**Astronomers Discover a Unique Icy Planetesimal: What’s So Special?**
*By Dwaipayan Roy | Sep 28, 2025, 03:13 PM*
Astronomers from the University of Warwick have made an exciting discovery: a frozen, water-rich planetary fragment being consumed by a white dwarf star. This groundbreaking finding was recently published in the *Monthly Notices of the Royal Astronomical Society*.
### Unveiling the Unique Find
Using ultraviolet spectroscopy from the Hubble Space Telescope, the research team analyzed the chemical composition of distant stars and identified a unique icy object. Among the stars studied, one in particular — WD 1647+375 — stood out due to its unusual atmosphere rich in “volatile” elements.
Unlike typical white dwarf atmospheres, which mostly consist of hydrogen and helium, WD 1647+375 showed high levels of carbon, nitrogen, sulfur, and oxygen. This volatile-rich atmosphere was the first hint that this star was unlike others in its class.
### White Dwarfs as Cosmic Crime Scenes
Lead author Snehalata Sahu explained that white dwarfs often display signatures of elements such as calcium and iron, which originate from the material they absorb. This material typically comes from planets and asteroids that stray too close to the star and are subsequently torn apart.
By studying the chemical footprints left behind, scientists can infer the composition of planetesimals beyond our solar system. Sahu likened white dwarfs to “cosmic crime scenes,” where analyzing the elements deposited by an accreted planetesimal helps reveal its identity.
### Signs of an Icy Origin
The ultraviolet spectroscopy data revealed a remarkably high nitrogen content in the material absorbed by WD 1647+375 — the highest nitrogen abundance ever detected in the debris of a white dwarf. Additionally, the star’s atmosphere contained more oxygen than expected for a typical rocky object, reinforcing the idea that this fragment originated from an icy body.
### What Could It Be?
The findings suggest that the object being consumed by the star is an icy, water-rich planetesimal, potentially resembling a comet like Halley’s or a fragment of a dwarf planet. Professor Boris T. Gänsicke, co-author of the study, noted that the volatile-rich nature of WD 1647+375 is similar to Kuiper Belt objects in our own solar system, hinting that this could be a fragment of a Pluto-like body.
### Why This Discovery Matters
This is the first clear case of a hydrogen-atmosphere white dwarf absorbing an icy planetesimal. However, key questions remain unanswered: did this icy object originate from the planetary system around the original star, or is it an interstellar comet captured from the depths of space?
As investigations continue, this discovery opens a new window into understanding the diversity of planetary debris around white dwarfs and sheds light on the fate of icy bodies in other star systems.
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