Are We Alone in the Universe? NASA Calls for New Framework

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Oct 27, 2021
Are We Alone in the Universe? NASA Calls for New Framework

How do we understand the significance of new scientific results related 
to the search for life? When would we be able to say, “yes, 
extraterrestrial life has been found?”

NASA scientists are encouraging the scientific community to establish a 
new framework that provides context for findings related to the search 
for life. Writing in the journal Nature, they propose creating a scale 
for evaluating and combining different lines of evidence that would 
ultimately lead to answering the ultimate question: Are we alone in the 
universe?

In the new article led by Jim Green, the agency's chief scientist, a 
NASA group offers 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 
possibilities of life elsewhere.

“Having a scale like this will help us understand where we are in terms 
of the search for life in particular locations, and in terms of the 
capabilities of missions and technologies that help us in that quest,” 
Green said.

The scale contains seven levels, reflective of the winding, complicated 
staircase of steps that would lead to scientists declaring they’ve found 
life beyond Earth. As an analogy, Green and colleagues point to the 
Technology Readiness Level scale, a system used inside NASA to rate how 
ready a spacecraft or technology is to fly. Along this spectrum, 
cutting-edge technologies such as the Mars helicopter Ingenuity begin as 
ideas and develop into rigorously tested components of history-making 
space missions.

The authors hope that in the future, scientists will note in published 
studies how their new astrobiology results fit into such a scale. 
Journalists could also refer to this kind of framework to set 
expectations for the public in stories about new scientific results, so 
that small steps don’t appear to be giant leaps.

“Until now, we have set the public up to think there are only two 
options: it’s life or it’s not life,” said Mary Voytek, head of NASA’s 
Astrobiology Program in at NASA Headquarters in Washington and study 
co-author. “We need a better way to share the excitement of our 
discoveries, and demonstrate how each discovery builds on the next, so 
that we can bring the public and other scientists along on the journey.”

It’s exciting each time a rover or orbiter finds proof that water once 
flowed on Mars. Each new finding shows us that Mars’ past climate was 
similar to Earth’s, and the red planet could have once supported life. 
But that doesn’t necessarily mean any sort of life ever lived there, or 
that anything lives there now. Discoveries of rocky planets orbiting 
stars beyond our Sun, especially those that could harbor liquid water on 
their surfaces, are similarly tantalizing, but not proof by themselves 
of life beyond Earth. So how do we understand these observations in context?

Scientists building a staircase that represents the search for life 
beyond Earth
Scientists worldwide collaborate, using different tools and methods, to 
search for life beyond Earth. NASA scientists propose having a scale to 
contextualize the significance of new results related to this search.
Credits: NASA/Aaron Gronstal
All of science is a process of asking questions, coming up with 
hypotheses, developing new methods to look for clues, and ruling out all 
alternative explanations. Any individual detection may not be completely 
explained by a biological process, and must be confirmed through 
follow-up measurements and independent investigations. Sometimes, there 
are problems with the instruments themselves. Other times, experiments 
don’t turn up anything at all, but still deliver valuable information 
about what doesn’t work or where not to look.

Astrobiology is no different. The field pursues some of the most 
profound questions that anyone could ask, regarding our origins and 
place in the universe. As scientists learn more and more about what 
kinds of signals are associated with life in diverse environments on 
Earth, they can create and improve upon technologies needed to find 
similar signs elsewhere.

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

At the first step of the scale, “level 1,” scientists would report hints 
of a signature of life, such as a biologically relevant molecule. An 
example would be a future measurement of some molecule on Mars 
potentially related to life. Moving up to “level 2,” scientists would 
ensure that the detection was not influenced by the instruments having 
been contaminated on Earth. At “level 3” they would show how this 
biological signal is found in an analog environment, such as an ancient 
lakebed 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 whether the environment 
could support life, and rule out non-biological sources. For Mars in 
particular, samples returned from Mars could help make this kind of 
progress. Perseverance will soon be collecting and storing samples with 
the goal of a future mission returning them one day. Since different 
teams on Earth would have the opportunity to independently verify hints 
of life in Mars samples with a variety of instruments, the combination 
of their evidence could achieve “level 6,” the second highest step on 
the  scale. But in this example, to reach level 7, the standard by which 
scientists would be most sure they had detected life on Mars, an 
additional mission to a different part of Mars may be required.

“Achieving the highest levels of confidence requires the active 
participation of the broader scientific community,” the authors write.

This scale would apply to discoveries from beyond the solar system, too. 
Exoplanets, planets outside our solar system,  are believed to outnumber 
the 300 billion stars in the Milky Way. But small, rocky planets are 
harder to study from afar than gas giants. Future missions and 
technologies would be necessary to analyze the atmospheres of Earth-size 
planets with Earth-like temperatures receiving adequate amounts of 
starlight for life as we know it. The James Webb Space Telescope, 
launching later this year, is the next big advance in this area. But it 
will likely take an even more sensitive telescope to detect the 
combination of molecules that would indicate life.

Detecting oxygen in the atmosphere of an exoplanet, a planet outside our 
solar system, would be a significant step in the process of searching 
for life. We associate oxygen with life because it is made by plants and 
we breathe it, but there are also geological processes that generate 
oxygen, so it is not proof by itself of life. To move upward on the 
scale, a mission team could demonstrate that the oxygen signal was not 
being contaminated by light reflected from Earth and study the chemistry 
of the planet’s atmosphere to rule out the geological explanation. 
Additional evidence of an environment that supports life, such as an 
ocean, would bolster the case that this hypothetical planet is inhabited.

Scientists who study exoplanets are eager to find both oxygen and 
methane, a combination of gases in Earth’s atmosphere indicative of 
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” milestone.

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

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

Upcoming missions such as Europa Clipper, an orbiter headed for 
Jupiter’s icy moon Europa later this decade, and Dragonfly, an 
octocopter that will explore Saturn’s moon Titan, will provide vital 
information about the environments in which some form of life may one 
day be found.

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

Learn more about the NASA Astrobiology Program at 
https://astrobiology.nasa.gov

Written by Elizabeth Landau
NASA Headquarters

Last Updated: Oct 28, 2021
Editor: Elizabeth Landau
Tags:  Ames Research Center, Astrobiology, Europa (Moon), Exoplanets, 
Goddard Space Flight Center, Mars, NASA Headquarters, Planets, Solar System