In 1980, astrophysicist Carl Sagan introduced people around the world to the possibilities of astrobiology – a scientific field dedicated to the search for life beyond our lonely blue planet – with a television series, Cosmos: A Personal Voyage. Wearing a scholarly beige jacket, Sagan traversed the universe, drawing viewers on a journey across the vastness of space and reviving interest in a question that had been brewing within humanity’s collective psyche since the beginning of civilization – has life arisen elsewhere in the Universe? With the maturation of space technology during the latter half of the 20th century, it finally became possible to begin a substantive investigation, but the road through astrobiology has not been without its rough stretches. Despite the revolutionary implications that astrobiology holds for humankind, scientists engaged in the search have occasionally encountered political and financial challenges. Through it all, UC Berkeley scientists scattered across numerous departments have been pursuing answers to some of the most profound questions our species has ever asked – what is life, how did it evolve, and are we alone?
Are we alone?
A committed quest to discover extraterrestrial life began in the 1960s with the birth of SETI (Search for Extraterrestrial Intelligence), a scientific field dedicated to scanning the sky for signals released into space by intelligent civilizations. Excited by SETI’s potential for discovery, on Columbus Day in 1992 NASA dedicated $100 million to the endeavor, but rumblings within Congress about overspending soon made NASA reconsider its commitment. Targeted as an example of wasteful spending and mocked as the “search for little green men,” SETI lost NASA’s financial support, forcing researchers around the country to find other avenues for funding their work. “We all started scrambling around,” says SETI at Berkeley chief scientist Dan Werthimer, “but we got some private support, companies gave us money, and so we were able to keep going, keep innovating.”
Despite the occasional setbacks, Berkeley’s SETI scientists have become pioneers in technological development and astronomical research. The scope of their creativity is reflected in their research programs – each with a different approach to tapping into the interstellar communications of distant civilizations – currently run by SETI at Berkeley. While they vary in their specific approaches, most of the projects work on the assumption that intelligent civilizations are emitting electromagnetic radiation into space, either intentionally to communicate with other intelligent beings, or accidentally as a byproduct of their daily lives. Electromagnetic radiation of varying energies corresponds to different types of detectable signals – radio waves, infrared waves, and visible light waves, to name a few. While waves from the entire electromagnetic spectrum are emitted by non-biological sources in the universe (radio waves, for instance, can be produced by stars and gases), SETI researchers argue that a concentrated, sustained, and repetitive release of waves from a narrow portion of the spectrum would suggest the presence of intelligent life. “We look for things that the universe doesn’t produce naturally,” says Andrew Siemion, a SETI graduate student from the Department of Electrical Engineering and Computer Sciences. “It can be a lot of energy in a very narrow time window, or a lot of electromagnetic energy in a very narrow frequency window.”
At the lowest end of the spectrum are radio waves, which were among the first to be scanned by SETI scientists for signs of alien intelligence, in part because they travel through space relatively unimpeded. One of SETI’s largest and longest-running radio-based research programs is UC Berkeley’s SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations), which began sifting through radio waves for signs of intelligent life over 30 years ago. In 1992, SERENDIP was installed at the Arecibo radio telescope, the largest and most sensitive radio telescope in the world, located in Puerto Rico. Like other radio telescopes, Arecibo works by gathering radio signals with an enormous curved dish lined with mirrors. When the signals bounce off of the dish, they’re directed toward a receiver, which collects the data and sends it along to researchers.
While the vast majority of SETI studies focus on narrow portions of the electromagnetic spectrum or on specific regions in space, SERENDIP takes a broader approach. “We try to look across the spectrum in the sense that we look at very long and very short wavelengths,” says Siemion. Werthimer adds, “There are different strategies in SETI. One of them is to find nearby stars that are kind of like our sun, point your telescope there, and look very carefully at that star. Our strategy typically is not to do that. We scan the sky, back and forth, looking at billions of stars, billions of galaxies.” While these tactics allow SERENDIP to search greater swathes of space and a wider portion of the electromagnetic spectrum, they have pitfalls – each region of space cannot be searched in fine detail, and with the influx of massive amounts of data, the system can only save the strongest signals for analysis, while the remaining majority of the data must be discarded. Berkeley’s SETI researchers responded to the latter challenge by creating SERENDIP’s complementary sibling project, SETI@home, which also collects data from the Arecibo radio telescope. While SERENDIP takes a rough look at a broad section, or bandwidth, of radio frequencies, SETI@home scans a much smaller bandwidth in exquisite detail, allowing it to pick up weak radio signals. The data collected by SETI@home are sent out in small chunks around the world to millions of personal computers, which process the data while they’re idle. Once finished, each computer sends its data back to SETI@home and receives a new data set to process. Since its inception in 1999, SETI@home has become the largest and most powerful supercomputer in the world, which has allowed it to facilitate the most sensitive SETI search in history.
Our microscopic neighbors
While SETI researchers seek signs of macroscopic, intelligent life beyond our solar system, other scientists at UC Berkeley are hoping to find microscopic organisms on our neighboring planets and moons. In the Department of Chemistry, Professor Richard Mathies’ group is developing the next iteration of the Mars Organic Analyzer (MOA), a miniaturized biochemical analyzer system with the ability to detect a variety of organic molecules with significant roles in life processes. The lab is especially interested in using the MOA to search for amino acids – the building blocks of proteins – on Mars, since the chiral structure of these molecules can provide additional information about the presence or absence of life. Two molecules are said to be a chiral pair when they’re mirror images of one another, asymmetrical, made of the same constituent elements, and non-superimposable (for an illustration of chirality, look at your hands – this is why chirality is also known as “handedness”). All known life on Earth uses left-handed amino acids. No one knows exactly why this is the case, but scientists agree that a mixture of left- and right-handed forms would probably interfere with biological processes, since combining the two types of amino acids creates a misshapen, tangled mess of a protein. In contrast, homochiral (all left-handed or all right-handed) amino acids can be strung into a well-defined and functional protein capable of carrying out life-sustaining reactions. When they’re not being manipulated by organisms, amino acids tend to exist in a nearly equal mixture of left- and right-handed forms, a state known as heterochirality. With the MOA, an instrument compact enough to fit on a Mars-bound rover, but powerful enough to discern the presence and chirality of amino acids, future missions to Mars could determine if the planet harbors concentrated amounts of either left-handed or right-handed amino acids. A sample with a preponderance of either type of amino acid would suggest the presence of life and probably send more than one champagne cork flying into a laboratory ceiling.
In the field, the MOA separates out organic molecules using a microfluidic device, or chip (see “Lab on a chip,” BSR Spring 2009), which allows researchers to determine the make-up of a solution using a sample as small as one microliter (to give you an idea of how small that is, consider that it would take nearly 5,000 microliters to fill up one teaspoon). Similar in diameter to a Petri dish, the chip consists of a flexible membrane sandwiched between two glass plates. Etched into the glass are separation channels and holes, each corresponding to a valve that allows scientists (or a machine) to move a sample around on the chip using pressure and vacuums. To identify the molecules within a sample, the MOA begins by passing an electric current through the microfluidic device. Since many organic molecules carry different charges, the current causes them to move down the separation channels at different rates, depending upon their charge-to-size ratio. At the end of the line, the molecules, which have been tagged using a fluorescent label, pass over a laser and fluoresce. A spectrometer then analyzes the signal and produces a spectrogram (a sort of identification key) for each molecule. “Basically, it’s like being on a conveyor belt at an airport,” says Mathies Lab staff scientist Tom Chiesl. “Sometimes you get people that run forward on it, and other people want to go backwards, and some just sit there. Every different type of amino acid is moving at a different rate on a different type of conveyor belt. At the very end, they go by the laser and they fluoresce and then we see the signal.”
Until recently, the MOA had “flight status” designation, which essentially meant that the instrument was on the cusp of being installed on the upcoming ExoMars mission, a joint endeavor between NASA and the European Space Agency (ESA). With an intended launch date of 2018, the mission’s goals are to search for signs of past or present life on Mars and to study the planet’s geochemistry. During the planning process, officials at ESA were mulling over three different rover design options – large, medium, or small – and the respective benefits (bigger means more space for more instruments) and drawbacks (bigger means higher cost) of each. In the end, the economic downturn made the decision for them – ESA decided to proceed with the least expensive design, which placed real estate on the rover at a premium. With the need to include instruments built by European labs, ESA “descoped,” or bumped, the MOA from the 2018 mission. Despite this setback, Mathies lab staff scientist Tom Chiesl and graduate student Amanda Stockton are moving forward with their work and continue to envision an instrument that will eventually be more compact, lightweight, and someday get its first taste of Martian soil.
Unraveling the history of life
While some scientists dream of discovering life beyond Earth, other researchers are investigating the only model of life we have – that of our home planet – to unveil answers to two important astrobiological questions: what is life and how does it arise? In particular, astrobiologists are interested in extremophiles, organisms that thrive under harsh environmental conditions, because many cosmic bodies harbor environments analogous to Earth’s most extreme places. In addition, the most inhospitable locations on Earth are thought to closely resemble our planet’s early history, when life first appeared. Studying Earth’s hardiest organisms provides scientists with an understanding of how life can emerge and survive on young or inhospitable planets, and offers a testing ground for the techniques that will allow us to detect life in other parts of the solar system and beyond.
In the Department of Earth and Planetary Science, members of Jill Banfield’s lab are studying the lives and remains of extremophiles living in Lake Tyrrell, a hypersaline (very salty) lake in southeastern Australia. With a salt content ten times that of seawater, the lake is home to a community of resilient microbes and offers a treasure trove of information on palaeoenvironments (that is, very old environments) and their long gone inhabitants. One of Banfield’s graduate students, Claudia Jones, is interested in characterizing the lake’s microbial residents, both current and extinct. To determine what lived in the lake in the past, Jones uses lipid biomarkers, molecular fossils that can act as an identity card for ancient organisms. Although there are numerous types of biomarkers, lipids are especially useful because they can persist in the environment for billions of years. “Simply, you may die,” Jones explains, “but your fat lives on (nearly) forever.” The longevity of lipids results from the fact that they contain a large proportion of carbon-carbon bonds, which are extremely stable and resistant to degradation unless conditions are either severely hot or severely oxidizing. Lipid fossils are extracted from rock or sediment samples using organic solvents held under high temperature and pressure and then passed through a gas chromatograph, which separates the molecules by weight and charge. From there, the fossils are sent through a mass spectrometer in single file, where they are pelted by electrons and broken into pieces. When depicted on a spectrogram, these fragments can be reconstructed like a puzzle, allowing scientists to determine the molecule’s identity. Taking it a step farther, Jones also measures the ratio of carbon-13 to carbon-12 (the two types of carbon differ in the number of neutrons they possess) to identify the lipid’s former owner. “These techniques tell us about the types of organisms extant in the geologic past, as well as the metabolic activities of those organisms,” says Jones. “Compound-specific isotopic measurements are important because some compounds, such as various fatty acids, can be produced by more than one type of organism. However, due to the different metabolic pathways by which microbes fix carbon and produce lipids, different ratios of carbon-13 to carbon-12 exist in the resulting molecules. In measuring this ratio, compound by compound, we can determine which type of organism produced which lipid.”
Using lipid biomarkers and geological data, Jones and her collaborators have managed to reconstruct Lake Tyrrell’s past. Although the region has gone through several cycles of drying and wetting throughout its history, conventional thought says that in recent times, the cycles have become more extreme due to disturbances caused by humans. Surprisingly, Jones’ findings suggest that in the distant past, the lake has been very similar to what it is now, both in terms of its aridness and its microbial communities. Discoveries like these show how it may someday be possible to use geological data and microbial fossils to reconstruct the evolution of habitats and organisms on other planets.
Another graduate student in the Banfield lab, Joanne Emerson, is helping to round out humanity’s understanding of extremophiles by focusing on a less talked about class of microbe – viruses that infect bacteria and Archaea living in hypersaline environments. Since so little is known about these viruses, Emerson’s goals are straightforward – she wants to characterize the viruses, figure out how they relate to other viruses, and understand their relationships with their hosts. Until very recently, biologists were unable to study 90 percent of the microorganisms living on Earth, since most are too poorly understood to be cultured in a laboratory. “We’ve been limited in our knowledge of microbiology based on what can be cultured, what can be grown in the lab, what can be manipulated,” says Emerson. “But with the advent of genome sequencing, we can actually go into an environment, take a sample, get all of the microbes on a filter, extract their DNA, sequence it, and then try to put the genomes back together again. In this manner, we can figure out who’s there and what’s going on without having to grow anybody in the lab.” These culture-independent techniques are especially exciting for the study of viruses since, until now, they could only be studied when their microbial hosts were thriving in a laboratory.
Although most speculations about the discovery of life on other planets have focused on bacteria, enhancing our understanding of viruses may prove equally important, since no one really knows what life outside of Earth will look like. In addition, viruses raise interesting questions regarding the definition of life and what it would mean to find a virus-like entity on another planet, as Jones points out: “Before we can discuss searching for life, we must specify what we mean by ‘life’. A microbiologist would tell you that a virus is not technically alive: it cannot reproduce or replicate on its own, it lacks much of the internal machinery necessary to do so. However, viruses are organic in nature, respond to organic stimuli, and behave in the fashion of predators. It may at first seem frivolous, but without a strong definition of the term ‘life,’ or what we’d consider a smoking gun for the same, we are likely to neglect fruitful lines of research.”
Ice begets life
Searching for life on other cosmic bodies assumes that it has likely originated elsewhere in the solar system, which begs the question: if extraterrestrial life exists, where did it come from? In the Department of Integrative Biology, Professor Jere Lipps has used knowledge garnered from his research in Antarctica to develop the novel unconventional idea that life can begin in ice. While Lipps admits that he is not the first to suggest the concept, he is currently one of only a handful of scientists promoting the idea among astrobiologists. “There are two problems for the origin of life,” says Lipps. “The first is concentrating the elements of life. The second problem is having the energy to get it going.” The formation of ice solves at least one of these problems – when it freezes, water becomes a crystal that excludes foreign molecules, which are pushed into and concentrated in tiny rivulets, called brine channels (this is why icebergs formed from seawater produce freshwater when they melt). Provided that there’s an energy source, like ultraviolet light, molecules squeezed together by freezing water may have created an ideal scenario for the appearance of the first amino acids and self-replicating nucleic acids, the building blocks of DNA.
Lipps began applying his knowledge and experience from working in icy environments to astrobiology when the Galileo spacecraft, launched in 1989 by NASA to investigate Jupiter and its moons, returned its first set of information on the moon Europa. Data from the spacecraft supported what planetary scientists had already suspected – that beneath its icy exterior, Europa possesses a salty ocean which likely holds about twice the amount of water contained in all of Earth’s oceans. Images from Galileo also revealed a craggy, icy surface, crisscrossed by numerous cracks and dotted with pits and domes. When Lipps viewed these images, he felt right at home. Trained as a geologist and with years spent working as a biologist, he had extensive experience using satellite images to identify sites that would likely harbor signs of life. “All of these geologic features fascinated me. This seemed to be an opportunity to look at the possibility of life based on my experience in Antarctica and to understand the geology and how we might be able to explore Europa for life.” While some scientists doubted that life could exist in the lightless environment beneath Europa’s surface, Lipps’s experiences in Antarctica told him otherwise. In the late 1970s, Lipps and a group of students drilled through 420 meters of ice on the Ross ice shelf (a mass of permanent, floating ice about the size of Texas) to determine what lived in the water beneath. Lowering a container filled with seal meat and a video camera, Lipps’ group discovered an astonishing diversity of organisms – fish, microbes, large crustaceans, thousands of tiny crustaceans known as amphipods, and trilobite-like isopods previously documented only in shallow waters. In addition, he found that the underside of the ice, with its crevices and brine channels, functioned like a nursery, sheltering living organisms from the extremes in their environment. With these discoveries in mind, Lipps proposed that similar habitats could exist on Europa.
Despite the exciting potential for life in Europa’s oceans, some significant challenges to conducting a search exist. To reach the Europan surface, spacecraft and their sensitive electronics would first have to survive the passage through the intense radiation surrounding Jupiter (see “Juno’s revenge,” current issue). Protecting a Europan lander from radiation is possible, but the price tag increases by millions of dollars as the level of protection is enhanced. Compound this with the need to equip a lander with heavy-duty drilling equipment to breach the ice, which is estimated to be many kilometers thick, and the cost for building a lander jumps even higher. Lipps suggests that it may be possible to reduce the hefty price of a mission to Europa by directing more effort to searching for life on the moon’s surface. Europa lacks a protective atmosphere, so prolonged exposure to the radiation assaulting the moon’s exterior would probably kill organisms dwelling in the open without at least 1.5 meters of ice overhead to shield them. But Lipps’s discovery of a diverse biological community in the most inhospitable regions of Antarctica, along with findings made by other scientists that have revealed the existence of organisms thriving under other difficult conditions (extreme heat, pressure, salinity, and radiation to name a few) have convinced him that life could exist on Europa’s surface, concealed and protected within caves and cracks, or beneath boulders and overhanging ledges. “Where there’s an opportunity, even the smallest opportunity, life takes advantage of it,” Lipps says.
Along with other researchers from various institutions, Jere Lipps is a member of the Europa Task Force, which planned to put an instrument package into orbit around Europa or to fly by the moon if dealing with the radiation issue proved too costly. Collaborators from Lockheed Martin hoped to equip the spacecraft with a telescope capable of one centimeter resolution from 100 kilometers away (if you could eliminate the curvature of the Earth and all visual obstructions, a telescope with this resolving power would allow you, while standing in Berkeley, to see a penny held out by your friend in Sacramento). Although the group received a grant to carry out their plans and move forward on the planned launch date in 2012, their contract was cancelled when President George W. Bush’s administration postponed all outer planetary missions for 50 years or more. Planning meetings have continued, but Professor Lipps admits that they’re of limited use: “How can you plan a mission in 50 years when you have no idea what kind of instrumentation there will be? What we can do is think about targets and objectives and keep them flexible, because those will probably change too, and then keep pushing to fly the mission.”
Why it matters
Despite the potentially revolutionary implications of astrobiology, its studies are often the first to lose funding during tough economic times. In defense of astrobiology, Professor Jere Lipps points out that the field has created an unprecedented platform for collaboration among scientists from many different disciplines and yielded advances that benefit non-astrobiological investigations. “If we discover life on another planet or moon,” he says, “we’ll have added a big cherry on the top of a substantial cake of good science.” Some of the technology employed by Berkeley scientists for astrobiological research has proven useful for other applications. The basic design of the Mars Organic Analyzer can be modified to aid in forensic investigations and identify medical conditions. Likewise, the technology used to create a massively powerful supercomputer, created for SETI@home, has benefited the study of other problems, like understanding cancer.
Some would also argue that astrobiology appeals to humanity for deeper reasons. “I think it’s worth doing because it satisfies that fundamental curiosity that we all have, that sent Columbus to America and Magellan around the world. We’ve been doing this since the history of mankind started,” Lipps says. Werthimer provides another interesting perspective: “I think it’s profound either way. If we find out that we are alone, the only intelligent civilization in the whole universe, that makes life on Earth an incredibly precious thing. If we find out that we’re not alone and that we’re part of a galactic club and thousands of civilizations are talking to each other, there’s a lot we could learn.” When asked about the value of astrobiology, other Berkeley scientists echoed what Carl Sagan stated over 20 years ago on Cosmos: A Personal Voyage: “The nature of life on Earth and the search for life elsewhere are two sides of the same question – the search for who we are.”
The following are inset boxes with supplemental background information. They are also found in the print edition of the article.
Protecting the unknown
After centuries of ecological blunders, humankind has discovered the hard way that introducing invasive species – organisms that did not evolve within a particular ecosystem – can disrupt the delicate balance of relationships between native species, lead to declines in biodiversity, and spread disease. It’s no wonder then that even during its earliest missions, NASA was deeply concerned about repeating the same mistakes on a much grander scale by depositing microbial stowaways on to other solar system bodies. Aside from disturbing the native ecology of other planets or moons, microbial contamination presents the additional problem of confusing efforts to identify new life-forms, necessitating the question, “Did that microorganism originate here, or did we plant it here by accident?”
To prevent the littlest Earthlings from hitching a ride to a new world, NASA enforces a set of rules known as its Planetary Protection Policy. Missions are divided into five categories, with increasingly stringent requirements for cleanliness depending upon the type of mission (lander, rover, orbiter, or flyby) and whether the destination is of astrobiological interest. Rovers and landers designed to seek signs of life or destined for places that may harbor life are placed into Category IV and subjected to strict cleaning protocols. As of now, NASA’s only approved method for sterilizing an entire spacecraft is “dry heat microbial reduction” – to put it simply, the spacecraft is placed into a container resembling a giant casserole dish and then baked in an oven at 111.7 degrees Celsius (that’s 233.1 degrees Fahrenheit) for 30 hours. Despite the best efforts of NASA scientists, a small number of spore-forming microorganisms survive the sterilization process, but spacecraft are generally considered safe to launch as long as they harbor an acceptably low microbial load.
Category V protection policies are designed to prevent the reverse situation – the contamination of our own planet by extraterrestrial life forms. We have yet to obtain terrestrial samples directly from a planet or moon (besides our own), but NASA is already brainstorming containment procedures, such as building specialized facilities for the storage and study of returned specimens, in preparation for the day when fragments from our celestial neighbors are delivered to Earth.