Erratic orbits of neighbouring planets may make life sustenance difficult

Astronomers have found that fluctuating orbits of surrounding planets around a seemingly habitable planet could render life impossible on it.

New findings from computer modelling show that the forces exerted by giant neighbours with eccentric orbits could cause extreme changes in temperatures and water availability and these changes would be constant.

A lone Earth-like, or terrestrial, planet with a generally circular orbit toward the inner edge of its sun's habitable zone could be expected to remain within that zone, said Rory Barnes, a University of Washington postdoctoral researcher in astronomy.

Adding a planet as big as Jupiter and giving it an elliptical orbit similar to most exoplanets discovered so far - can cause strange things to happen to the smaller planet, possibly causing it to cycle between habitable and uninhabitable conditions.

"For part of the time liquid water could exist on the surface, but at others it would boil off," said Barnes.

The effect would be similar for an Earth-like planet at the outer edge of its habitable zone, except that its altered orbit likely would, at times, take it too far from its star, possibly resulting in planetary glaciation.

"The bigger issue here is that the habitable zone is very complicated," Barnes said. "Earth's climate is affected slightly over tens of thousands of years by the orbits of other planets in the solar system, but it is possible that in many exoplanetary systems the layout of the planets is very important to habitability."

And this issue gets compounded for stars with low mass - in such systems, the habitable zone is much closer to the smaller star, and tidal forces from the star's gravity are critical in determining whether the planet is habitable.

"There could be planets out there that have their geological properties change over very long timescales," Barnes said. "You can imagine planets that cycle in and out of intense volcanism and earthquake stages.

"The length of the day changes almost day to day," he said. "It's fascinating to think about how evolution occurs on such a world."

The findings will be presented on Wednesday at a meeting of the American Astronomical Society in Miami.