James Webb MIRI image of exoplanet Epsilon Indi Ab. Image: ESA/Webb, NASA, CSA, STScI, E Matthews (Max Planck Institute for Astronomy)
The exoplanet is one of the coldest observed exoplanets to date, with an estimated temperature of 2 degrees Celsius.
An international team of astronomers using the James Webb Space Telescope captured an image of a nearby cold exoplanet that is more than three times the mass of Jupiter – the largest planet in our solar system.
The exoplanet, known as Epsilon Indi Ab, is only 12 light-years away from Earth and orbits the K-type star Epsilon Indi A, which the astronomers say is roughly the same age as our sun but slightly cooler.
Most exoplanets (planets outside our solar system), including Epsilon Indi Ab, orbit other stars, while some orbit the galactic centre untethered to any star.
This is one of the coldest exoplanets observed to date with an estimated temperature of 2 degrees Celsius, which is colder than any other imaged planet beyond our solar system and colder than all but one free-floating brown dwarf, known as Wise 0855.
Previously imaged exoplanets have tended to be the youngest and hottest exoplanets, as they still radiate a lot of their energy from when they first formed. They become fainter and harder to image as they cool and contract over time, which is where James Webb’s Mid-Infrared Instrument (MIRI) comes in handy.
“Cold planets are very faint, and most of their emission is in the mid-infrared,” explained Dr Elisabeth Matthews of the Max Planck Institute for Astronomy, who is lead author of the study that observed the exoplanet. “Webb is ideally suited to conduct mid-infrared imaging, which is extremely hard to do from the ground. We also needed good spatial resolution to separate the planet and the star in our images, and the large Webb mirror is extremely helpful in this aspect.”
The discovery has excited the astronomers due to its similarity to Jupiter. “It is a little warmer and is more massive, but is more similar to Jupiter than any other planet that has been imaged so far,” said Matthews.
From imagining to imaging
The exoplanet was observed using the coronograph of the James Webb’s MIRI where masks are placed in front of bright objects – in this case, Epsilon Indi A – to allow scientists to study their surroundings without being blinded by the bright object itself.
“Our prior observations of this system have been more indirect measurements of the star, which actually allowed us to see ahead of time that there was likely a giant planet in this system tugging on the star,” said team member Prof Caroline Morley of the University of Texas. “That’s why our team chose this system to observe first with Webb.
“Astronomers have been imagining planets in this system for decades; fictional planets orbiting Epsilon Indi have been the sites of Star Trek episodes, novels and video games like Halo,” added Morley. “It’s exciting to actually see a planet there ourselves and begin to measure its properties.”
The exoplanet is the twelfth closest exoplanet to Earth observed to date and the closest planet bigger than Jupiter. Matthews said that it’s twice as massive as the team expected, as well as being a little further from its star, while its atmosphere appears to differ from model predictions.
“So far we only have a few photometric measurements of the atmosphere, meaning that it is hard to draw conclusions, but the planet is fainter than expected at shorter wavelengths,” she said.
This may mean that there is a significant presence of methane, carbon monoxide and carbon dioxide in the exoplanet’s atmosphere – which the team believes are absorbing the shorter wavelengths of light. This also suggests that the planet has a cloudy atmosphere.
Going forward, the team intends to revisit the exoplanet with Webb to conduct photometric and spectroscopic observations, as well as searching for similar planets to unearth trends about their atmospheres.
Recently, the James Webb celebrated its two-year anniversary, which we commemorated with a list of 10 of the telescope’s most iconic images, ranging from cosmic fireworks to phantom galaxies.
Find out how emerging tech trends are transforming tomorrow with our new podcast, Future Human: The Series. Listen now on Spotify, on Apple or wherever you get your podcasts.
