Astronomers using the NASA/ESA/CSA James Webb Space Telescope have analyzed the atmosphere of a massive exoplanet orbiting the white dwarf WD 1856+534, offering a rare glimpse into what may happen to giant planets like Jupiter when the Sun exhausts its nuclear fuel billions of years from now. The findings, published in a new study, mark the first time that the atmospheric composition of a planet around a white dwarf has been directly examined, shedding light on the survival and evolution of planetary systems after their host stars die.
The exoplanet, designated WD 1856+534 b, is a gas giant roughly the size of Jupiter but several times more massive. It orbits its white dwarf star at a distance of about 2.5 million kilometers — an extremely close orbit that places it well within the zone where the star’s gravitational pull would have torn apart smaller objects. The system is located approximately 80 light-years from Earth in the constellation Draco. The white dwarf itself is the remnant of a star that was once similar to the Sun, having shed its outer layers and collapsed into a dense, Earth-sized core after running out of nuclear fuel.
Using Webb’s near-infrared spectrograph, the research team detected water vapor and other molecules in the planet’s atmosphere, confirming that it is a gas giant with a composition similar to Jupiter’s. The presence of water vapor is particularly significant because it indicates that the planet’s atmosphere has remained intact despite the violent death of its star. The white dwarf’s intense radiation and gravitational forces would have stripped away any lighter elements, but the planet’s massive size and strong gravity have allowed it to retain a substantial atmosphere.
The discovery provides a direct analog for what may happen to Jupiter and Saturn when the Sun becomes a white dwarf in about 5 billion years. As the Sun exhausts its hydrogen fuel, it will expand into a red giant, engulfing Mercury, Venus, and possibly Earth. Its outer layers will drift into space, leaving behind a white dwarf. During this process, the orbits of the remaining planets will shift, and some may be pulled inward by gravitational interactions. The WD 1856+534 system suggests that gas giants like Jupiter could survive this chaotic phase and end up in close orbits around the white dwarf, their atmospheres largely preserved.
The study also raises questions about the long-term habitability of any moons that might orbit such a planet. While the white dwarf itself no longer produces energy through fusion, it remains extremely hot for billions of years, radiating residual heat. A gas giant in a close orbit could provide a temperate environment for its moons if the planet’s own heat and the white dwarf’s radiation combine to create a habitable zone. However, the intense radiation from the white dwarf would likely sterilize any surface life, and the planet’s proximity to the star would subject any moons to powerful tidal forces.
The Webb telescope’s ability to analyze the atmosphere of a planet orbiting a white dwarf marks a significant milestone in exoplanet science. Previously, such observations were impossible because white dwarfs are so faint and their planets are so close that they are difficult to distinguish from the star’s glare. Webb’s infrared sensitivity and high-resolution spectroscopy allow astronomers to separate the planet’s signal from the star’s, enabling detailed atmospheric studies. This technique could be applied to other white dwarf systems, potentially revealing a population of surviving planets that were previously hidden.
The findings also have implications for understanding the fate of our own solar system. While the Sun’s transformation into a white dwarf is billions of years away, the WD 1856+534 system provides a natural laboratory for testing models of planetary system evolution. If Jupiter and Saturn can survive the Sun’s red giant phase and end up in close orbits around the white dwarf, they would become the last surviving planets in the solar system, orbiting a dim, cooling ember of a star. The study suggests that such a scenario is not only possible but likely, based on the evidence from this distant system.
The research team plans to continue observing WD 1856+534 b with Webb to search for additional molecules, such as carbon dioxide and methane, which could provide further clues about the planet’s formation and history. They also hope to find other similar systems to determine how common such survivors are. The discovery underscores the versatility of the James Webb Space Telescope, which continues to deliver groundbreaking results across a wide range of astronomical topics, from the atmospheres of exoplanets to the most distant galaxies in the universe.
