Illustration of exoplanet LHS 475 b and its star. Photo: Supplied / NASA, ESA, CSA, L. Hustak (STScI)
The new James Webb Space Telescope has discovered its first planet orbiting another star - an exoplanet.
The rocky planet, LHS 475 b, measures 99 percent of Earth's diameter and is 41 light-years away, in the Octans constellation.
But it is not yet clear if the planet has an atmosphere at all, let alone one like Earth, and researchers also could not rule out one made of purely carbon dioxide.
Research co-leader Jacob Lustig-Yaeger, from Johns Hopkins University Applied Physics Laboratory, said a pure carbon dioxide would be incredibly compact and challenging to detect.
The team did, on the other hand, rule out the planet having a thick methane-dominated atmosphere, like Saturn's moon Titan.
Webb also revealed the planet is a few hundred degrees warmer than Earth, so if clouds are spotted, it may mean the planet is more like Venus - which has a carbon dioxide atmosphere and is constantly shrouded in thick clouds.
Although LHS 475 b is closer to its star than any planet in our solar system, the red dwarf star is less than half the temperature of the Sun, so the researchers project it still could have an atmosphere.
The planet completes an orbit in just two days.
Illustration of exoplanet LHS 475 b. Photo: Supplied / NASA, ESA, CSA, L. Hustak (STScI)
Webb was the only operating telescope that was capable of characterising the atmospheres of Earth-sized exoplanets, NASA said.
Since the beginning of its operation in July, the telescope has offered glimpses of the universe that were inaccessible to us before.
Research co-leader Kevin Stevenson said the telescope's data also showed LHS 475 b was "a small, rocky planet".
NASA astrophysics division director Mark Clampin said the discovery opened the door to future possibilities for studying rocky planet atmospheres with Webb.
"Webb is bringing us closer and closer to a new understanding of Earth-like worlds outside our solar system, and the mission is only just getting started."
"With this telescope, rocky exoplanets are the new frontier," Lustig-Yaeger added.
The researchers are scheduled to obtain more data in upcoming observations.