GJ 436b: Mystery and Its Uses

by Paul Gilster on April 27, 2010

Yesterday’s musings on extraterrestrial contact were inspired both by Stephen Hawking and the surrealist painter Giorgio de Chirico (1888-1978). Whereas Hawking opined that an encounter with an alien culture could be dangerous, my own hunch was that it would be deeply mysterious and perhaps not even understood as contact, given the huge differences in technology between us. That called De Chirico’s strange cityscapes to mind, what Walter Wells calls ‘their deep and often irrational shadows, their empty walkways and portentous silences.’

It helped, of course, that years ago I had reviewed V.S. Naipaul’s The Enigma of Arrival, which draws heavily on the De Chirico painting of the same name (shown above). Naipaul’s book is a strange, autobiographical meditation whose subject is consciousness confronted with mystery. He imagines one of the two figures in the painting as a traveler and conceives a story based on the scene, one set in what he calls a ‘dangerous classical city,’ but he soon becomes caught up in autobiographical introspection and The Enigma of Arrival turns into an exercise in self-indulgence.

Too bad, because Naipaul at his best is a great writer. Even so, both the De Chirico painting and Naipaul’s treatment of it stayed with me, and it has often occurred to me that our scientific ‘arrivals’ can in their own way be just as enigmatic. A case in point: Last week we learned that the Spitzer Space Telescope, in its studies of the Neptune-sized planet GJ 436b, had performed an analysis of the distant world’s atmosphere. The result was unusual. GJ 436b should, by our current theories, show the clear signature of methane in its atmosphere. In fact, an atmospheric mix of hydrogen, carbon and oxygen in a temperature range up to 1000 Kelvin (726 degrees Celsius) should feature just tiny amounts of carbon monoxide and a large supply of methane.

But GJ 436b gives us just the opposite. Spitzer can detect its carbon monoxide but finds a clear deficiency of methane. In fact, the amount of methane here is 105 times less than predicted for a planet in thermochemical equilibrium. H2O is also present, as is CO2 in trace amounts. The technique, using the secondary eclipse as the planet moves behind its star as seen from Earth, has been proven sound and used on several ‘hot Jupiters.’ Spitzer worked with six infrared wavelengths and simply didn’t come up with what was expected. Joseph Harrington (University of Central Florida) is principal investigator on this work:

“In this case, we expected to find methane not because of the presence of life, but because of the planet’s chemistry. This type of planet should have cooked up methane. It’s like dipping bread into beaten eggs, frying it, and getting oatmeal in the end.”

Not a satisfying result in one sense, but of course from the scientific perspective, unusual results are all the more fascinating because they challenge us to improve our theories. GJ 436b is located in the constellation Leo some 33 light years away, orbiting an M-dwarf in a 2.64 day orbit. And while we figure out how to account for this planet’s atmosphere, we can also look forward with excitement to the extension of these techniques to smaller and cooler worlds, rocky planets not that much bigger than the Earth that could conceivably house life.

De Chirico’s art is all about showing life’s mystery and dwelling upon our aesthetic response. Science, on the other hand, uncovers mysteries like that of GJ 436b, but its aim is to resolve the tension they create by adjusting our models to fit incoming data. Good scientists rejoice in mystery even as they set about understanding it, much as the reader of suspense novels turns pages in anticipation of untangling the plot. What new enigmas may turn up when we have the ability to detect biomarkers on Earth-class worlds? And who will be the new De Chirico to capture the scene?

The paper is Stevenson et al., “Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b,” Nature 464 (22 April 2010), pp. 1161-1164 (abstract).

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{ 11 comments }

kurt9 April 27, 2010 at 12:56

Maybe its a harvested planet. The first sign of advanced alien intelligence.

Daniel April 27, 2010 at 14:42

talk about M dwarf star planets,one new sarturn mass planet was found in the habitable zone of the star Gliese 1148.

The Lick-Carnegie Exoplanet Survey: A Saturn-Mass Planet in the Habitable Zone of the Nearby M4V Star HIP 57050

http://arxiv.org/abs/1004.4608

i wonder if this planet have habitable moons

andy April 27, 2010 at 15:33

There’s already been some research done as to how relative abundances of elements can affect the bulk compositions of planets. Some planetary systems may have very different chemical make-ups to our own. For example, see this paper and this one. Unfortunately M-dwarfs are quite challenging targets for this kind of analysis, but it would be nice to know the relative abundances across a wide range of elements for this system.

As for habitable moons in M-dwarf systems, I’m quite sceptical. You have relatively small Hill radii, which means tidal evolution can rapidly cause a moon to become unstable or fall into the planet. Plus you have to consider that the stellar tides will be much stronger than tides on Earth, as the moon is going to be rotating with respect to the star. To make matters worse, the star’s gravity will probably also keep the moon’s orbit significantly eccentric, leading to planet-induced tides à la Io.

You’ve also got the ~0.02% scaling law for satellite system masses to contend with. If this applies to HIP 57050 as it does in our solar system, you wouldn’t expect to find moons more than a couple of times bigger than our own moon there. HIP 57050′s planet probably rules out Earth-type (liquid water oceans at the surface) habitable worlds in that system.

Phil April 27, 2010 at 23:34

Obviously it is complicated but I wouldn’t be surprised if this is all related to the initial composition of the solar system and how it formed planets after as Andy mentioned… 33 light years seems relatively close for things to be radically different though??

Of course there is no way to prove it has any connection to life at the moment but I think we can see from our own solar system that moons around gas planets can be very interesting and dynamic places (Titan, Triton, Io, Enceladus, and Europa come to mind). You don’t need a huge imagination to see these moons hosting life of some sort since the energy is apparently there.

It’s sci fi but I think it’s a cool idea… a civilization emerges around a gas giant and realizes it is within reach of a nearly infinite supply of methane… they reach down and grab it and then they proceed to use it all up and that’s how we find them in the end!! Right on our doorstep of all places….

Eniac April 28, 2010 at 1:26

In fact, an atmospheric mix of hydrogen, carbon and oxygen in a temperature range up to 1000 Kelvin (726 degrees Celsius) should feature just tiny amounts of carbon monoxide and a large supply of methane.

At high temperatures like that I do not see how the atmosphere cannot be in chemical equilibrium. If there is free hydrogen and carbon, equilibrium amounts of methane should form in very short order. I think for there to be methane we need hydrogen in excess of 2:1 with respect to oxygen.

Do we know for sure that there is enough hydrogen there?

Adam April 28, 2010 at 3:46

Hi andy

What about a captured Trojan planet? That’d by-pass the mass restriction – which I’m not convinced by a yet, in spite of my immense respect for Robin Canup’s work – and would be a natural outcome of a migration process.

Mark Phelps April 28, 2010 at 11:09

Paul,
Could it be that Hopper was influenced by Chirico? Certainly I see, now,hints of Chirico in Powers art too. Two very different approaches to making the intangible realized.

Best,

Mark

andy April 28, 2010 at 13:30

Adam: perhaps that’d work, but such a moon would still be subject to severe tides. In any case there is still the requirement to brake the moon into orbit around the gas giant: you have to transfer some of the momentum and kinetic energy somewhere, preferably to something with comparable mass. It’s interesting to note that Triton, which shows all the signs of being captured, still fits the mass ratio rule. Perhaps the proximity of the star would make the capture process easier, but not sure about this.

Administrator April 28, 2010 at 16:21

Mark Phelps writes:

Could it be that Hopper was influenced by Chirico? Certainly I see, now,hints of Chirico in Powers art too. Two very different approaches to making the intangible realized.

Good point, and I notice that the Wikipedia article on De Chirico makes this connection. You have a good eye! And yes, I agree about Powers.

Gary Williams April 28, 2010 at 16:35

Fascinating stuff. My first thought is that something chemical is going on due to it being so close to it’s star and then I saw kurt9′s response about it being a harvested planet and whilst I really, really, really don’t believe that it still makes an interesting thought exercise – As you have said – would we recognise something alien?

stephen April 29, 2010 at 16:11

Some stars have unusually high abundances of elements. Would that make it more likely for the planets to have high abundances, enough to have life with unusual biochemistries?

Fomalhaut has an unusually high level of flourine. Isaac Asimov suggested life based on fluorosilicones. Although the star is very young, maybe there could be precursors.

Could there be enough fluorine for lakes or oceans of fluorosilicones?

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