Let’s see what else we can see on our little traveler:
https://www.astronomerstelegram.org/?read=17726
Bockelee-Morvan, D. Langevin, Y. Poulet, F. et al. Detection of H2O in the coma of interstellar comet 3I/ATLAS with MAJIS/JUICE
ATel #17726; on 23 Mar 2026; 14:32 UT
3I/ATLAS is our visitor of interest, JUICE is ESA’s probe to Jupiter, MAJIS is the visible-to-near-infrared spectrometer instrument on that probe, and H2O is water. Put them all together, and what do you have? Measurement of cometary activity!
Comets have many volatile gases, but typically water ice leads all other “ices.” (We think 3I’s high CO2 level may be a radiation processed ‘crust,’ from water plus organics.) Tracking emission levels and changes tells us of e. g., compositions, depths, thermal properties, and perhaps mechanical issues like fissures vs. crusts. Unfortunately, water does not have lots of nice, visible spectral emissions. We must view in the infrared, and by chance, the JUICE trajectory to Jupiter brought it “near” 3I. The authors brief us on what exactly JUICE saw from 3I.