One of the many goals of the James Webb Space Telescope is to help characterize the atmospheres of exoplanets using a technique called spectroscopy, which splits light into different wavelengths allowing scientists to determine the elemental makeup of a distant object.
Astrobiologists like Dr. Giada Arney from the NASA Goddard Space Flight Center are excited about this capability because it allows scientists to continue collecting evidence for possible biosignatures, or remotely observable signs of life. Some important biosignatures on Earth include oxygen and methane, which are direct results of biological processes of plants and animals. However, when looking at exoplanets, scientists must rule out other non-life methods of creating those signatures, like volcanism and atmospheric processes.
Extraordinary claims, such as finding life on another planet, must have extraordinary evidence, and while Webb will help contribute to that effort, it alone will not be enough to truly detect life on an exoplanet.
We’re really excited to use the James Webb Space Telescope to look for signs of life in the atmospheres of potentially habitable planets. And, in particular, we’re searching for signatures called biosignatures, which are remotely observable signs of life.
Now on Earth, some of the important biosignatures of our own planet are oxygen, which is produced by oxygenic photosynthesis, that of course, we all know plants do that. But there’s all sorts of microbes that also do oxygenic photosynthesis, and a lot of people consider it to be the dominant metabolism of our planet.
Another important biosignature of Earth is methane. Methane on our planet is produced by microbes that live in a variety of places, ranging from hydrothermal vents at the bottom of the ocean to the guts of cows. And they produce most of the methane that’s in our planet’s atmosphere.
So, these are important gases that we want to look for in the atmospheres of exoplanets with the James Webb Space Telescope. But you also have to really carefully interpret that gas. That is, does it make sense for life to produce that given biosignature in that given environment.
And then, really importantly, you also want to rule out what are called biosignature false positives.
Biosignature false positives are non-life ways that a planet can fool you by producing something that looks like a biosignature, but it’s not actually a biosignature because it’s not produced by life; it’s produced by some other process like volcanism or atmospheric chemistry or any other process that doesn’t involve life.
So, all of this together means this is a really exciting search, but it’s going to be complicated.
And, if we detect something that we think is a biosignature when we look at an exoplanet, it might not immediately be definitive. It might be ambiguous until we collect more data to better understand it in the context of its environment.