Astronomers utilizing NASA/ESA/CSA’s James Webb Space Telescope have conducted an in-depth analysis of the atmosphere of a massive exoplanet orbiting the white dwarf star WD1856+534. Their findings offer vital insights into the ultimate fate of giant planets orbiting stars similar in mass to our Sun.
WD 1856b is a gas giant planet that orbits its star 50 times closer than Earth orbits the Sun. Image credit: NASA/ESA/CSA/Ralf Crawford, STScI.
“Most stars, including the Sun, eventually expire, resulting in a white dwarf,” explained Dr. Ryan McDonald, an astronomer from the University of St. Andrews, along with his colleagues.
“The impact of this stellar evolutionary process on orbiting planets remains incompletely understood.”
“Various planet candidates have been discovered surrounding white dwarfs, suggesting that planets can survive the transition of stars evolving into red giants before becoming white dwarfs.”
“However, the atmospheric composition of these planets is still largely unknown.”
In their latest study, Dr. McDonald and his team concentrated on WD1856b, a giant exoplanet identified in 2020 by astronomers using NASA’s TESS and Spitzer Space Telescopes.
This exoplanet has a radius measuring 0.9 times that of Jupiter and its mass ranges between 4.3 and 10.9 times that of Jupiter.
Orbiting the 10-billion-year-old white dwarf star WD 1856+534, this celestial body is located 80 light-years away in the constellation Draco.
“This planet is similar in size to Jupiter, while the white dwarf star it orbits is as small as Earth, making the planet seven times larger than the star,” said Dr. McDonald.
Astronomers employed Webb’s Near Infrared Spectrometer (NIRSpec) to detect hydrocarbons and aerosols, including methane, within the atmosphere of WD 1856b.
They also observed thermal radiation emanating from the planet’s night side.
“We observed small cloud particles and distinct signs of hydrocarbons (possibly methane),” stated Cornell University astronomer Victoria Boehm. “This is the first instance of observing the atmosphere of a planet transiting a deceased star.”
“We’ve recently conducted four additional observations of WD 1856b with Webb to analyze its atmospheric chemistry further, and we eagerly anticipate the results.”
Webb measured the composition of WD 1856b as it passed in front of the star and found signs of methane. Image credit: NASA/ESA/CSA/Joseph Olmsted, STScI.
Researchers estimate that the atmospheric temperature of the planet is around 390-412K, significantly above the anticipated average for a giant planet (160K).
This thermal activity likely occurred between 3 billion and 5.5 billion years after the star transitioned into a white dwarf.
In this framework, it is believed the planet originally had a wider orbit that kept it shielded from the star during the destructive red giant phase, gradually moving to its current position.
“As the planet drew closer, its interaction with the white dwarf’s strong gravitational pull would have led to a notable temperature rise, which has since cooled,” explained Northwestern University astronomer Dr. Christopher O’Connor.
“The key question is how WD 1856b became what it is today, and two primary theories exist.”
“The first is that the planet was engulfed by its host star during its terminal phase yet somehow persevered within.”
“The alternative theory posits that the planets’ movement resulted from gravitational influences from other objects within the system.”
Notably, the white dwarf is part of a triple star system, and its companion star might have significantly influenced WD 1856b’s orbit.
In roughly 5 billion years, the Sun will exhaust its hydrogen fuel and expand to over 100 times its current size, entering its red giant phase.
During this process, it will shed its outer layers and culminate its life as a white dwarf, leading to the destruction of Mercury, Venus, and possibly Earth.
The destinies of the more distant planets, particularly gas giants, remain uncertain.
“While we typically utilize telescopes to examine the past, this represents the first opportunity to look forward and witness the potential outcomes for exoplanets surrounding the remnants of Sun-like stars,” Dr. McDonald remarked.
“It’s akin to using a time machine to glimpse the future of our solar system.”
These findings were featured in this week’s issue of Nature.
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RJ McDonald et al. 2026. Aerosols and hydrocarbons in the atmosphere of a white dwarf star. Nature 655, 76-80; doi: 10.1038/s41586-026-10514-7
Source: www.sci.news
