Cristiano Batalli Cosmovici

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

Abstract 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 6 16 →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.

Water masers in the Kronian system

The presence of water has been considered for a long time as a key condition for life in planetary environments. The Cassini mission discovered water vapour in the Kronian system by detecting absorption of UV emission from a background star (Hansen et al. 2006). Prompted by this discovery, we started an observational campaign for search of another manifestation of the water vapour in the Kronian system, its maser emission at the frequency of 22 GHz (1.35 cm wavelength). Observations with the 32 m Medicina radio telescope (INAF-IRA, Italy) started in 2006 using Mk5A data recording and the JIVE-Huygens software correlator. Later on, an on-line spectrometer was used at Medicina. The 14 m Metsahovi radio telescope (TKK-MRO, Finland) joined the observational campaign in 2008 using a locally developed data capture unit and software spectrometer. More than 300 hours of observations were collected in 2006-2008 campaign with the two radio telescopes. The data were analysed at JIVE using the Doppler tracking technique to compensate the observed spectra for the radial Doppler shift for various bodies in the Kronian system (Pogrebenko et al. 2009). Here we report the observational results for Hyperion, Titan, Enceladus and Atlas, and their physical interpretation. Encouraged by these results we started a campaign of follow up observations including other radio telescopes.

The puzzling detection of the 22 GHz water emission line in Comet Hyakutake at perihelion

Abstract We observed Comet Hyakutake C/1996 B2 during the period 26 April–4 May 1996 around perihelion searching for the 22 GHz neutral water line by using a fast multichannel spectrometer coupled to the 32 m dish of the Medicina radiotelescope. We report here not only the first certain detection of this radio spectral line in a comet and the unique detection of water in a celestial body at a distance of 0.23 AU from the Sun, but also strong physical anomalies in the behavior of the water molecule velocities. The line is split into two clear and bright components and is positively shifted with respect to the comet rest velocity at velocities varying from 22 to 44 km/s during the four days of observation. As far as we know, a similar behavior of neutral molecules in comets has never been observed before as the outflow velocity should normally not exceed 1 km/s. A qualitative analysis of the data seems to support sublimation of excited water molecules from accelerated icy grains which form an extended source around the nucleus. The strong coronal activity observed by the SOHO spacecraft in the same period may have contributed to the acceleration mechanism. A future quantitative analysis would be very useful for the study of the complex plasma-grain interaction problem and of the cometary activity at very close distances from the Sun.

Water masers in the Saturnian system

Context. The presence of water has long been seen as a key condition for life in planetary environments. The Cassini spacecraft discovered water vapour in the Saturnian system by detecting absorption of UV emission from a background star. Investigating other possible manifestations of water is essential, one of which, provided physical conditions are suitable, is maser emission. Aims. We report detection of water maser emission at 22 GHz associated with several Kronian satellites using Earth-based radio telescopes. Methods. We searched for water maser emission in the Saturnian system in an observing campaign using the Metsahovi and Medicina radio telescopes. Spectral data were Doppler-corrected over orbital phase for the Saturnian satellites, yielding detections of water maser emission associated with the moons Hyperion, Titan, Enceladus, and Atlas. Results. The detection of Saturnian water molecules by remote astronomical observation can be combined with in situ spacecraft measurements to harmonise the physical model of the Saturnian system.