Unexplained IFU position offset in JWST maps of 3I/ATLAS

Determine the origin and physical cause of the remaining 0.7 arcsec offset between the brightest pixel (assumed nucleus location) in the JWST NIRSpec IFU gas/dust maps of 3I/ATLAS and the predicted ephemeris position, beyond the 0.5 arcsec explained by a 1.7σ ephemeris error, at r_H = 3.32 au.

Background

The JWST NIRSpec IFU observations produced spatial maps of dust-scattered light and gas emissions (CO2, H2O, CO). These maps showed a well-defined coma peak displaced by 1.2 arcsec from the IFU center.

A later ephemeris reconstruction accounted for 0.5 arcsec of this displacement via a 1.7σ ephemeris prediction error, leaving 0.7 arcsec unaccounted for. The authors explicitly note that this residual offset remains under investigation, indicating an unresolved issue potentially linked to pointing, reconstruction, calibration, or coma morphology effects.

References

As shown by a later ephemeris reconstruction, about $0\farcs5$ of the offset can be explained by a $1.7\sigma$ error on the predicted ephemeris, while the remaining $0\farcs7$ offset remains under investigation.

— JWST detection of a carbon dioxide dominated gas coma surrounding interstellar object 3I/ATLAS (2508.18209 - Cordiner et al., 25 Aug 2025) in Section 3 (Results), paragraph describing gas and dust maps near Figure 2