NASA Field-Tests the First System Designed to Drill for Subsurface Martian Life
Mars is desert-like and much colder than Earth's Antarctica. Nearly all the time, the temperature on Mars is far below zero. Its surface is much too frigid, and the martian air is too thin for liquid water to occur. Life as we know it requires liquid water.
A pair of NASA Voyager spacecraft landed on Mars in the 1970s to look for life. They scooped and tested the martian soil, but they did not find solid evidence of life. In addition, various spacecraft have observed clouds and dust devils in the very thin atmosphere that is mainly carbon dioxide.
What is more, spacecraft have seen empty riverbeds that indicate that water once flowed on the surface, according to many scientists. More recently, two NASA Mars Exploration Rovers (MERs) landed in early 2004 and found geologic evidence that liquid water had indeed existed long ago on Mars.
So, if there were life on Mars today, where would we find it? By drilling for it, according to Carol Stoker, principal investigator for the Mars Astrobiology Research and Technology Experiment (MARTE). She also is a scientist at NASA Ames Research Center, located in California's Silicon Valley. Astrobiology is the study of life in the universe.
"Drilling deep below the martian surface offers the best opportunity to find evidence of current, living organisms on Mars because liquid water may exist there today," Stoker ventured.
"We can find evidence of ancient environments that may have hosted liquid water on the surface of Mars by exploring the surface with rovers, and that's what NASA is currently doing," Stoker said. "Liquid water environments on the ancient martian surface might have hosted living organisms, and it is possible that life may have left a fossil record that can be discovered on the martian surface."
"However, the current surface of Mars is really a very nasty place for living organisms. It's very cold, well below freezing. The atmosphere is very thin, and liquid water can't occur," Stoker explained.
In order to seek life in the martian subsurface, robotic drilling, extraterrestrial sample handling and life-detection technologies must be developed, according to Stoker. "Robotic drilling for Mars exploration is in its technological infancy, and key technologies have yet to be demonstrated even in a terrestrial environment," Stoker noted.
To advance the state of the art of robotic drilling technology, Stoker is overseeing development of a prototype drilling system. Using this newly developed drilling system, NASA researchers plan to simulate a Mars mission later in 2005 near the Rio Tinto, a river in southwestern Spain.
Marte is the Spanish word for Mars, and the Rio Tinto area in Spain is also where Stoker and her team earlier performed drilling experiments to search for subsurface life in a Mars analog environment—an environment that may well be similar to one within the martian subsurface. Researchers used these earlier experiments to guide development of technology for Mars drilling and for searching for life in subsurface samples.
Before returning to Spain, the team tested the new robotic drill and sample handing system for the first time in Bonny Doon, Calif., near NASA Ames.
Describing the MARTE drill, Stoker said, "I think it may be one of the most complex robotic devices ever built—certainly, the most complex robotic drilling system ever built."
The drill platform includes a suite of scientific instruments that is able to search for evidence of life in samples the robotic drill has extracted from below ground. The drill rig is about 8 feet (2.4 meters) tall and sits on a three-legged platform about 7 feet (2.1 meters) in diameter. The six-sided, hexagonal drill platform is in the shape of a Mars lander, much like the Phoenix lander that is scheduled to go to Mars in 2007.
"The drill uses less than 150 watts of power when it is drilling with carbide-diamond cutters, and the drill uses no drilling fluid," Stoker said. She also noted that the drill "makes core," plugs of rock that are about 8 inches (about 20 centimeters) long, and brings them to the surface.
"Other things mounted on the lander platform include a device called the core sample handling system," she continued. The system processes cores after the drill brings them to the surface, according to Stoker.
The drill's robotic machinery transfers each core to a clamp, which is mounted on a rail. "And the clamp, then, moves along the rail and runs the core under a set of instruments--cameras and spectrometers--that look at the core, examining it for interesting features that might indicate biological activity has occurred," explained Stoker.
A reflectance spectrometer is an instrument that measures reflected light from a given material to determine what that material is made of. Many spectrometers include a narrow slit that splits incoming light into its components, much like a prism splits white light into a rainbow of colors. Somewhat like a fingerprint that helps identify people, 'spectral data' from a rock can enable scientists to identify minerals that comprise it.
After the cameras and spectrometers gather data from the cores, the core sample handling mechanism stores the cores in a rack on top of the platform until scientists have a chance to examine the data in more detail and can decide what core material to examine more closely.
"The data can be transmitted to scientists located in another site," Stoker explained. "If the drill rig were on Mars, those scientists would be located on Earth. They would look at those images and spectra and decide if there's anything interesting in those cores that warrants further sampling."
"If scientists decided that a location on a specific core was particularly interesting, that core would be retrieved from the rack, and then sub-sampled using a saw that would cut a piece out the core. That piece is next placed in a crusher that crushes the rock into powder," Stoker said.
"Then the powder is placed into another set of instruments that look for evidence of biological activity–signs of life. In fact, one such instrument is called the 'Signs of Life Detector.' This automated life detection instrument can identify many kinds of biochemical compounds, microorganisms and their metabolic products," Stoker added.
"The subsurface of Mars might have abodes that life could be thriving in at the present time," Stoker explained. "There is quite a bit of evidence that liquid water exists in the subsurface of Mars, at least in some locations. And so, you have the best chance of finding extant life today by getting into that subsurface environment where there's liquid water," Stoker said.
Forms of life that might be beneath the surface of the planet would be shielded from harmful ultraviolet light that penetrates the thin martian atmosphere and bathes the martian surface, according to scientists. But ultraviolet light can kill life.
"On the Earth we're shielded from ultraviolet light by the atmosphere, but on Mars there isn't enough atmosphere, and there isn't enough of the right kind of compounds in the atmosphere to shield the surface from very intense ultraviolet light. So the surface of Mars is not a nice place for life," Stoker noted.
Researchers also think that—as on Earth—microbial life on Mars may be able to exist underground, without the benefit of sunlight, by living off of chemical energy. There are such microbes deep inside Earth—life forms that scientists call 'extremeophiles' because they live in extreme environments of heat, cold, acidic or alkaline conditions.
The NASA Astrobiology Science and Technology for Exploring Planets program and the Centro de Astrobiologia, Madrid, Spain, sponsor MARTE.
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NASA Ames Research Center, Moffett Field, Calif.