Even with powerful ground-based observatories and advanced space telescopes, directly imaging exoplanets remains a challenging feat. These planets beyond our solar system are incredibly distant and faint compared to their host stars, making direct observation extremely difficult. This is why most exoplanet studies rely on observing their stars. However, the James Webb Space Telescope has achieved a remarkable feat – directly imaging a gas giant exoplanet, marking one of the coldest exoplanets observed to date.
This newly imaged planet, named Epsilon Indi Ab, resides 12 light-years away and boasts an estimated temperature of just 35 degrees Fahrenheit (2 degrees Celsius). This relatively cool temperature, compared to most exoplanets, necessitated the use of Webb’s sensitive instruments for its study. “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, captured by Webb’s MIRI instrument, utilizes a coronagraph, a disk that blocks out light from bright sources like the host star, allowing for the observation of nearby dimmer objects, such as the planet. The proximity of this particular planet to Earth, relatively speaking, enabled a clear separation between the planet and its star, further facilitating this rare direct observation.
Epsilon Indi Ab shares similarities with Jupiter, though it is slightly warmer and larger. Preliminary observations hint at the presence of a cloudy atmosphere or potentially high concentrations of heavy elements like carbon. However, the research team intends to gather more data using spectrographs to delve deeper into the planet’s atmospheric composition before drawing definitive conclusions.
This groundbreaking observation holds immense potential for advancing our understanding of gas giants in our own solar system and the vast number of exoplanets that remain too faint and distant for direct observation. “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 findings have been published in the journal Nature.
