Astronomers using Webb’s MIRI (Mid-Infrared Instrument) have imaged Epsilon Indi Ab, a gas giant several times the mass of Jupiter located around 12 light-years away from Earth.
This image of Epsilon Indi Ab was taken with the coronagraph on Webb’s MIRI instrument. Image credit: NASA / ESA / CSA / Webb / STScI / E. Matthews, Max Planck Institute for Astronomy.
Of the 25 directly imaged planets to date, all are younger than 500 million years and all but six are younger than 100 million years.
The newly-imaged planet orbits Epsilon Indi A (HD 209100, HIP 108870), a K5V star of roughly solar age (between 3.7 and 5.7 billion years old).
“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 University of Texas at Austin astronomer Dr. Caroline Morley.
“That’s why our team chose this system to observe first with Webb.”
“This discovery is exciting because the planet is quite similar 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 Dr. Elisabeth Matthews, an astronomer at the Max Planck Institute for Astronomy.
“Cold planets are very faint, and most of their emission is in the mid-infrared. 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.”
Epsilon Indi Ab is one of the coldest exoplanets to be directly detected, with an estimated temperature of 2 degrees Celsius (35 degrees Fahrenheit) — colder than any other imaged planet beyond our Solar System, and colder than all but one free-floating brown dwarf.
The planet is only around 100 degrees Celsius (180 degrees Fahrenheit) warmer than gas giants in our Solar System.
This provides a rare opportunity for astronomers to study the atmospheric composition of true solar system analogs.
“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,” Dr. Morley said.
“It’s exciting to actually see a planet there ourselves, and begin to measure its properties.”
Epsilon Indi Ab is the twelfth closest exoplanet to Earth known to date and the closest planet more massive than Jupiter.
The astronomers chose to study Epsilon Indi A because the system showed hints of a possible planetary body using a technique called radial velocity, which measures the back-and-forth wobbles of the host star along our line of sight.
“While we expected to image a planet in this system, because there were radial velocity indications of its presence, the planet we found isn’t what we had predicted,” Dr. Matthews said.
“It’s about twice as massive, a little farther from its star, and has a different orbit than we expected. The cause of this discrepancy remains an open question.”
“The atmosphere of the planet also appears to be a little different than the 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.”
“This may mean there is significant methane, carbon monoxide, and carbon dioxide in the planet’s atmosphere that are absorbing the shorter wavelengths of light. It might also suggest a very cloudy atmosphere.”
A paper on the findings was published in the journal Nature.
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E.C. Matthews et al. A temperate super-Jupiter imaged with JWST in the mid-infrared. Nature, published online July 24, 2024; doi: 10.1038/s41586-024-07837-8
This article was adapted from an original release by NASA.
