James Webb telescope peers at the atmosphere of a rocky hell world

This artist’s concept shows what the exoplanet 55 Cancri e could look like. Also called Janssen, 55 Cancri e is a so-called super-Earth, a rocky planet significantly larger than Earth but smaller than Neptune, which orbits its star at a distance of only 2.25 million kilometres (0.015 astronomical units), completing one full orbit in less than 18 hours. In comparison, Mercury is 25 times farther from the Sun than 55 Cancri e is from its star. The system, which also includes four large gas-giant planets, is located about 41 light-years from Earth, in the constellation Cancer.
This artist’s concept shows what the exoplanet 55 Cancri e could look like. Also called Janssen, 55 Cancri e is a so-called super-Earth, a rocky planet significantly larger than Earth but smaller than Neptune, which orbits its star at a distance of only 2.25 million kilometers (0.015 astronomical units), completing one full orbit in less than 18 hours. NASA, ESA, CSA, R. Crawford (STScI)

When it comes to learning about exoplanets, or planets beyond our solar system, the James Webb Space Telescope is providing more information than ever before. Over the last decade or so, thousands of exoplanets have been discovered, with details available about these worlds, such as their orbits and their size or mass. But now we’re starting to learn about what these planets are actually like, including details of their atmospheres. Webb recently investigated the atmosphere around exoplanet 55 Cancri e, finding what could be the first atmosphere of a rocky planet discovered outside the solar system.

The planet in question, 55 Cancri e, isn’t a welcoming place. The star that hosts it is sun-like, but the planet orbit is so close to it, at just 1.4 million miles away, that its surface is likely to be a bubbling ocean of magma. It’s even known as the “hell planet.” But despite the extreme conditions there, astronomers have long wondered if the planet could host an atmosphere or if it is too hot and bombarded by too much radiation.

“I’ve worked on this planet for more than a decade,” said co-author of the new research, Diana Dragomir of the University of New Mexico, in a statement. “It’s been really frustrating that none of the observations we’ve been getting have robustly solved these mysteries. I am thrilled that we are finally getting some answers!”

It’s harder to spot atmospheres around rocky planets than around big, puffy gas giants because they are thinner, but researchers using Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) were able to see indications of a volatile-rich atmosphere, indicating there could be carbon monoxide or carbon dioxide.

The researchers also found that the side of the planet that faces its star, called the dayside, is cooler than expected. That suggests that heat is being transferred to the cooler nightside, possibly by an atmosphere. Now the question is how that atmosphere formed, as the extreme temperatures would likely have stripped away any gases present when the planet formed. The atmosphere could be forming from gases coming up from inside the planet, the researchers theorize.

“The primary atmosphere would be long gone because of the high temperature and intense radiation from the star,” said co-author Aaron Bello-Arufe of NASA’s Jet Propulsion Laboratory. “This would be a secondary atmosphere that is continuously replenished by the magma ocean. Magma is not only crystals and liquid rock, there’s a lot of dissolved gas in it, too.”

The research is published in the journal Nature.

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