Possible distributed H2O source from sublimating icy grains in the outer coma

Ascertain whether there is a significant contribution to the H2O gas in the outer coma of 3I/ATLAS from sublimating icy grains acting as a distributed source, as suggested by the non-asymptotic H2O production-rate curve within the JWST NIRSpec IFU field.

Background

Production-rate (Q) curves derived from spectral modeling show CO2 and CO leveling off with distance from the nucleus, indicating near-nuclear sources. In contrast, the H2O Q curve does not clearly asymptote within the IFU field, leaving open the possibility of extended production.

The authors explicitly state that they cannot rule out H2O production from sublimating icy grains in the outer coma, consistent with their detection of coma H2O ice. Resolving whether such a distributed source exists would clarify water production mechanisms and help reconcile differences with ultraviolet OH imaging measurements.