Are we alone in the universe? NASA calls for a new scientific framework for the search for extraterrestrial life



This artist’s concept allows us to imagine what it would be like to stand on the surface of the exoplanet TRAPPIST-1f, located in the TRAPPIST-1 system in the constellation Aquarius. Credit: NASA / JPL-Caltech

How to understand the importance of new scientific results linked to the search for life? When would we be able to say, “yes, alien life has been found?” “

">Nasa scientists are encouraging the scientific community to establish a new framework that provides a context for discoveries related to the search for life. Write in the journal Nature, they propose to create a scale for evaluating and combining different data sources that would ultimately lead to answering the ultimate question: are we alone in the universe?

In the new article published in Nature, led by Jim Green, the agency’s chief scientist, a NASA group is proposing a sample scale to use as a starting point for discussions among anyone who would use it, such as scientists and communicators. They envision a scale informed by decades of experience in astrobiology, a field that probes the origins of life on Earth and the possibilities of life elsewhere.

“Having such a scale will help us understand where we are in terms of finding life in particular places, and in terms of mission capabilities and technologies that help us in that quest,” Green said.

The ladder contains seven levels, mirroring the winding, complicated staircase of steps that would lead scientists to claim they have found life beyond Earth. As an analogy, Green and his colleagues point to the Technological Readiness Level Scale, a system used inside NASA to assess how ready a spacecraft or technology is to fly. In this spectrum, advanced technologies such as ">March Helicopter ingenuity begins with ideas and develops into rigorously tested components of historic space missions.

The authors hope that in the future scientists will note in published studies how their new astrobiology results fit on such a scale. Journalists could also refer to this type of framework to define audience expectations in articles about new science, so that small steps don’t seem like giant leaps.

“So far, we’ve been leading the public to believe that there are only two options: it’s life or it’s not life,” said Mary Voytek, head of the astrobiology program at NASA at NASA Headquarters in Washington and co-author of the study. “We need a better way to share the excitement of our discoveries and to demonstrate how each discovery builds on the next, so that we can bring the public and other scientists on the journey.”

It’s exciting whenever a rover or orbiter finds evidence that water has already flowed on Mars. Each new discovery shows us that Mars’ past climate was similar to that of Earth, and that the Red Planet could once have supported life. But that doesn’t necessarily mean that no sort of life ever lived there, or that anything lives there now. The findings of rocky planets orbiting stars beyond our Sun, especially those that might harbor liquid water on their surfaces, are equally enticing, but do not in themselves prove life beyond. beyond Earth. So how do you understand these observations in context?

Scientists from all over the world collaborate

Scientists around the world are collaborating, using different tools and methods, to search for life beyond Earth. NASA scientists suggest having a scale to contextualize the importance of new findings related to this research. Credit: NASA / Aaron Gronstal

All science is a process of asking questions, formulating hypotheses, developing new methods of looking for clues, and ruling out any alternative explanation. Any individual detection may not be fully explained by a biological process and must be confirmed by follow-up measures and independent investigations. Sometimes there are problems with the instruments themselves. Other times, the experiments don’t reveal anything at all, but still provide valuable insight into what doesn’t work or where not to look.

Astrobiology is no different. The field pursues some of the deepest questions anyone can ask themselves about our origins and our place in the universe. As scientists learn more and more about the types of signals associated with life in various environments on Earth, they can create and improve the technologies needed to find similar signs elsewhere.

While the exact details of the scale will evolve as scientists, communicators and others step in, Nature’s article offers a starting point for discussion.

At the first rung of the ladder, “level 1”, scientists would report clues to a signature of life, such as a biologically relevant molecule. An example would be a future measurement of a potentially life-related molecule on Mars. By moving to “level 2”, scientists would ensure that detection is not influenced by instruments that have been contaminated on Earth. At “level 3,” they would show how this biological signal is found in an analog environment, such as an ancient lake bed on Earth similar to the Perseverance rover’s landing site, Jezero Crater.

To add evidence to the middle of the scale, scientists would supplement those initial detections with information about the environment’s ability to support life and exclude non-biological sources. For Mars in particular, samples returned from Mars could help make that kind of progress. Perseverance will collect and store samples soon for the purpose of a future mission to bring them back one day. Since different teams on Earth would have the ability to independently verify clues of life in samples from Mars with a variety of instruments, the combination of their evidence could reach “level 6”, the second highest rung in the world. ‘ladder. But in this example, to reach level 7, the standard that scientists are most sure they have detected life on Mars, an additional mission to another part of Mars may be required.

“Achieving the highest levels of trust requires the active participation of the scientific community at large,” write the authors.

This scale would also apply to discoveries beyond the solar system. It is believed that exoplanets, planets located outside our solar system, outnumber the 300 billion stars in the Milky Way. But small rocky planets are more difficult to study from afar than gas giants. Future missions and technologies would be needed to analyze the atmospheres of Earth-sized planets with Earth-like temperatures receiving sufficient amounts of starlight for life as we know it. The James Webb Space Telescope, launched later this year, is the next big step forward in this field. But it will likely take an even more sensitive telescope to detect the combination of molecules that would indicate life.

Detect oxygen in the atmosphere of a exoplanet, a planet outside of our solar system, would be an important step in the process of seeking life. We associate oxygen with life because it is made by plants and we breathe it in, but there are also geological processes that generate oxygen, so it is not in itself proof of life. To climb the ladder, a mission team was able to demonstrate that the oxygen signal was not contaminated by light reflected from the Earth and study the chemistry of the planet’s atmosphere to rule out the geological explanation. Further evidence of a supportive environment for life, such as an ocean, would strengthen the hypothesis that this hypothetical planet is inhabited.

Scientists studying exoplanets are eager to find both oxygen and methane, a combination of gases in Earth’s atmosphere indicating life. Because these gases would lead to reactions that cancel each other out unless there are biological sources of both present, finding both would be a key “level 4” step.

To reach level 5, astronomers would need a second independent detection of a hint of life, such as global images of the planet with colors suggesting forests or algae. Scientists would need additional telescopes or longer-term observations to be sure they’ve found life on an exoplanet.

The authors of the study stress that the ladder should not be seen as a race to the top. The scale emphasizes the importance of the groundwork that many NASA missions do without directly detecting possible biological signals, such as characterizing environments on other planetary bodies.

Upcoming missions like Europa Clipper, an orbiter in Jupiterthe icy moon Europa later this decade, and Dragonfly, an octocopter that will explore Saturnthe Titan moon, will provide vital information about the environments in which a certain form of life may one day be found.

“With each measurement, we learn more about biological and non-biological planetary processes,” Voytek said. “The search for life beyond Earth requires a broad participation of the scientific community and many types of observations and experiments. Together, we can be stronger in our efforts to search for clues that we are not alone. “

Reference: “Call for a framework for reporting evidence for life beyond Earth” by James Green, Tori Hoehler, Marc Neveu, Shawn Domagal-Goldman, Daniella Scalice and Mary Voytek, October 27, 2021, Nature.
DOI: 10.1038 / s41586-021-03804-9


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