Drilling for Life on Mars

Much has been said about the life that once may have existed on Mars (see

our review of Donald Goldsmith's The Hunt for Life on Mars in our Winter 1998

issue). But what about life that exists on Mars now? This is an ongoing

part of NASA's explanation of Mars, and how it is being done was explained by

Carol Stoker of the NASA Ames Research Center on 4 August 2004 at the American

Association of Physics Teachers meeting in Sacramento (CA).

In her talk on "Drilling for Life on Mars," Stoker began by describing

how the present conditions on Mars dictate where to search for life there.

Because the atmospheric pressure on Mars is close to that of the triple point of

water, water passes from solid to vapor state there; the liquid water

considered to be essential to a life-producing and sustaining environment can exist on

Mars only below ground. Moreover, Mars lacks atmospheric ozone to absorb

solar ultraviolet radiation which destroys organic compounds that might form on

the surface of the planet.

In fact, Mars Odyssey neutron spectrometry shows that an ice-rich layer

is known to lie 1-5 km below the ice-free layer on the surface of Mars,

especially in high latitudes (above 60 degrees). Below that, said Stoker, the ice

should be melted by internal heating. Drilling a couple of kilometers on Mars

is an ambitious project. But, Stoker noted, gullies may expose outcropping of

the underground aquifer layer 100 meters below ground level, after they are

cleaned off by a "Dust Devil." Finding extant life, she added, is more

important and more likely than recognizing extinct life, which may require multiple

missions or (more likely) human exploration.

Before trying this out on Mars, NASA is testing their drilling strategy

at Rio Tinto in Spain in their MARTE (Mars Astrobiology Rio Tinto Experiment).

Stoker said that the Rio Tinto area in the Iberian pyrite belt was chosen

because of its red color. There conventional drilling technology, sampling, and

analysis will look for living organisms whose metabolism is based on the

reduction of iron (to ferrous ion) and oxidation of sulfur (from sulfide to

sulfate). Such anaerobic bacteria have been found in the Rio Tinto, which has a pH

of 2.3, but they had never been found underground.

Formation of sulfate in acidic environment would produce sulfuric acid, a

eutectic solution of which has a freezing point of -16oC. Such a depressed

freezing point would enhance its likelihood on Mars. The detection of

jarosite (a hydrous sulfate of iron and potassium) on Mars further encourages Stoker

to believe that an ecosystem like that at Rio Tinto exists there, because

jarosite doesn't form above a pH of 3.

Stoker continued by pointing out problems in drilling for subsurface life

on Earth that will not occur on Mars:

1) introduction of surface organisms into the subsurface.

2) alteration of chemical properties.

3) destruction of anaerobic life by exposure to aerobic environment.

She said that the core samples are protected against atmospheric oxygen by

plastic liners and are analyzed in an anaerobic glove chamber. Cultures have

been grown from the rock both aerobically and anaerobically, with identification

of possible bacteria in SEM (Scanning Electron Microscope) photos. Microbes

have been identified both above and below the water table, she reported, with

resources to sustain them in the same layer.

Those interested in learning more about MARTE can avail themselves of

eight hour-long on-line lectures (in either English or Spanish) -- at the

following website: The lecture titles are "Mission to Mars, the MARTE Project and

an Introduction to Rio Tinto, Spain," "The Wonders of a Mars Analog: Biology

at Rio Tinto," "Subsurface Life," "Spain's Iberian Pyrite Belt," "Issues and

challenges for Robotic Drilling," "Drilling on Mars," "Molecular Biology

techniques for discovering life on Mars," and "Sample Handling while Searching for

Life." The first 18 frames of PowerPoint for the first lecture match those for

Stoker's talk to AAPT.