For years, astronomers have scoured the cosmos for rocky exoplanets with atmospheres, a key criterion for potential life. Recently, they’ve identified such a planet, though it turns out to be a nightmarish world with a molten rocky surface, unsuitable for life.
On Wednesday, scientists announced that the planet, termed a “super-Earth,” is notably larger than Earth yet smaller than Neptune, and it orbits perilously close to a star dimmer and slightly less massive than our sun, rapidly completing an orbit every 18 hours or so.
The James Webb Space Telescope, using two of its instruments, has detected signs of a significant, though hostile, atmosphere that might be constantly replenished from an extensive magma ocean.
“The atmosphere is likely rich in carbon dioxide or carbon monoxide, but can also have other gases such as water vapor and sulfur dioxide. The current observations cannot pinpoint the exact atmospheric composition,” explained Renyu Hu of NASA’s Jet Propulsion Laboratory and Caltech, the study’s lead author, published in the journal Nature.
The data from Webb leaves the atmospheric thickness unclear, but Hu suggests it might be comparable to Earth’s or even exceed Venus’s dense and toxic atmosphere. Named 55 Cancri e or Janssen, the planet is roughly 8.8 times the mass of Earth and twice its diameter. It orbits its star at a mere one-25th the distance between Mercury and the Sun, heating its surface to approximately 3,140 degrees Fahrenheit (1,725 degrees Celsius). “Indeed, this is one of the hottest-known rocky exoplanets,” remarked astrophysicist and co-author Brice-Olivier Demory of the University of Bern’s Center for Space and Habitability, “There are likely better places for a vacation spot in our galaxy.”
Uninhabitable Super-Earth: Closest to its star, yet maintains an atmosphere
Likely tidally locked, the planet consistently shows the same side to its star, similar to the Earth-moon relationship. It is situated in the Milky Way, about 41 light-years away in the constellation Cancer. Alongside 55 Cancri e, four gas giants orbit the same star, which is part of a binary system with a red dwarf. The stars are separated by a distance a thousand times that between the Earth and the Sun, with light taking six days to travel between them. Despite its proximity to its star, which typically would strip away any atmosphere, the planet seems to maintain one, likely fueled by gases from its extensive magma oceans, Hu indicated. “The planet cannot be habitable,” Hu noted, due to the extreme heat preventing the presence of liquid water, essential for life.
Previously, only gas giants had been found with atmospheres. The discovery of an atmospheric rocky planet by Webb marks a significant advancement in exoplanet research. On Earth, the atmosphere is vital for life, warming the planet, providing oxygen, shielding against solar radiation, and maintaining pressure necessary for liquid water. “On Earth, the atmosphere is key for life,” Demory observed. “This result on 55 Cnc e entertains the hope that Webb could conduct similar investigations on planets that are much cooler than 55 Cnc e, which could support liquid water at their surface. But we are not there yet.”