Astronomers have discovered the remains of an icy, water-rich world being swallowed by a white dwarf star outside our solar system.
The finding provides some of the strongest evidence yet that the building blocks for life—like water and nitrogen—exist in planetary systems far beyond our own.
In our solar system, scientists believe comets and icy objects called planetesimals once delivered water to Earth, helping create the conditions needed for life.
Detecting similar icy objects around distant stars, however, has been extremely difficult.
They are small, faint, and can only be identified by studying their chemical “fingerprints.”
Researchers from the University of Warwick, along with colleagues in Europe and the US, used the Hubble Space Telescope to examine the chemical makeup of distant stars.
One star in particular, known as WD 1647+375, revealed something extraordinary.
Unlike most white dwarfs, which have atmospheres dominated by hydrogen and helium, this star’s atmosphere contained large amounts of carbon, nitrogen, sulfur, and oxygen—clues that it was consuming a volatile-rich object.
White dwarfs are the collapsed, burnt-out cores of stars like our Sun. When planets or asteroids stray too close, they are ripped apart and absorbed by the star.
These events leave behind telltale chemical traces in the star’s atmosphere, allowing astronomers to reconstruct what kind of object was destroyed.
Normally, astronomers see rocky material being pulled in—rich in calcium, iron, and other metals. But in this case, the debris was rich in volatile elements, especially nitrogen, which is a key marker of icy bodies.
The study found that nitrogen made up about 5% of the debris being absorbed by WD 1647+375—the highest nitrogen level ever detected in such a system. The star’s atmosphere also showed far more oxygen than would be expected from rocky debris. Both clues point to the object being icy and water-rich, rather than solid rock.
The feeding has been going on for at least 13 years, with the star consuming roughly 200,000 kilograms every second—the weight of a blue whale—of the frozen body.
This means the object was at least 3 kilometers across, about the size of a comet, though it could have been much larger, even up to 50 kilometers wide. The team estimates the planetesimal was made of about 64% water ice.
The icy fragment resembles objects in our own Kuiper Belt, the region beyond Neptune where Pluto and many frozen worlds orbit. In fact, the researchers think it may have been a piece of a Pluto-like dwarf planet.
Its unusually high ratio of ice to rock—about 2.5 times greater than most Kuiper Belt objects—suggests it may have come from the outer layers of such a planet.
This is the first clear evidence of a hydrogen-rich white dwarf consuming an icy planetesimal. Whether the icy world formed in the star’s original planetary system or was captured from interstellar space is still unknown.
Either way, the discovery shows that frozen, water-rich objects—capable of delivering life’s essential ingredients—exist in distant planetary systems.
It also highlights the unique power of ultraviolet observations. Only UV light can reveal the signatures of elements like nitrogen, making telescopes like Hubble essential for uncovering the hidden chemistry of alien worlds.
