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Epsilon Indi Ab is colder than any other depicted planet outside our solar system.

If extraterrestrial astronomers in a nearby star system had a telescope like NASA‘c James Webb Space Telescopeand then pointed it towards our solar system Jupiter may look a lot like this new Webb image of exoplanet Epsilon Indi Ab. It is one of the coldest exoplanets directly detected, with an estimated temperature of 35 degrees Fahrenheit (2 degrees Celsius). Epsilon Indi Ab is only about 180 degrees Fahrenheit (100 degrees Celsius) warmer than the gas giants in our solar system. With so many known exoplanets that look nothing like the planets in our solar system, Epsilon Indi Ab provides astronomers with a rare opportunity to study the atmospheric composition of true solar system counterparts.

This image of the gas giant exoplanet Epsilon Indi Ab was taken with the MIRI (Mid-Infrared Instrument) coronagraph on NASA’s James Webb Space Telescope. A star symbol marks the location of the host star Epsilon Indi A, whose light is blocked by the coronagraph, resulting in the dark circle marked by the dashed white line. Epsilon Indi Ab is one of the coldest exoplanets ever imaged directly. Light at 10.6 microns is defined as a blue color, while light at 15.5 microns is defined as an orange color. MIRI did not resolve the planet which is a point source. Courtesy: NASA, ESA, CSA, STScI, Elizabeth Matthews (MPIA)

Webb Space Telescope images A cold exoplanet 12 light years away

An international team of astronomers using NASA’s James Webb Space Telescope has directly imaged an exoplanet approximately 12 light-years from Earth. The planet Epsilon Indi Ab is one of the coldest exoplanets ever observed.

The planet is several times the mass of Jupiter and orbits the K-type star Eps Ind A (Eps Ind A), which is about the age of our Sun but slightly cooler. The team observed Epsilon Indi Ab using Webb’s coronagraph MIRI (Mid-infrared instrument). Only a few dozen exoplanets have been directly imaged before by space and ground-based observatories.

“Our previous observations of this system were more indirect measurements of the star, which actually allowed us to see beforehand that there is probably a giant planet in this system that is pulling on the star,” said team member Caroline Morley of the University of Texas at Austin. “That’s why our team chose this system to observe with Webb first.”

“This discovery is exciting because the planet is quite similar to Jupiter – it’s a bit warmer and it’s more massive, but it’s more Jupiter-like than any other planet that’s been imaged so far,” added lead author Elizabeth Matthews of Max Planck Institute for Astronomy in Germany.

From its launch in 2021, the James Webb Space Telescope is peering into the earliest moments of the universe with its advanced infrared capabilities and large mirror. It provides a detailed view of galaxies, stars and exoplanets, greatly improving our cosmic understanding. Credit: NASA

An analogue of the solar system

Exoplanets imaged earlier tend to be the youngest, hottest exoplanets that are still emitting much of the energy from their formation. As planets cool and contract throughout their lives, they become significantly fainter and therefore more difficult to image.

“Cool planets are very faint and most of their radiation is in the mid-infrared range,” Matthews explained. “Webb is ideally suited for conducting mid-infrared imaging, which is extremely difficult to do from the ground. We also needed good spatial resolution to separate the planet and star in our images, and the Webb Large Mirror is extremely useful in this aspect.

Epsilon Indi Ab is one of the coldest exoplanets that has been directly detected, with an estimated temperature of 35 degrees Fahrenheit (2 degrees Celsius)—colder than any other imaged planet outside our solar system, and colder than all free-floating brown dwarfs except for one . The planet is only about 180 degrees Fahrenheit (100 degrees Celsius) warmer than the gas giants in our solar system. This provides a rare opportunity for astronomers to study the atmospheric composition of real analogs of the solar system.

“Astronomers have been imagining planets in this system for decades; fictional planets orbiting Epsilon Indi have been the locations of episodes, novels and video games such as Star Trek’s Halo,” Morley added. “It’s exciting to actually see a planet there ourselves and start measuring its properties.”

Not quite as expected

Epsilon Indi Ab is the twelfth closest exoplanet to Earth known to date, and the closest planet more massive than Jupiter. The science team chose to study Eps Ind A because the system showed hints of a possible planetary body using a technique called radial velocity, which measures the back-and-forth wobble of the host star along our line of sight.

“Although we expected to capture a planet in this system because there were indications of its presence at radial velocity, the planet we found was not what we had predicted,” Matthews said. “It’s about twice as massive, slightly farther from its star, and has a different orbit than expected. The reason for this discrepancy remains an open question. The planet’s atmosphere also looks a bit different than the model’s predictions. So far we only have a few photometric measurements of the atmosphere, which means it’s hard to draw any conclusions, but the planet is fainter than expected at shorter wavelengths.

The team believes this could mean that the planet’s atmosphere has significant amounts of methane, carbon monoxide and carbon dioxide that absorb the shorter wavelengths of light. It can also suggest a very cloudy atmosphere.

Direct imaging of exoplanets is particularly valuable for characterization. Scientists can directly collect light from the observed planet and compare its brightness at different wavelengths. So far, the science team has only detected Epsilon Indi Ab at a few wavelengths, but they hope to revisit the planet with Webb to conduct both photometric and spectroscopic observations in the future. They also hope to find other similar planets with Webb to find possible trends about their atmospheres and how these objects form.

NASA’s upcoming Nancy Grace Roman Space Telescope will use a coronagraph to demonstrate direct imaging technology by photographing Jupiter-like worlds orbiting Sun-like stars—something that has never been done before. These results will pave the way for future missions to explore worlds that are even more Earth-like.

These results were taken with Webb’s Cycle 1 General Observer 2243 program and are published in the journal Nature.

For more on this discovery, see JWST’s Super-Jupiter Breakthrough: Oldest, Coldest Exoplanet Ever Imaged.

Reference: “A moderate super-Jupiter imaged with JWST in the mid-infrared” by EC Matthews, AL Carter, P. Pathak, CV Morley, MW Phillips, S. Krishanth PM, F. Feng, MJ Bonse, LA Boogaard, JA Burt , IJM Crossfield, ES Douglas, Th. Henning, J. Hom, C.-L. Ko, M. Casper, A.-M. Lagrange, D. Petit dit de la Roche and F. Philipot, 24 July 2024, Nature.
DOI: 10.1038/s41586-024-07837-8

The James Webb Space Telescope (JWST), launching on December 25, 2021, represents a monumental leap forward in astronomical capabilities. As the successor of Hubble Space Telescope, JWST is designed to observe the universe primarily in the infrared spectrum, allowing it to peer through cosmic dust and peer into the universe’s earliest moments. Its large, segmented primary mirror spanning 6.5 meters and an advanced array of science instruments allow the telescope to capture extremely detailed images of distant galaxies, star-forming nebulae and exoplanets, providing unprecedented insight into the origins of stars, planetary systems and the universe itself. JWST is a joint venture involving NASA, European Space Agency (ESA) and the Canadian Space Agency (CSA) and is expected to fundamentally change our understanding of space.