Future historians might look back on this time and call it the ‘exoplanet age.’ We’ve found over 5,000 exoplanets, and we’ll keep finding more. Next, we’ll move beyond just finding them, and we’ll turn our efforts to finding biosignatures, the special chemical fingerprints that living processes imprint on exoplanet atmospheres.
But there’s more to biosignatures than atmospheric chemistry. On a planet with lots of plant life, light can be a biosignature, too.
Finding oxygen in an exoplanet’s atmosphere is a clue that life may be at work. On Earth, photosynthetic organisms absorb carbon dioxide, sunlight, and water and produce sugars and starches for energy. Oxygen is the byproduct of that process, so if we can detect oxygen elsewhere, it’ll generate excitement. But researchers have also put pressure on the idea that oxygen in an exoplanet’s atmosphere indicates life. It’s only evidence of life if we can rule out other pathways that created the oxygen.
When the James Webb Space Telescope aims at exoplanet atmospheres, it’ll use spectroscopy to identify chemical elements. One of the things it’s looking for is methane, a chemical compound that can indicate the presence of life.
Methane is a compelling biosignature. Finding a large amount of methane in an exoplanet’s atmosphere might be our most reliable indication that life’s at work there. There are abiotic sources of methane, but for the most part, methane comes from life.
But to understand methane as a potential biosignature, we need to understand it in a planetary context. A new research letter aims to do that.
The next step to understanding exoplanets is to understand their atmospheres better. Astronomers can determine a planet’s mass, density, and other physical characteristics fairly routinely. But characterizing their atmospheres is more complicated.
Astronomers have had some success studying exoplanet atmospheres, and spacecraft like the James Webb Space Telescope and the ESA’s ARIEL mission will help a lot. But there are thousands of confirmed exoplanets with many more to come, and the Webb has many demands on its time.
Can smaller, ground-based telescopes play a role in understanding exoplanet atmospheres?
Uranus and Neptune are similar planets in many ways. Both are ice giant worlds, both have atmospheres rich in methane, and both have a bluish color. But while Uranus has a pale blue-green hue, Neptune has a deep blue color. But why? Why would two planets so similar in size and composition appear so different? According to a recent study, the answer lies in their aerosols.
Red dwarf stars are the most common kind of star in our neighbourhood, and probably in the Milky Way. Because of that, many of the Earth-like and potentially life-supporting exoplanets we’ve detected are in orbit around red dwarfs. The problem is that red dwarfs can exhibit intense flaring behaviour, much more energetic than our relatively placid Sun.
So what does that mean for the potential of those exoplanets to actually support life?
The search for exoplanets has revealed types of planets that are nothing like the worlds in our own Solar System. One such type is the hot-Jupiter. They’re gas giants like Jupiter that orbit their host star very closely. That proximity raises their temperatures to extreme heights.
Hot-Jupiters can be hot enough to vaporize metals, making their atmospheres un-Earthlike. A team of astronomers examining one exoplanet has found 7 different gaseous metals in its atmosphere.
Can the galaxy’s dead stars help us in our search for life? A group of researchers from Cornell University thinks so. They say that watching exoplanets transit in front of white dwarfs can tell us a lot about those planets.
Thanks to the success of the Kepler mission, we know that there are multitudes of exoplanets of a type called “Hot Jupiters.” These are gas giants that orbit so close to their stars that they reach extremely high temperatures. They also have exotic atmospheres, and those atmospheres contain a lot of strangeness, like clouds made of aluminum oxide, and titanium rain.
A team of astronomers has created a cloud atlas for Hot Jupiters, detailing which type of clouds and atmospheres we’ll see when we observe different Hot Jupiters.
The last few years has seen an explosion of exoplanet discoveries. Some of those worlds are in what we deem the “habitable zone,” at least in preliminary observations. But how many of them will have life-supporting, oxygen-rich atmospheres in the same vein as Earth’s?
A new study suggests that breathable atmospheres might not be as rare as we thought on planets as old as Earth.