Artistic concept of a cold gas giant exoplanet
The James Webb Space Telescope has taken a direct image of Epsilon Indi Ab, a cold Jupiter-like exoplanet located 12 light-years from Earth. The discovery is crucial because it gives us insight into the atmospheric properties of a planet that is colder than most known exoplanets and helps refine our understanding of planetary systems beyond our own. (Artist’s concept.) Credit: SciTechDaily.com
Epsilon Indi Ab is colder than any other planet imaged beyond our solar system.
If alien astronomers in a nearby star system had a telescope like NASA‘s James Webb Space Telescopeand they pointed it at our solar system, then Jupiter might look a lot like this new Webb image of the exoplanet Epsilon Indi Ab. It is one of the coldest exoplanets to have been 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) hotter than the gas giants in our solar system. With so many known exoplanets that look nothing like planets in our solar system, Epsilon Indi Ab offers astronomers a rare opportunity to study the atmospheric composition of true solar system analogues.
Exoplanet Epsilon Indi Ab (Webb MIRI image)
This image of the gas giant exoplanet Epsilon Indi Ab was taken with the coronagraph on NASA’s James Webb Space Telescope MIRI (Mid-Infrared Instrument). A star symbol indicates the location of the host star Epsilon Indi A, whose light was blocked by the coronagraph, resulting in the black circle with a dashed white line. Epsilon Indi Ab is one of the coolest exoplanets ever directly imaged. Light at 10.6 microns was colored blue, while light at 15.5 microns was colored orange. MIRI was unable to distinguish the planet, which is a point source. Credit: NASA, ESA, CSA, STScI, Elisabeth Matthews (MPIA)
Webb Space Telescope Photographs Cold Exoplanet 12 Light-Years Away
An international team of astronomers using NASA’s James Webb Space Telescope has obtained a direct image of an exoplanet located about 12 light-years from Earth. This planet, Epsilon Indi Ab, is one of the coldest exoplanets observed to date.
The planet has a mass several times that of Jupiter and orbits the K-type star Epsilon Indi A (Eps Ind A), which is about the same age as 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 photographed so far by space and ground-based observatories.
“Our previous observations of this system were indirect measurements of the star, which allowed us to see in advance that there was likely a giant planet in this system that was 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 first with Webb.”
“This discovery is exciting because the planet is quite similar to Jupiter: it’s a bit hotter and more massive, but it’s more similar to Jupiter than any other planet that has been imaged so far,” added lead author Elisabeth Matthews of the Max Planck Institute for Astronomy in Germany.
The Webb Telescope in Space
Since its launch in 2021, the James Webb Space Telescope has been peering into the early moments of the universe with its advanced infrared capabilities and large mirror. It provides detailed information about galaxies, stars, and exoplanets, greatly improving our understanding of the cosmos. Credit: NASA
An analogy with the solar system
The exoplanets that have already been photographed are generally the youngest and hottest, those that still give off much of the energy from their formation. As planets cool and contract over the course of their lives, they become significantly fainter and therefore more difficult to photograph.
“Cool planets are very faint and most of their emissions are in the mid-infrared,” Matthews says. “Webb is ideally suited to imaging in the mid-infrared, 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 large Webb mirror is extremely useful for this.”
Epsilon Indi Ab is one of the coldest exoplanets ever directly detected, with an estimated temperature of 2 degrees Celsius, colder than any other planet imaged beyond our solar system and colder than all but one of the free-floating brown dwarfs. The planet is only about 100 degrees Celsius warmer than the gas giants in our solar system. This offers astronomers a rare opportunity to study the atmospheric composition of true solar system analogues.
“Astronomers have been imagining planets in this system for decades; fictional planets orbiting Epsilon Indi have been featured in Star Trek episodes, novels and video games like Halo,” Morley added. “It’s exciting to see a planet there 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 evidence of a possible planetary body using a technique called radial velocity, which measures the host star’s wobbles back and forth along our line of sight.
“We expected to image a planet in this system because there were radial velocity indications of its presence, but the planet we found is not the one we predicted,” Matthews explained. “It is about twice as massive, a little further from its star, and has a different orbit than we expected. The cause of this discrepancy remains an open question. The planet’s atmosphere also appears to be a little different from what the model predicted. So far, we only have a few photometric measurements of the atmosphere, which means it’s hard to draw conclusions, but the planet is fainter than expected at shorter wavelengths.”
The team thinks this could mean the planet’s atmosphere contains a significant amount of methane, carbon monoxide and carbon dioxide, which absorb the shorter wavelengths of light. It could also suggest a very cloudy atmosphere.
Direct imaging of exoplanets is particularly useful 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 perform photometric and spectroscopic observations in the future. They also hope to detect other similar planets with Webb to discover possible trends in their atmospheres and how these objects form.
Nancy Grace, the future star of NASA 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 study even more Earth-like worlds.
These results were obtained using Webb’s Cycle 1 General Observer 2243 program and were published in the journal Nature.
To learn more about this discovery, check out JWST’s Super-Jupiter Breakthrough: The Oldest, Coldest Exoplanet Ever Imaged.
Reference: “A temperate super-Jupiter photographed with JWST in the mid-infrared” by EC Matthews, AL Carter, P. Pathak, CV Morley, MW Phillips, S. Krishanth P. M, F. Feng, MJ Bonse, LA Boogaard, JA Burt, IJM Crossfield, ES Douglas, Th. Henning, J. Hom, C.-L. Ko, M. Kasper, 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), launched on December 25, 2021, represents a monumental leap forward in astronomical capabilities. As the successor to the The Hubble Space TelescopeJWST is designed to observe the universe primarily in the infrared spectrum, allowing it to peer into cosmic dust and observe the earliest moments of the universe. Its large, segmented primary mirror, with a span of 6.5 meters, and its advanced suite of scientific instruments enable the telescope to capture extraordinarily detailed images of distant galaxies, star-forming nebulae, and exoplanets, providing unprecedented insights into the origins of stars, planetary systems, and the universe itself. JWST is a collaborative project involving NASA, the European Space Agency (ESA), and the United States National Aeronautics and Space Administration (IAEA). European Space Agency (ESA) and the Canadian Space Agency (CSA), and is expected to fundamentally transform our understanding of the cosmos.
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