NASA’s Webb Detects First Atmosphere on a Jupiter-Sized Planet Orbiting a Dead Star

The Anatomy of WD 1856 b and its Host Star

The system, located approximately 80 light-years from Earth, presents one of the strangest silhouettes in the sky. The planet, WD 1856 b, is roughly the size of Jupiter, while its host star, WD 1856+534, is a white dwarf approximately the size of Earth. This creates a stark physical disparity where the planet is seven times wider than the star it orbits.

According to Space Daily, the planet blocks more than half of the star’s light during a transit. The white dwarf itself is a dense, cooling core that remains after a Sun-like star exhausts its fuel, expands into a red giant, and sheds its outer layers. WD 1856+534 has been cooling for roughly six billion years.

The orbital dynamics are equally extreme. WD 1856 b completes a full orbit every 34 hours, positioned 50 times closer to its star than Earth is to the Sun.

How Webb Detected Methane and Cloud Haze

To analyze the planet, researchers utilized transmission spectroscopy. This process involves splitting starlight into colors as it filters through the planet’s atmosphere during a transit, allowing scientists to identify molecules based on missing wavelengths. NASA Science reports that the James Webb Space Telescope observed a transit on 27 April 2023 using its Near-Infrared Spectrograph in PRISM mode.

The observation lasted about two hours, though the transit itself took only eight minutes. The resulting data revealed a chemical composition that challenges previous assumptions about planets orbiting dead stars.

“We saw the telltale signatures of small cloud particles and hydrocarbons, most likely methane, which is the first time we have seen an atmosphere on a planet transiting a dead star,”
Victoria Boehm, Cornell University, via Space Daily

The analysis indicates that methane and hydrocarbons make up roughly seven percent of the atmosphere, accompanied by a haze of tiny particles.

Solving the Survival Mystery via Planetary Temperature

The primary puzzle for astronomers was how WD 1856 b survived its star’s red giant phase. At its current proximity, the planet should have been swallowed or obliterated as the star expanded billions of years ago.

The key to the mystery lay in the planet’s infrared signature. Webb found that the planet blocked less infrared light than expected, meaning WD 1856 b was emitting its own heat from its night side. This allowed researchers to determine the planet’s temperature is about 126 degrees Celsius (260 degrees Fahrenheit).

This temperature is significantly higher than what would be expected if the white dwarf were the planet’s only heat source. According to NASA Science, this thermal data provides the evidence needed to trace the planet’s orbital history. Christopher O’Connor of Northwestern University, a co-author of the study, noted that the temperature helps distinguish between theories of whether the planet was partially swallowed by the dying star or migrated into its current position.

Implications for the Future of the Solar System

The existence of WD 1856 b serves as a preview of the potential fate of our own solar system. In about 5 billion years, the Sun is expected to expand into a red giant before collapsing into a white dwarf.

While the prevailing view among astrophysicists was that Earth would be vaporized during the Sun’s expansion, new research suggests a different possibility. As reported by Wired, a study in Astronomy & Astrophysics indicates that Earth may survive the transition. The study suggests that tidal dissipation—the process that drains orbital energy—might be less effective than previous models indicated, while the Sun’s loss of mass through stellar winds could cause Earth’s orbit to drift outward.

The discovery of WD 1856 b proves that giant planets can not only survive the death of their stars but can maintain atmospheres and reach stable, albeit tight, orbits around the resulting white dwarfs.

Technical Data Summary: WD 1856 b

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