This artist's conception shows the inner four planets of the Gliese 581 system and their host star. The large planet in the foreground is Gliese 581g, which is in the middle of the star's habitable zone and is only two to three times as massive as Earth. Some researchers aren't convinced Gliese 581g exists, however.
Image: Lynette Cook
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The controversial exoplanet Gliese 581g is the best candidate to host life beyond our own solar system, according to a new ranking of potentially habitable alien worlds.
Gliese 581g shot to the top of the list — which was published Thursday (July 19) by researchers at the University of Puerto Rico at Arecibo’s Planetary Habitability Laboratory (PHL) — after a new study marshaled support for its long-debated existence.
The exoplanet was discovered in September 2010, but other astronomers began casting doubt on its existence just weeks later. Now Gliese 581g's discoverers have rebutted their critics' charges in a new paper, and have done so effectively enough to get the PHL onboard.
Here's a brief rundown of the PHL's top five habitable alien planets:
Gliese 581g
This rocky world — if it does indeed exist — is just 20 light-years away from our solar system. It's likely two to three times as massive as Earth and zips around its parent star, the red dwarf Gliese 581, every 30 days or so. [Gallery: The Strangest Alien Planets]
This orbit places the planet squarely in the star's "habitable zone" — that just-right range of distances where liquid water, and perhaps life as we know it, could exist.
Gliese 581g has at least four, and possibly five, planetary neighbors. The team that spotted Gliese 581g also detected another planet, known as 581f, circling much farther away from the star. But scientists are still arguing about that world's existence, too.
Gliese 667Cc
Gliese 667Cc, which was discovered in February 2012 by the same core team that spotted Gliese 581g, orbits a red dwarf 22 light-years away, in the constellation Scorpius (The Scorpion).
The alien world is a so-called "super Earth" that's at least 4.5 times as massive as our planet, and it completes an orbit every 28 days. At least one other planet resides in the 667C system.
Gliese 667Cc's parent star is part of a triple-star system, so the planet's night sky would probably be a sight to behold.
Kepler-22b
Kepler-22b was spotted by NASA's planet-hunting Kepler space telescope, which has detected more than 2,300 potential exoplanets since its March 2009 launch. Only a small number have been confirmed so far, but the vast majority should end up being the real deal, researchers have said.
Kepler-22b, whose discovery was announced in December 2011, is a super Earth about 2.4 times as wide as our planet. If the greenhouse effect operates on Kepler-22b like it does on Earth, the alien world would have an average surface temperature of 72 degrees Fahrenheit (22 degrees Celsius), researchers have said.
The exoplanet is found about 600 light-years away, and it orbits a star very much like our own sun.
HD 85512b
HD 85512b is another super Earth, one that's thought to be about 3.6 times as massive as our planet. The alien world is found about 35 light-years from us, in the direction of the constellation Vela (The Sail).
Astronomers announced the discovery of HD 85512b — and about 50 other alien planets spotted by the HARPS spectrograph on a telescope in Chile — in September 2011. The planet's estimated average surface temperature is 77 degrees Fahrenheit (25 degrees Celsius).
Gliese 581d
This world, which is about seven times as massive as Earth, orbits a bit farther out than its planetary sibling Gliese 581g.
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16 Comments
Add CommentI still don't understand the intense search for a habitable planet. By the time we develop the technology to live in space for centuries, if not 1000's of years, traveling to another planet, why on would we need a planet? Who wants to be stuck on a planet when you can explore the galaxy?
Reply | Report Abuse | Link to thisWhat does 'habitable' mean? Life as we know it?...some bacteria or a multi-celled organism? Quintillions of planets in the Universe probably have life. No planet will have life as we know it...it will be some continuum between 'a lot' like our life to 'not as much'.
Reply | Report Abuse | Link to thisLife based on DNA might be versatile...especially at the bacteria-level. What's vital are the seminal conditions in which which life can begin and then be able to evolve to adapt. Evolution will take it off on tangents.
sparcboy: "By the time we develop the technology to live in space for centuries, if not 1000's of years, traveling to another planet, why on would we need a planet?'
Reply | Report Abuse | Link to thisSo true. Inter stellar travel would require such a vast generation infrastructure that they would be civilizations unto themselves. By that time man will be manipulating matter and energy at the quantum level. No idea why we'd go to a planet other than to wave as we went by. Our technology will know everything about it long before we got there and the building blocks we need...subatomic particles will be the same everywhere.
In a couple thousand years i doubt if man will be 'location' dependent for anything. Earth, our solar system, etc. will be historical but largely irrelevent. Physical 'stuff' will be produced from anything. The restrictions will be as they are now... the physical properties of matter and energy.
As I understand, without a single large moon to stabilize planetary axial rotation it is likely to shift significantly, so that given locations on the planet do not provide a stable, seasonal climate. Complex life forms are unlikely to develop in wildly varying climatic conditions.
Reply | Report Abuse | Link to thisThe comments here regarding space travel remind me of the movie, 2001 A Space Odyssey. We had colonies on the Moon back then, found a funny looking monolith, and sent a mission to Jupiter to figure out what the darn thing was. If only that frigging HAL 9000 had worked right.
Reply | Report Abuse | Link to thisSince then our technology has gone backwards. So, I predict that, in about 1000-years, we will be throwing bamboo spears harvested from Alaska at rusty ICBMs we don't understand.
Not only do you have the problems of no lunar stabilization (unless a moon or moons are later discovered for these planets) - but think of the gravitational problems involved. A "super-Earth" that is up to 4 times the size of our planet would make life for we "puny" humanoids very unbearable.
Reply | Report Abuse | Link to thisI just don't think that there is a planet yet that would be a true "Class M" (nod to Gene Roddenberry) planet for us to visit. But all of this will be a moot point anyway when the black hole at the center of the Milky Way galaxy sucks us and all the other stars in.
That is why I just say, sit back and enjoy the ride!
Martin: "Since then our technology has gone backwards'
Reply | Report Abuse | Link to thisNo, 2001 Space Odyssey was a movie. Our technology is far in advance of anything I grew up with during the Apollo era....otherwise you'd be using snail mail to post your comments to a monthly hand type-set magazine.
Those concerned by the mass of these worlds need to remember that surface gravity is not the same thing as mass or 'size', meaning that a planet of 4 Earth masses does not necessarily have a surface gravity 4 times what we experience on Earth. Density and radius are other factors in the equation.
Reply | Report Abuse | Link to thisFrom Wikipedia:
" g = m/r2, where g is the surface gravity of an object, expressed as a multiple of the Earth's, m is its mass, expressed as a multiple of the Earth's mass (5.976·1024 kg) and r its radius, expressed as a multiple of the Earth's (mean) radius (6,371 km). "
"The exoplanet is found about 600 light-years away, and it orbits a star very much like our own sun."
Reply | Report Abuse | Link to thisThat may be fine but we will likely never get that far.
Add the fact everything is spreading ever farther apart
Though it's fun to discover none the less.
kienhau
Reply | Report Abuse | Link to thisYes we won't be going, However, as for 'everything is spreading ever farther apart'...that's only on the grander level. Local 'stuff' is more varied...thus why our Galaxy and Adromeda will collide in a few billion years. Stars in our own galaxy can become closer or farther depending on a few variables.
Missed the point?
Reply | Report Abuse | Link to thisObviously, there are a lot of variables to habitability that we don't have the information to determine yet, for instance, perhaps toxic elements exist in the atmosphere. But it's likely that a number of the planets listed have moons stabalizing climates, we just can't see items of that size yet. It's also an assumption that a planet 5 times the size of earth gives a significantly greater gravitational pull than that of Earth.
But, the Industrial revolution wasn't that long ago, to suggest that space (whatever) is that far off as thousands of years seems a little far fetched to me. Overpopulation and overpollution may focus most of the minds on such solutions at some point in the nearer future. Wasn't so long ago we were inferring that stars existed by monitoring wobbles of stars and suggesting gravitational pull.
You say "it's likely that a number of the planets listed have moons stabalizing climates," but based on the sample of planets found in our Solar system (for which the presence of moons can be reasonably determined) and the method by which our moon is thought to have been formed from collision with another rocky protoplanet, it seems hardly likely at all to me. Do you have some basis for your assessment?
Reply | Report Abuse | Link to thisNo matter how many billions of unfortunate souls might wish move to a better 'New World', we were already granted and wasted that opportunity right here on Earth. Even if all our collective efforts were used to send humans to some other, much less welcoming 'New World', only a 'lucky' few could go, leaving wistful billions behind to suffer the horrible consequences of our mismanagement of reproduction and resource consumption.
By the time we get to another star, we may not want to visit except for scientific research. Barring major breakthroughs in ftl propulsion, we will likely spread slowly through the outer planets, Kuiper belt, and the trillions of objects in the Oort Cloud, building colonies as we go. Eventually reaching and moving into the Oort clouds of our neighboring star systems and proceeding on, passing the inner systems by, except for exploration and possible mining. Those spaces between the stars may be where we need to look for alien life forms.
Reply | Report Abuse | Link to thisAssuming comparable densities, the surface gravities of 2 planets will be in proportion to the ratio of the cube roots of their masses, not the masses themselves.
Reply | Report Abuse | Link to thisThere is one very important thing that did not get mentioned. Since Gliese 581G is a red dwark like 70% of all stars in every galaxy, it means planets would have to be extremely close to their parents in order to gather enough heat for liquid water. But red dwarfs are very unstable and are prone to violent releases in radiation. So 581G whizzing around its parent in 30 days clues that athought the temp may be correct, the radiation would toast any and everything. Ummm....just sayin'.
Reply | Report Abuse | Link to thisGood point!
Reply | Report Abuse | Link to thisThere's a few other issues mentioned here:
http://en.wikipedia.org/wiki/Red_dwarf#Habitability