It’s a Small (Habitable) World After All

by Molly Bentley on September 30, 2010

On “Are We Alone,” we often talk about the possibility for life elsewhere in the cosmos.

We haven’t found biology beyond Earth yet, but one thing that would increase the chances for cosmic company would be the discovery of planets that are at least somewhat similar to our own.  Until now, such terrestrial cousins have been in short supply.

But astronomers using the Keck Telescope on Hawaii’s big island have just announced their discovery of a planet that might well qualify as desirable real estate.

The planet is located in the star system Gliese 581 – a mere 20 light-years away – and visible in the constellation of Libra to anyone wielding a small telescope or a good pair of binoculars. 

Mind you, this isn’t Earth’s identical twin.  Gliese 581 is a small dwarf star, only a fraction the size and brightness of our Sun. Therefore, any planets that are in its so-called “habitable zone”, which is to say at the right distance to possibly have liquid oceans on their surfaces, will be in smaller orbits than for the much hotter Sun.  The new planet is in such a tight track around its star that it has succumbed to what’s called “tidal locking”.  This means that one side perpetually faces Gliese 581, much as one side of the Moon faces Earth. 

So one hemisphere of this new world, which has a diameter only about 50 percent larger than Earth, will be substantially and permanently warmer than the other.  But tidal locking need not rule out life, which might establish itself somewhere in the sweet spot straddling the sunny and dark sides of this world.

The obvious question is: could this new planet have inhabitants?  We don’t yet know, although there’s been at least one attempt to find out. The SETI Institute, as part of a decade-long survey of nearly a thousand star systems known as Project Phoenix, used antennas in both Australia and West Virginia to examine Gliese 581, hoping to pick up radio signals that would prove that someone was there.  No transmissions were detected.

That should provoke disappointment, but not discouragement.  After all, you could have looked at Earth with a radio telescope for most of its 4-1/2 billion-year history, and failed to find any signals. Even if this newly discovered world is carpeted with creatures, they might not yet be of the sort able to build a radio transmitter.

The important thing about Gliese 581’s newly discovered habitable planet is not that we should expect to find some Glieseans, but that planetary cousins of the Earth may, indeed, be as common as corn flakes.  And if that’s true, then our expectations for finding our opposite numbers among the stars will get a significant boost.

                                                                                                – Seth                                                  

(Stay tuned for an episode of AWA in October that discusses habitable worlds!  -Molly)

{ 4 comments… read them below or add one }

avatar Dr Science October 1, 2010 at 7:12 am

How long has this red dwarf star been around? Is it older or younger than our Sun? Has it been probed for any laser optical signals?

avatar Seth Shostak October 19, 2010 at 9:02 pm

Hey, Dr. Science,

Well, the age of this star is, like that of most stars, fairly uncertain. But it’s roughly twice as old as the Sun, which means that any inhabitants could be billions of years more advanced than we are. Of course, we don’t know if this planet even has liquid oceans and an atmosphere, let alone life.

I don’t know of any optical SETI observations of Gliese 581, other than the attempt by Ragbir Bhathal, in Australia. He saw a single flash, but that could be an instrumental effect. He didn’t see it ever again, and he doesn’t claim that it was an actual signal from Gliese 581.

avatar Alexander K October 20, 2010 at 11:22 am

Is not Gliese 581 d gravitationally bound to it’s star? if one side is very hot and very cold, it might mean that if there is life producing oxygen that binds oxygen with other substances on the warm side because of chemistry. And if no oxygen is there, so … how can a muscle function? And you need muscle to build a radio antenna. But they might have telepathic brain powers like Darth Vader. Greetings from Sweden

avatar Danny October 20, 2010 at 12:02 pm

Pardon my layman terms on approaching this, but… What would be our options to find out more about this planet on a “reasonably short” term? (the how and how long). Are there any plans made, or in the making about exploring this earths-twin-planet? And what impact did this planet’s discovery have on “searching for extraterrestrial life” in matters of government/NASA support or research fundings etc? (and do you as institute benefit from this discovery at all?)…

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