Life in Extreme Environments: the Atacama Desert
Nested between the Andes and the coastal mountain ranges of Chile lies the Atacama Desert: the driest and most lifeless place on earth. Until recently, the lack of moisture and nutrients, thin atmosphere, and intense radiation led scientists to believe that the Atacama was uninhabitable by any kind of life. Five years ago, though, a team of NASA scientists disproved that theory: they found one rock with bacteria. Now, that discovery has caused the scientific community to re-evaluate their assumptions.
Carnegie Mellon was among the few institutions to receive NASA grants in order to search for “Life in the Atacama,” as the project is titled. “Life in the Atacama” began in February 2003 as a combined effort between CMU’s biology and robotics departments, analogous teams at NASA, and a few other universities and supporting organizations. The project had a two-part goal: to build an autonomous rover capable of traversing the desert, and to equip that rover with instruments that would search for evidence of life. “Our project was the very first remote, robotic search for life, ever,” said Shmuel Weinstein, research biologist at CMU.
NASA’s ultimate agenda with the project is to use the knowledge gained from these projects to understand how life in extreme environments evolves and to apply this technology to future expeditions to Mars, where they will use the same tactics to search for extraterrestrial life.
In the vanguard of this interdisciplinary project is Zoë, a compact, capable, completely autonomous robotic astrobiologist. Zoë is designed to map out her location — she must characterize terrain, environment, and the surrounding life.
Though not unlike the autonomous Hummers developed by Red Team at the Robotics Institute, Zoë has a variety of programming and applications that differ. Zoë cannot use global positioning to navigate because she may not be restricted to earth. Instead, she uses a sun tracker to communicate her location based on the tilt of the rover and the location of the sun.
With regard to communication, during the most recent trip to the Atacama in late 2005, Zoë only needed to be told a destination. How to get there was completely up to her. She identified life autonomously, as well, and relayed her findings back to the remote control center in Pittsburgh.
Her current automatization puts Zoë far ahead of her predecessor, Hyperion, the robot used in the first mission to the Atacama in 2003. All navigation for Hyperion was done manually on site, and earlier prototypes of Zoë were controlled at all times from the Pittsburgh control center. Although soil sampling is still done manually, it is not inconceivable for Zoë to be able to do all of that herself in the future. Lauren Ernst, a senior research scientist envisions multiple rovers deployed over Mars, collecting, bagging, and sealing soil samples to be taken back to a centralized robotic analysis center.
The assumption that life exists in space is based on the ability to find environments similar to Earth. This does not put Mars out in left field in terms of looking for organisms. “Right now they are looking for evidence of primitive water, and they have found it,” said Waggoner. “What we would consider life, reproducible organisms that can move and exist and maybe evolve into higher organisms, probably have [elements] just like we have on earth…. You get the kind of bond breaking and bond making that occurs on a time scale that is reasonable for having life.”
The aforementioned elements are available on Mars, but they may not be the same as those on Earth. In fact, since Mars’ atmosphere is mostly carbon dioxide, any found organisms could instead resemble life on primitive Earth, when it had a CO2 atmosphere as well.
In order to achieve the second goal of the project and search for life in the Atacama, a team of biologists headed by Alan Waggoner, Director of the Molecular Biosensor and Imaging Center, developed four fluorescent dyes that tag the macromolecules indicative of life: proteins, carbohydrates, lipids (fats), and nucleic acids (DNA and RNA). The dyes are designed to fluoresce only when bound to the target molecule to prevent mistaking random, background fluorescence for data.
Besides the 4 classes of macromolecules, the team was also able to search for chlorophyll due to its natural fluorescence.
The project goals may have conflicted were the biology and robotics departments not able to collaborate and create solutions together. While the engineers needed Zoë to cover a certain amount of ground, the biologists cannot sample if the rover is moving. Also, recording the fluoresence pattern on the ground created problems because capturing fluorescence is done in the dark. David Pane recalled that “[they] wanted to put a shroud over [the instrument]... and the rover guys said no way… it’s too difficult.” A shroud would have made Zoë too bulky, particularly when facing strong desert winds.
Responding to the crisis, Waggoner’s team was able to develop a daytime fluorescent imager, capable of recording fluorescence in broad daylight. “It was a multidisciplinary type of effort…,” Pane said. “As a result, we developed something very novel in this daytime fluorescent imager. I think it was a big plus to have input from two different types of people.”
The fluorescent pattern, compared to the image of the patch of ground from which they came, can provide valuable information about the presence of life relative to terrain, albeit on an extreme microscale. For example, a medium sized rock appeared, when examined under fluorescent lighting, to have patterns of protein, carbohydrates, lipids, and DNA all along its ridges. Though it is unclear what this particular rock indicates, it does imply that terrain has a lot to do with the presence of life, and that to study the geography of an area is a good tool for predicting where life might be.
“One of the ultimate goals of this project to aid in astrobiology… is to learn how to look for those teeny-weeny microhabitats that would support life in the driest areas,” Weinstein said. “That would aid in their strategy on how to look for life somewhere else. Mars is one prime example.”
Back on earth, while identifying macromolecules on the surface of the Atacama Desert was a breakthrough in itself, conducting “ground truth experiments” was important for verification that the macromolecules indicated life. That task fell to Edwyn Minkley, microbiologist and director of the Center for Biotechnology and Environmental Processes.
“Ground truth involves analyzing the soil sample to determine if and how many microorganisms are present,” said Minkley. While the average soil sample might contain about 108 or 109 microbes per gram, samples from the Atacama contain about 1000 microbes, many orders of magnitude less. But they were still there: In fact, microbes were present in every single soil sample analyzed.
The organisms found were mostly bacteria and some lichens. The interesting question to ask, according to Minkley, is what are these organisms surviving on? He proposed that they might exist in relationships where one organism’s byproducts help others to grow.
So, having developed a rover capable of autonomously traversing difficult terrain and detecting life in extreme environments, when will this technology be going to Mars? Apparently not for a while. Weinstein declared that the next mission to Mars has already been selected, but that if Zoë continues to mature, she might be touching down in 2015 or 2016.
Even if the technology never makes it to Mars, implications of the “Life in the Atacama” research over the last three years are far reaching. The ease of using a rover to explore and test places on earth where a human cannot or should not go will expand knowledge about life in different kinds of environments.
“The greater knowledge you have of how [an] organism manages to survive in its ridiculous environment… may lead to scientific discoveries to understand how life works…” said Weinstein. “[Maybe] its metabolism is based on something we had no clue before, it eats iron… or its good for oil spills because it consumes [oil]. We could spin off new technologies or we can utilize biotechnology to do other things we need to do….”
For now, the NASA grant is up, and the various teams involved with the project will be presenting their findings to their peers soon. However, that is not to say that the work is over. The goals of this particular project may have been met, but they spark many new questions about where we can look for life, how to do it, and what we can learn from the myriad of organisms that, in all probability, exist in plenty. Searching for answers to these questions under the polar ice caps or in underwater sink-holes is only the beginning. As Weinstein said: “There is the scientific thing that is of value, and then [there is] what you can do with that knowledge that is of value.”