An exoplanet approximately 12 light-years away from Earth has been directly imaged by an international team of astronomers using NASA’s James Webb Space Telescope.
Epsilon Indi Ab is a planet that has been observed to be one of the coldest exoplanets.
Larger Mass
The planet, whose mass is several times that of Jupiter, revolves around the K-type star Epsilon Indi A (Eps Ind A), which is about the same age as our Sun but is slightly cooler.
Using Webb’s MIRI (Mid-Infrared Instrument) coronagraph, the team observed Epsilon Indi Ab.
“Indirect Measurements”
Space and ground-based observatories have only previously imaged a small number of exoplanets directly.
Caroline Morley, a member of the team from the University of Texas at Austin, stated, “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.”
Similarity to Jupiter
Morley continued by stating, “That’s why our team chose this system to observe first with Webb.”
Lead author Elisabeth Matthews of the Max Planck Institute for Astronomy in Germany added, “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.”
Energy Radiation
Exoplanets that have been seen before are usually the newest and hottest ones, and they are still emitting a lot of the energy they had when they formed.
Over their lifetime, planets become significantly fainter, making them more difficult to visualize.
Pros of Webb
Matthews elaborated, “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.”
Coldest Exoplanets
With an estimated temperature of 35 degrees Fahrenheit (2 degrees Celsius), Epsilon Indi Ab is one of the coldest exoplanets that has been directly observed.
This makes it colder than any other imaged planet outside of our solar system and colder than all but one free-floating brown dwarf.
Atmospheric Conditions
The gas giants in our solar system are only about 180 degrees Fahrenheit (100 degrees Celsius) warmer than the planet. Astronomers can now examine the atmospheric composition of true solar system analogs, a rare opportunity.
“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,” Morley continued. “It’s exciting to actually see a planet there ourselves, and begin to measure its properties.”
Possible Planetary Body
Epsilon Indi Ab is the 12th closest known exoplanet to Earth and the closest planet with a mass greater than Jupiter.
Using a method known as radial velocity, which measures the host star’s back-and-forth wobbles along our line of sight, the scientific team decided to investigate Eps Ind A because the system offered hints of a possible planetary body.
“Twice as Massive”
Matthews shared, “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.”
“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.”
Atmospheric Contents
The team thinks that this could indicate that the planet’s atmosphere contains a lot of methane, carbon monoxide, and carbon dioxide that are absorbing the shorter wavelengths of light. Additionally, it might suggest a very cloudy environment.
Exoplanet characterization greatly benefits from direct imaging. Researchers are able to directly collect light from the planet being observed and evaluate its brightness at various wavelengths.
Plans to Return
The scientists have only detected Epsilon Indi Ab at a few wavelengths thus far, but they plan to return to the planet with Webb in the near future to carry out photometric and spectroscopic observations.
They also hope to use Webb to find other planets that are similar to theirs so they can look for patterns in their atmospheres and learn how these things form.
A coronagraph will be used by NASA’s upcoming Nancy Grace Roman Space Telescope to demonstrate direct imaging technology by photographing Jupiter-like worlds orbiting Sun-like stars.
