The atmospheres on seven newly discovered planets orbiting the ultra-cool dwarf star TRAPPIST-1, are mostly likely dense and deadly, but new research has confirmed a previously noted exception: One planet might be an ocean world with a habitable atmosphere for life as we know it.
Research published this month in the Astrophysical Journal shows radiation and chemistry models detailing the different atmospheres of TRAPPIST-1’s seven Earth-sized planets, and one of them, TRAPPIST-1 e, is the planet that might be just right for humans one day, assuming they can safely make the 39-light-year journey to the star system.
Andrew P. Lincowski, a doctoral student at the University of Washington and lead author of the research paper, says the planet “could be a water world, completely covered by a global ocean. In this case, it could have a climate similar to Earth.”
The star system’s differing planets can also tell us more about how planets age and change, Lincowski says.
“This is a whole sequence of planets that can give us insight into the evolution of planets, in particular around a star that’s very different from [the sun], with different light coming off of it,” Lincowski says. “It’s just a gold mine.”
TRAPPIST-1 is a tiny M-class dwarf star, first spotted by the Two Micron All-Sky Survey in 1999 (and subsequently named to celebrate Trappist Belgian beer, which the Belgian researchers profess to appreciate).
It wasn’t until 2015 that scientists discovered TRAPPIST-1’s exoplanets (a name for another planet outside our solar system), and announced the discovery of three in May 2016.
In 2017, the NASA Spitzer Space Telescope discovered that TRAPPIST-1 had not three, but seven planets, publishing findings with the evaluation that three could be habitable. (I know, we had the perfect chance to name them after the seven dwarves or the colors of the rainbow, and we went with letters. TRAPPIST-1 Indigo? Let me hunt for extraterrestrial life on that planet.)
Modeling the climates of a star so different from our own sun helps guide scientists to research other stars unlike ours. The models identify signature wavelengths connected to atmospheric gases, which the James Webb telescope could then document, allowing researchers to discern a planet’s composition and environment. Understanding how different stars form broadens our ability to identify which processes could form the habitable promised land of planets.
We may be able to identify a habitable planet, but we don’t have the technology to make a visit to test it out. Even if the speedy spacecraft New Horizons attempted to stop by (it’s traveling at 14.31 kilometers per second), it would still take 817,000 years to make it to the star from Earth.
The TRAPPIST-1 planetary system provides an unprecedented opportunity to study terrestrial exoplanet evolution with the James Webb Space Telescope (JWST) and ground-based observatories. Since M dwarf planets likely experience extreme volatile loss, the TRAPPIST-1 planets may have highly evolved, possibly uninhabitable atmospheres. We used a versatile, 1D terrestrial planet climate model with line-by-line radiative transfer and mixing length convection (VPL Climate) coupled to a terrestrial photochemistry model to simulate environmental states for the TRAPPIST-1 planets. We present equilibrium climates with self-consistent atmospheric compositions and observational discriminants of postrunaway, desiccated, 10–100 bar O2- and CO2-dominated atmospheres, including interior outgassing, as well as for water-rich compositions. Our simulations show a range of surface temperatures, most of which are not habitable, although an aqua planet TRAPPIST-1 e could maintain a temperate surface given Earth-like geological outgassing and CO2. We find that a desiccated TRAPPIST-1 h may produce habitable surface temperatures beyond the maximum greenhouse distance. Potential observational discriminants for these atmospheres in transmission and emission spectra are influenced by photochemical processes and aerosol formation and include collision-induced oxygen absorption (O2–O2), and O3, CO, SO2, H2O, and CH4 absorption features, with transit signals of up to 200 ppm. Our simulated transmission spectra are consistent with K2, Hubble Space Telescope, and Spitzer observations of the TRAPPIST-1 planets. For several terrestrial atmospheric compositions, we find that TRAPPIST-1 b is unlikely to produce aerosols. These results can inform JWST observation planning and data interpretation for the TRAPPIST-1 system and other M dwarf terrestrial planets.