The James Webb Space Telescope (JWST) has discovered a “hot Jupiter” planet with two long tails made of helium. For a planet to sport such tails is strange, and it is the first time that the gases leaking from an exoplanet have been studied during one of its complete orbits. This planet, named WASP-121b, also known as “Tylos,” is located around 858 light-years away. Earlier observations have shown that it is an “ultrahot Jupiter.” WASP-121b is a gas giant planet that orbits extremely close to its star and completes an orbit in only 30 hours. Its host star’s intense radiation heats its atmosphere to around 2,300 degrees Celsius. This heating causes the lighter elements to escape the planet, flowing into space, creating these tails.
This process of atmospheric escape lasts millions of years and changes the planet in several ways – its size, composition and even the way it evolves. In the past, researchers were only able to observe atmospheric escape when exoplanets passed in front of their parent stars. However, they weren’t sure whether planetary atmospheres continued to leak when the planet was not in transit. This created a gap in the understanding of atmospheric escape in such exoplanets.
But JWST’s Near-Infrared Spectrograph (NIRSpec) observed WASP-121b for more than 37 consecutive hours, revealing for the first time how helium acts on a planet and how it leaks during a complete orbit. “We were incredibly surprised to see how long the helium escape lasted,” study author Romain Allart, of the University of Montreal, said in a statement. The researchers noted that the gas around WASP-121b stretches to an extreme distance outside the hot Jupiter. The helium signal lasted for over half the orbit of the planet.