The James Webb Space Telescope has confirmed its first exoplanet, a rocky Earth-size planet, and attempted to take the measure of its atmosphere.
The planet formerly known as TOI 910.01, now LHS 475b, is real, according to new observations by the James Webb Space Telescope. Although roughly Earth-like in size, this world is nevertheless completely uninhabitable, roasting in its two-day orbit around its middle-aged red dwarf star.
NASA’s TESS mission first pinpointed this planet as a candidate worth follow-up, detecting the blip as the world crossed its star. In the follow-up Webb observations on August 31st and September 4th, the telescope caught two such transits, in which the planet blocked a mere 0.1% of the star’s light for 40 minutes.
“These pristine data help to validate and confirm the discovery of this Earth-size exoplanet,” says Jacob Lustig-Yaeger (Johns Hopkins University), who presented the as-yet unpublished results at the 241st meeting of the American Astronomical Society in Seattle, Washington.
“Our ultimate goal here was to search for the atmosphere of this planet,” he adds. To do this, the team relied on a technique known as transmission spectroscopy. The team basically measures the planet’s size at different wavelengths. When there are particles in the atmosphere absorbing the star’s light at particular wavelengths, the planet will appear bigger at those wavelengths; at wavelengths for which there’s no atmospheric absorption, the planet will appear smaller.
Drake Deming (University of Maryland), who was not involved with the study, says the team made the right observations for the job: “They have picked the best spectral region — the 4.3-micron carbon dioxide absorption line has great intrinsic strength, and that’s the most sensitive probe.”
Such observations are difficult at best, and in this case inconclusive. Lustig-Yaeger reported that while they can match the data with an atmosphere dominated by carbon dioxide, those data are also consistent with a completely airless world. Zero atmosphere for a planet several hundred degrees warmer than Earth wouldn’t be a great surprise, especially around the type of star known for its atmosphere-stripping flares.
Further observations with Webb will help disentangle these possibilities, and Lustig-Yaeger is excited for upcoming time already scheduled to look at a third transit.
Whether this world has air or not, perhaps the more important take-away is what the current data mean for future observations. “Our measurements meet the sensitivity requirements to be able to detect the atmospheres of Earth-size planets,” Lustig-Yaeger notes.
Those planets probably won’t be habitable either, Deming points out. “I think that eventually carbon dioxide in a rocky planet’s atmosphere will be detected using this technique,” he says. “But in my opinion the best prospects are hotter than LHS 475b, which is already well above a habitable temperature.”
Future observations of both types of worlds, airless and not, will help shed light on what conditions cause a planet to lose its atmosphere. “We’re interested in where this dividing line might be between planets with and without atmospheres,” Lustig-Yaeger says. “It’ll be really interesting, I think, to learn about the processes that make these very different stars and their planetary systems different from our own solar system.”