Gliese 581d
Published on Jun 16, 2007 at 11:39 pm.
9 Comments.
Filed under extrasolar planets.
Back in April, I posted about the star Gliese 581, and in particular about one of its planets, Gliese 581c. In that post, I reported on Udry et al’s announcement of a potentially habitable planet, Gliese 581c. In my previous post, I presented my doubts as to the habitability of this planet. Now, I find that Manfred Cuntz, an astronomer at the University of Texas at Arlington, along with colleagues from the Potzdam Institute for Climate Impact Research, has submitted a paper to Astronomy and Astrophysics with mathematical analysis supporting my impression of this planet. The problem, you see, is that planetary atmospheres tend to have a greenhouse effect. Our own Earth does, in fact. Without the Earth’s atmospheric greenhouse effect, Earth would have an average temperature well below the freezing point of water. According to Cuntz and his colleagues’ paper, Gliese 581c turns out to be far too hot once you include the effect of a greenhouse effect in its atmosphere.
In fact, this is a most likely scenario. Gliese 581c has a mass of about 5 times the mass of Earth. This would imply that the planet would have a higher gravity than Earth. That would suggest a thicker atmosphere. And, that thicker atmosphere would have a greenhouse effect on the planet, and that greenhouse effect would likely be bigger than Earth’s. That would mean that the planet would be far too hot to sustain life.
But, Cuntz and his colleagues did not stop there. They also looked at another recently discovered planet orbiting Gliese 581. This planet, Gliese 581d is larger, nearly 8 times the mass of Earth. It also orbits quite a bit farther from the star, at nearly 0.25 Astronomical Units. In earlier things written about Gliese 581 and its planets, this outer planet was generally discounted as being a possible haven for life. But, interestingly, Cuntz et al have found that may have been a premature dismissal of the planet. With 8 times the mass of the Earth, Gliese 581d would most certainly have a thicker atmosphere, and that would surely contribute to a significant greenhouse effect. Their analysis shows that for certain concentrations of CO2 in the atmosphere, and sufficient water coverage, the planet Gliese 581d may be habitable. Now, by habitable, I mean that some life may exist. They also show that this planet, even much farther from the star than Gliese 581c, will still likely be tidally locked to its parent star. This will make the lit side of the planet likely unbearably hot. And, the night side would be punishingly cold. But, again, with water and enough carbon dioxide, calculations suggest that the temperature extremes, while quite extreme, would not necessarily render the planet uninhabitable. That would be particularly true along the terminator. But, let’s be clear: the climate would be extremely severe. This new study makes the statement that while the planet may be habitable, complex life is unlikely due to the severity of the climate.
But, this study does seem to make the case that Gliese 581d may, in fact, be the first habitable exoplanet discovered to date. And, that is exciting, even if it is only barely habitable. This is still not a certainty, of course, but it is intriguing.
-Astroprof
Image, courtesy ESA.
A Ler…-- Rastos de Luz on June 18, 2007 at 7:49 am: 1
[…] “Science and the Press“, no Astroprof’s Page. Também a ler neste blog, “Gliese 581d“; […]
Shaun on June 29, 2007 at 6:53 am: 2
I’m must readily confessed to being not much of an expert here, more of a novice astro buff to be exact, so do pardon me for my ignorance. But I do have some questions.
What has gravity got to do with the ability of a planet to possess a thick atmosphere or not? Do correct me if I’m wrong but both Venus’s gravity (8.87 m/sec^2 for Venus Vs 9.78 m/sec^2 for Earth, see*1) and its mass (4.869 * 10^24 Vs Earth’s 5.976 * 10^24, see*2) is lower than Earth’s but yet it has a much much thicker atmosphere, why is this so?
While G 581d may indeed be a tidally locked planet given that it is but a mere 0.25 AU (see *3) from its SpT M2.5V (see *4) primary, am I not wrong to say that so long as there is some kind of a greenhouse effect at work, there will not be the kind of extreme Teff variations between its lit and dark sides if the circulation mechanisms there are effective enough?
Sources:
http://www.solarviews.com/eng/venus.htm
http://www.solarviews.com/eng/earth.htm
http://exoplanet.eu/planet.php?p1=Gl+581&p2=d
http://en.wikipedia.org/wiki/Gliese_581
Astroprof on June 29, 2007 at 10:56 am: 3
Yes, a greenhouse effect, if it is strong enough, can mitigate the temperature extremes.
The higher a planet’s gravity, the easier it can hold onto an atmosphere. The higher the temperature of the (upper portions) of the atmosphere, the easier it is for the gasses to leave, particularly the light ones. The Moon, for example, is the same distance from the Sun as the Earth, but it does not have enough gravity to hold an atmosphere. But, Titan, nearly the same gravity as the Moon holds an atmosphere because it it ten times farther from the Sun. Earth and Venus have gravity enough to hold an atmosphere, but not enough to hold the lightest of gasses: hydrogen and helium. Earth and Venus both have the ability to hold an atmosphere like Venus’; however, oceanic and biologic activity have removed most of the CO2 from Earth’s atmosphere. If you were to remove the CO2 from Venus, what would be left would have a thickness like Earth’s. Conversely, if you were to free up the CO2 bound up in rocks on Earth, then Earth’s atmosphere would be very much like Venus’.
Amy on November 16, 2007 at 1:46 pm: 4
please send info on Gliese 581d to aamanda39@yahoo.com
Amy on November 16, 2007 at 1:47 pm: 5
please send info on Gliese 581d to aamanda39@yahoo.com, Thanx!
The Guild of Scientific Troubadours » Goodbye, alien neighbors. on December 1, 2007 at 12:22 am: 6
[…] Unfortunately, Nature has shifted that article into its paid subscriber-only archive, but you can get the gist of the story here, here and here. Gliese 580d is the new most-likeliest-to-be-alivest planet Earth people have seen in space. In fact, it’s technically a super-Earth. […]
Nicki Gloden on January 30, 2008 at 3:54 pm: 7
omg i cant belive there is a new planet!! we could actually live there??? Twnety years 2 get there is a little long dont you think!?
If it is 8 times the size of earth that gives me an idea. Rule the Planet. Some of it could be a mall, some of it could be the little stone houses that everyone would live in and then the rest of it could be my palace!! Just Kidding. Can’t wait to hear more
thirst4knowledge on May 16, 2008 at 12:45 pm: 8
realitive to what you were saying about earth being able to hold an atomosphere compared to venus.We know that the early earth comprised of mainly iron concentrated water which was turned to iron oxide (rust) with the introduction of oxygen,the same can be said to carbon dioxide due mainly to water and oxygen.We know where there is water there is life and where there is life oxygen may exist so if there is enough water and oxygen can’t this lower the effects of greenhouse gases and thus make 581d hospitable to carbon based life forms. Please reply to let me know if I’m behind the 8 ball.
thirst4knowledge on May 16, 2008 at 1:23 pm: 9
but then again all 3 planets of the gliese 581 system orbits too close to there parent star and will almost certainly be tidally locked and therefore all these analysis is irrelevant but what of the poles where less solar radiation reaches. Would it be possible for there to be a habitable zone?and if it is 8 times the mass of earth close to the poles should be fairly large for a civilization to reside comfortably but I suppose all of this is wishful thinking the universe is just too large for mankind to discover an earth-like planet within the reach of humans within our lifetime but I am content with the fact that my children or my grandchildren will live to see it if god spare there lives