The hunt for habitable exoplanets is on, and with the James Webb Space Telescope, we finally have a tool that can not only detect the presence of a planet in another star system, but can also look at the composition of its atmosphere. That ability will eventually allow us to find Earth-like planets wthat are good candidates for searching for life, but measuring the atmosphere of something so far away isn’t an easy matter.
Webb recently saw exciting signs in the form of water vapor detected in the vicinity of the exoplanet GJ 486 b. That could indicate the presence of water in its atmosphere, but it could also be from another source: the outer layer of the planet’s host star. Researchers are working through the data and hope to use another of Webb’s instruments to make the final call.
The planet GJ 486 b is rocky, a bit larger than Earth, and more massive, so it would have heavier gravity than we experience. And the star it orbits is quite different from our sun, as it is a type called a red dwarf, which is a dim, cool star that is approaching the end of its life. The planet is close enough to the star, orbiting in just 1.5 days, that its surface temperature would be around 800 degrees Fahrenheit, so it isn’t in the habitable zone where liquid water can exist on the surface.
However, Webb’s NIRSpec instrument detected water vapor, which could mean that the planet does have an atmosphere even though it’s so close to its star.
“We see a signal and it’s almost certainly due to water. But we can’t tell yet if that water is part of the planet’s atmosphere, meaning the planet has an atmosphere, or if we’re just seeing a water signature coming from the star,” explained Sarah Moran of the University of Arizona, lead author of the research, in a statement.
The reason that the star could be the source of the water vapor is that there are cool spots on the star’s surface, similar to the sunspots seen on our sun. The cool areas around these regions are more likely to collect water vapor compared to the hot regions around them, so there could be enough water vapor to give a signal to Webb’s instrument.
Finding water in the atmosphere of this rocky planet would be exciting since astronomers haven’t seen this before, and it could help to find habitable exoplanets in the future. But to be sure of the source of the water vapor, the researchers need to make more measurements using Webb’s NIRISS and MIRI instruments.
“Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science,” said fellow researcher Kevin Stevenson of the Johns Hopkins University Applied Physics Laboratory. “But we must be careful and make sure that the star is not the culprit.”
The research will be published in The Astrophysical Journal Letters.
