Lecture of the Week: Part VII: Astrobiology

The Evolutionary Biology Lecture of the Week for June 26, 2006 is now
available at:

http://aics-research.com/lotw/

The talks center primarily around evolutionary biology, in all of its
aspects: cosmology, astronomy, planetology, geology, astrobiology,
ecology, ethology, biogeography, phylogenetics and evolutionary biology
itself, and are presented at a professional level, that of one
scientist talking to another. All of the talks were recorded live at
conferences.

This is the sixth lecture in a summer-long series on the new science of
astrobiology.

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July 3, 2006

Part VII: Astrobiology

The MER Mission and the Stratigraphic History
of the Meridiani Planum
Steven Squyres, Cornell University
34 min.

"If Mars be capable of supporting life, there must be water upon his
surface; for, to all forms of life, water is as vital a matter as air.
On the question of habitability, therefore, it becomes all-important to
know whether there be water on Mars."
- Percival Lowell, 1895

A "sol" is a Martian day, which by chance is very nearly the same
length as an Earth day, 24 hrs 40 min. The Spirit and Opportunity
rovers were sent to Mars to be the robotic hands and eyes of geologists
left on Earth to out seek evidence for ancient water. But Mars is a
challenging environment. The rovers were only "warrantied" to work for
90 sols, but against all odds they've continued to function far beyond
their original expectations, having just now passed the 900 sol mark.

Steven Squyres, the principal investigator for the rovers, was
informally interviewed on CNN last week and was asked how things were
going. He said, "We're very tired. Very happy, but very tired."

The Spirit Rover, as described by Matt Golombek in last week's lecture,
landed on the floor of Gusev Crater, which was found to have been dry
and dessicating since the late Hesperian (approximately 3.5 billion
years).

Opportunity was sent to the other side of Mars, into the lowlands at
Meridiani Planum. The intention of both rovers was to seek out evidence
of ancient water. While Gusev was discovered to have been dry for at
least three-quarters of Mars' existence, Meridiani gives every evidence
to have been once deep in water.

Hematite is an iron mineral that forms in the presence of water,
although volcanic genesis can also occur. The landing site at Meridiani
Planum was selected partly because coarse gray hematite was expected to
be present on the basis of orbital data.

As Squyres explains in the talk, microscopic images of undisturbed
surface soil showed that one component of the soil is fine (~100
micron) sand, and that Mössbauer spectra of the sand show two iron
doublets (one of them due to olivine), a ferric doublet, and a weak
magnetic sextet. APXS and Mini-TES data on this sand are consistent
with a composition dominated by basalt.

A second component of the soil consists of coarse (several mm)
granules. These range in shape from subangular to rounded to remarkably
spherical. The granules are finely laminated, with typical layer
thicknesses of only a few mm. The texture of the outcrops as viewed in
microscopic images suggests that it is fine-grained. APXS results on
this fine-grained matrix suggest an unusual composition, including
sulfur concentrations significantly higher than any observed elsewhere
on Mars. All of these conditions are consistent with water
mineralization processes.

At the time of this talk, about 200 sols into the mission, the
Opportunity rover had just entered Endurance crater, a crater 150 m in
diameter, 750 m from the landing area. Endurance is a crater of
spectacular topography. Sedimentary structures dominate its upper rim.
Because the mechanism responsible for the observed banding is not
perfectly understood, rock abrasion tool (RAT) holes were drilled
frequently as Opportunity descended into the crater.

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