Meet Janssen, A World 41 Light-Years Away That May Have An Atmosphere

Scientists using the James Webb Space Telescope may have detected an atmosphere around an exoplanet—a planet that orbits a star other than our own—relatively close to the solar system.

Just 41 light-years distant in the constellation of Cancer, Janssen (also called 55 Cancri e) is presently the best evidence to date for an atmosphere around a terrestrial, rocky planet outside the solar system.

However, this is no “Earth 2.0” because Janssen is a hot, hellish world.

‘Super-Earth’

One of five known planets orbiting a sun-like star, Janssen has a diameter nearly twice that of Earth. It’s also slightly denser. That puts it in the category of “super-Earth” or “sub-Neptune.”

Published this week in Nature, a new paper contains observations that show the exoplanet may sustain a gaseous atmosphere. That’s despite it being a super-hot lava world with a likely sea of liquid magma.

Unlike anything we have in our solar system, Janssen whizzes around its star in just 18 hours, so it receives intense radiation. “The planet is so hot that some of the molten rock should evaporate,” said team leader Renyu Hu at NASA’s Jet Propulsion Laboratory (JPL).

Night And Day

The team used JWST’s Near-Infrared Camera and Mid-Infrared Instrument to measure infrared light coming from Janssen’s dayside and nightside simultaneously. Analysis of the light showed that the planet might be surrounded by an atmosphere of carbon monoxide or carbon dioxide. It likely bubbles up from the planet’s interior.

If proven, the findings hugely extend the scope of planets that may contain an atmosphere, though nobody is expecting to find signs of life on a world as hot as Janssen.

Enigmatic Exoplanet

“Despite enormous amounts of observing time obtained with a dozen ground and space facilities in the past decade, its very nature has remained elusive, until today,” said Brice-Olivier Demory from the Center for Space and Habitability CSH of the University of Bern and member of the NCCR PlanetS, and co-author of the study. He called it “one of the most enigmatic exoplanets.”

It’s hoped that Janssen can provide insights into the early Earth, Venus and Mars, all of which are thought to have been covered in oceans of lava in the past. “Ultimately, we want to understand what conditions make it possible for a rocky planet to sustain a gas-rich atmosphere: the key ingredient for a habitable planet,” said Hu.

Wishing you clear skies and wide eyes.