July 3, 2006

Part VII: Astrobiology

The MER Mission and the Stratigraphic History
of the Meridiani Planum
Steven Squyres, Cornell University
34 min. (slideshow requires QCShow Player)
Audio only (mp3 format)
View as a webpage (quicktime, real player) (notes)

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 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 search for 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 it can be created throught volcanic genesis as well. 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 (Alpha Particle X-Ray Spectrometer) and Mini-TES (Mini-Thermal Emission Spectrometer) 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.

— Wirt Atmar

About the Speaker

Steven Squyres's research focuses on the large solid bodies of the solar system: the terrestrial planets and the satellit es of the Jovian planets. His work involves analysis of data from both spacecraft and ground-based telescopes, as well as a variety of types of geophysical modeling. Areas of particular interest include the tectonics of Venus, the history of water on Mars, and the geophysics of the icy satellites of the outer planets. Data analysis and theory are used together to examine the processes that have shaped the surfaces and interiors of these bodies.

Squyres has participated in a number of planetary spaceflight missions. From 1978 to 1981 he was an associate of the Voyager imaging science team, participating in analysis of imaging data from the encounters with Jupiter and Saturn. He was a radar investigator on the Magellan mission to Venus, a member of the Mars Observer gamma-ray spectrometer flight investigation team, and a co-investigator on the Russian Mars `96 mission. Dr. Squyres is currently the scientific Principal Investigator for the Mars Exploration Rover Project. He is also a co-investigator on the Mars Express mission, and on the Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment. He is a member of the Gamma-Ray Spectrometer Flight Investigation Team for the Mars Odyssey mission, and a member of the imaging team for the Cassini mission to Saturn.

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