Discovery: A White Dwarf and an Icy Pluto-Like World
Astronomers using the Hubble Space Telescope have identified a white dwarf in the Milky Way that carries chemical traces of having swallowed an icy body similar to Pluto. The star sits about 255 light-years from Earth and weighs roughly 0.57 solar masses. White dwarfs are the exposed cores of dead stars, typically only Earth-sized in diameter, but with masses comparable to the Sun. The new finding, published in Monthly Notices of the Royal Astronomical Society, sheds light on what can survive the tumultuous end stages of planetary systems and hints at how common water-rich worlds might be beyond our solar system.
The Observation
The team analyzed ultraviolet light from the white dwarf using the Cosmic Origins Spectrograph aboard Hubble. They detected unusual chemical fingerprints on the star’s surface, notably an abundance of nitrogen that does not match what would be expected from rocky, asteroid-like material alone. The proportions suggest the white dwarf accreted fragments from an icy body rather than a dry rocky asteroid.
Interpreting the Evidence
Lead author Snehalata Sahu explains that the observed nitrogen and other trace elements point to material that originated in a world dominated by icy, nitrogen-rich ices, possibly a Pluto-like object. The team estimates the current delivery rate of debris to the white dwarf equals the mass of a blue whale per second, sustained for at least 13 years, illustrating a long-term feeding frenzy on the stellar corpse.
The Mechanism
As white dwarfs age, their strong gravity can tear apart passing rocky bodies that wander too close. The resulting debris forms a disk around the star, with fragments gradually spiraling inward and being accreted onto the white dwarf’s surface. The observed nitrogen-rich, ice-dominated signature is consistent with this picture, implying that icy planets or dwarf planets can orbit other stars and later contribute material to their dead suns.
Why This Matters for Habitable Worlds
One of the big questions in exoplanet science is how common water-rich bodies are around other stars. On Earth, comets and other ices are thought to have delivered water and prebiotic compounds, perhaps shaping the emergence of life. The new findings show that water-bearing debris is not unique to our solar system but may be a widespread feature of planetary architectures. If Pluto-like moons or icy planets exist around other stars, they could play roles in delivering volatiles to inner, potentially habitable worlds and influence planetary habitability in ways we are only beginning to understand.
Future Directions
Further observations of white dwarfs with similar debris signatures will help quantify how common icy, Pluto-like bodies are in the galaxy and how such material contributes to the chemistry of surrounding planetary systems. The Hubble Space Telescope and next-generation observatories will be pivotal in painting a broader picture of the volatile inventory in exoplanetary systems.
