Over the past 30 years, astronomers have found nearly 6,000 “exoplanets” (planets around other stars). In almost all cases, these are indirect discoveries. For example, a planet may intercept a small amount of starlight as it passes in front of its star, as seen from Earth. Or it causes the star to wobble a little due to its gravity.
Both techniques work particularly well if the planet is very close to its “parent star.” Planets in wider orbits are much harder to find. The existence of the new planet, called Epsilon Indi Ab, was already deduced in 2019 from the star’s minimal speed variations. But now it is real.
‘seen’ by the James Webb telescope’s Miri camera, developed in part in the Netherlands. And it turns out to be much heavier and much further from its star than previously thought.
About the Author
Govert Schilling is a science journalist. He prescribes of Volkskrant on astronomy.
“A fantastic result,” said Leiden exoplanet expert Ignas Snellen, who was not involved in the research.
Miri does not look in visible light, but in infrared wavelengths. The camera captured the low-lying heat radiation of the planet, which has a temperature close to freezing. It moves in a wide, elongated orbit around an orange star that is considerably smaller, cooler and dimmer than our own sun.
Old and cold
In trade magazine Nature The researchers (led by Elizabeth Matthews of the Max Planck Institute for Astronomy in Heidelberg) convincingly show that the spot of infrared light in the Miri photographs really does belong to the star and is not a distant object in the universe that simply happens to be in roughly the same direction.
Massive giant planets in wide orbits have been photographed before, but they were always young specimens, with ages of no more than a few hundred million years. Such a newborn planet has not yet cooled down and therefore emits much more infrared light.
Thanks to James Webb’s sensitivity, Epsilon Indi Ab is now the oldest and coldest ‘super Jupiter’ ever recorded. Measurements seem to indicate that there is a relatively large amount of carbon in the atmosphere, probably in the form of methane and carbon dioxide.
“This is really a milestone,” says Snellen. “For the first time we are learning something about the atmosphere of an ancient, cooled exoplanet.” According to Matthews and his colleagues, this helps to better understand the evolution of gas giant planets.
Extraterrestrial life is unlikely to exist
It is hoped that such massive planets will also be found in wide orbits between other nearby stars in the future, not only with the James Webb telescope, but also with the European Extremely Large Telescope under construction and NASA’s future Habitable Worlds Observatory.
It’s doubtful that the new discovery is good news for the search for extraterrestrial life. Epsilon Indi Ab is a gaseous world with no solid surface or water. It may be accompanied by moons that might look a bit more like Earth, but whether anything could live there is highly speculative, according to Snellen. “It’s very cold at such a great distance from the star.”