The Europa Clipper mission under development is driven in large part by astrobiology, including determining if the icy moon of Jupiter could support life. (credit: NASA/JPL-Caltech)
by Jeff Foust
A quarter-century ago, astrobiology was struggling to find credibility. After past disappointments in the search for life beyond Earth, such as the Viking missions to Mars, not to mention the controversies and funding battles in efforts linked to the search for extraterrestrial intelligence (SETI), astrobiology did not seem like a vibrant field at the time.
How times have changed. Astrobiology has become an active, interdisciplinary field, driven by a greater understanding about how life can thrive in niches once thought inhabitable on Earth, as well as better understanding of the potential habitability of worlds in our solar system—not just Mars but also Europa, Enceladus, and Titan—and the bounty of exoplanets discovered since the mid 1990s, many of which have sizes and orbits similar to the Earth.
A new report calls on NASA to make astrobiology an even more central part of its science mission. The report, released by the National Academies earlier this month and mandated by language in NASA’s 2017 authorization act, praised what NASA has done in its astrobiology program in recent years, but called on it to do even more.
One of the themes of the report, said Barbara Sherwood Lollar, university professor in the department of Earth sciences at the University of Toronto and chair of the committee that prepared the report, is to “go broad” in the search for life. “When we say ‘go broad,’ it’s not the same as saying, ‘do everything,’” she said at an October 10 press conference in Washington to unveil the report. “This is a strategic approach to going broad.”
That includes, she said, a “broad intellectual attack at the problem” of the search for life. “Successful search strategies for life must integrate the idea that no one biomarker is infallible, no single geochemical scenario or environment is the key, and life, of course, need not be as we know it.”
The report recommended “outside-the-box thinking” in the search for life, including life as we don’t know it. That includes the concept of the “agnostic biosignature” not tied to a specific biological process.
“It’s an attempt to get at something that is more universal, an understanding, a search strategy that might capture life as we know it but also potentially life as we don’t know it,” she said. “We would be excited about any set of chemical redox parameters that might indicate a disequilibrium, a presence of processes different from what we might expect from abiotic processes alone.”
A second theme of the report, Sherwood Lollar said, is to “go deep,” as in go deep below the surface of worlds to search for life. The report recommends “a dedicated focus on research and exploration of subsurface habitability” given increased understanding of the existence of life well below the Earth’s surface and our knowledge of potential habitats below the surface of Mars and icy moons in the outer solar system.
“All of these discoveries over the last few years has definitely provided an idea that what we systematically need to do is incorporate a broader focus on our understanding of subsurface environments and subsurface processes in the search for life,” she said.
The third theme of the report, she said, is “go high contrast.” That’s a reference to the importance of high-contrast direct imaging of exoplanets, a critical technology to enable scientists to look for evidence that planets are inhabitable, or even inhabited.
“We want to push NASA to develop the technology needed to take direct imaging pictures of these planets,” said Alan Boss of the Carnegie Institute of Science, a member of the report committee, at the briefing. “That requires a space-based direct-imaging mission.”
Two approaches exist for direct imaging. One, a coronagraph, blocks out sunlight within an instrument on a telescope. The other, a starshade, places a large disk, with flower-like petals, in front of the space-based telescope to block the starlight. Both have been under study for some time. NASA’s Wide Field Infrared Survey Telescope (WFIRST) will have a coronagraph instrument, although cuts to the program to decrease its cost turned the coronagraph from a full-fledged science instrument to a technology demonstrator. WFIRST is also intended to be compatible with any future starshade spacecraft.
“NASA should basically keep doing what it’s doing, and in particular try to get this technology developed as soon as one can,” Boss said, “hopefully in time for the next decadal survey to seriously consider such a large, expensive mission in its priorities for the next ten years.”
The report emphasized the interdisciplinary nature of astrobiology, as well as the interagency cooperation the field requires. “The question we’re trying to answer is, ‘are we alone?’” Boss said. “That is a big question of interest to practically everyone on the planet, if not everyone, and that also means that is an expensive question to try to answer, and one shouldn’t expect any one agency or perhaps one country to answer it all on its own.”
One example of such partnerships, he said, is with the National Science Foundation, which funds some large groundbased telescopes. Those observatories, he noted, are critical for follow-up observations of planets discovered by space missions, like Kepler and TESS.
There’s also partnerships with private organizations, like philanthropic organizations that privately fund astrobiology research. The report recommended that NASA “actively seek new mechanisms to reduce the barriers to collaboration with private and philanthropic entities, and with international space agencies, to achieve its objective of searching for life in the universe.”
Those philanthropic efforts, most notably the Breakthrough Listen program funded by Russian billionaire Yuri Milner, have focused on new SETI efforts. A week before the report’s release, Breakthrough Listen announced a new agreement with the South African Radio Astronomy Observatory to use the MeerKAT radio array in South Africa, a precursor for the Square Kilometer Array radio telescope, to carry out SETI searches.
Those SETI efforts fall into a category called “technosignatures” that has recently gained support in Congress, particularly the House. NASA recently held a workshop on the topic of detecting technosignatures, which would include radio and optical signals as well as other evidence of technological activity, such as the presence of “megastructures” around other stars.
Technosignatures are discussed only briefly in the report, primarily in a one-page sidebar. “The search for technosignatures is a high risk, high reward approach to the search for life, and its probability of success is poorly understood,” the report stated, emphasizing this as one area of collaboration with private groups.
“It’s certainly an important part of astrobiology,” said Sherwood Lollar. “This is a particularly important opportunity to take advantage of some of these partnerships issues. This is clearly one of the examples where the philanthropic partner investment has really enabled the technosignatures aspect to go forward.”
The focus of the report, though, was more on detecting biosignatures rather than technosignatures, something that the committee thought should be infused throughout NASA’s science work.
“I think one of the top messages of our report is that we’re asking NASA to make sure it keeps astrobiology in mind when it is doing mission planning, especially within our own solar system,” said Boss. “If you’re going to be sending a probe or an orbiter someplace, don’t just simply go for water or methane, but think about looking for biosignatures.”