Tips in the search for life
Report offers advice for NASA scientists hunting for what’s out there
It’s one of the biggest questions there is: Are we alone in the universe?
NASA scientists in the field of astrobiology are looking for answers. A new report from the National Academies of Sciences, Engineering and Medicine has some advice to help them along.
“Out of every 10 stars, six of them have an Earth-like planet,” said Alan Boss, an astronomer at the Carnegie Institution for Science who worked on the report. That means the odds of finding extraterrestrial life are much better than scientists once thought.
The report was released Wednesday at the National Academies’ headquarters in Washington. Here are some of its recommendations.
Scientists searching for life on other worlds should look beneath the surface
If you were to look at Earth from space with an extremely powerful telescope, the signs of life would be obvious: trees clustered in rainforests, herds of elephants roaming across the savanna, the distinctive colors of algae blooms on the water.
But there’s also plenty of life beneath the surface. Consider the soil microbes that produce natural antibiotics, or the giant tube worms (they’re actually mollusks) that thrive on the freezing ocean floor, fueled by hydrothermal vents instead of light from the sun.
Other worlds that may look dormant on the surface could harbor life in their interiors.
Enceladus, Saturn’s sixth-largest moon, is a prime example. Its frozen exterior may give the impression that it’s nothing more than a giant ice cube.
But you can’t judge a world by its outer shell. NASA’s Cassini spacecraft revealed that Enceladus has a briny subsurface ocean with complex organic molecules. That, along with heat generated by tidal forces, makes scientists think that the moon could be hospitable to life.
Scientists need a better idea of how they would recognize alien life if they were to find it
If astrobiologists detect evidence of life, how would they know? Are there certain essential features that any form of life must have? Are some of them unique to living things?
In science-speak, the thing astrobiologists are looking for is a “biosignature” — a detectable sign that life is (or was) present. It may be a particular shape that only a living being could produce. It may be a distinctive pattern of chemical compounds that must have had a biological origin. It may be a gas (or mixture of gases) in a planet’s atmosphere that couldn’t exist in a lifeless system.
Ideally, it would be a combination of several of these, said Barbara Sherwood Lollar, a professor of Earth sciences at the University of Toronto who chaired the committee that produced the report. “No one biomarker is infallible,” she said.
There is still much debate about what would qualify as a biosignature. The report recommends that astrobiologists buckle down and figure this out.
In doing so, they need to consider what would distinguish an actual biosignature from a false alarm. They also need a way to tell whether they’ve seen a true biosignature but accidentally rejected it.
Scientists need to invent some kind of life-detection technology and make sure it really works
One possibility for detecting life is to focus on biosignatures in exoplanet atmospheres. In the last decade, new technologies have greatly improved scientists’ ability to analyze the contents of these distant atmospheres, and NASA should do what it can to accelerate this work, the report said.
It’s also important to look closer to home. Potential biosignatures from some of Earth’s oldest sedimentary rocks can provide scientists something to practice on.
When NASA sends robotic explorers into space, they should be capable of analyzing DNA and RNA with great precision. Ideally, they should be able to study a single sample using a multitude of techniques. In designing test equipment, engineers should focus more on getting the science right than on building something quickly or saving a few bucks.
Another important consideration: Any technologies used on other worlds should tread as lightly as possible. And no matter what, they should not contaminate any other part of the universe with life from Earth.
Scientists can’t look at a planet or a moon in isolation
Any world that hosts (or hosted) life didn’t become habitable on its own. The conditions that make a place life-friendly depend on what’s around it.
The most obvious of these is the star at the center of its solar system: How much energy does it provide? Is that energy source stable?
“You can’t just study the planet — you also have to study the star,” Boss said. “You need to understand the stellar properties in order to understand habitability.”
Other objects in the solar system are important too. The orbits of nearby planets and moons may help keep a habitable world in a lifefriendly zone. Their gravitational forces may also contribute to tidal heating, as scientists suspect is the case with Enceladus.
Astrobiologists need better “starlight suppression” tools to take pictures of other worlds
It’s becoming increasingly important to be able to point a camera at an exoplanet and take a detailed picture. The problem is that the light from a nearby star will typically make it hard to see.
The report suggested two ways to get around this.
One is to build more advanced coronagraphs. These can be built right into a telescope to block the light of a nearby star. Coronagraphs were originally designed to study the outer atmosphere of the sun (called the corona), which would normally be invisible except during an event such as a solar eclipse. In recent years, scientists have started adapting coronagraphs for exoplanet studies.
Another option is to invent some kind of external “star shade” that would block a star’s light directly. These would fly in tandem with space-based telescopes and function like a piece of paper you might hold up to the sun before snapping a picture with your phone.
NASA should make sure that astrobiologists are involved in planning future missions
And they shouldn’t wait to be consulted until after key decisions are made — astrobiological factors should be baked in from the very beginning, when a mission is still in the conceptual stage.
People with expertise in astrobiology should remain involved every step of the way. That includes the operational phase, when a space probe is actually carrying out its assigned work.
Don’t be afraid to ask for help
Astrobiologists have stepped up their collaboration with NASA experts in astronomy, Earth science, planetary science and heliophysics. But why stop there?
NASA should coordinate its research efforts with the National Oceanic and Atmospheric Administration and the National Science Foundation, the report advises. It should also team up with space agencies from other countries.
NASA should even rely on nonprofit initiatives that search for signs of technologically advanced civilizations, such as the SETI Institute and Breakthrough Listen.