First evidence of planetary water maser emission induced by the comet/Jupiter catastrophic impact

The comet Shoemaker-Levy 9/Jupiter event gave a unique opportunity to study the consequences of a catastrophic impact in a planetary atmosphere and the subsequent changes in the chemistry and in the excitation conditions of atomic and molecular species. In particular previous attempts to detect molecular radio lines from the Jupiter atmosphere gave negative results. By using a new fast multichannel spectrometer (up to 128,000 channels), coupled with the 32 m dish of the Medicina Radiotelescope, three molecular lines observable in the available region of our system were searched for: water at 22.235 GHz, formaldehyde at 4.830 GHz and ammonia at 23.694 GHz. The detection of the 616→5 23 rotational transition of the 1.35 cm water line from blob E on July 19, 1994, 2 days after impact is reported. A possible detection of water emission from blobs A and C on the same day may be given only with a 3-sigma level. Emission from blob E was probably detected also on August 3 and September 9, i.e. up to 54 days after impact. The very narrow line width (40 kHz) and the high brightness temperature (20,000 K) of the water emission detected cannot be explained in terms of usual thermal emission when taking into account thermal and/or collisional broadening. In this paper it is shown that only a MASER effect could explain the observed values. This would be the first detection of a water MASER in the Solar System and the first evidence of masing effects induced by catastrophic impacts.