Nearby exoplanet could offer clues about atmospheres around hot, rocky alien worlds

A nearby Earth-size planet beyond our solar system could soon join the ranks of worlds with confirmed atmospheres, according to new research.

The exoplanet, L 98-59 c, is a hot, rocky world slightly larger than Earth that orbits a bright, young star about 35 light-years away from us. While the planet itself was discovered back in 2019, a new analysis of Hubble Space Telescope observations suggests it may be capable of hosting an atmosphere, adding to the diversity of known terrestrial worlds with clearly defined "air."

If confirmed, the new findings would also make L 98-59 c the first planet of its size with a detected atmosphere, astronomers say, potentially setting new constraints on the atmospheres of worlds with this size and their ability to endure extreme environments created by the harsh conditions of young, flaring stars.

"L 98-59 c could be the first planet smaller than 2 Earth radii with a definitively detected atmosphere," a team of astronomers led by Thomas Barclay, a scientist at NASA Goddard Space Flight Center in Maryland, stated in a new paper reporting the findings.

Previous data gathered by NASA's exoplanet hunter TESS (short for Transiting Exoplanet Survey Satellite) suggest the exoplanet's host star, L 98-59, is more active than previously thought and showers significantly more energy on its system of four, potentially five, planets than the sun does on Earth. As such, "L 98-59 c provides an excellent opportunity to probe the atmospheres of planets smaller than 1.5 Earth radii that formed and evolved in the same stellar environment," the new study reports.

In April of 2020, the researchers observed the world as it transited in front of its star with the goal of detecting faint spectral features that might reveal the presence of an atmosphere. Over the course of four Hubble orbits, the team found compelling evidence that the planet's transmission spectrum is not flat, which they suspect could be indicative of atmospheric components, such as clouds or hazes, that absorb or scatter light.

The study notes that the detection is not yet totally confirmed, as the single transit of L 98-59 c, while promising, limits the conclusions that can be drawn. Determining the presence of the world's atmosphere in telescope data is no easy task, particularly due to the contamination of spectral signals from its host star, which can obscure the sought-after atmospheric signals from the planet.

Forthcoming observations of the planet scheduled with Hubble — and potentially even the James Webb Space Telescope — could help determine whether the signals seen so far are due to stellar spectral contamination or are actually caused by a planetary atmosphere, the study reports.

These findings are described in a paper published April 2 in the Astronomical Journal.