Thursday, September 30, 2010

Gliese 581g: An extrasolar planet sitting in a "habitable zone"

Okay - so astronomers are getting close. Up until the mid-1990s, we did not have any confirmed detection of planets outside our Solar system. And now the number is close to 500 planets (and in the mean time we even managed to take away the planetary status of one of our own planets. Pluto is still a planet, Dammit! :) ). But then all of the detections were of planets much bigger than the Earth, with most of them orbiting close to their parent stars (this was mostly the consequence of the wobble detection technique being used - the parent star wobbles because of the tug from a big planet, orbiting close by).

Now astronomers have detected a planet, Gliese 581g, only three times the mass of the Earth and located smack in the middle of the habitable zone. Habitable zone only means that the planet is orbiting at a distance where water can potentially exist in liquid form. And water, we think, is essential for life.

Very cool! We are not talking about any intelligent lifeforms here - but simply the potential of simple life (though, of course, it would be absolutely amazing if there was complex life there - but we can't say any thing about it from the information we have).

Couple of quick things: This is the sixth planet discovered orbiting the star Gliese 581 (yes, such names are very sexy for astronomers) - in fact this is the most planets discovered (so far) around a star other than the Sun. Gliese 581 is located only 20 light years form us or about 200 trillion kms (crap - it sounds much closer in light years - so lets stick with that).

But here is the cool thing (literally). Gliese 581 is a red dwarf - which means that it is relatively cooler than the Sun (couple of thousand degrees on the surface, versus 6000 degrees for the Sun). The newly discovered planet, Gliese 581g, is quite close to its parent star and it takes only 37 days to make one full orbit. One consequence of this is that the planet is tidally-locked with its star - i.e. the same side of the planet always faces the star and the other star never sees any light from the star (our Moon is tidally locked with the Earth - this is the reason we only see the same side of the Moon from the Earth - and thus Pink Floyd could come up with their cool album name).

Here is a schematic of the habitable zone before the discovery of Gliese 581g. It would sit smack in between the planets c and d:

So can there be life on a planet - where there is perpetual light on one side and perpetual darkness on the other? Very hot on one side and very cold on the other. We don't know (yet). Some have speculated that the border between the shadow and light may be a good place for life to originate and evolve. One can also imagine local terrestrial features, such as mountains, cracks, or crevices that may shield organisms from the blazing heat and may provide a suitable environment to thrive.

Okay, we'll have to eventually take a field trip there. But this is certainly the first of many planets discovered that will be good candidates for hosting other lifeforms.

Read the press release here and a story from the Washington Post here. If you are interested in Gliese 581, you can more information here.


Anonymous said...

hm thats intersting.
Is it necessary the parameters which we think are important for life are same for all the forms in the universe? May be the requirement of life over there or at any other planet is not water, light etc. Universe is far more vast than our imagination. Anything is possible

M. Akbar Hussain said...

If a planet has an atmosphere, I think tidal locking should not be a huge problem, as atmospheric tides due to temperature difference (and pressure diference as a result) should result in massive atmospheric current shifts maintaining an equillibrium. Like on Venus, where temperatures and pressures are same all over the planet, from poles to equator and from day side to night side (A day is longer than a year on Venus). Again extremophiles on Earth display remarkable ability to sustain in harsh and seemingly impossible 'alien-like' environments.

M. Akbar Hussain said...

(...sorry to comment was left in the middle as I had to rush to the theatre, one case after another).
Right, talking of extremophiles, thay are everywhere on Earth, from the deep trenches of Pacific Ocean, where pressures are far more crushing than on Venus, High up in the clouds in very low temperature, pressure, and high radiations, in volcanic vents in oceans with temperatures in excess of 120 degrees, dessicating chemical pools of sulphur in Yellow Stone NP, and miles under the ice sheets of Antarctica with no sunlight. I am a big fan of Tardigrades too who survived vacuum of space for months. Inshort, life is everywhere on Earth from poles to equator, from ocean depths to the top of high clouds, from freezing glaciers to boiling pools. The only places which are devoid of virtually any life are a few sterile patches in Atacama Desert that lack any trace of moisture...presence or absence of water makes real difference.
Now the presence of life is one thing, and the origin of it is another. Take a few tardigrades and some tough algae and bacteria to Gliese planet system, and the planets will be teaming with life (of course with a different ecosystem). But I still don't get over the odds involved in the creation of a simple prokaryotic cell, which is still much more complex than anything you can think or name.

Salman Hameed said...

Oh absolutely. Life can be in a form that we currently cannot imagine. However, we have to start with places/environments for which we know life exists - at least the one we know.


The possibility of a thick atmosphere is a great point - and that will indeed modulate the temperature differences to a certain degree. Also, because of the larger mass Gliese518g, there is also an increases likelihood of it retaining an atmosphere (because of increased gravity). Though too much atmosphere - and we run into a runaway greenhouse effect...

Ali said...

Interesting post Salman.
Discoveries such as this one makes me happy and they make me sad too.

Happy because it obviously gives us the impression we can abndon the Earth should the need arise. Sad because I realise this is such a false impression. Nevertheless, it is an excitement for everyone and I am sure a bigger one for the astronomers (who also teach evolution?).

Can a planet that is tidally locked with its sun even harbour an atmosphere? This question have been lingering in my mind ever since I saw Akbar's first comment here. So thought might as well ask.
Hi Akbar,
"But I still don't get over the odds involved in the creation of a simple prokaryotic cell, which is still much more complex than anything you can think or name."

Well, panspermia (if the word can be used for planets other than the Earth) on Gleise 581g is always an option. And we also know that there is more than one variety that we can choose from for this purpose.

If inhabitants are already there at Gliese 581g, we can even start an exchange programme. Any volunteers?

M. Akbar Hussain said...

Good thought about presence or absence of atmosphere on a planet that is tidally locked. I think most likely all the atmosphere will freeze and snow down on the night side of a tidally locked body. and the the planet would have been stripped off of an atmosphere altogether. The case for Venus is surely different in this case.
Perhaps we can dream about Earth or Mars sized moons orbiting a tidally locked gas giants in habitable zone circling Gliese581. Even though the moons may themeselves be tidally locked to the parent planet, but they will get equal cycles of day and night all over the surface, just like Jupiter's moons.
About creation of even the simplest (yet incredibly complex) prokaryotic cell, did you notice that I deliberately omitted the word 'Earth' for a purpose?