Discovery of an icy and nitrogen-rich extrasolar planetesimal

Abstract

White dwarfs accreting planetary debris provide detailed insight into the bulk composition of rocky exo-planetesimals. However, only one Kuiper-Belt analogue has been identified in that way so far. Here, we report the accretion of an icy extra-solar planetesimal onto white dwarf WD 1647+375 using ultraviolet spectroscopy from the Hubble Space Telescope. The accreted material is rich in the volatiles carbon, nitrogen, and sulphur, with a chemical composition analogous to Kuiper-belt objects (KBOs) in our solar system. It has a high nitrogen mass fraction ($5.1\pm 1.6$ per cent) and large oxygen excess ($84\pm 7$ per cent), indicating that the accreted planetesimal is water-rich (a water-to-rock ratio of $\simeq 2.45$), corroborating a cometary- or dwarf planet-like composition. The white dwarf has been accreting at a rate of $\approx 2\times 10^8$ g s${}^{-1}$ for the past 13 years, implying a minimum mass of $\sim 10^{17}$ g for the icy parent body. The actual mass could be several orders of magnitude larger if the accretion phase lasts $\sim 10^5$ yr as estimated in the literature from debris disc studies. We argue that the accreted body is most likely a fragment of a KBO dwarf planet based on its nitrogen-rich composition. However, based on the chemical composition alone, it is difficult to discern whether this icy body is intrinsic to this planetary system, or may have an interstellar origin.

Published in MNRAS on 18th September 2025, see https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/staf1424

References in corpus (43)

• Gaia Data Release 3: Summary of the content and survey properties
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• The frequency of planetary debris around young white dwarfs
• The Chemical Composition of an Extrasolar Minor Planet
• Formation of planetary debris discs around white dwarfs I: Tidal disruption of an extremely eccentric asteroid
• The Chemical Composition of an Extrasolar Kuiper-Belt-Object
• Initial Characterization of Interstellar Comet 2I/2019 Q4 (Borisov)
• The carbon monoxide-rich interstellar comet 2I/Borisov
• Earth shaped by primordial H${}_2$ atmospheres
• Likely detection of water-rich asteroid debris in a metal-polluted white dwarf
• The unbiased frequency of planetary signatures around single and binary white dwarfs using $Spitzer$ and $Hubble$
• Cool DZ white dwarfs I: Identification and spectral analysis
• Hydrogen delivery onto white dwarfs from remnant exo-Oort cloud comets
• New white dwarf envelope models and diffusion. Application to DQ white dwarfs
• Tidal disruption of planetary bodies by white dwarfs I: A hybrid SPH-analytical approach
• A new perspective on interiors of ice-rich planets: Ice-rock mixture instead of ice on top of rock
• Evaporation and Accretion of Extrasolar Comets Following White Dwarf Kicks
• Does a Differentiated, Carbonate-Rich, Rocky Object Pollute the White Dwarf SDSSJ104341.53+085558.2?
• An ultra-massive white dwarf with a mixed hydrogen-carbon atmosphere as a likely merger remnant
• 1I/'Oumuamua as an N2 ice fragment of an exo-pluto surface. II. Generation of N2 ice fragments and the origin of 'Oumuamua
• Interstellar comet 3I/ATLAS: discovery and physical description
• Discovery of Beryllium in White Dwarfs Polluted by Planetesimal Accretion
• Horizontal spreading of planetary debris accreted by white dwarfs
• 1I/'Oumuamua as an N2 ice fragment of an exo-Pluto surface: I. size and compositional constraints
• Exocomets from a Solar System Perspective
• The lifetimes of planetary debris discs around white dwarfs
• Icy Exomoons Evidenced by Spallogenic Nuclides in Polluted White Dwarfs
• New chondritic bodies identified in eight oxygen-bearing white dwarfs
• Data Release 1 of the Dark Energy Spectroscopic Instrument
• GD424 -- a helium-atmosphere white dwarf with a large amount of trace hydrogen in the process of digesting a rocky planetesimal
• PEWDD: A database of white dwarfs enriched by exo-planetary material
• Unusual Abundances from Planetary System Material Polluting the White Dwarf G238-44
• Asynchronous accretion can mimic diverse white dwarf pollutants II: water content
• The Source of Hydrogen in Earth's Building Blocks
• Can comets deliver prebiotic molecules to rocky exoplanets?
• Capture of interstellar objects I: the capture cross-section
• Capture of interstellar objects II: by the Solar system
• An impact-free mechanism to deliver water to terrestrial planets and exoplanets
• Two substellar survivor candidates; one found and one missing
• Characterizing planetary material accreted by cool helium atmosphere white dwarfs using an exponentially decaying disc model
• White dwarf magnetospheres: Shielding volatile content of icy objects and implications for volatile pollution scarcity
• Hubble Space Telescope Observations of the Interstellar Interloper 3I/ATLAS
• Spectral Characteristics of Interstellar Object 3I/ATLAS from SOAR Observations