Astronomers employing NASA/ESA/CSA’s James Webb Space Telescope have successfully analyzed the atmosphere of a giant exoplanet, WD1856+534, which orbits a white dwarf star. These groundbreaking findings provide insight into the ultimate fate of giant planets surrounding stars with masses akin to our Sun.
WD 1856b is a gas giant planet orbiting its star 50 times closer than Earth does the Sun. Image credit: NASA/ESA/CSA/Ralf Crawford, STScI.
“Most stars, including our Sun, eventually exhaust their fuel, leaving behind a white dwarf,” noted Dr. Ryan McDonald, an astronomer at the University of St. Andrews, along with colleagues.
“The implications of this stellar evolution on orbiting planets remain largely unclear.”
“Multiple planet candidates have been discovered around white dwarfs, suggesting that planets can endure the transition period when stars evolve into red giants before becoming white dwarfs.”
“However, there is still limited knowledge regarding the atmospheric composition of such planets.”
The new study focused on WD1856b, identified in 2020 by astronomers using NASA’s TESS and Spitzer Space Telescopes.
This exoplanet boasts a radius of 0.9 times that of Jupiter and a mass between 4.3 and 10.9 times Jupiter’s mass.
It orbits the 10-billion-year-old white dwarf star WD 1856+534, which is situated 80 light-years away in the Draco constellation.
“This planet is approximately the same size as Jupiter, while the white dwarf star it orbits is the size of Earth, making this planet seven times larger than its star,” Dr. McDonald stated.
Utilizing Webb’s Near Infrared Spectrometer (NIRSpec), astronomers detected hydrocarbons and aerosols, including methane, in WD 1856b’s atmosphere.
They also measured thermal radiation emanating from the planet’s night side.
“We observed tiny cloud particles and clear indications of hydrocarbons (possibly methane),” shared Cornell University astronomer Victoria Boehm. “This marks the first instance of observing the atmosphere of a planet transiting a dead star.”
“We have recently executed four additional observations of WD 1856b with Webb to delve deeper into the chemistry of its atmosphere, and we’re eager to analyze the results.”
Webb evaluated the composition of WD 1856b as it transited in front of the star, revealing signs of methane. Image credit: NASA/ESA/CSA/Joseph Olmsted, STScI.
Researchers estimate that the planet’s atmosphere has a temperature ranging from 390-412K, significantly higher than the expected temperature of a giant planet (160K).
This heating likely transpired between 3 billion and 5.5 billion years after the star converted into a white dwarf.
In this context, the planet would have initially occupied a wider orbit, safeguarding it from the star during its cataclysmic red giant phase, only to eventually move to its current position.
“As the planet migrated inward, interactions with the white dwarf’s formidable gravity would have induced a significant temperature spike, which has been decreasing ever since,” stated Dr. Christopher O’Connor of Northwestern University.
“The primary question is how WD 1856b evolved into its current state, and there are two prevailing theories.”
“One hypothesis suggests the planet was engulfed by its dying host star and somehow persisted within.”
“The alternative theory posits that the movement was influenced by gravitational dynamics of other bodies within the system.”
The white dwarf is part of a triple star system, where its companion star may play a role in shaping WD 1856b’s orbital path.
In approximately 5 billion years, our Sun will exhaust its hydrogen fuel, expanding to over 100 times its current dimensions, entering the red giant phase.
Following this, it will shed its outer layers, ultimately becoming a white dwarf.
Mercury, Venus, and potentially Earth may be obliterated during this transition.
However, the fates of outer planets, particularly gas giants, remain uncertain.
“We typically rely on telescopes to examine the past, but for the first time, we can observe what may happen to exoplanets around remnants of Sun-like stars,” Dr. McDonald remarked.
“It’s akin to employing a time machine to glimpse into the distant future of our own solar system.”
For further details, see the findings outlined in this week’s edition 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
