The Key to Unlocking the Mysteries of the Universe? Ice Planetesimals Discovered in the Atmosphere of a White Dwarf

The latest research reported by Phys.org on September 27, 2025 (U.S. time) has provided definitive evidence of fragments from an "ice-rich, particularly nitrogen-rich" exoplanetary body (planetesimal) raining down on the atmosphere of the white dwarf WD 1647+375. Using ultraviolet spectroscopy from the Hubble Space Telescope (HST), a nitrogen mass fraction of about 5% and an oxygen excess (+84%) were detected, suggesting a high water content (approximately 2.45 times more water relative to rock). This represents the highest level of nitrogen ever observed in debris around a white dwarf, and it was concluded that the properties are more akin to Pluto and Kuiper Belt Objects (KBOs) than to comets. Phys.org

The research team estimated that material has been accreting at a rate of approximately 2×10^8 g per second for at least 13 years. The target is a white dwarf located at a relatively close distance of about **78.5 parsecs (approximately 255 light-years)** from Earth. The announcement is supported by a pre-peer-reviewed paper by an international team led by the University of Warwick (arXiv), NASA/HST commentary, and major media reports. arXiv

What Was Found: Key Observations

• Instrument: Observations in the far ultraviolet were made with HST's **COS (Cosmic Origins Spectrograph). It directly read the "chemical fingerprint" showing the characteristic absorption lines of nitrogen (N)**, which are difficult to capture in visible light. Follow-up observations used data analysis from the VLT X-shooter. arXiv

• Elemental Composition: Rich in carbon, nitrogen, sulfur, and oxygen, with nitrogen at about 5.1±1.6%. Additionally, the oxygen excess of 84±7% cannot be explained by minerals alone, indicating the presence of a large amount of water (ice). The ratio of water to rock ≈ 2.45 suggests a depiction closer to **"crust and mantle fragments of a dwarf planet"** than to a comet. arXiv

• Identity of the Parent Body: The hypothesis of a "cometary origin" is weak due to the excessive nitrogen compared to typical comets. It was interpreted that fragments of a Pluto-like KBO were shredded by the white dwarf's gravity and accreted. Reuters
  
  

Why It Matters: Indicating the "Spread" of Life Materials

1. Sources of Water and Volatile Elements
   to Young Exoplanetary Earth-like Planets. The delivery agents of water and organics were likely icy bodies from the Kuiper Belt in our solar system. This time, the study demonstrated the universal existence of similar "water carriers" beyond the solar system through elemental ratios, marking a groundbreaking point. Reuters

2. Advancement in "White Dwarf Archaeology"
   The atmosphere of a white dwarf is typically dominated by hydrogen or helium. The presence of heavy elements in large quantities indicates recent consumption of solid bodies. This allows for the reverse calculation of the chemical composition of planetary systems in the "stellar graveyard," directly linking to the reconstruction of exoplanet formation history. NASA Science

3. Possibility of "Dwarf Planet Fragments" Rather Than "Comets"
   The abundance of nitrogen and the ratio of water were decisive. The nitrogen ice covering Pluto's surface is consistent, becoming one indicator of **"crust and mantle origin."** Sky at Night Magazine
   
   

Details of the Study: Reading WD 1647+375 by the Numbers

• Distance: Approximately 78.5 pc (~255 light-years)arXiv

• Accretion Rate: ~2×10^8 g/s (equivalent to the mass of an adult blue whale per second as introduced in reports)Reuters

• Duration: Continued for at least 13 years (the actual phase could theoretically be on the order of 10^5 years)arXiv

• Elements: Rich in C, N, S, O / Detected the highest N in white dwarf debrisarXiv
  
  

Voices from the Field: A Glimpse into SNS Reactions

• Spread of the News: The official post by Phys.org spread widely. The headline **"Detection of Ice Fragments Rich in Nitrogen and Water in a White Dwarf"** sparked discussions. X (formerly Twitter)

• Threads by Researchers and Commentators:

  • Astronomy commentary accounts explained it as the **"first clear example of 'ice fragments' rich in water, nitrogen, sulfur, and carbon accreting onto a hydrogen-atmosphere white dwarf."** They also summarized that **"it's more likely fragments of a Pluto-like body's crust and mantle than a comet."** X (formerly Twitter)

• Reddit/r/space, r/astronomy:

  • A thread titled "Cosmic Crime Scene" was created, and comments like "It's interesting that nitrogen is the key and it can be called Pluto-like" and "We're peeking into the future of our solar system (when the Sun becomes a white dwarf)" fueled the discussion. Reddit

• Mainstream Media Coverage:

  • Reuters reported that "a white dwarf swallowed a 'Pluto-like icy world'," emphasizing the implications for the **"universality of life-essential substances."** The topic spread beyond the scientific community. Reuters

Note: The SNS text is a summary, and individual post wording avoids long quotations (refer to the links above for sources).

How the Conclusion Was Reached: Spectroscopy as "Fingerprinting"

Spectroscopy shows unique lines for each element, serving as a means to "weigh the chemical composition" of debris remotely. The decisive detection of nitrogen is only reliably done in the far ultraviolet, making HST/COS the clear winner. The value of 5% nitrogen is relatively high compared to typical cometary ice and aligns with the nitrogen ice on Pluto's surface. HST revealed components that might be overlooked by ground-based telescopes focused on visible light. NASA Science　Sky at Night Magazine

Falsifiability and Cautious Implications

The paper states that **"based on chemical composition alone, it is difficult to definitively determine whether the original parent system is within the same planetary system or of interstellar origin", clearly indicating a cautious stance. Nevertheless, the abundance of nitrogen and water is more naturally explained by KBO dwarf planet fragments** and is the most promising working hypothesis. arXiv##HTML_TAG_