Weird orbits of neighbors can make 'habitable' planets not so habitable

May 24, 2010
An exoplanet with a mass similar to that of Jupiter but with a highly elliptical orbit could have dramatic effects on the orbit of a planet in the same system comparable to Earth, possibly even determining whether the smaller planet is habitable. Credit: NASA

Astronomers hunting for planets orbiting nearby stars similar to the sun are looking for signs of rocky, Earth-like planets in a "habitable" zone, where conditions such as temperature and liquid water remain stable enough to support life.

New findings from computer modeling indicate that some of those exoplanets might fluctuate between being habitable and being inhospitable to life because of the forces exerted by giant neighbors with eccentric orbits.

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 comparable to to the system, however, and giving it a highly 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.

The smaller planet's orbit will elongate and then become more circular again, all in as little as 1,000 years, and could do so repeatedly. That raises the possibility, for example, that its average yearly temperature could change significantly during each millennium.

"For part of the time could exist on the surface, but at others it would boil off," said Barnes, who will present the findings Wednesday at a meeting of the American Astronomical Society in Miami.

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."

The problem becomes even more complex for what could be habitable planets orbiting low-mass stars, perhaps one-third the mass of the sun. In such systems, the is much closer to the smaller star, and tidal forces from the star's gravity are critical in determining whether the planet is habitable. Adding an eccentric orbit of a Jupiter-like planet could greatly alter conditions on the smaller planet as its orbit changes.

"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."

Tidal forces also fix the planet's rotation period, and as the orbit becomes more elongated the length of day can change significantly, Barnes said.

"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 work, funded by NASA's Virtual Planetary Laboratory, was conducted with Brian Jackson of NASA's Goddard Space Flight Center, Richard Greenberg of the University of Arizona and Sean Raymond of the Laboratoire d'Astrophysique de Bordeaux in France.

"There is this crazy zoo of planets out there that probably are habitable," Barnes said, "but their properties are very different from Earth and they're different from Earth because of their eccentric neighbors."

Explore further: Image: Orion crew module at the Neil Armstrong Operations and Checkout Building, Kennedy Space Center

Related Stories

Wobbly planets could reveal Earth-like moons

Dec 11, 2008

Moons outside our Solar System with the potential to support life have just become much easier to detect, thanks to research by an astronomer at University College London (UCL).

Planet-Finding by Numbers

Oct 18, 2006

More than a decade after the first planets beyond our solar system were found, astronomers have discovered about 200 of these "extrasolar planets," as they're called. Using a common-sense definition of potentially ...

Scientists discover a nearly Earth-sized planet (Update)

Apr 21, 2009

(PhysOrg.com) -- Exoplanet researcher Michel Mayor announces the discovery of the lightest exoplanet found so far. The planet, "e," in the system Gliese 581, is only about twice the mass of our Earth. The ...

Missing planets attest to destructive power of stars' tides

Apr 27, 2009

During the last two decades, astronomers have found hundreds of planets orbiting stars outside our solar system. New research indicates they might have found even more except for one thing - some planets have fallen into ...

Will Kepler find habitable moons?

Sep 03, 2009

(PhysOrg.com) -- Since the launch of the NASA Kepler Mission earlier this year, astronomers have been keenly awaiting the first detection of an Earth-like planet around another star. Now, in an echo of science ...

Recommended for you

New launch date set for ISS delivery vessel

8 hours ago

A robot ship will be launched from Kourou, French Guiana, after a five-day delay on July 29 to deliver provisions to the International Space Station, space transport firm Arianespace said Tuesday.

The heart of an astronaut, five years on

10 hours ago

The heart of an astronaut is a much-studied thing. Scientists have analyzed its blood flow, rhythms, atrophy and, through journal studies, even matters of the heart. But for the first time, researchers are ...

Image: Kaleidoscopic view of Mars

16 hours ago

Astrophotographer Leo Aerts from Belgium took advantage of the recent opposition of Mars and captured the Red Planet both "coming and going" in this montage of images taken from October 2013 to June of 2014. ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

gunslingor1
not rated yet May 25, 2010
"There is this crazy zoo of planets out there that probably are habitable," Barnes said, ...

habitable by carbon based life forms would be a better way to put it, we still do not know for certain if carbon based is the only form of life. I suspect under various harsh conditions, other elements may display very similar properties to this substance. Just don't rule out the possibility of Jupiter, asteroids, pluto and even nebula from having some sort of "self replicating macro molecules", i.e. life. heck, I wouldn't even rule out a star at this point, we know nothing of exolife, we have a molecule in an ocean.

On another note, this is slightly interesting. We've known about planets affecting each others orbits for a long time. I would have prefered to see more simulations and extreme conditions.