Researchers using NASA’s James Webb Space Telescope may have discovered atmospheric gases surrounding 55 Cancri e, a hot, rocky exoplanet 41 light-years from Earth. This is the best evidence for the existence of an atmosphere on a rocky planet outside our solar system.

Renew Hu of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, is the lead author of the paper published May 8. Nature. “Webb pushes the boundaries of exoplanet characterization all the way to rocky planets,” Hu said. “It really paves the way for a new kind of science.”

Super Hot Super World 55 Cancri e

55 Cancri e, also known as Janssen, is one of five known planets orbiting the sun-like star 55 Cancri in the constellation Cancer. With a diameter nearly twice that of Earth and a slightly higher density, the planet is classified as a super-Earth: larger than Earth, smaller than Neptune, and likely similar in composition to the rocky planets in our solar system.

But describing 55 Cancri e as “rocky” might give the wrong impression. The planet orbits so close to its star (about 2.4 million miles, or one twenty-fifth of the distance between Mercury and the Sun) that its surface is likely molten, a seething ocean of magma. With such a narrow orbit, the planet is also likely to be tidally locked; The day side is always facing the star, and the night side is always in darkness.

Despite numerous observations since the transit was discovered in 2011, it remains unclear whether 55 Cancri e has an atmosphere or not. May It remains open whether this is possible, given its high temperature and the constant onslaught of stellar radiation and wind from its star. remained unanswered.

“I’ve been working on this planet for over a decade,” said Diana Dragomir, an exoplanet researcher at the University of New Mexico and co-author of the study. “It’s very frustrating that none of the observations we’ve received have been able to solve these mysteries. I’m so glad we finally have some answers!

Unlike the atmospheres of gas giant planets, which are relatively easy to see (the first were detected by NASA’s Hubble Space Telescope more than two decades ago), the thinner, denser atmospheres surrounding rocky planets remain elusive.

Previous studies of 55 Cancri e, using data from NASA’s defunct Spitzer Space Telescope, suggested an atmosphere significantly rich in volatiles (molecules found as gases on Earth) such as oxygen, nitrogen and carbon dioxide. But researchers can’t rule out another possibility: The planet is bare except for a thin layer of vaporized rock rich in elements such as silicon, iron, aluminum and calcium. “The planet is so hot that some of the molten rock has to evaporate,” Hu explained.

Measurement of subtle changes in infrared colors

To distinguish between the two possibilities, the team measured infrared light from the planet between 4 and 12 microns using Webb’s NIRCam (Near Infrared Camera) and MIRI (Mid Infrared Instrument).

Although Webb cannot take a direct image of 55 Cancri e, it can measure subtle changes in the light coming from the system as the planet orbits the star.

By subtracting the brightness during a secondary eclipse (see image above) when the planet is behind the star (starlight only) from the brightness when the planet is near the star (light from the star and planet together), the team was able to calculate the number of different wavelengths of infrared light coming from the daytime side of the planet.

The technique, known as secondary eclipse spectroscopy, is similar to that used by other research groups to search for atmospheres on other rocky exoplanets such as TRAPPIST-1b.

colder than expected

The first indication that 55 Cancri e might have a significant atmosphere came from temperature measurements based on its thermal radiation (see image above), or heat energy emitted in the form of infrared light. If the planet is covered in dark molten rock with a thin blanket of vaporous rock, or if there is no atmosphere at all, the daytime temperature should be around 4000 degrees Fahrenheit (~2200 degrees Celsius).

“Instead, MIRI data showed a relatively low temperature of approximately 2,800 degrees Fahrenheit [~1540 градусів за Цельсієм]Hu said. “This is a very strong indication that energy is distributed from the day side to the night side, most likely through a volatile-rich atmosphere.” Although lava flows can transfer some of the heat to the night side, they cannot move it efficiently enough to account for the cooling effect.

“When the team looked at the NIRCam data, they saw patterns consistent with a variable atmosphere.”

“We see signs of a drop in the spectrum between 4 and 5 microns; less of this light reaches the telescope,” said co-author Aaron Bello-Aruffe of NASA JPL. “This suggests the presence of an atmosphere containing carbon monoxide or carbon dioxide that absorbs these wavelengths of light.” A planet with no atmosphere or an atmosphere consisting only of vaporized rocks would not have this specific spectral feature.

“We’ve spent the last decade modeling different scenarios, trying to imagine what this world might look like,” said co-author Yamila Miguel from the Leiden Observatory and the Netherlands Institute for Space Research (SRON). “Finally having our work validated is priceless!”

Bubbling magma ocean

The team believes that the gases covering 55 Cancri e would have come from within, rather than having been present since the planet’s formation. “The primitive atmosphere would have disappeared long ago due to the high temperature and intense radiation coming from the star,” Bello-Aruffe said. “There will be a secondary atmosphere that is constantly replenished by the magma ocean. Magma is not just crystals and liquid rocks; “There’s also a lot of dissolved gas.”

Although 55 Cancri e is too hot to be habitable, researchers believe it could provide a unique window into the interactions between the atmospheres, surfaces, and interiors of rocky planets and possibly provide insight into the early conditions of Earth, Venus, and Mars. It is believed to have been covered by oceans of magma in the distant past. “Ultimately, we want to understand what conditions allow a rocky planet to maintain a gas-rich atmosphere: the essential ingredient of a habitable planet,” Hu said. said.

This study was conducted as part of the Webb General Observers (GO) Program 1952. Analysis of additional secondary observations of the 55 Cancri e eclipses is currently ongoing.