Astronomers have announced a breakthrough discovery made with the James Webb Space Telescope: It is a planet more than six times the size of Jupiter, orbiting one of the closest stars to our solar system. Eps Ind Ab is the coldest exoplanet imaged to be dated, therefore representing a milestone in astronomy.
“This is a cold planet,” said Elisabeth Matthews, a planet hunter at the Max Planck Institute for Astronomy in Heidelberg, Germany. The results were published in the journal Nature on July 24. A planet within the triple star system Epsilon Indi, a mere 12 light years away from Earth. That’s six Jupiter’s worth of mass, circling its red dwarf parent at about the distance Neptune orbits the Sun. This means Eps Ind Ab has a surface temperature of around 0 degrees Celsius.
The exoplanet was then discovered using the James Webb Space Telescope’s Mid-Infrared Instrument (MIRI). The MIRI offers the telescope a fine imaging cross-section at the thermal infrared spectrum, enabling it to pinpoint the planet hidden within the glare of its host star. “We were excited when we realized we had imaged this new planet,” said Matthews. Previous studies misjudged the mass and orbital separation of the said super Jupiter gas giant, but the JWST rectified this misconception.
This is in making the first time JWST has taken an image of a previously unseen exoplanet from the ground. Markus Janson, an astronomer at Stockholm University, explains the importance of this study: In this respect, it is a step towards the ability to image planets in mature, mature systems. So far, all direct imaging work is limited to young star systems, whereas Epsilon Indi A is almost as old as the Sun.
The orbit of the planet is highly elliptical, being kicked back and forth between 20 and 50 times the Earth-Sun distance. Its wide orbit makes it hard to find it with conventional techniques, either with a transit or a radial detection method. But with JWST’s coronagraphic capability of blocking the star’s light, astronomers were able to take a clear image of Eps Ind Ab.
The star Epsilon Indi A forms a triple system with two brown dwarfs, objects that never grew big enough to initiate hydrogen fusion in their cores. These brown dwarfs orbit the star over 1,000 times farther away than the super Jupiter. “We have a very peculiar kind of system that we are fortunate to have in our backyard,” Matthews said.
The finding of Eps Ind Ab holds the promise of new possibilities and opportunities associated with cold gas-giant planets. In fact, with the information supplied by direct imaging and spectral observations, a unique database will be compiled about the atmospheric composition and conditions of the planet in question, thus tracing the evolution of the planetary systems. This may eventually help with a thorough understanding of planet formation and evolution, especially for planets in fully settled planetary systems.
The team now hopes to make follow-up observations to measure the spectrum of light from Eps Ind Ab. This should yield the composition of its atmosphere and, fortunately, provide them with some of the first answers to where and how such a big, fearsome-looking planet could have taken shape. “Our next goal is to obtain spectra that provide us a detailed fingerprint of the planet’s climatology and chemical composition,” explained Thomas Henning, emeritus director at the Max Planck Institute for Astronomy.
In the longer term, the team hopes to estimate other planetary systems within reach in its search for hidden, cold, and gas-giant fugitives. This survey would yield the foundational data necessary to comprehend the process of gas-planet formation and its evolution.
This finding represents not just the potential of the James Webb Space Telescope but also a foundation for the future exploration of the secrets of our universe.