Webb telescope closely observes mysterious planet outside our solar system

The James Webb Space Telescope (JWST) recently took a close look at a mysterious exoplanet with a steamy, hazy atmosphere. It's the closest look yet at the mini-Neptune that was largely impenetrable to previous observations.

The planet, named GJ 1214 b, is too hot to harbor liquid-water oceans, but water in a vaporized state may still play a significant role in its atmospheric composition. To peer through the planet's thick atmosphere, the researchers used a novel approach - they tracked GJ 1214 b through nearly its entire orbit around the host star.

"The planet is totally blanketed by some sort of haze or cloud layer. The atmosphere just remained totally hidden from us until this observation. If indeed water-rich, the planet could have been a “water world,” with large amounts of watery and icy material at the time of its formation," said Eliza Kempton, a researcher at the University of Maryland and lead author of a new paper, published in Nature, on the planet.

True to its name, a mini-Neptune is kind of like Neptune, but fun-sized. These exoplanets have thick, hazy atmospheres that can be difficult to peer through. Now Webb has lifted the curtain with the closest look yet at mini-Neptune GJ 1214 b (illustrated): https://t.co/ecY6lPioYV

— NASA Webb Telescope (@NASAWebb) May 10, 2023

This observation highlights the remarkable capabilities of Webb's Mid-Infrared Instrument (MIRI), which views light wavelengths beyond the range of human vision in the electromagnetic spectrum. Using MIRI, the team successfully generated a "heat map" of the planet while it was orbiting its star. This heat map provided valuable insights into the planet's atmospheric composition - just before the planet's orbit carried it behind the star, and as it emerged on the other side – both its day and night sides.

According to the researchers, such a significant shift can only occur in an atmosphere consisting of heavier molecules, such as water or methane, which appear similar when observed through MIRI. This suggests that the atmosphere of GJ 1214 b is not composed mainly of lighter hydrogen molecules - a potentially crucial clue to the planet's watery start.

Further, Kempton noted that while the planet is hot by human standards, it is much cooler than expected. This unexpectedly lower temperature is attributed to its remarkably shiny atmosphere, which surprised the researchers. Instead of absorbing the light from its parent star and consequently heating up, the planet's atmosphere reflects a substantial portion of the star's light.

"For the last almost decade, the only thing we really knew about this planet was that the atmosphere was cloudy or hazy. This paper has really cool implications for additional detailed climate interpretations – to look at the detailed physics happening inside this planet’s atmosphere," said Rob Zellem, an exoplanet researcher who works with co-author and fellow exoplanet researcher Tiffany Kataria at NASA's Jet Propulsion Laboratory in Southern California.

Future observations will help pin down more details about GJ 1214 b and the formation histories of other planets belonging to the mini-Neptune category.