For centuries, humanity has wondered whether the recipe for life exists elsewhere in the cosmos. Now, a team of astronomers led by the University of Warwick has uncovered a dramatic new clue: the chemical fingerprint of a frozen, water-rich planetary fragment being devoured by a white dwarf star hundreds of light years away.
This discovery is more than an astronomical curiosity. It is a direct sign that icy bodies—similar to the comets and dwarf planets that may have delivered water to Earth—also exist in distant planetary systems. These frozen worlds are critical ingredients in the story of habitability. Without them, planets like Earth would remain dry, barren rocks. With them, the possibility of oceans, atmospheres, and perhaps even life itself emerges.
The Role of Icy Planetesimals
In our own solar system, comets and icy planetesimals are thought to have played a central role in shaping the Earth’s habitability. Billions of years ago, they bombarded the young Earth, seeding it with water and volatile elements. Without their contribution, our oceans and atmosphere might never have formed.
But while we see these icy bodies close to home—in the Kuiper Belt beyond Neptune or in the form of long-period comets streaking across the sky—detecting them outside our solar system has been nearly impossible. They are small, faint, and elusive. Proving their existence requires analyzing their chemistry, something that is extraordinarily difficult at interstellar distances.
That is why the new finding is so remarkable. For the first time, astronomers have identified the clear chemical signature of a volatile-rich, water-bearing planetary fragment beyond the solar system.
White Dwarfs as Cosmic Crime Scenes
The star at the center of this breakthrough is WD 1647+375, a white dwarf—the dense, cooling remnant of a once sun-like star. White dwarfs are usually composed of hydrogen and helium, but they sometimes display “pollution” from other elements. This happens when unlucky planets, moons, or asteroids stray too close to the star, get torn apart by its gravity, and are slowly consumed.
Astronomers call these stars “cosmic crime scenes.” Like forensic detectives, scientists examine the star’s atmosphere for chemical fingerprints, reconstructing the identity of the destroyed objects. Typically, the evidence points to rocky debris: calcium, iron, magnesium—the ingredients of shattered planets and asteroids.
But WD 1647+375 was different. Using ultraviolet spectroscopy from the Hubble Space Telescope, researchers detected an unusual set of volatiles—chemical substances that evaporate at low temperatures. Its atmosphere contained large amounts of carbon, nitrogen, sulfur, and oxygen. These were the first signs that the white dwarf was not consuming a typical rocky fragment but something colder, wetter, and more exotic.
The Nitrogen Clue
One element in particular stood out: nitrogen. Nitrogen is a hallmark of icy bodies, rare in rocky debris but common in comets and dwarf planets. The study revealed that the debris falling into WD 1647+375 was unusually rich in nitrogen, making up about 5% of its mass. This is the highest nitrogen abundance ever detected in material accreted by a white dwarf.
The star’s atmosphere also contained 84% more oxygen than expected if the fragment had been purely rocky. Together, the nitrogen and oxygen levels told a clear story: the star was consuming a frozen, water-rich object, strikingly similar to the icy worlds on the fringes of our solar system.
A Feeding Star and a Dying World
The destruction of this icy fragment has not been a fleeting event. Data show that WD 1647+375 has been accreting material for at least 13 years—likely far longer—at a staggering rate of 200,000 kilograms per second, roughly the mass of an adult blue whale swallowed every heartbeat.
This feeding frenzy implies that the icy world was at least three kilometers across, the size of a comet, and possibly much larger. If accretion has been ongoing for hundreds of thousands of years, as is likely, the original object could have been closer to 50 kilometers in diameter and weighed more than a quintillion kilograms.
Chemical modeling suggests that the fragment was made of about 64% water ice, with a high ice-to-rock ratio, far beyond what is typical for smaller comets. Instead, the composition resembles the outer layers of Pluto or other dwarf planets. In essence, WD 1647+375 may be consuming a piece of a Pluto-like world.
Echoes of the Kuiper Belt
This resemblance to Kuiper Belt objects in our solar system is striking. Beyond Neptune, worlds like Pluto, Eris, and Makemake linger in frozen darkness, rich in nitrogen and methane ices. The fragment at WD 1647+375 shares these traits, suggesting that distant planetary systems may harbor their own Kuiper Belt analogs.
Professor Boris T. Gänsicke, co-author of the study, emphasized that the fragment’s nitrogen-rich, ice-heavy composition points to a dwarf planet origin. The material may have come from the crust or mantle of such a body, shattered and drawn into the star’s fatal pull.
Implications for Life in the Universe
The discovery is more than an isolated cosmic spectacle. It carries profound implications for our understanding of planetary systems and the potential for life elsewhere. If icy planetesimals like this one are common beyond our solar system, then so too is the delivery of water and volatiles to rocky planets. That means Earth’s story—the transformation from dry rock to blue world—might not be unique.
The detection also highlights the crucial role of ultraviolet spectroscopy in searching for life’s raw ingredients. Only by probing the ultraviolet spectrum could astronomers detect volatile elements such as nitrogen and sulfur. Future missions equipped with advanced UV instruments may uncover more icy worlds being shredded by dying stars, further revealing the chemistry of distant systems.
A Window into Cosmic Origins
The mystery of where life begins is inseparable from the question of where water and volatiles come from. On Earth, icy planetesimals delivered these essentials. Now, by catching WD 1647+375 in the act of consuming a frozen planetary fragment, astronomers have glimpsed the same process unfolding in a distant star system.
It is a reminder that planetary systems, even after their suns have died, continue to bear the fingerprints of life’s ingredients. Somewhere out there, other rocky planets may have received their own watery gifts, waiting under alien skies.
The icy fragment devoured by WD 1647+375 will never see the light of life again, but its chemical story brings us closer to answering one of humanity’s oldest questions: Are we alone, or is life written into the universe itself?
More information: Snehalata Sahu et al, Discovery of an icy and nitrogen-rich extrasolar planetesimal, Monthly Notices of the Royal Astronomical Society (2025). DOI: 10.1093/mnras/staf1424
