Astronomers have been on the hunt for years for rocky planets beyond our solar system with an atmosphere—a characteristic deemed essential for any chance of supporting life. Finally, it seems they’ve pinpointed one. However, this fiery planet—reportedly covered in molten rock—holds no promise for habitability.
On Wednesday, last week, researchers revealed that the planet is a “super-Earth”—a rocky world significantly larger than our own but smaller than Neptune—and it orbits dangerously close to a star fainter and slightly less massive than our sun, completing an orbit roughly every 18 hours. Infrared observations conducted using two instruments aboard the James Webb Space Telescope suggest the presence of a substantial, though unwelcoming, atmosphere, perhaps constantly replenished by gases released from a vast magma ocean.
“The atmosphere is likely abundant in carbon dioxide or carbon monoxide, but could also contain other gases such as water vapor and sulfur dioxide. However, the current observations cannot determine the exact composition of the atmosphere,” explained Renyu Hu, a planetary scientist from NASA’s Jet Propulsion Laboratory and Caltech, who led the study published in the journal Nature.
The data from the Webb telescope also did not clarify the thickness of the atmosphere. Hu speculated that it could be as thick as Earth’s or even thicker than that of Venus, which boasts the densest, toxic atmosphere in our solar system.
This planet, known as 55 Cancri e or Janssen, is about 8.8 times more massive than Earth, with a diameter roughly twice as large. It orbits its star at about one-25th the distance between Mercury and the sun in our solar system. Consequently, its surface temperature soars to approximately 3,140 degrees Fahrenheit (1,725 degrees Celsius or 2,000 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 likely tidally locked, meaning it continuously presents the same side to its star, akin to how the moon behaves towards Earth. Situated in our Milky Way galaxy approximately 41 light-years from Earth, within the Cancer constellation, it spans a distance of 5.9 trillion miles, equivalent to a light year. Its host star is accompanied by four gas giants in orbit.
This star is gravitationally linked to another in a binary system, the latter being a red dwarf, the smallest type of typical star. The separation between these stellar companions is 1,000 times greater than that between Earth and the sun, requiring six days for light to traverse the gap.
Despite extensive searches, the rocky exoplanet showcasing evidence of an atmosphere isn’t the ideal candidate. Proximity to its star suggests atmospheric stripping by stellar radiation and winds. However, gases from the vast lava ocean believed to envelop the planet may continuously replenish the atmosphere, as suggested by Hu.
“The planet isn’t conducive to habitability,” Hu emphasized, due to its scorching temperatures unsuitable for liquid water, a prerequisite for life.
Previous discoveries of exoplanetary atmospheres predominantly featured gas giants, not rocky ones. Thus, the identification of a rocky exoplanet with an atmosphere signifies progress as Webb expands the horizons of exoplanetary exploration.
On Earth, the atmosphere plays crucial roles: warming the planet, providing breathable oxygen, shielding against solar radiation, and sustaining the pressure necessary for surface water to remain in liquid form.
