Largest Methane Spike Ever, Curiosity Rover to Examine it Further Options

[dudley]

It's been reported today that a release of methane on Mars, three times larger than ever detected before, was discovered on Wednesday. On Friday the Curiosity rover had its plans altered, in order to concentrate on this phenomenon, it's said. Preliminary results of this investigation are expected on Monday. Further information is available in the article, linked below:

Link

[marsbug]

Ahem. If I might pedant.... many moons ago I used to build GCMS. So, for the uninitiated (feel free to skip this first paragraph if you already know how GCMS work): The Gas Chromatograph stage works by flash heating the sample and seeing how long the components of the vapour take to travel down a long, thin, column (more like a rolled capillary tube, usually) with one of a range of coatings on it's inner surface that slow the different vapour components down by differing amounts. The GC gives you a rough idea of what is in the sample based on how long different pulses of vapour components take to hit the detector at the end of the column. In the GCMS the Mass Spectrometer is the detector. This takes the material in the pulses exiting the GC stage, ionises it (aiming to average 1 charge per molecule), and separates the molecules in it according to their charge to mass ratio. So, crudely speaking, you get a rough idea from the GC, then a more detailed analysis from the MS.

OK, here's why I'm pedanting at you all: The important point for large molecules is that when you ionise them they almost always break apart - and for a given type of ionisation method most large molecules break apart in a predictable, repeatable, fashion. So you don't get a big signal at the charge to mass ratio for the parent molecule, you get a 'fingerprint' of smaller peaks that is unique to a given high mass molecule. For example, even something fairly light weight like the amino acid glycine (mass 75 AMU) yields a fingerprint like the one I've attached when ionised by electron bombardment (see attached file). Notice that the biggest peak isn't at 75 AMU, but at 30.

So the MS isn't simply analysing heavy molecules by their charge / mass ratio - in fact that almost certainly wouldn't work. It's using these heavy molecule specific fingerprints. It can be very, very, specific as long as the molecule is known or modelled in how it breaks down under ionisation. When combined with the GC stage, and a database of known GC and MS 'fingerprints' this can be a very precise process for identifying heavy molecules.

It can go wrong : Getting the right rate of GC heating, GC column type, ionisation process and mass to charge ratio analyser stage all needs some idea to start with of what type of thing you'll be analyzing. But in this case the team behind the GCMS on the rover will have had that from previous missions.

Now, that's probably clear as mud. And, if my old boss is here he will probably now tear me apart for that explanation anyway... go ahead Vic, I'm sure I deserve it.

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[JRehling]

That's a superb explanation, marsbug! Thanks for elevating the discussion!