After years of relentless search, astronomers have finally stumbled upon a rocky exoplanet beyond our solar system boasting an atmosphere—a critical feature deemed essential for supporting life. However, this newly discovered world, with its infernal landscape of molten rock, dashes any hopes of habitability.
According to researchers, the planet identified as a “super-Earth”—a rocky behemoth larger than our own planet but smaller than Neptune—orbits dangerously close to a star dimmer and less massive than our sun, completing a blistering orbit every 18 hours or so. Infrared observations from the James Webb Space Telescope have unveiled the presence of a substantial yet harsh atmosphere, likely sustained by gases emitted from a vast ocean of magma.
“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,” said planetary scientist Renyu Hu of NASA’s Jet Propulsion Laboratory and Caltech, the lead author of the study, published in the journal Nature.
The thickness of the atmosphere remained ambiguous in the Webb data. Hu suggested it could rival Earth’s in density or even surpass Venus, which boasts the densest and toxic atmosphere in our solar system.
Dubbed 55 Cancri e or Janssen, the planet is approximately 8.8 times more massive than Earth, with a diameter twice as large. Its close orbit around its star, at just one-25th the distance between Mercury and the sun, scorches its surface to temperatures around 3,140 degrees Fahrenheit (1,725 degrees Celsius or 2,000 degrees Kelvin).
“Indeed, this is one of the hottest-known rocky exoplanets,” said astrophysicist and study co-author Brice-Olivier Demory, of the University of Bern’s Center for Space and Habitability in Switzerland. (Exoplanet is the term for planets beyond our solar system.) “There are likely better places for a vacation spot in our galaxy.”
The planet is probably tidally locked, meaning it perpetually has the same side facing its star, much like the moon does toward Earth. It is located in our Milky Way galaxy about 41 light-years from Earth, in the constellation Cancer. A light year is the distance light travels in a year, 5.9 trillion miles. Four other planets, all gas giants, are known to orbit its host star.
That star is gravitationally bound to another star in a binary system. The other one is a red dwarf, the smallest kind of ordinary star. The distance between these companions is 1,000 times the distance between Earth and the sun, and light takes six days to get from one to the other.
After all their searching, the rocky exoplanet for which scientists finally found evidence of an atmosphere turned out to be one that probably should not even have one. Being so close to its star, any atmosphere should be stripped away by stellar irradiation and winds. But gases dissolved in the vast lava ocean thought to cover the planet may keep bubbling up to replenish the atmosphere, Hu said.
“The planet cannot be habitable,” Hu said, because it is too hot to have liquid water, considered a prerequisite for life.
All of the previous exoplanets found to have atmospheres were gaseous planets, not rocky ones. As Webb pushes the frontiers of exoplanet exploration, the discovery of a rocky one with an atmosphere represents progress.
On Earth, the atmosphere warms the planet, contains the oxygen people breathe, protects against solar radiation and creates the pressure needed for liquid water to remain on the planet’s surface.
“On Earth, atmosphere is key for life,” Demory said. “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.”
