FIRST EVIDENCE OF PLANETARY WATER MASER EMISSION INDUCED BY THE COMETJUPITER CATASTROPHIC IMPACT/

The comet Shoemaker-Levy 9/Jupiter event gave a unique opportunity to study the consequences of a catastrophic impact in a planetary atmosph ere and the subsequent changes in the chemistry and in the excitation conditions of atomic and molecular species. In particular previous att empts 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 Radiote lescope, three molecular lines observable in the available region of o ur system were searched for: water at 22.235 GHz, formaldehyde at 4.83 0 GHz and ammonia at 23.644 GHz. The detection of the 6(16) --> 5(23) rotational transition of the 1.35 cm water line from blob on July 19, 1994, 2 days after impact is reported. A possible detection of water e mission 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 l ine width (40 kHz) and the high brightness temperature (20,000 K) of t he water emission detected cannot be explained in terms of usual therm al emission when taking into account thermal and/or collisional broade ning. 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 MAS ER in the Solar System and the first evidence of masing effects induce d by catastrophic impacts. Copyright (C) 1996 Elsevier Science Ltd