016/01/31/solar-systems-like-ours-remain-scarce/#73d456b01d58-" Solar systems like ours, in which Jupiter-like planets orbit their parent stars at Jupiter-like distances, remain scarce in the local stellar neighborhood, says an Australian-led team of astronomers.-***-"They confirms that 17 years of data taken with the 3.9-meter Anglo-Australian Telescope in Australia, indicates that only some 6.2 percent of 202 nearby solar type harbor Jupiter analogs. That is, gas giant planets that would circle their stars on Jupiter-like orbits of 3 to 5 astronomical units (AU), or Earth-Sun distances. Our own Jupiter lies at 5.2 AU, which means it orbits our Sun roughly once every 12 years.-"As Robert Wittenmyer, an astronomer at the University of New South Wales in Sydney and the paper's lead author told me, NASA 's Kepler space telescope has shown us that small planets appear to be ubiquitous. But he says very few observers are looking at what he terms the other half of the question, the long-period gas giants.-***-"The findings are important because conventional theories of planet formation have usually dictated that gas giants like Jupiter parked in a stable, rather distant, orbit from its parent star were thought to be key to the onset of life on closer-in Earth-like planets.-***-"As Wittenmyer notes their latest results confirm earlier data from 2010 that statistically few systems harbor true Jupiter analogs.-“'This tells us that the architecture of our solar system, with nearly-circular outer gas giants and room for inner terrestrial planets, is relatively uncommon?? ,” said Wittenmyer.-"Even so, Jupiter's presence can be a double-edged sword.-"As the paper points out, although Jupiter can act to shield Earth from incoming comets and asteroids, it can also act to “control the flux of small bodies to the inner solar system, acting to perturb” such objects onto Earth-crossing orbits.-“'Jupiter doesn't just eject things from the solar system, taking them off Earth-crossing orbits,” said Horner. “But it also throws things our way that would otherwise have come nowhere near our planet.”-"So, are habitable extrasolar Earths possible without such Jupiters?-“'You could certainly have Earth-sized planets without [gas giants] beyond,” said 
Horner. “But without a Jupiter-like planet to throw volatile-rich objects toward that planet, it may not be able to get a significant amount of water. Earth without Jupiter might be a very different place with fewer impacts perhaps, but far more arid and inhospitable.'”-Comment: Our Earth is very different and very special, and it looks like our solar system is quite unusual, which fits the pattern that life needs a very special place to develop. The Earth is two-thirds of the way out on the second spiral arm, a quiet place in the Milky Way without too much radiation or explosions.