Search for the 22GHz water maser emission in selected comets

• Published in: Planetary and space science 2014-06, Vol.96, p.22-28
• Main Authors: Cosmovici, C.B., Pluchino, S., Montebugnoli, S., Pogrebenko, S.
• Format: Article
• Language: English
• Subjects: Acceleration; Comets; Emission; Radiospectrometry; Searching; Spectra; Spectrometers; Water maser emission; Water masers; Water vapor
• ISSN: 0032-0633; 1873-5088
• DOI: 10.1016/j.pss.2014.03.004

Following the first evidence of planetary water maser emission induced by the collision of comet Shoemaker/Levy with Jupiter and the puzzling detection of the 22GHz water emission line in Comet Hyakutake we started in the period 2002–2008 systematic observations of selected comets at 22GHz (1.35cm) with the aim of clarifying the unusual behavior of the maser line in the cometary “scenario”. Using a fast multichannel spectrometer coupled to the 32m dish of the Medicina (Bologna, Italy) Radio Telescope we investigated 6 bright or sungrazing comets down to a heliocentric distance of 0.11AU: 96P/Machholz, 153P/ Ikeya–Zhang, C/2002 V1 (NEAT), C/2002 X5 (Kudo–Fujikawa), C/2002 T7 (Linear), and 73P/Schwassmann–Wachmann 3. All of them, similarly to Comet Hyakutake, demonstrate spectral features that, if real and due to the 1.35cm water vapor transition, are strongly (up to tens of km/s) shifted relative to the radial velocity of the nucleus and, at least sometimes, seem to be present as two separate peaks. If our interpretation of these spectral peaks is correct, there must be some mechanism of acceleration of neutral water molecules up to the velocities of ions. We discuss here the results achieved and the possible explanation of the chemo-physical constraints. •First possible detection of the water maser emission line at 22GHz in sun-grazing comets•Observed puzzling acceleration of neutral water molecules at ion velocities and split of the line in two components.•Evidence of plasma–grain interaction in sun-grazing comets.•Possible new detections in six peculiar comets.