Discovering a Barren Exoplanet
Astronomers have made a groundbreaking discovery, offering their clearest view yet of the surface of an exoplanet. This achievement is attributed to NASA’s James Webb Space Telescope, which has provided unprecedented insights into the nature of this distant world.
The exoplanet in question, known as LHS 3844 b or Kua’kua, is a rocky planet with a diameter approximately 30% larger than Earth. It is described as a desolate and airless world, bearing a striking resemblance to Mercury, our solar system’s innermost planet. The absence of a discernible atmosphere and its extreme temperature variations—scorching on one side and freezing on the other—make it highly unlikely to support life.
Kua’kua orbits a star that is smaller and less luminous than the Sun, located about 49 light-years from Earth. A light-year is the distance light travels in a year, equating to roughly 5.9 trillion miles (9.5 trillion kilometers).
A Hellish World
Laura Kreidberg, an astronomer and managing director of the Max Planck Institute for Astronomy in Germany, who was the senior author of the study published in the journal Nature Astronomy, described the planet as “not a nice place.” She likened it to a “hellish, barren rock,” emphasizing that it is more similar to Mercury than to Earth.
“The planet has no trace of an atmosphere. Instead, we’re seeing a dark surface, likely old. Picture a bare rock hurtling through space for billions of years. You wouldn’t want to go there,” Kreidberg said.
The observations suggest an ancient planetary surface covered by darkened regolith, which is loose, fragmented rocky material formed over eons due to continuous bombardment by stellar radiation and micrometeorite impacts.
Advancements in Exoplanet Research
The James Webb Space Telescope, launched in 2021 and becoming operational in 2022, has revolutionized the understanding of exoplanets. Its advanced infrared observational capabilities have enabled scientists to discern the chemical composition and internal dynamics of exoplanet atmospheres, even identifying the types of clouds present.
Sebastian Zieba, an astronomer and lead author of the study from the Center for Astrophysics, Harvard & Smithsonian in Massachusetts, highlighted that the telescope now allows astronomers to directly study the geology and surface composition of exoplanets.
“This was very challenging before the James Webb Space Telescope. This, therefore, also puts the Earth and the solar system as a whole into greater context, allowing us to check if processes or surface compositions familiar within the solar system are common around other stars, too,” Zieba said.
“It’s like we suddenly cleaned our glasses and can see the planets clearly for the first time,” Kreidberg added.
Characteristics of the Star and Planet
The star that Kua’kua orbits is a common type known as a red dwarf. It has a mass of about 15% that of the Sun and a luminosity of approximately 0.3%. Kua’kua is extremely close to its star, orbiting it once every 11 hours. It is also tidally locked, meaning one side always faces the star while the other side remains in perpetual darkness, similar to how the Moon is tidally locked to Earth.
The planet’s “dayside” surface, perpetually exposed to the star, reaches temperatures of about 1,340 degrees Fahrenheit (725 degrees Celsius). No detectable heat was found on the “nightside.”
Surface Composition and Implications
Webb enabled researchers to detect light, specifically in the infrared region of the electromagnetic spectrum, coming directly from the planet’s surface. Different rocks have unique spectral fingerprints, much like atmospheres do. Dark volcanic rocks like basalt matched the observations better than brighter, silica-rich rocks like granite.
The surfaces of Mercury and the moon are dominated by basalt. On Earth, widespread granite formation is linked to water and plate tectonics, a geological process involving the gradual movement of the immense plates that make up Earth’s surface. If granite-like surfaces were robustly identified on an exoplanet, it would not necessarily mean life but could suggest a more Earth-like geological history.
Another possibility matching the observations was a solid surface of relatively recent volcanic rock, but the researchers searched for volcanism-related gases like sulphur dioxide and found none.
Without an atmosphere, there is minimal protection from stellar radiation or charged particles from the star, and no chance for liquid water, considered fundamental for life.
“So overall, this is almost certainly not a habitable world,” Zieba said.
