James Webb Telescope sights distant small planets

BALTIMORE — When the James Webb Space Telescope was first imagined, exoplanets hadn’t even been discovered yet. Now the observatory is showing astronomers what it can learn about planets orbiting other stars, including smaller ones.

Since its launch in December 2021, JWST had already “sniffed” the atmospheres of Jupiter-sized planets orbiting extremely close to their stars (SN: 08/26/22). These intense worlds are interesting, but not the places astronomers hope to look for signs of life. The telescope is now getting glimpses of atmospheres on known exoplanets from the more terrestrial persuasion, astronomers reported Dec. 13-14 at JWST’s First Science Results conference.

And JWST is also starting to find new rocky worlds.

These first glimpses of distant worlds don’t yet reveal much about these distant places. But the researchers are encouraged by what JWST’s sharp vision in infrared wavelengths could eventually uncover about smaller planets beyond our solar system.

“The main message is that we are in business,” said University of Montreal astronomer Björn Benneke. “We don’t even have all the sightings yet, but they’re exciting enough.”

One of the smallest planets JWST has examined is GJ 1214b, which has frustrated astronomers since its discovery in 2009 (SN: 12/16/09). The planet is a sub-Neptune, which means that its size is somewhere between that of a rocky world like Earth and that of a gaseous world like Neptune.

“What are sub-Neptunes?” asked astronomer Eliza Kempton of the University of Maryland in College Park. They could be balls of rock with thick atmospheres of hydrogen and helium, or maybe water worlds (SN: 02/22/12). “What we would like to do with atmospheric characterization is measure their atmospheres and see which is which,” Kempton said.

Previously, astronomers tried to observe the composition of GJ 1214b’s atmosphere by watching how starlight passed through it. But the atmosphere is thick and hazy, blocking astronomers’ ability to detect individual molecules in it.

Instead of watching the planet pass in front of its star, Kempton and his colleagues used JWST to search for the planet’s glow just before it disappeared. behind the star. And it worked: After 38 hours of observation, the researchers detected the planet’s infrared glow, Kempton said in a Dec. 13 presentation.

There is still work to be done, but initial data suggests that the planet contains many chemical constituents, including possibly water and methane. It is also enriched with elements heavier than hydrogen and helium.

As for what kind of world GJ 1214b is, “I would say we’re not there yet,” Kempton said. It could be a watery planet, she said, or a gaseous planet that has lost a fair amount of its lighter elements.

The telescope also got its first glimpse of the tantalizing TRAPPIST-1 system, Benneke said in another December 13 presentation (SN: 12/13/17). Discovered in 2017, the system contains seven Earth-sized worlds that are likely rocky. Three of these planets could have the right temperatures for liquid water to exist on their surfaces, making them particularly attractive targets for the JWST and other telescopes to search for signs of life.

But TRAPPIST-1 is a small red star called an M dwarf, a type of star known for its violent flares and strong radiation. For years, astronomers debated whether the planets around these stars would be hospitable to life, or whether the stars would strip the atmospheres of their planets (SN: 06/14/17).

“If the TRAPPIST planets don’t have atmospheres, then we have to move on” from M dwarfs to searching for extraterrestrial life, says astronomer Mercedes Lόpez-Morales of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., who was not involved in the new JWST observations.

JWST’s first look at one of these potentially habitable worlds, TRAPPIST-1g, revealed no clear signs of an atmosphere. But the telescope only looked at the planet for about five hours. With more observations, an atmosphere should be detectable if it’s there, Benneke said.

JWST is also getting into the planet-hunting game, astronomer Kevin Stevenson said Dec. 14. The telescope rechecked a potentially interesting sighting from another telescope and confirmed that it had seen an Earth-sized rocky world around a nearby M dwarf. This proves that JWST has the accuracy to find such worlds.

“This is an exciting result, possibly JWST’s first discovery of an exoplanet,” said Stevenson of the Space Telescope Science Institute in Baltimore. The planet orbits its dim star every other day, so it’s probably around 225° Celsius on the surface – probably too hot to be habitable, he says. “It looks more like an exo-Venus than an exo-Earth.”