June 26, 2006

Part VI: Astrobiology

Surficial Geology of the Sprit Rover Traverse
in Gusev Crater: Dry and Desiccating
Since the Hesperian
Matt Golombek, Jet Propulsion Laboratory, Caltech
20 min. (slideshow requires QCShow Player)
Audio only (mp3 format)
View as a webpage (quicktime, real player) (notes)

To set foot on the soil of the asteroids, to lift by hand a rock from the Moon, to observe Mars from a distance of several tens of kilometers, to land on its satellite or even on its surface, what can be more fantastic? From the moment of using rocket devices a new great era will begin in astronomy: the epoch of the more intensive study of the firmament.
— Konstantin E. Tsiolkovsky, 1896

The geological column on Earth has been divided and subdivided again into increasingly finer segments, so that we now know the age of the strata to three or four decimal points.

Yet less than 200 years ago, we only had the crudest estimates of the age of the Earth. We identified the epochs by the kinds of fossils we found in particular rocks, giving the strata the names of the places in which they were found: Devon, Cambria, Siluria, Ordovicia and the like, only later sorting out which were older.

Mars is a new world to us geologically, and our current knowledge of Mars is as rudimentary as Earth once was. Armed with the first topographic maps of Mars derived from orbiting spacecraft, three crude epochs in the history of Mars were outlined based on cratering intensities at three locations: Amazonis Planitia, Hesperia Planum and Noachis Terra. These names mean nothing; they were assigned to regions of Mars by earth-bound astronomers early in the 20th Century, long before we had the capacity to see the regions in detail.

The Noachis region is ancient cratered highlands, Moon-like, a region left essentially undisturbed from the time of heavy bombardment during the formation of the solar system, ending ca. 3.9 billion years ago. Hesperia is a lower, much less cratered region, while Amazonis lies in the lowland half of Mars in which the craters have been erased.

Originally, in the absence of any other information, the three epochs were assigned roughly equal ages, but as recent evidence has accumulated, it has become increasingly more clear that the first two epochs were reasonably short, and that the current dry, dessicating epoch, the Amazonian, has dominated for three-quarters of Mars' life.

In this week's lecture, Matt Golombek, one of the principals responsible for choosing the landing sites for the Spirit and Opportunity rovers, speaks wistfully about the traverse of Gusev Crater by the Spirit rover. Layered sediments are the gold a geologist seeks. They tell a sequential story, but none were found on the floor of Gusev. Rather, the plains of Gusev were discovered to be a heavily impacted basaltic (lava) regolith, perhaps 10 meters or more in depth.

Although no clear evidence of rain-driven or lake activity was identified in the cratered plain, its surface geology still tells an important story. Gusev's geology strongly limits any warmer and/or wetter period of Mars history to be only pre-Late Hesperian at best. The surface geology of Gusev observed by Spirit, as it traversed the crater's floor, strongly argues for a dry and desiccating environment since the Late Hesperian. The geological history of Mars essentially died at that time. Erosion rates at Gusev are measured to be less than 0.1 billionth of a meter per year over the last 3.5 billion years, approximately 1/10,000th of what they were during the Noachian.

As we'll see in next week's lecture, we now have very strong evidence that Mars once had oceans, but the measurements at Gusev greatly constrain how long those oceans could have persisted, and by consequence the likelihood that Mars had sufficient time to evolve life.

— Wirt Atmar

About the Speaker

Dr. Matt Golombek is a research geologist at the Jet Propulsion Laboratory, California Institute of Technology, the lead NASA center for planetary exploration. He received his undergraduate degree in geology from Rutgers College, Rutgers University and his M.S. and Ph.D. in geology from the University of Massachusetts, Amherst. Golombek was a post-doctoral fellow at the Lunar and Planetary Institute, Houston after which he joined JPL as a Research Scientist. Since joining JPL he has worked on a variety of Mars developmental flight project studies, was the Mars Pathfinder Project Scientist, and is the Mars Exploration program Landing Site Scientist.

Golombek’s research focuses on Mars geology in general and the prediction of surface characteristics at a lander scale from orbital remotely sensed data. In his career, he has worked on a variety topics related to the structural geology and tectonics to the Earth, terrestrial planets and outer planet satellites.

Golombek was the chief scientist for the Mars Pathfinder Mission, which successfully landed a spacecraft and the Sojourner rover on Mars on July 4, 1997. As Project Scientist, Dr. Golombek chose the landing site for the spacecraft and was responsible for the overall scientific content of the mission.

As a research scientist at JPL, Golombek has worked in Earth and planetary (including satellites) structural geology and tectonics, with recent emphasis on Mars geology in general. This work has been funded via peer review from a wide variety of NASA programs, including the Planetary Geology and Geophysics and the Solid Earth Science Programs, as well as advanced mission studies and the operation phases of other Mars missions. The techniques used in this research include: field and structural mapping, brittle fracture analysis, paleomagnetic analysis, space-based geodesy, planetary mapping and analysis, and modeling of planetary structures and lithospheres. Dr. Golombek has served as editor or associate editor of professional journals, as convener of scientific workshops and special sessions at national and international meetings, as a member of many NASA science advisory groups, and has been invited nationally and internationally to speak as a contributing member of the science community.

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