Astronomers Discover an Atmosphere on a Hot, Rocky Exoplanet With an Ocean of Magma

Astronomers have spotted signs of an atmosphere on an exoplanet 41 light-years away from Earth—the best evidence to date for a rocky planet with an atmosphere outside our solar system, according to a statement from NASA.

The exoplanet, called 55 Cancri e, likely has an atmosphere rich in carbon dioxide or carbon monoxide, emitted from its bubbling ocean of magma, the researchers reported Wednesday in the journal Nature.

“It’s probably the firmest evidence yet that this planet has an atmosphere,” Ian Crossfield, an astronomer at the University of Kansas who was not involved in the work, tells Adithi Ramakrishnan of the Associated Press (AP).

At around 2,800 degrees Fahrenheit, the planet is too toasty to support life, and its surface is likely liquefied and covered in magma. Earth, Venus and Mars may also have been covered with magma long ago, so studying this distant world could help astronomers better understand our own planet’s early days.

“Earth probably went through at least one magma-ocean stage, maybe several,” Laura Schaefer, a planetary geologist at Stanford University who did not contribute to the findings, tells Nature News’ Sumeet Kulkarni. “Having actual present-day examples of magma oceans can help us understand the early history of our solar system.”

55 Cancri e is about eight times the mass of Earth and close to two times as wide. It’s one of five planets astronomers have spotted orbiting the star 55 Cancri in the constellation Cancer. The distant world’s composition is likely similar to that of rocky planets in our solar system, per NASA.

But the exoplanet resides only 1.4 million miles from its star—less than one-sixtieth the distance from Earth to our sun—and completes an orbit roughly every 17 hours. The planet likely has one side that permanently faces its sun, eternally baking in the heated glow.

Astronomers first discovered the planet in 2004, but solid evidence of an atmosphere has eluded them for decades. It’s easier to spot an atmosphere on a gas giant planet, compared to on a rocky world. As such, researchers have been unsure whether 55 Cancri e has a substantial, rich atmosphere or if it only has a small amount of evaporated molten rock around it.

To answer this question, researchers turned to the James Webb Space Telescope. They measured infrared light from the system at various times—when the planet was behind its star, the telescope would capture light from just the star, and when the planet was next to the star, Webb could image light from both bodies. By comparing the data from each of these situations, the scientists were able to isolate how much infrared light came from only the planet.

This technique revealed that even though the planet’s dayside was hot, it was much cooler than expected—rather than the predicted 4,000 degrees Fahrenheit, it was measured at only 2,800 degrees Fahrenheit. This strongly suggested that an atmosphere was spreading some of that heat to the planet’s darker and cooler side.

The researchers also found that certain wavelengths of light were not reaching the telescope, indicating molecules in the atmosphere were blocking this light. Since carbon dioxide and carbon monoxide can absorb light of these particular wavelengths, the team suggests the planet’s atmosphere is composed of these gases.

But the atmosphere around 55 Cancri e was likely different in the past—the planet’s original atmosphere would have been eroded away by its host star’s heat and radiation long ago. What scientists have now observed is its so-called secondary atmosphere, created by gases “bubbling out” from its magma ocean, as Renyu Hu, a co-author of the study and planetary scientist at NASA’s Jet Propulsion Laboratory (JPL), tells Space.com’s Robert Lea.

“Magma is not just crystals and liquid rock; there’s a lot of dissolved gas in it, too,” says study co-author Aaron Bello-Arufe, an astrophysicist at JPL, in the statement. These gases continuously replenish the planet’s atmosphere.

In the future, researchers could use 55 Cancri e and its magma ocean to better understand what Earth and its neighbors were like in their youth.

“It’s a rare window,” Hu tells the AP. “We can look into this early phase of planet evolution.”

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.