TRAPPIST-1e is a rocky, close-to-Earth-sized exoplanet orbiting within the habitable zone around the ultra-cool dwarf star TRAPPIST-1 approximately 40 light-years away from Earth in the constellation of Aquarius.
It is the fourth of seven planets in the TRAPPIST-1 system, which is the most studied planetary system outside our own. Astronomers are intensely interested in these planets because all seven of them are roughly Earth-sized and rocky, and three of them – including TRAPPIST-1e – are located in the habitable zone, where liquid water could exist on their surfaces. it has a mass about half that of the Earths and it’s about the same size. All of these planets orbit close to the star. It takes only 6 days for this one to complete one orbit, and is so close that it’s about 30 times closer than Earth is to the Sun!
TRAPPIST-1e was discovered in 2017 based on observations from various telescopes, including NASA’s Spitzer Space Telescope, which detected the periodic dimming of light from the star as the planet transits, or passes in front of it. Since then, it has been studied by other telescopes, including NASA’s James Webb Space Telescope, which is beginning to probe the atmosphere and surface conditions of all the planets.
TRAPPIST-1e is a fascinating example of how diverse and complex exoplanets can be, and of all the planets in this system, it may be the most suitable exoplanet found yet for life.
If it is found to have an atmosphere, which would be a huge deal in and of itself and something the Webb Space Telescope is uniquely equipped to do, then by studying it, we can learn more about its climate and potential for habitability. For example, a detailed study by Webb could detect signs of water vapor and ozone in the planet’s atmosphere, which could provide a protective layer against harmful radiation from the star. Webb could also measure the planet’s dayside temperature to give an indication of just what sort of organisms, if any, could survive there.
Running models of rocky planets like this suggests that TRAPPIST-1e may not be uniformly hot. Because it is tidally locked to its star, meaning it always shows the same face to it, one side of the planet may be much hotter than the other. The night side may be cold enough to freeze water, creating a stark contrast between day and night. The planet may also have strong winds that circulate heat around the globe, creating a more moderate climate.
What’s more, astronomers are starting to think that life on tidally locked planets might even be found nestled in Terminator Zones, the region where the night side of the planet is separated from the day side.
TRAPPIST-1e is an enormously promising target for future observations with Webb, not only to further understand the physical characteristics of the planet, but Webb has instruments on board which may be able to detect signs of life if they exist. Astronomers call these biosignatures, and are compounds in the atmosphere that could only be put there by living organisms, such as certain types of methane or oxygen. This would indicate biological activity on the planet’s surface or subsurface.