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To date, scientists have listed more than 3,500 exoplanets, some of which could even promote life. But we simply do not know. The ability to detect life in distant worlds is still elusive, but a new project coordinated by NASA is now making a significant step towards realizing this goal.
Six new articles published in the scientific journal astrobiology provide a starting point for scientists looking for signs of life on planets outside our solar system. The new articles describe the different ways in which extraterrestrial "biosignatures" could be detected using current and future technologies, and what scientists should look for in the data. It is encouraging that the atmospheric biosignatures of potentially habitable planets will be detected by 2030, while warning that the definitive proof of extraterrestrial life will come only later, after a more rigorous analysis and more powerful telescopic techniques. .
This project, called Nexus for Exoplanet Systems Science or NExSS, is the culmination of two years of work. It started with online discussions and a workshop in Seattle in July 2016. NExSS is coordinated by NASA, but is globally accessible. scientists from the University of Washington, the University of California-Riverside, the Tokyo Institute of Technology, the University of Glasgow and many other institutions. The project is rooted in astrobiology, but it involves an impressive team of interdisciplinary experts, including planetary scientists, Earth scientists, heliophysicists (who study the effects of stars on their planetary systems) , astrophysicists, chemists and biologists. Indeed, if we will ever find life on other planets, it will take a village.
The purpose of the project and the six new articles is to provide a comprehensive overview of what we know about life and how it begins in the Universe, as well as how we could detect the biosignatures of the Earth using the current and the future. technologies. The researchers say that an integrated and multidisciplinary approach is needed, as well as an open mind to a variety of ideas and perspectives. However, because of the distances, and given the limited state of our telescopic technologies, these biosignatures will have to be very visible.
"In order for life to be detectable in a distant world, it must dramatically alter its planet in a way that we can detect," said Victoria Meadows astronomer of the University of Washington, DC. author of two of the six new articles. "But for us to properly recognize the impact of life, we must also understand the planet and the star – that the environmental context is the key."
In the first article, lead author Nancy Kiang of the NASA Goddard Institute for Spatial Studies (GISS) and her colleagues consider the types of biosignatures that scientists should look for. A key conclusion of the paper is the recognition of two main types of signals: atmospheric gases produced by life (eg oxygen produced by plants or photosynthetic microbes) or light reflected by life (eg the color of leaves or pigments). The second paper, led by Meadows, is a discussion of possible false positives and false negatives, and the different ways in which astrobiologists might be fooled into thinking that they have detected a planet with a discernible biosignature, or vice versa. As a result, the article examines the ways in which a planet could produce a biosignature like oxygen without the presence of life, and how the planets with life could produce biosignatures far removed from what we see here on Earth.
"There are many things in the universe that could potentially put two oxygen atoms together, not just photosynthesis, let's understand what they are," Meadows said. "Under what conditions are they more likely to happen, and how can we avoid being fooled?"
The third paper, led by Edward W. Schwieterman of the Department of Earth Sciences at the University of California at Riverside, examines what we have learned on our own planet and how life has emerged on Earth. . In the fourth article, University of Washington astronomer David C. Catling and his colleagues provide a framework for evaluating exoplanetary biosignatures, including variables such as chemicals in the atmosphere of the planet, the presence of oceans and continents. The authors also provide a systematic way to evaluate a potential biosignature, allowing researchers to assign confidence levels for a planet to accommodate life, ranging from "very likely" (90 to 100%) to " very unlikely "(> 10%). The fifth and sixth papers assess our current observational perspectives, while proposing future directions, such as the design of powerful space telescopes capable of detecting distant exoplanet biosignatures.
Collectively, these papers, together with NExSS, show that the field of astrobiology is maturing; it has become a rigorous scientific enterprise in its own right. Scientists are finally formalizing the quest for extraterrestrial life, while providing entry points for scientists from different fields to come together. The strategies proposed in these documents require a rigorous process and solid science, but not to the detriment of allowing scientists to think creatively about other types of life that may exist elsewhere.
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