Astronomers using the James Webb Space Telescope have identified a Jupiter-sized exoplanet, WD 1856 b, orbiting a white dwarf 80 light-years from Earth. The discovery, detailed in the journal Nature, provides a rare glimpse into the future of solar systems after their host stars die and leave behind dense remnants.
How WD 1856 b survived its star’s death
Photo: Nature
The existence of WD 1856 b challenges previous assumptions about planetary survival during a star’s transition into a red giant. According to NASA Science, a Sun-like star nearing the end of its life swells tremendously, typically engulfing and destroying any nearby planets. Yet this Jupiter-sized gas giant persists in an incredibly tight orbit, completing a revolution every 34 hours.
The planet’s current position is 50 times closer to its host star than Earth is to the Sun. This proximity creates a cosmic paradox: if the planet had started its life at this distance, it would have been obliterated during the red giant phase.
To explain this, researchers are weighing two primary theories. As Space.com reports, one theory suggests the planet was swallowed by the dying star and managed to survive on the inside. The alternative is that gravitational influence from other objects in the system triggered a migration. The white dwarf is part of a triple star system, and outer companion stars may have pushed WD 1856 b inward.
The ‘oddball’ proportions of the system
Photo: Space
The physical scale of the system is an anomaly in astrophysics. While the planet is roughly the size of Jupiter, the white dwarf it orbits, WD 1856+534, is approximately the size of Earth.
“The planet is quite the oddball. It’s about the size of Jupiter, but the white dwarf it orbits is the size of Earth, so the planet is seven times larger than its star,”
Ryan MacDonald, University of St Andrews, via Space.com
This massive size disparity means that when the planet transits the star, it blocks a significant portion of the white dwarf’s light. First discovered in 2020 by the Transiting Exoplanet Survey Satellite (TESS) and the Spitzer Space Telescope, WD 1856 b was the first intact planet ever found closely orbiting a white dwarf.
What Webb’s temperature data reveals
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The James Webb Space Telescope (JWST) provided the critical evidence needed to trace the planet’s history by measuring its heat. By observing the planet’s transit, the team detected that the planet is significantly warmer than expected.
The data indicates a temperature of approximately 260 degrees Fahrenheit (126 degrees Celsius). This heat is higher than what would be produced if the planet relied solely on the light from the white dwarf. According to NASA, this temperature discrepancy is the key to understanding the planet’s migration.
“As the planet moved inward, its interactions with the strong gravity of the white dwarf will have caused it to warm up considerably, and it has been cooling ever since,”
Christopher O’Connor, Northwestern University, via Space.com
The research team utilized the NIRSpec PRISM instrument to extract transmission spectra, employing two independent codes—FIREFLy and Juniper—to ensure the accuracy of the light curve fitting and the planetary emission data.
The long-term fate of Earth and the Sun
While WD 1856 b serves as a “time machine” for the outer planets, the fate of the inner rocky planets remains a subject of debate. Standard models suggest that in about 5 billion years, the Sun will exhaust its hydrogen, expand into a red giant, and eventually shrink into a white dwarf.
Historically, astrophysicists believed Earth would be pulled into the expanding red sun and vaporized. However, a study published in Wired suggests a different outcome based on new models of tidal dissipation and stellar mass loss.
The survival of Earth depends on a cosmic tug-of-war between two forces:
Stellar Winds: As the Sun loses mass, its gravitational pull weakens, potentially allowing Earth to drift outward.
Tidal Drag: The Sun’s extended gaseous envelope creates drag and tidal forces that act as a brake, pulling the planet inward.
The new research indicates that tidal dissipation—the process that circularizes orbits—may be less effective than previously thought. This suggests that Earth might avoid being swallowed, though it will be rendered uninhabitable within the next two billion years as the Sun’s increasing luminosity evaporates all surface water.
Implications for the search for ‘life after death’
The study of WD 1856 b proves that planetary systems can survive the violent death of their host stars, albeit in transformed states. This opens a new frontier for the JWST to explore other white dwarf systems to see if such survivors are common or rare.
“We’re used to looking back in time when we use telescopes, but this is the first time we have been able to look forward to what might happen to the outer planets around the remnant of a sun-like star; it’s like using a time machine to peer into the distant future of our solar system,”
Ryan MacDonald, University of St Andrews, via Space.com
The discovery shifts the narrative from total cosmic destruction to one of survival and migration. While the inner planets of our system face an uncertain end, the outer giants like Jupiter may find a “vibrant and lively future” orbiting the smoldering remains of the Sun.
