Author: Natasha Hochlowski
Institution: Princeton University
Date: May 2010
For decades, people have been grappling with the question: could life have ever existed on Mars? Although NASA scientists have found ways to test Martian material, many of their methods actually destroy the materials they are testing, making it difficult to obtain accurate results.
Just a few weeks ago, NASA/Goddard Space Flight Center scientist Jennifer Eigenbrode discovered an improved way to test rocks on Mars for evidence of carbon, the building block of life. Using current methods, the materials that scientists test for signs of life are damaged or even destroyed. This makes it difficult to be sure that there are signs of life, because repeat tests can't be done and thus measurement errors are never be discovered. With the use of Eigenbrode's new procedure, samples will be protected from the dangers of heat, and scientists can then test them without fear of damage.
Goddard scientists will employ her methods in the construction of the Sample Analysis at Mars (SAM) instrument, set to launch from Earth in late 2011 and land on Mars in the year 2012.
Flow of a sample through SAM http://ael.gsfc.nasa.gov/marsSAM.shtml
SAM is essentially a package of assorted instruments designed to study Mars. These instruments are all packed inside a car-sized rover that will collect and examine rock and soil samples in an attempt to answer three pressing questions: Are there carbon compounds that indicate potential habitability? What other elements on Mars tell us about its ability to support life? Were past conditions on Mars different from those today? The answers to these questions will not tell us whether life DID exist on Mars, but rather whether conditions favorable for life have existed in the past or exist today.
The question of whether life exists outside our planet is an age-old one. Getting an answer to this question would reveal much about our own planet and its evolution. "We don't have a record of this time on Earth and it may have witnessed the dawn of life. The conditions of Mars may have been more like Earth back then, so Mars may be a "window" into Earth's earliest years," says Eigenbrode.
On our planet, most of our fossil record doesn't date much older than the time of the dinosaurs that roamed the planet several hundred million years ago. Plate tectonics,the motion of the huge plates that make up the Earth's surface,have done much to damage Earth's rock record. However, such movement never occurred on Mars, allowing scientists to study numerous rocks that are over three and a half billion years old.
Due to the Martian conditions, life on Mars would exist very differently than life on Earth. Here on Earth, we are protected from harmful UV radiations by the ozone layer,a thin, semi-mobile region of the atmosphere. It exists at different altitudes at different parts of the Earth, ranging from approximately 12-30 miles above the Earth's surface. The special form of oxygen found here protects all living organisms. Without it, all life on Earth would essentially burn up. Since such a layer does not exist on Mars, any life form that could have existed would have had to have been extremely robust, or would have to be found deep below Mars' surface.
The same adaptations that make it possible for life to exist on Mars make it especially challenging for scientists to determine whether life exists. Just as plants or bacteria form nearly impenetrable spores when faced with unfavorable conditions such as extreme heat or lack of food supply, molecules on Mars would have had to exist in a similar hardened form in order to be protected from UV radiation. When testing samples of soil or rock, there's a metaphorical seal on these materials that must be broken, so that scientists can penetrate into the inside of the sample. To do this, scientists heat samples in an oven, and the heated molecules, in turn, release gases. Although molecules are tiny, with each of them releasing a small puff of gas, scientists are able to measure this gas and analyze it for potential signs of carbon-based molecules
Until now, the process of "baking" the samples caused problems for NASA. Although analysts need to apply heat in order to penetrate the samples, heat also breaks down carbon bonds and other chemical bonds. With the bonds broken, it is difficult to tell which molecules were present in the samples.
However, Eigenbrode has found a way to overcome this hurdle. She has developed a technique to prep samples with a small amount of tetramethylammonium hydroxide in methanol (TMAH), a poisonous, flammable chemical mixture that is used presently in different laboratory instruments to study organic, or carbon-based, compounds. Previously this year, NASA scientists conducted experiments utilizing rocks similar to those found on Mars. In all of the experiments, they discovered that the TMAH was able to both preserve the structure of the samples when they were heated, as well as to survive extremely high levels of radiation, such as those that would be found on Mars.
"An instrument is only as good as the sample, and there is no single method for identifying all molecular components," says Eigenbrode. In other words, if the methods used to analyze a sample don't keep it intact, then it's of less use to the scientists that are studying it. Because scientists must test substances numerous times in order to account for testing error, tests are not considered very accurate unless they can be tested more than once. These samples may be studied in many different ways, and Eigenbrode's mission was to find a way that did the least amount of damage to the sample being studied.
However, just like the concerns expressed in so many science fiction films, scientists worry that the vehicles that we send to explore other planets may damage the very samples they are set out to test. NASA's instruments, like any other objects, are covered in tiny molecules that have been picked up from Earth. Contamination such as spores, if it goes undetected, could pollute the Martian surface immediately on contact. This would lead to the possibility of obtaining false results in soil tests, as well as causing irreparable damage to the potentially vital rock record of Mars.
"Because this mission will specifically be testing for organic molecules, terrestrial contaminants also include synthetic organic polymers, such as plastics, and residues of life, such as cell wall lipids and proteins. The cleaning method used for SAM is effective at removing most of these contaminants but we will never get rid of all of them," Eigenbrode explains. To attempt to combat this difficulty, the team working on the SAM mission has been cataloging potential contaminants from the SAM instrument
Amongst the many advantages of the SAM is that all of the sample testing will be done on Mars, without needing to bring samples back to the Earth-life-rich (and thus, contaminant-rich) atmosphere. However, it can only go so far,some of the more accurate tests to determine life need to be done on Earth, using more complicated and immobile equipment. Therefore, samples will be brought back so that a wider range of equipment can be used to test the materials. Samples returning to Earth may be contaminated, sparking results that will give us false information about the possibility of Martian life.
NASA scientists hope that the SAM mission may help to shed some light on the age-old question of whether there is evidence of potential life on Mars. Just as importantly, they are still trying to determine the effects our experiments could have on the future of the Martian landscape. Will we be able to discover new insights into the geological evolution of our planet without damaging Martian rock records? Only time will tell.