Astronomers have announced the discovery of a planet with about three times the Earth’s mass orbiting the nearby red dwarf star Gliese 581. That in itself is cool news; a planet like that is very hard to detect.
Not too far from its star, not too close. So it could contain liquid water. The planet itself is neither too big nor too small for the proper surface, gravity and atmosphere.The new planet sits smack in the middle of what astronomers refer to as the habitable zone, unlike any of the nearly 500 other planets astronomers have found outside our solar system. And it is in our galactic neighborhood, suggesting that plenty of Earth-like planets circle other stars.
Finding a planet that could potentially support life is a major step toward answering the timeless question: Are we alone?
Scientists have jumped the gun before on proclaiming that planets outside our solar system were habitable only to have them turn out to be not quite so conducive to life. But this one is so clearly in the right zone that five outside astronomers told The Associated Press it seems to be the real thing.
Life on other planets doesn't mean E.T. Even a simple single-cell bacteria or the equivalent of shower mold would shake perceptions about the uniqueness of life on Earth.But there are still many unanswered questions about this strange planet. It is about three times the mass of Earth, slightly larger in width and much closer to its star — 14 million miles away versus 93 million. It's so close to its version of the sun that it orbits every 37 days. And it doesn't rotate much, so one side is almost always bright, the other dark.
Temperatures can be as hot as 160 degrees or as frigid as 25 degrees below zero, but in between — in the land of constant sunrise — it would be "shirt-sleeve weather," said co-discoverer Steven Vogt of the University of California at Santa Cruz.
It's unknown whether water actually exists on the planet, and what kind of atmosphere it has. But because conditions are ideal for liquid water, and because there always seems to be life on Earth where there is water, Vogt believes "that chances for life on this planet are 100 percent."
The astronomers' findings are being published in Astrophysical Journal and were announced by the National Science Foundation on Wednesday.
The planet circles a star called Gliese 581. It's about 120 trillion miles away, so it would take several generations for a spaceship to get there. It may seem like a long distance, but in the scheme of the vast universe, this planet is "like right in our face, right next door to us," Vogt said in an interview.
That close proximity and the way it was found so early in astronomers' search for habitable planets hints to scientists that planets like Earth are probably not that rare.
Vogt and Butler ran some calculations, with giant fudge factors built in, and figured that as much as one out of five to 10 stars in the universe have planets that are Earth-sized and in the habitable zone.
With an estimated 200 billion stars in the universe, that means maybe 40 billion planets that have the potential for life, Vogt said. However, Ohio State University's Scott Gaudi cautioned that is too speculative about how common these planets are.
But the amazing thing is that the planet’s distance from the star puts it in the Goldilocks Zone: the region where liquid water could exist on its surface!
First, a few things: 1) Gliese 581 is a dinky, cool red dwarf about 20 light years away. That’s pretty close as stars go; only a handful are closer. Bear in mind it’s still 200 trillion kilometers (120 trillion miles) away, and that’s still a bit of a drive.
2) The planet is one of six now known to orbit the star. Apparently, all the planets have neat, circular orbits, so the system seems to be stable. This new planet takes 37 days to orbit the star once, and orbits at a distance about 1/6 the distance of the Earth from the Sun. As far as we know, it’s the fourth planet from its star.
3) The planets have all been found by the Doppler method: as they orbit the star, they tug on it. This causes a shift in the wavelength of emitted light from the star. The mass of the planet, its distance from the star, and the shape of the orbit all determine how the light shifts, which is how astronomers found those properties of the new planet.
* Too big? 55 Cancri appears to have a planet in the Goldilocks zone, but it's 45 times as massive as Earth. That's probably too massive for life as we know it, but life could conceivably exist on a moon (such as Pandora in the movie "Avatar").
* Too hot? As mentioned above, Gliese 581c might be on the edge of the Goldilocks zone, but astronomers are coming around to the view that it's too hot to sustain life. The planet is at least five times as massive as Earth.
* Too cold? When Gliese 581c fizzled, astronomers suggested that Gliese 581d might be on the other side of the star system's habitable zone. Astronomers say life could be a possibility if the planet had a thick atmosphere to hold onto heat. Otherwise, it's probably too cold. It's also seven times as massive as Earth.
