Looking for Water
Belgian astronomers [1], part of Deep Impact at ESO campaign, observing with the UVES spectrograph attached to VLT Kueyen 8.2m telescope, found from pre-impact high-quality, high-resolution spectra, convincing evidence for the presence of water in Comet Tempel 1.
The astronomers have detected among many other species [2] the light emitted at 308-316 nm by the OH molecule, the direct decay product of water.
More than a half century ago, Fred Whipple, suggested the "dirty snowball" model as a fait representation of comets. This model pictures the nucleus as a mixture of dark organic material, rocky grains and water. The presence of water ice seemed natural since it had been long noticed that most comets became active when they came within 2 AU of the Sun. This is exactly the limit of the warm zone where water ice sublimes in vacuum.
In 1970 UV satellite observations of Comet Tago-Sato-Kosaka 1969 IX and Bennett 1970 II detected vast amounts of hydrogen extending over millions of kilometers. The detection of OH lines near 310 nm (already known from ground-based spectra of the brightest comets) and of the Lyman-alphaline of H validated the Whipple model. H and OH are the daughter species of the parent molecule H2O.
Among other molecules, the fluorescence bands of OH were expected to brighten following Tempel 1 impact, since a huge amount of gas was expected to be released into the coma from the crater. There remained an uncertainty, however, on the observability of this phenomenon, as in its normal state the comet already releases extremely high quantity of gas. Would it be enough to induce a significant change in the intensity of the bands?
The answer seems to be an unqualified yes.
Notes
[1]: Emmanuel Jehin (ESO, Paranal) and Jean Manfroid (U. Liège, Belgium).
Leading scientists of the ESO DI campaign: H. Boehnhardt (MPI, Lindau, Germany), O. Hainaut (ESO), H.U. Kaufl (ESO), H. Rauer (DLR, Germany).
Members of the ESO DI observing team on site: N. Ageorges (ESO, Chile), S. Bagnulo (ESO, Chile), L. Barrera (UMCE, Chile), H. Boehnhardt (MPS, Germany), T. Bonev (Astr. Inst. Sofia, Bulgaria) , O. Hainaut (ESO, Chile), E. Jehin (ESO, Chile), H.U. Kaufl (ESO, Germany), F. Kerber (ESO, Germany), J. Manfroid (U.Liège, Belgium), O. Marco (ESO, Chile), E. Pantin (CEA, France), E. Pompei (ESO, Chile), C. Sterken (Vrije Universiteit Brussel, Belgium), G.P. Tozzi (Obs. Arcetri, Italy), M. Weiler (DLR, G ermany)
Members of the ESO DI observing team not on site: C. Arpigny (U.Liège, Belgium), A. Cochran (McDonald, USA), C. Delahodde (Univ. Florida, USA), Y. Fernandez (Univ. Hawaii, USA), D. Hutseme kers (U.Liège, Belgium), H. Kawakita (Gunma, Japan), J. Knollenberg (DLR, Germany), L. Kolokolova (Univ. Maryland, USA), M. Kretlow (MPS, Germany), M. Kueppers (MPS, Germany), E. Kuehrt (DLR, Germany), L. Lara (IAA, Spain), J. Licandro (IAC, Spain), C. Lisse (Univ. Maryland, USA), K . Meech (U.Hawaii, USA), R. Schulz (ESTEC, The Netherlands), G. Schwehm (ESTEC, The Netherlands), M. Sterzik (ESO, Chile), J.A. Stüwe (Leide n, The Netherlands), I. Surdej (Univ. Liège, Belgium and ESO, Garching), D. Wooden (Ames, USA), J.-M. Zucconi (Besancon, France)
[2]: more...