perfidy

The roll of extra solar planets has reached north of 200 in just over a decade. The vast majority of the worlds we have detected circling other suns are Jupiter sized or better, and quite frequently orbiting very close to their primary – often completing a yearly circuit in a matter of days. The preponderance of large, close in worlds is of course an artifact of the means we use to find them – measuring the wobble in the movement of the star caused by the planet. Planets too small, or too far away cannot produce a big enough wobble for us to discern.

The proof that there are extra solar planets was wonderful news for those who hoped that the universe outside our own comfortable backwater might contain life. Even if the planets that we have found so far would be unsuitable for life as we know it, the fact that we were finding planets everywhere we were able to look seemed to indicate that somewhere, conditions would be right for another Earth.

Back in 2002, astronomers determined that there were several Jupiter sized worlds circling the star 55 Cancri, some 41 light years from here. The amazing thing was that all of these worlds were (compared to most of the planets detected previously) far away from the star. As best we can determine, there are four worlds around 55 Cancri. Three are large Gas Giants, and the fourth a solid object, composed of rock or perhaps ice and about the size of Neptune. Since this star is of the same approximate age and composition as our own sun, astronomers immediately said that this could be the home of an earthlike world.

A recent computer simulation has put that speculation on slightly firmer ground. The exercise took four candidate star systems, each with two or more worlds, and placed hypothetical moon sized objects around them for a 100 million simulated years. The simulation for 55 Cancri consistently yielded and Earth sized rocky world smack dab in the middle of the star’s habitable zone.

"Our models show a habitable planet, a planet with mass, temperature and water content similar to Earth's, could have formed," said Rory Barnes, a postdoctoral researcher at the University of Arizona…

"Our simulations typically produced one terrestrial planet in the habitable zone of 55 Cancri, with a typical mass of about half an Earth mass," said Sean Raymond, a postdoctoral researcher at the University of Colorado who worked on the project while a doctoral student at the University of Washington. "In many of the simulations, these planets accreted a decent amount of water-rich material from farther out in the disk." …

"In terms of the systems we looked at, 55 Cancri has the largest zone between giant planets in which terrestrial planets may form and remain on stable orbits," Raymond said. "So, I think the chance of other planets existing in the system is pretty good, but it's certainly not definitive at the moment."

Other modeling by Raymond has shown that only about 5 percent of the known giant-planet systems are likely to have Earth-like planets. But, he and others have said, there may well be many solar systems similar to our own, in which the giant planets are all on the outskirts, that simply can't be detected yet.

Next thing, clearly, is to build a honking big telescope that can find other planets visually. There have been proposals for a space telescope that would block the light of a star, allowing planets circling it to be detected directly. We need one of those, and then we can get on with the task of finding an alternate home in case the giant robots take over here on Earth.