The James Webb Space Telescope (JWST) has taken a deeper have a look at a mysterious planet outside the solar system that’s unlike anything in our planetary system.
The extrasolar planet, or exoplanet, called Gliese 1214 b (GJ 1214 b), is an example of a “mini-Neptune,” a planet less massive than the solar system ice giant Neptune but still around two to 4 times the scale of Earth. Despite being essentially the most common form of planet found throughout the Milky Way, mini-Neptunes are curiously absent from our solar system. Because of this, astronomers know little about these worlds. Likewise, Gliese 1214 b has proven difficult to watch as a result of its highly reflective atmosphere — until JWST turned its powerful gaze towards the alien world.
“The planet is completely blanketed by some kind of haze or cloud layer,” research lead creator and University of Maryland exoplanet astronomer Eliza Kempton said in a press release. (opens in latest tab) “The atmosphere just remained totally hidden from us until this commentary.”
Kempton added that if GJ 1214 b indeed proves to own a water-rich atmosphere, the exoplanet could have been a “water world” in its distant past, an exoplanet replete with large amounts of watery and icy material on the time of its formation.
Related: Exoplanets: Worlds Beyond Our Solar System
Unlike the icy planet that offers the category of planets to which GJ 1214 b belongs its name, this exoplanet found 48 light-years from Earth is scorching hot. Because of this, astronomers don’t look forward to finding liquid water oceans on GJ 1214 b, but imagine that the planet’s atmosphere should be composed of a considerable amount of water vapor. This thick, steamy envelope has helped this highly-reflective exoplanet maintain its aura of mystery.
The team used a novel combination of approaches to gaze through the thick atmospheric shell of GJ 1214 b because it orbits its red dwarf star parent star Gliese 1214, which it circles in only 1.6 Earth days.
GJ 1214 b is tidally locked, meaning it has a permanently star-facing “day side” and a perpetual “night side” that at all times stares out into space. Watching the planet because it disappeared behind its star and later emerged on the opposite side let astronomers see each its day and night sides and thus higher detail its atmosphere.
“The flexibility to get a full orbit was really critical to grasp how the planet distributes heat from the day side to the night side,” Kempton said. “There’s lots of contrast between day and night. The night side is colder than the day side.”
Using the JWST’s Mid-Infrared Instrument (MIRI) that sees light from the infrared portion of the electromagnetic spectrum, just beyond wavelengths of visible light our eyes can see, the team created a “heat map” of GJ 1214 b because it orbited the star.
This showed that dayside temperatures on the planet are as great as 535 degrees Fahrenheit (279 degrees Celsius), while temperatures on the night side of GJ 1214 b drop to 326 degrees Fahrenheit (65 degrees Celsius).
This significant shift in temperature told the team that its atmosphere should be composed of heavier molecules, reminiscent of water or methane, moderately than lighter hydrogen molecules. MIRI’s observations also backed this up, offering a clue regarding the formation of GJ 1214 b.
“This shouldn’t be a primordial atmosphere,” Kempton said. “It doesn’t reflect the composition of the host star it formed around. As a substitute, it either lost lots of hydrogen, if it began with a hydrogen-rich atmosphere, or it was formed from heavier elements to start with — more icy, water-rich material.”
One surprise that met the team after they studied GJ 1214 b with JWST was the incontrovertible fact that the mini-Neptune, despite being much hotter than a planet like Earth, remains to be much cooler than they expected. They think this relative coolness is since the exoplanet’s “shiny” atmosphere reflects a considerable amount of the sunshine that falls on it from its parent red dwarf star.
The astronomers also found clues that GJ 1214 b could have formed further away from its star than its close orbit brings it currently. Because it spiraled inwards, temperatures could have increased dramatically on the planet, boiling away ice and liquid water and making a water vapor-filled atmosphere.
“The best explanation, in case you discover a very water-rich planet, is that it formed farther away from the host star,” Kempton said.
The team will now try and collect more data regarding GJ 1214 b to handle a number of the lingering questions on the planet. This may occasionally eventually allow astronomers to higher understand how mini-Neptunes form and evolve. Observing a broader population of such exoplanets could even reveal why our solar system was deprived of such a world.
“By observing a complete population of objects like this, hopefully, we are able to construct up a consistent story,” Kempton concluded.
An early version of the team’s research is published within the journal Nature. (opens in latest tab)
