Jupiter-like planet more massive than first thought, according to new space telescope images

Astronomers using the James Webb Space Telescope (JWST) have imaged a planet that is, relatively speaking, in our galactic backyard — and that fresh data has led to new details about this massive "cold" Jupiter.

The gas giant exoplanet has the unceremonious name of Epsilon Ind Ab. Epsilon (or "Eps") is the fifth letter in the Greek alphabet or — in this case — the fifth-brightest star in the constellation Indus, which is where the "Ind" comes from. "A" is the star, and "b" denotes the planet.

Eps Ind Ab (sometimes referred to as Eps Indi Ab) orbits in a three-body system. But hold on: it's not like the best-selling book and the hit Netflix series 3 Body Problem: two are very close brown dwarfs — bodies that lie somewhere between planets and stars and are often referred to as failed stars — while the other is a red dwarf star.

While the main star lies two billion kilometres away from the planet, the two brown dwarfs are more than 224 billion kilometres away, or about more than 40 times farther than Pluto is from Earth.

The planet was known — but not well

This planet was known to astronomers, but as the researchers write in their new study, published Wednesday in the journal Nature, a lot of information about Eps Ind Ab was incorrect.

With no ground-based images, however, astronomers had little to go on.

But with the incredible "eyes" of JWST, a group of astronomers from around the world were able to finally see this massive Jupiter-like planet. And while it may be just a bright dot in a photograph, that white dot contains a lot of information. 

When astronomers first looked at the JWST photograph of Eps Ind Ab, they immediately knew something was wrong: It wasn't where it was supposed to be.

"We looked at it and did all the measurements, like rotated it so that it's aligned to the north and everything like that. And we're like, 'Wait a minute, it's in completely the wrong place,'" said lead author of the paper, Elisabeth Matthews of the Max Planck Institute for Astronomy in Germany.

"So then we had to do all of this work to confirm that it really was a planet and not a background galaxy."

JWST a 'wild horse'

Using the JWST data, they made some more discoveries.

Initial data from the ground suggested the planet was 3.25 times the mass of Jupiter. With data from the new images, they found that it was six times Jupiter's mass. In astronomy, references to mass relate to the weight of a particular body. 

As well, they learned that the planet orbits the star every 200 years, instead of every 45.2 years.   

Scientists were also able to measure its temperature, estimated at roughly 0 C. That's considered quite cold when it comes to exoplanet discoveries.

This is particularly exciting for astronomers studying exoplanets. Most of the ones that have been discovered are young and hot, still radiating much of the energy from their formation.

Detecting cooler, older ones is more difficult.

"We're fairly good at detecting planets, especially with the transit and the radial velocity measurement, but then characterizing their atmospheres as much harder," Matthews said.

"So this is kind of opening up that new parameter space. It's allowing us to actually characterize a cold atmosphere for the first time. And then I think — like really long-term — we also want to be able to push toward characterizing cold but much smaller planets, so things more like the Earth."

The planet was initially found through a process called radial velocity, where a star wobbles slightly due to the tug of a nearby planet, but it had never before been imaged. Most exoplanets are discovered using the transit method where there is a slight dip in a star's brightness as a planet passes in front of it. 

Paul Delaney, an astronomer and professor emeritus at York University's department of physics and astronomy in Toronto, said it's a great illustration of JWST's capabilities.

"It's a finely tuned telescope, and it is producing data that is of such a high quality, that it's making headlines," said Delaney, who was not involved in the study.

"Everybody is always sort of hanging now on James Webb's next observation. I think it's great for astronomy."

Delaney said in just two years, the amount of data collected by the telescope has already outpaced what was gathered by its predecessor, the Hubble Space Telescope, which was launched in 1990. 

"It's like a wild horse. It's just running away furiously."

And while JWST may not be used for detecting planets — its focus will be to study already-discovered ones to get more information on these distant worlds — it's helping astronomers better understand how planets like our own form.

Matthews said scientists will be further studying Eps Ind Ab to determine its atmosphere. 

"I still find it kind of incredible that we have such a big planet so close to us. It's just a little less than 12 light-years away. So it's like right there," said Matthews.

"It's really accessible to study in more detail. And it's a really strange planet, honestly, but I think a really exciting planet that will hopefully be able to use to learn a lot more physics as well."