Even with huge ground-based observatories and the latest technology in space-based telescopes, it’s still relatively rare for astronomers to take an image of an exoplanet. Planets outside our solar system are so far away and so small and dim compared to the stars they orbit that it’s extremely difficult to study them directly. That’s why most observations of exoplanets are made by studying their host stars. Now, though, the James Webb Space Telescope has directly imaged a gas giant — and it’s one of the coldest exoplanets observed so far.
The planet, named Epsilon Indi Ab, is located 12 light-years away and has an estimated temperature of just 35 degrees Fahrenheit (2 degrees Celsius). The fact it is so cool compared to most exoplanets meant that Webb’s sensitive instruments were needed to study it.
“Cold planets are very faint, and most of their emission is in the mid-infrared,” explained lead researcher Elisabeth Matthews of the Max Planck Institute for Astronomy in Germany. “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 image of the planet, seen above, was taken by Webb’s MIRI instrument. This has a tool called a coronagraph, which is a disk that blocks out light from very bright sources (in this case, the planet’s host star) so that nearby dimmer objects (like the planet) can be observed. It was also possible to make this rare direct observation of the planet because it is so nearby to us, relatively speaking, so there was more visible separation between the planet and the star.
The planet is rather similar to Jupiter, though a little warmer and a little larger. There are some indications that it could have a cloudy atmosphere, or it could have lots of heavy elements like carbon. But the researchers want to collect more data using spectrographs to get a better look at the planet’s atmosphere before drawing conclusions.
Studying the planet could help astronomers understand more about the gas giants in our own solar system, as well as the many exoplanets that are farther away and are too faint and distant to be observed in this manner.
“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,” said team member Caroline Morley of the University of Texas at Austin. “It’s exciting to actually see a planet there ourselves, and begin to measure its properties.”
The research is published in the journal Nature.
