BMSIS Scientists Involved with NExSS Strategies to Search for Life on Exoplanets

NASA’s Nexus for Exoplanet Systems Science (NExSS) has gathered researchers from around the world to support and accelerate NASA’s programs created techniques to answer the question: “Are we alone?” To this end, NExSS has produced a comprehensive series of papers outlining the past, present, and future of research on how to search for signs of life on exoplanets (planets around other stars). BMSIS Scientists Eddie Schwieterman, Sara Walker, Betul Kacar, and Daniel Angerhausen are contributors to these articles.

The pace of exoplanet discoveries has been so rapid—over 3,500 since the first in 1992— that a meeting of scientists from many disciplines was urgently needed to synthesize our knowledge and to advance our ability to find signs of life on exoplanets. Formed by NASA three years ago, NExSS is an international network of researchers that brings a variety of disciplines to understand how we can characterize and eventually search for signs of life, called biosignatures, on exoplanets.

These major review papers are the result of two years’ worth of work by some of the world’s leading researchers in astrobiology, planetary science, Earth science, heliophysics, astrophysics, chemistry, and biology. It began with online meetings followed by an in-person workshop held in Seattle, Washington (July 27-29, 2016), where scientists exchanged and debated new plans on how to best identify life on worlds beyond our solar system. These discussions formed the basis of the research articles that are being published in the June 2018 issue of the journal Astrobiology. These papers will serve as a reference for future research into how scientists can search for signs of life in the data they collect from future telescope observations. Since we are currently unable to visit exoplanets, scientists must use telescopes to examine them for biosignatures.

An artist’s concept of what life could look like on the surface of a distant planet (Credit: NASA)

“In less than 30 years, we’ve gone from not knowing whether planets existed outside our solar system to being able to pinpoint potentially habitable planets and collect data that will enable us to look for the signatures of life,” said BMSIS Scientist Dr. Eddie Schwieterman, a postdoctoral researcher in the Department of Earth Sciences at UC Riverside. “These advances offer unprecedented opportunities to answer the age-old question, ‘are we alone?’, but at the same time demand that we move forward with great care by developing robust models that allow us to seek and identify life with a high degree of certainty.”

The first of these papers, authored by Dr. Schwieterman, reviews the types of signatures that astrobiologists have previously proposed as ways we could identify life on an exoplanet. There are two major types of signals scientists plan to look for. One type comes in the form of the gases that life produces, for example the oxygen you are breathing right now, which was made by plants or by photosynthetic microbes. Second, they plan to look for the light reflected by life itself, such as the color of leaves or the pigments that give color to blooms in the oceans and to the hot springs of Yellowstone. These kinds of signatures can all be seen on Earth from orbit, and astronomers are studying designs of telescope concepts that may be able to detect them on planets around nearby stars.

The second review paper, co-authored by Dr. Schwieterman, discusses more recent research on ways nature could “trick” scientists into thinking a planet without life was alive, or vice versa. In this manuscript, the scientists review ways that a planet could make oxygen without life, and how planets with life may have signatures other than the oxygen that is abundant on modern-day Earth. By thinking about such kinds of planets in advance, scientists are now better prepared to distinguish such worlds from planets that are truly alive, and how to expand our catalogue of signatures scientists can look for in the future.

Two more papers show how scientists try to formalize the lessons we have learned from Earth, and expand them to the wide diversity of worlds we have yet to discover. One of these articles was authored by BMSIS Scientist Dr. Sara Walker and co-authored by BMSIS Scientist Dr. Betul Kacar, while the other was co-authored by Dr. Schwieterman.

“Discovering planets that are outside of our solar system provides evolutionary and molecular biologists new opportunities to think outside of the box.” Says Dr. Kacar of the work. “Is life a fluke accident? How repeatable is life? What are the chances of encountering similar life forms elsewhere in the Universe? One way to answer this question is to increase our understanding of the link between biology and the environment. It surely is an exciting time to tackle big questions that relate to life’s possibilities- the discovery of new exoplanets seemingly every day makes understanding planetary biology a must.”

Trying to solve the quandary of how and where to look for signs of life led the team of scientists to set another goal for the community: to quantify the chances for life and the clarity of its signals on other worlds. “For the first time in human history we will no longer need to satisfy ourselves only speculating about the possibility life on other worlds – we may finally be able to assign confidence level to how likely it is we’re not alone,” said Dr. Walker of this important step in the search for extraterrestrial life.

A consistent theme throughout these papers is the need to consider planets in an integrated way, which includes multiple disciplines and perspectives. “Because life, planet, and parent star change with time together, a biosignature is no longer a single target but a suite of system traits,” said Nancy Kiang, a biometeorologist at NASA’s Goddard Institute for Space Studies (GISS), New York City. “More biologists and geologists are needed to direct how to interpret observations where life processes will be adapted to the particular environmental context.”

The final article, co-authored by BMSIS Scientist Dr. Daniel Angerhausen, discusses the telescopes that will make the observations necessary to conduct this search for life beyond our Solar System. This includes a variety of observatories, both ground-based and space-based, those in operation today and those that will be built decades in the future. Taken together, this paper demonstrates how the exoplanet community will evolve from their current assessments of the sizes and orbits of these faraway worlds, to thorough analysis of their chemical composition, and eventually whether they harbor life. Critical to this endeavor is coordination between these different observatories, all of which convey unique advantages to scientists.

Speaking of his involvement, Dr. Angerhausen commented, “When people ask what my biggest dream is, I always say that I want to be part of the team that finds life in space. These reviews feel like a big step in that direction and show the path we will take. I am proud and happy to be a little gear in this amazing and diverse community.”

Dr. Shawn Domagal-Goldman, an astrobiologist at NASA’s Goddard Space Flight Center and a member of the Board of Advisers of Blue Marble Space says of this work, “NExSS has created a diverse network of scientists. That network will allow the community to more rigorously assess planets for biosignatures than would have otherwise been possible.”

The workshop discussions and review papers lead to the hopeful assessment that, given upcoming technologies and current knowledge from the known distributions of exoplanets, the detection of atmospheric signatures of a few potentially habitable planets may possibly come before 2030. 

NExSS is funded by NASA’s Astrobiology Program.