In the News: Exoplanet Missing Methane

[CraigS]

In the news:
Lack of methane to blame for planet's 'smell'

To the surprise of astronomers who have been studying the Neptune-sized planet using NASA's Spitzer Space Telescope, GJ 436b (33 light years) has very little methane (CH4).
..
"Methane should be abundant on a planet of this temperature and size, but we found 7000 times less methane than what the models predict,"
…
Finding methane was a foregone conclusion.
…
But what if planetary atmospheres don't always follow the rules of our own Solar System? GJ 436b certainty doesn't. Investigators might have to go back to the drawing board and re-figure their chemistry.
"GJ 436b is telling us something important," says Harrington: "We’re not in Kansas anymore."

Note the underlined part. The 'Pathological Science' part of me is not surprised by this statement.

Cheers

[renormalised (Carl)]

Here's the data for the planet....GJ 436b

There could be another reason for the deficit of methane....the presence of a catalyst in the atmosphere. Given it's density, if this planet doesn't have a well defined core (i.e. it's relatively well mixed in its interior), then that catalyst maybe Fe, in the form of small particles floating around in the atmosphere). I'd suggest they try and get both spectroscopic and albedo measurements done on this planet as soon as they can.

[renormalised (Carl)]

Just had a quick read on methane...I might have an idea. See if it works

[CraigS]

Don't blow yourself up there, fella !


Cheers

[renormalised (Carl)]

Nah, that won't happen. It's all in the head....just equations

[renormalised (Carl)]

Here's the article on GJ436b straight from the horse's mouth

http://planets.ucf.edu/research/exoplanets/GJ436b-Wheres-the-methane

The reactions for the methane are just as I suspected

[CraigS]

i) They're obviously pretty confident of their lightcurve readings, in the first place. This is still a fairly new measurement technique. They only have a total of six observations to go on at the moment, also.

ii) They're chasing only a few disequilibrium processes as a possible explanation. There could be others (?);

This seems to be a preliminary finding. Heaps more for them to do, and find out, methinks .

Let's face it … there's lots of things going on on the surface of this thing because of its close proximity to the star.

Cheers

[renormalised (Carl)]

We know the base reaction which is occurring is this...

CH4 + H2O------>CO + 3H2

Under normal circumstances, this will drive towards the CH4 end, but the addition of a catalyst will prevent that. However, you've got to get the water in the first place. The way to get that is through oxydative pyrolysis of the CH4....

CH4 + O2------>CO + H2 +H2O

So, in order for the equations to produce the amounts of H2 and such we see, they need to be balanced as such...

3CH4 + 3O2----->3CO + 3H2 + 3H2O (1)

3H2O + CH4----->CO + 5H2 (2)

What has to be prevented is the CO oxidising to CO2, which means the CH4 must react with the water before it photodissociates in any UV light. The way to do that is to have one reaction occur higher up in the atmosphere than the other....in this case reaction (1) occurring in the upper atmosphere and (2) further down. That would mean large scale rapid vertical atmospheric turnover...strong convection. Some water would have to be broken up to get the O2, so not all of it is getting away. In lieu of the UV, the heat should breakup the water molecules.

[CraigS]

Ok ... But surely strong convection happens elsewhere in our observations ?

What's so special about this one ?
(Ie: that we can't see the CH4 => requiring the strong convection/catalyst ?).

Cheers

[renormalised (Carl)]

This is just one particular case...there maybe more we haven't really looked at, yet. Also, they haven't yet fully explored this planet's orbital history. It maybe this way because it was still quite convective within the body of the planet when it arrived in its present orbit. Which means it's been there since early on. The planet was well mixed early on whilst it was forming, and has stayed that way now, due to its proximity to its parent star.

Every planet has to be taken on a case by case basis. There is most likely a "standard" way of forming these planets, but there is always variations to the standard and not all planets will necessarily follow the standard to the letter (if, in truth, any planet really does).

[CraigS]

There is a lot of conjecture about his planet.

It has an eccentric orbit, so it got a partner planet:

This planet should not be as eccentric as is measured. To have maintained its eccentricity over time requires that it be accompanied by another planet. In September 2008, a formerly-unrecognised transit signature at NMSU from January 11, 2005 was incorporated into the data up to then, consistent with a planet at 0.08 AU and under 12 Earth masses.

It has a period of about 2 days (only !)… but:

Whatever energy that tidal effects deliver to the planet does not notably affect its temperature.

This isn't what happens around Saturn & Jupiter !

The planet could have formed further from its current position, as a gas giant, and migrated inwards with the other gas giants. As it arrived in range, the star would have blown off the planet's hydrogen layer via coronal mass ejection

.. and now a previously unknown convection to account for missing CH4.

I realise that the variability in our own Solar System is immense but it seems that each planet is destined to have its own formation theory !

Surely true scientific value comes from when there is a 'class' of planets which have something(s) in common (?).

We must have a long, long way to go to see the horizon on all this stuff !!

Cheers

[renormalised (Carl)]

Well, it would have to have a partner planet or some other large body in the system to maintain the eccentric orbit it has, otherwise tidal forces between it and its parent star would've circularised it over time. It needs those gravitational tugs to keep it in that elliptical orbit (which is less eccentric than Mercury's).

Two days isn't all that uncommon amongst these close in planets. There are a number around that orbit their stars in even less time...WASP 18b for example.

This particular planet does have some tidal effects due to it's closeness to the star, but not enough to adversely affect its temp...remember it orbits a small star (an M dwarf).

No, because Saturn and Jupiter formed a long way from the Sun...way outside the ice line and a long way from all that heat and solar activity. They did change their orbits as they were forming but the accretion disk around the Sun was neither massive enough to create enough drag on the planets to slow them down, nor did it last long enough to give these effects time to take hold. After the little game of "billiard balls" finished after their formation, they settled into the orbits they're now in. In many systems, this process keeps on going till you get the situations we see.

These planets do have initial histories in common, but it's what happens after they form that is important. What occurs around the star and the environment that is present, which determines the fate of the planet. It all depends on a lot of factors, least of which is where the planet initially forms and how that occurs. That builds the planet...then it's up to the gravitational and other dynamic conditions present as to where it may orbit eventually.

[avandonk]

The paucity of data is directly/inversly proportional to the conjecture!

Berts law.

[renormalised (Carl)]

Originally Posted by avandonk

The paucity of data is directly/inversely proportional to the conjecture!

Berts law.

True

[CraigS]

Originally Posted by renormalised

This particular planet does have some tidal effects due to it's closeness to the star, but not enough to adversely affect its temp...remember it orbits a small star (an M dwarf).

No, because Saturn and Jupiter formed a long way from the Sun...way outside the ice line and a long way from all that heat and solar activity. They did change their orbits as they were forming but the accretion disk around the Sun was neither massive enough to create enough drag on the planets to slow them down, nor did it last long enough to give these effects time to take hold. After the little game of "billiard balls" finished after their formation, they settled into the orbits they're now in. In many systems, this process keeps on going till you get the situations we see.

Sorry .. I was drawing analogy from moons close to large objects such as Jupiter's moon Io - the most volcanically active object in the Solar System, which I believed was due to Jupiter's tidal pull on it. (I now realise its a resonance effect, due to it being between Jupiter and the other Galilean moons).

I was also thinking of Enceladus, but I now understand they think the cryovolcanism there results from mean motion resonance with Dione.

I have a feeling both of these explanations, (from Wiki), have been updated since I last looked.

Cheers
PS: The diversity of all this is astounding !! Which hooks into my thoughts about the chances of finding life on a single, given planet (other than Earth), perhaps, may not be at all significant, even when taking into account the numbers of planets which are clearly out there.

Who is to say that the planet environment diversity times the biological near-'fluke' of life, is outweighed by the numbers of planets times the same chances-of-life probability ?

Does that make sense ? I hope so. Cheers.

[CraigS]

Err .. I think Bert's law takes care of my last question ..
(His post beat mine).

Cheers

[renormalised (Carl)]

Here's something interesting...

http://arxiv.org/PS_cache/arxiv/pdf/...007.0324v2.pdf

A paper by Beaulieu etal, which goes to say that the study by Stevenson etal may have observational or analytical flaws and that maybe why they never detected any methane in the atmosphere of GJ436b.

[CraigS]

It would appear that the journos (& NASA) may be the cause of any confusion on this one.

The original paper by Stevenson etal was received by 'Nature' on 18 Nov 2009, accepted on the 5th March, and then published in Nature on April 22, 2010.

The first article about this appeared (in Physorg) on April 21, 2010 (source material provided by NASA/JPL/Spitzer).

The rebuttal paper was then published arXiv on 28th July, 2010.

Then Physorg again republished the original Stevenson article on Sept 14 and it doesn't seem to include any more info/detail. The Sept 14 article was sourced from Science@NASA (Dr. Tony Phillips and Dauna Coulter). This is the one which kicked off this thread.

Apart from the confusing multiple articles (being superseded, as well), the content is interesting, none-the-less.

From the rebuttal paper Beaulieu etal:

This collection of data strongly suggests that methane is the dominant species in such an atmosphere. An opposing scenario was proposedby Stevenson et al. (2010), when they interpreted secondary transit data recorded with Spitzer at multiple wavelengths. We have shown here, though, that a methane- rich atmosphere and the presence of a stratosphere could produce a similar effect: spectroscopic data are necessary to test this hypothesis.

In my own defence, I did say after reading the original Stevenson paper: "They're obviously pretty confident of their lightcurve readings, in the first place. This is still a fairly new measurement technique. They only have a total of six observations to go on at the moment, also."

Beaulieu et al are now saying they need good 'ol spectroscopic readings.

Good fun. Apologies for the confusion but 'twas worthwhile going 'round the loop. Thanks for the 'heads-up' on the Beaulieu paper, Carl.
Interesting.

Cheers

[renormalised (Carl)]

Yep, whip out the ol' grating and get me some colours

Start looking for the tiger stripes

[CraigS]

Originally Posted by renormalised

Start looking for the tiger stripes

Add light curve analysis to the heap …. no time dilation from pulsars {EDIT: quasars} …. fine structure constant anomalies … all governed by Bert's law, huh ?



Cheers
Edits done following Carl's correction above.