Subaru Telescope Study of 'Naked' Comet 28P/Neujmin Challenges Asteroid Distinctions

• New analysis using archival Subaru Telescope data reveals that comet 28P/Neujmin possesses a surface microstructure distinct from C- and D-type asteroids despite spectral similarities.
• As a 'naked' comet with virtually no coma when far from the Sun, 28P/Neujmin serves as a critical test case for blurring the lines between cometary and asteroidal classifications.

Research Context

• Led by Takafumi Ootsubo, the research team analyzed images from the Subaru Telescope (Mauna Kea, Hawaii) to study the 21 km wide comet at a heliocentric distance exceeding 10 AU.
• Observing the comet at this distance minimizes coma contamination, allowing researchers to study the nucleus directly.

Findings

• Opposition Effect: By analyzing the brightness surge at small phase angles, researchers assessed surface albedo, grain size, and porosity.
• Spectral vs. Structural Differences: While the comet’s color matches that of D-type asteroids, its grain-packing and small-scale porosity are significantly more 'fluffy' or loosely packed.
• Evolutionary Links: These results suggest that while comets and asteroids may form in similar environments, their physical properties differ significantly from established asteroid taxonomic groups.

Implications

• The traditional binary model of 'icy' comets versus 'rocky' asteroids is becoming increasingly outdated as evidence of hydrated minerals in comets and comet-like asteroids grows.
• Understanding these structural nuances is essential for reconstructing the 4.5 billion-year history of the Solar System and defining the origins of different small-body populations.