Astronomers have for years searched for rocky planets outside our solar system with atmospheres, a characteristic considered essential for any possibility of life. Well, they finally seem to have found one.
But this hellish planet – apparently with a surface of molten rock – offers no hope of habitability.
Researchers said Wednesday that the planet is a “super-Earth” — a rocky world significantly larger than our planet but smaller than Neptune — and it’s orbiting dangerously close to a star darker and slightly more massive than our own. sun, rapidly completing an orbit every 18 hours or so.
Infrared observations using two instruments aboard the James Webb Space Telescope have shown the presence of a substantial—albeit inhospitable—atmosphere, likely continuously replenished by gases released by a vast ocean of magma.
“The atmosphere is probably rich in carbon dioxide or carbon monoxide, but there may also be other gases such as water vapor and sulfur dioxide. Current observations cannot determine the exact composition of the atmosphere,” said planetary scientist Renyu Hu of NASA’s Jet Propulsion Laboratory and Caltech, the lead author of the study published in the journal Nature.
Webb’s data also did not clarify the thickness of the atmosphere. Hu said it could be as thick as Earth’s, or even thicker than that of Venus, whose toxic atmosphere is the densest in our solar system.
The planet, called 55 Cancri e or Janssen, is about 8.8 times more massive than Earth, with a diameter about twice that of our planet. It orbits its star at one-25th the distance between our solar system’s innermost planet Mercury and the sun. As a result, its surface temperature is about 3140 degrees Fahrenheit (1725 degrees Celsius or 2000 degrees Kelvin).
“This is indeed one of the hottest rocky exoplanets known,” said astrophysicist and study co-author Brice-Olivier Demory of the Center for Space and Habitability at the University of Bern in Switzerland. (Exoplanet is the term for planets outside our solar system.) “There are probably better places in our galaxy for a vacation spot.”
The planet is likely tidally locked, meaning that it always has the same side facing the star, much like the moon faces 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 one year, 5.9 trillion miles (9.5 trillion km). Four other planets, all gas giants, are known to orbit their star.
This star is gravitationally bound to another star in a binary system. The other is a red dwarf, the smallest type of ordinary star. The distance between these moons is 1,000 times the distance between Earth and the sun, and light takes six days to travel 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 shouldn’t even have one. Because it is so close to its star, any atmosphere must be stripped away by stellar radiation and winds. But gases dissolved in the vast lava ocean believed to cover the planet may continue to bubble 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 previous exoplanets found to have atmospheres were gas planets, not rocky. As Webb pushes the boundaries of exoplanet research, the discovery of a rocky one with an atmosphere represents a breakthrough.
On Earth, the atmosphere warms the planet, contains the oxygen that humans breathe, shields from solar radiation, and creates the pressure needed to keep liquid water on the planet’s surface.
“On Earth, the atmosphere is key to life,” Demory said. “This result for 55 Cnc e gives hope that Webb can conduct similar studies on planets much cooler than 55 Cnc e that could support liquid water on their surfaces. But we’re not there yet.”
