A white dwarf star has recently been observed in the act of consuming a planetary relic, offering groundbreaking insights into the fate of planetary systems following the death of their stars. Approximately three billion years ago, a sun-like star reached its end, shedding its outer layers during its red giant phase. This process left behind an inert core, which we now identify as the white dwarf known as LSPM J0207+3331, located an impressive 145 light-years away from Earth.
What happened to the planets that once orbited this star? Spectroscopic observations conducted by several telescopes, including the Magellan Baade 6.5-meter telescope in Chile and the 10-meter Keck I telescope on Hawaii's Mauna Kea, have unveiled a fascinating revelation: fragments of planets and asteroids have remarkably endured for three billion years. However, for one particular fragment, its time is rapidly running out.
The spectroscopic data revealed that gravitational tidal forces from the white dwarf have torn this fragment apart, scattering debris from the planetary body across the surface of the white dwarf. The measurements identified a total of 13 elements from this doomed object, including aluminum, carbon, chromium, cobalt, copper, iron, magnesium, manganese, nickel, silicon, sodium, strontium, and titanium, predominantly found in Earth-like abundances.
The observations indicate that the white dwarf features a hydrogen-rich envelope. Typically, any elements that are deposited onto the white dwarf should sink into this hydrogen envelope and become invisible. The fact that such a large number of elements are still detectable suggests that their accretion onto the white dwarf must have occurred relatively recently—within the past 35,000 years. In fact, LSPM J0207+3331 could still be dismantling this object, which is estimated to be around 120 miles (193 kilometers) across, even as we speak.
While heavy elements from destroyed planets and asteroids have been previously detected on white dwarfs, it is unusual for this process of debris accumulation to continue after three billion years. According to Patrick Dufour from the Trottier Institute for Research on Exoplanets at Université de Montréal, the amount of rocky material present is exceptionally high for a white dwarf of this age.
LSPM J0207+3331 is also surrounded by a probable debris disk rich in silicates, which was discovered through an excess mid-infrared glow detected by NASA's Wide-field Infrared Survey Explorer (WISE). This leads to the hypothesis that the object recently torn apart by the white dwarf may have originated from this debris disk, which contains material that survived the star's death.
Future observations using the James Webb Space Telescope (JWST) could allow researchers to analyze this disk further, determining its mineralogy and total mass. Such findings could provide additional clues about the nature of the object that the white dwarf has destroyed.
One of the pressing questions that arises from this discovery is why this object faced its demise now, rather than at any point in the previous three billion years. This finding challenges our understanding of planetary system evolution, as noted by Érika Le Bourdais, the lead author of the research. The ongoing accretion suggests that white dwarfs may still retain planetary remnants that are undergoing dynamic changes.
When a sun-like star begins its death throes and expands into a red giant, the inner planets are typically consumed and destroyed. However, celestial bodies located farther away, such as asteroids, comets, and gas giant planets, can survive this cataclysm, albeit in a changed gravitational environment. The shifting gravitational field as the star sheds mass can disrupt orbits, leading to collisions among asteroids, comets, and surviving planets over billions of years, producing dust and small chunks that fill the debris disk surrounding LSPM J0207+3331.
What is particularly surprising is that substantial solid bodies still exist within that debris disk, and something must have triggered one of those solid bodies to drift toward the white dwarf. John Debes of the Space Telescope Science Institute commented, "Something clearly disturbed this system long after the star's death." This suggests that there remains a reservoir of material capable of polluting the white dwarf, even after billions of years.
However, the exact cause of this instability is still unclear. Surviving gas giant planets could potentially be responsible, with interactions among multiple planets gradually destabilizing the orbits of smaller bodies over eons. This points to long-term dynamical processes that we do not yet fully understand. Proving this theory, however, will be a challenge, as gas giant planets would likely be too distant and cool to be clearly imaged. Nevertheless, the JWST may have some capability in this regard.
More likely, the European Space Agency's Gaia astrometric mission may have detected a wobble in the motion of the white dwarf caused by the gravitational influence of orbiting gas giant planets. The first batch of exoplanet data from Gaia is expected to be released in December 2026—perhaps then, we will finally solve this cosmic mystery.