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Gullies on Mars: unravelling the mystery
AS the flow of information from the Red Planet continues to unfold several mysteries, scientists are learning to put together the pieces of the puzzle with the help of the orbiters, surveyors and, of course, the two most important emissaries sent from the Earth, the twin rovers. Instead of theorising the unusual terrain and surface features, researchers are now able to view things in “real time”.
At present the most intriguing feature is the presence of gullies on surface, which are recent and likely to be formed by the flow of water. Some scientists think that the ground water seeping may have formed these gullies.
These observations are triumph for astrobiologists and it adds in excitement about the prospect of present biology thriving somewhere in the crevices of the mysterious planet. It all started in June 2000, when the pictures of landforms sent by the Mars Global Surveyor, first hit the news. For the last five years, these orbiting spacecraft have been sending the appealing facts and observations. The answers to the gully formations are now being debated and weighed by researchers, astronomers and scientists so as to unravel the mystery and confusion.
The real picture
Regarding these landforms, the Mars Reconnaissance Orbiter (MRO), has been given a new target. Its state-of-the-art High Resolution Imaging Science Experiment, also known as HiRISE, will now figure the gullies. Alfred McEwen, Director of the Planetary Image Research Lab at the University of Arizona in Tucson and MRO’s HiRISE principal investigator states, “HiRISE can do an excellent job of change detection due to the high resolution”. Detection targets will include polar layered deposits, gullies and dunes. “Viewing angles will differ, but we plan to acquire stereo images and produce digital elevation models of any site that shows evidence for change…so we can correct for any viewing effects and make precise measurements of changes. We will of course see changes in colour and albedo (variations in the amount of sunlight reflected by the Martian surface) but interpretation of surface changes can be controversial. So our hope is to detect and measure actual changes in the topography” stated McEwen. The Mars Reconnaissance Orbiter’s capability to point-and-shoot includes re-imaging of surface features and terrains at exactly the same season of different Mars years in order to match the illumination angles.
According to Linda Martel, a geologist and educational outreach staffer at the Hawaii Institute of Geophysics and Planetology, “most researchers are still favouring two models of formation for gullies on Martian slopes --- erosion caused by groundwater discharge or by the melting of near surface ice or snow”. Meanwhile, scientists are mapping the gullies and examining atmospheric condition and temperature in the sub-surface gully crevices and recesses where liquid water is thought to exist. The exposure of these regions to the sunshine and its effects on the surface are also being evaluated. “They are coming up with very convincing reasons why either model makes sense. But when researchers say that gullies are recent, they aren’t talking about today, right now,” stated Martel. She explains that it is not possible that the large gullies, which are approximately four miles long. But water does not seem to be the cause of the surface carvings, say some scientists. According to them, the Moon too has formations on its surface, which resemble to those on Mars, but as we know, the Moon has been a dry world. The gullies on Mars have a kind of “collapsed region” at the top while the other end features a kind of “alcove” with an apron-like area of debris accumulated by stuff from the top of the slope. University of Arizona’s lunar and planetary scientist, Gwendolyn Bart, has made a comparison of the gullies on the lunar surface to that of Mars. “Because the Moon is devoid of geologically active water, we know the lunar features formed by dry landslides. As a result, it is impossible to rule out dry landslides as the formation mechanism for Martian gullies, based solely on the alcove-channel-apron morphology,” she stated. At present though, scientists are not sure whether the Moon has the kind of variety in gullies similar to Mars. Researchers can only be sure after the Lunar Reconnaissance Orbiter, to be launched in 2008 by NASA, which will identify more of the lunar surface.
It would be a dream come true for astrobiologists to examine any evidence of bacteria in an alien world. But only a rover made especially for this purpose and fitted with the right kind of instruments, can do the job. Rummel suggested that exploration of the gullies could even be done from orbiting around the planet or by robotic airplanes or balloons flying through the martian atmosphere.
Snowy packs and dusty toppings
On the other hand, some scientists theorise that it is more expected that Mars might still be a wet world. According to leading Mars researcher, Philip Christensen from Arizona State University in Tempe, the gullies on Mars have been caused by water released from snow packs, which remain covered by dust, and when winds or landslides cause the dustcovers to move, the snow begins to melt. “It is my opinion that there could be an active melting or release of water from sub-surface aquifers. The main argument against a lot of current activity is that these snow packs likely formed during the previous climate cycles and are 50,000 to 300,000 years old. If they had remained active all that time they would have completely gone by now,” Christensen states, supporting his theory that due to the covering of the snow by dust, the snow has remained protected and thus melting is activated only when the dust cover is removed. He also adds, “Alternatively, if the water is coming from sub-surface aquifers or ground ice…local heating or other local changes could also release water and these gullies could also be active”.
But even for supporters of the wet Mars theory, a lot of questions still remain. What is the nature of the snow or water on Mars in the mid-latitude regions today? Christensen says, “these regions are extremely interesting because they’re cold enough for snow and ice to accumulate during climate cycle – but warm enough for melting and release of liquid water to occur at other times…perhaps current times”. Talking about the Polar Regions, he thinks that they are very cold throughout the year and the equatorial regions look very dry. “The gullies indicate that there is snow or water near the surface in the mid-latitudes. That is where I think a lot of action and excitement on Mars is occurring today,” explained Christensen in his interview to SPACE.com.
A restraining order
While all this confusion and speculation persists along with the theories regarding the gullies NASA plans to send the Mars Science Laboratory (MSL) in 2009. But the answer seems to be “no” as far as gully probing is concerned. The reason being that planetary protection rules do not allow any kind of contamination of possible native Martian bacteria by stowaway bacteria from Earth as the MSL will not be up to the sterility standards to go on snuffing tours to the gullies. So near future robotic wheeling on the gullies is “off-limits”. According to John Rummel, NASA’s Senior Scientist for Astrobiology in the Science Mission Directorate at Washington D.C, “gullies appear to be the best chance we will have – or perhaps could have – for seeking present-day life on the Martian surface”.
It would be a dream comes true for astrobiologists to examine any evidence of bacteria on an alien world. But only a rover made especially for this purpose fitted with the right kind of instruments can do the job. Rummel suggested that exploration of the gullies could even be done from orbiting around the planet or by robotic airplanes or balloons flying through the martian atmosphere. “But the most important phase of the exploration of the gullies can only be done by visiting them and making measurements on site. It requires an agile, sterile rover and finely tuned analytical instruments … but with those tools, we have perhaps the best chance of this century to discover whether or not Mars is alive,” states Rummel. So, will rovers ever be sterile enough to meddle with any possible Martian bacteria? Any kind of contamination might lead to dire circumstances on the undisturbed life forms on the Red Planet even any hitchhiking bacteria brought back on Earth possibly be worse. But scientific exploration is a natural human trait for progress and adventure, the only way to unravel the mystery of the carved features on the Martian surface is to take a closer look.
The writer is a freelance contributor
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