Near-Earth Object Shows Comet-Like Non-Gravitational Acceleration

The diameter of 1998 SH2 is established to be about 380 meters, consistent with the infrared data obtained by NEOWISE, which estimates the diameter at 380 ± 60 m. The radar observations with 1-μs ranging resolution span 2 range bins (rows), corresponding roughly to a spatial extent of about 300 meters (1,500 m × 2 bins × 0.5 illumination fraction), confirming the size estimate from the infrared data. This agreement reinforces the interpretation that 1998 SH2 is a sub-kilometer object with a diameter near 380 m.

Summary of Key Findings from Radar and Optical Analysis:

• Diameter: Approximately 380 meters from NEOWISE and radar constraints.
• Rotation Period: Upper limit estimated at 5.4 hours from radar bandwidth and diameter equation.
• Surface Characteristics: Low circular polarization ratio (SC/OC = 0.09 ± 0.03) suggests a smoother near-surface at decimeter scales compared to many other NEAs.
• Non-gravitational Effects: Modeled via a transverse acceleration proportional to (1 au / r_H)^2 consistent with Yarkovsky effect assumptions.
• Cometary Activity: Detected at multiple epochs (Sep 13, 17, and 30, 2025) with increasing activity suggested by excess flux over PSF profiles.
• Dust Tail Analysis: Tail emission between Aug 29 and Sep 7, 2025 with large grains (~300-600 µm) dominated, indicating a narrowly limited grain size distribution rather than a typical power-law.
• Gas Production: Approximate water production rate Q_H2O ≈ 1.2 × 10^24 molecules/s, sufficient to lift observed large grains.
• No Binary Companion: Radar data show no convincing evidence for a satellite or binary companion.
• No Detectable Coma Echo: Radar observations reveal no broad coma echo, consistent with low-level cometary activity.

If you want, I can help summarize the orbital fitting approach, photometric or tail analysis, or provide interpretations for any more specific parts of the findings.