Saturday, June 26, 2004

Images and news from the Spirit and Opportunity Rovers

After 170 martian days (none of this "sol" stuff for me...), the Spirit rover has joined Opportunity in detecting rocks with significant hematite content. Further analysis of the mineralogy is still needed to make the case that the hematite was deposited in an aqueous environment as appears to be the case for Opportunity's detection, but the rocks are _truly_ unusual in any case:

Some Crazy-Ass Rocks.

The rock getting some media attention yesterday and today is "Pot of Gold" and is located just above and to the left of the center of that image. It appears to be morphologically similar to the group of rocks exposed at the far right of the image. You can clearly see resistant, thin shells around knobby, decayed looking rock.

One Crazy-Ass Rock.

Displays the profile of "pot of gold" in shadow, and

Close view of a Crazy-Ass Rock.

shows the texture of the rock on the ~1 inch scale.

----

Speaking of the Opportunity detections, keep your ears peeled for hints of astrobiological investigations at that site. The mineralogy of the Opportunity landing site is strongly suggestive of a hydrothermal depositional environment with temperatures and redox conditions known to be highly conducive to bacterial activity on earth. Further, the precise mineral phases precipitated in such environments on earth are very strongly mediated by microbiological activity, and the Mossbauer spectrometers that the rovers carry are, by their very nature, sensitive to subtle variations in Fe-bearing minerals like those found in such environments.


Mossbauer spectroscopy:

The Mossbauer effect refers to the utilization of a cold crystal matrix to stiffen the recoil of a nucleus as it emits or absorbs a gamma radiation photon. Absent that effect from the matrix, an emitted (or absorbed) photon loses sufficient energy to the recoil of the nucleus to take it out of resonance with the opposite energy level change in a potential absorbing (emitting) nucleus of the same isotope.

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/mossfe.html

for more information on why the Mossbauer effect is particularly useful for studying Fe minerals. In a Mossbauer spectrometer, Co-57 is used as a gamma source. The actual gamma emission is not from the decay of Co-57 to Fe-57, but from the relaxation of the resultant Fe-57 nuclei to lower energy states. The gamma source is vibrated to sweep the emitted gamma energy over the range expected to be resonant with the Fe nuclei in the sample given the sample's anticipated temperature, chemistry, and crystalline structure. The specific gamma emitting transition utilized, the mass of the Fe nucleus, and the characteristics of typical Fe-bearing crystals make the source velocities required and the resolution obtainable particularly attractive for Fe relative to other elements.

-Ethan, very sorry for the too-long post.

2 Comments:

Blogger finou said...

wow! the pictures are so pretty.
The rover is pretty darn cool. I feel like we are living in one of those futuristic movies :)-

6/27/2004 01:51:00 PM  
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