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ScienceDaily: Astronomers Find First Habitable Earth-like Planet

Science Daily -- Astronomers have discovered the most Earth-like planet outside our Solar System to date, an exoplanet with a radius only 50% larger than the Earth and capable of having liquid water. Using the ESO 3.6-m telescope, a team of Swiss, French and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbour a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses.

This exoplanet - as astronomers call planets around a star other than the Sun -- is the smallest ever found up to now [1] and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581 [2], is smaller and colder than the Sun -- and thus less luminous -- the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid!

"We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stéphane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result. "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky -- like our Earth -- or covered with oceans," he adds.

"Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X."

The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the constellation Libra ("the Scales"). It has a mass of only one third the mass of the Sun. Such red dwarfs are intrinsically at least 50 times fainter than the Sun and are the most common stars in our Galaxy: among the 100 closest stars to the Sun, 80 belong to this class.

"Red dwarfs are ideal targets for the search for low-mass planets where water could be liquid. Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun," emphasizes Xavier Bonfils, a co-worker from Lisbon University. Planets lying in this zone are then more easily detected with the radial-velocity method [3], the most successful in detecting exoplanets.

Two years ago, the same team of astronomers already found a planet around Gliese 581 (see ESO 30/05). With a mass of 15 Earth-masses, i.e. similar to that of Neptune, it orbits its host star in 5.4 days. At the time, the astronomers had already seen hints of another planet. They therefore obtained a new set of measurements and found the new super-Earth, but also clear indications for another one, an 8 Earth-mass planet completing an orbit in 84 days. The planetary system surrounding Gliese 581 contains thus no fewer than 3 planets of 15 Earth masses or less, and as such is a quite remarkable system.



The fact is that what we're experiencing right now is a top-down disaster. -Paul Krugman
by dvx (dvx.clt ät gmail dotcom) on Wed Apr 25th, 2007 at 03:04:01 AM EST
[ Parent ]
the smallest ever found up to now

Smaller ones have been found around a pulsar, but that one is often forgotten by the optical exo-planet hunters.

Regaring habitability, two further issues beyond temperature:

  • Since this planet orbits beyond a Neptune-sized planet (which could get that close only by spiralling inward from much further out), it must have been exposed to sizeable perturbations, which makes it likely that its orbit is not very circular. Changing radiation input on a 13-day orbit, I wonder what atmospheric features this could drive.

  • A small red dwarf is not only less luminous overall, but its spectra differs, too. At 3250K-> peak luminosity around 900nm, at the wavelengths preferred by our plants it falls off to about a third.


*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Apr 25th, 2007 at 06:12:48 AM EST
[ Parent ]
In other words - very warm, very windy, and very flat.

Not quite a home from home yet. Although finding something so earth-like so close given the limits of technology does suggest there will be more Earth-like objects/planets (ELOs? ELPs?) in the immediate area.

by ThatBritGuy (thatbritguy (at) googlemail.com) on Wed Apr 25th, 2007 at 06:59:43 AM EST
[ Parent ]
In other words - very warm, very windy, and very flat.

No, no, no :-) 0-40°C --- not necessarily very warm, I don't get the flat reference, and what I meant isn't necessarily being very windy: there could be brutal wind direction/precipitation changes, maybe even global phase shifts in every orbit, or alternatively (depending on rotation period, axis tilt) there could be stark regional differences, which in turn can drive planet-wide circulation systems. The more interesting if there is water and there is coupling between the atmosphere and oceans, like on Earth but possibly on a grander scale.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Wed Apr 25th, 2007 at 07:14:28 AM EST
[ Parent ]
Five times the mass? That's not going to be easy to run around on, even if with a wider diameter. (1.7g?)

0-40°C is an estimate, but I'd guess with water vapour and energy input shading into infra red wavelengths there would be more chance of the latter.

there could be brutal wind direction/precipitation changes, maybe even global phase shifts in every orbit, or alternatively (depending on rotation period, axis tilt) there could be stark regional differences, which in turn can drive planet-wide circulation systems.

Yep - windy. :)

by ThatBritGuy (thatbritguy (at) googlemail.com) on Wed Apr 25th, 2007 at 07:41:27 AM EST
[ Parent ]
Astronomers are busy decoding a message received yesterday from the newly discovered planet in the Gliese 581 solar system...

Dear Earth:  As much as we'd like to have you over for drinks & dinner, please excuse the delay in extending an invitation to our newly-aware-of-us neighbors.

Honestly, our reluctance to invite you over for a chat has absolutely nothing to do with the chaos you've wrought of your own neck of the universe, either environmentally or militarily.  Really.  We're just a little, um, busy at the moment.  And the house is just a mess.  We've been having work done on the plumbing, and now they're having to take up the floors.    And it seems that there could be some, um, contagious mold growing behind the radiator, so perhaps it's in your own best interest if you just don't come visit right now.

To be perfectly honest, we were kind of hoping you wouldn't notice we were here for a few more millenia.  But it has nothing to do with you, really.

Signed,
The Gilesians

by the stormy present (stormypresent aaaaaaat gmail etc) on Wed Apr 25th, 2007 at 08:08:52 AM EST
[ Parent ]

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