Continuing into Glenelg, Leaving Rocknest behind, sols 102-166 (Nov 18 2012-Jan 23, 2013) Options

[Astro0]

New frontiers Sol 102



Larger

[marsophile]

"A determination about how much time passed between the emplacement of the water-formed rocks and then a second episode of water flowing through cracks in the rocks can not be determined with Curiosity's instrument suite," she said.

http://spaceref.com/mars/curiousmars-tripl...production.html

If APXS readings were obtained for the vein material, would not the relative amounts of deuterium give an estimate of the time intervening between the two events?

[dvandorn]

If APXS readings were obtained for the vein material, would not the relative amounts of deuterium give an estimate of the time intervening between the two events?

Ummm... can the APXS detect deuterium at all, much less analyze its relative abundance? An Astronomy Online review of the MER APXSes (which, as I understand it, are quite similar to the one on Curiosity) says the following:

The x-ray mode is sensitive to major elements, such as Mg, Al, Si, K, Ca, and Fe, and to minor elements, including Na, P, S, Cl, Ti, Cr, and Mn. The alpha mode is sensitive to lighter elements, particularly C and O. The depth of analysis varies with atomic number, ranging from approximately 10 to 20 micrometers for sodium, to approximately 50 to 100 micrometers for iron. The detection limit is typically 0.5 to 1 weight percent, depending on the element. The APXS is insensitive to small variations of the geometry of the sample surface because all major and minor elements are determined, and can be summed to 100 weight percent.

I don't see H mentioned anywhere in the list of elements to which the APXS is sensitive. Obviously, it's not a definitive list, but... just sayin', I thought APXS only gave relative atomic abundances and only for a selected set of elements to which the detectors are sensitive. I didn't think it actually gave molecular abundance information.

-the other Doug

[DFortes]

Ummm... can the APXS detect deuterium at all, much less analyze its relative abundance? An Astronomy Online review of the MER APXSes (which, as I understand it, are quite similar to the one on Curiosity) says the following:

I don't see H mentioned anywhere in the list of elements to which the APXS is sensitive. Obviously, it's not a definitive list, but... just sayin', I thought APXS only gave relative atomic abundances and only for a selected set of elements to which the detectors are sensitive. I didn't think it actually gave molecular abundance information.

-the other Doug

There are two answers to the question of this instrument's ability to detect light element. Firstly, hydrogen (and deuterium) do not fluoresce in the X-ray portion of the spectrum - their most energetic emissions unpon excitation are in the UV.
Secondly, progressively lighter elements emit lower energy X-ray (from 525 eV for oxygen, down to 54 eV for lithium), and these are more readily absorbed by any 'air' between the sample and detector. I haven't sat down to do the calculations, but I suspect that even the relatively thin martian atmosphere will substantially block these low-energy emissions along path lengths of mm to cm in air (to say nothing of through solid rock!)
And this is before you even begin to worry about what the detector is sensitive to....