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Illustration of the twin tails of WASP-121b. | Credit: B. Gougeon/UdeM
Astronomers have used the James Webb Space Telescope (JWST) to discover that a distant “hot Jupiter” planet has two surprisingly long tails made of helium that currently defy explanation. The observations represent the first study of gases escaping from an extrasolar planet during its full orbit, and help paint the most complete picture of the atmosphere yet.
Extrasolar planets, or exoplanet, The one in question is WASP-121b, also known as “Tylos,” located about 858 light-years away. WASP-121b is an example of an “ultrahot Jupiter”, a giant The gas giant The planet was found so close to its parent star that it can complete one orbit in a few hours. As WASP-121b orbits its star once every 30 hours, intense radiation from its stellar parent heats its atmosphere to about 4,200 degrees Fahrenheit (2,300 degrees Celsius).
When a planet undergoes this type of warming, it releases gasses of lighter elements like hydrogen and helium into space, a slow atmospheric component lasting millions of years that changes the planet’s shape, composition and how it will evolve. Previously, scientists had glimpsed atmospheric escape when exoplanets passed in front of their parent stars, known as “transits.” But that left a gap in our understanding of the process because scientists couldn’t be sure whether the leakage continued beyond those few hours when the planets’ atmospheres were observed during transit.
These new observations, made over nearly 37 consecutive hours using JWST’s Near-Infrared Spectrograph (NIRSpec), represent the first most comprehensive continuous observations of the presence of helium on a planet and how it leaks out over a full orbit.
“We were surprised by how long the helium release lasted,” said team leader Romain Allert of the University of Montreal. said in a statement. “This discovery reveals the complexity of the physical processes that shape exoplanet atmospheres and their interactions with stellar environments. We are only beginning to uncover the true complexity of these worlds.
A tale of two tails
Helium is one of the most important tracers of atmospheric escape from exoplanets, and JWST’s incredible sensitivity allows the element to be observed at great distances. By tracking light absorbed by helium atoms, the researchers discovered that the envelope of gas surrounding WASP-121b extends far beyond this hot Jupiter. The helium signal lasted for more than half the planet’s orbit, making it the longest continuous detection of an atmospheric escape to date.
Most remarkable about this research is the fact that helium leakage from WASP-121b forms two distinct tails, one of which is pushed behind the exoplanet by radiation and stellar winds from its parent star. Another tail carries the planet into its orbit, possibly pulled toward the star by its gravity.
Combined, the helium tails are 100 times the length of WASP-121b’s width, and three times the distance between hot Jupiter and its star. And double tails are something that scientists can’t explain with current models.
“Very often, new observations reveal the limitations of our numerical models and push us to explore new physical mechanisms to advance our understanding of these distant worlds,” said team member Vincent Borrier of the Department of Astronomy at the Faculty of Science of the University of Geneva.
The team’s research was published in the journal Monday (Dec. 8). Nature communication.
