Water and related chemistry in the solar system. A guaranteed time key programme for Herschel

Abstract

This Guaranteed Time Key Programme, approved by the European Space Agency, aims at determining the distribution, the evolution and the origin of water in Mars, the Outer Planets, Titan, Enceladus and Comets, using the three Herschel instruments HIFI, PACS and SPIRE. It addresses the broad topic of water and its isotopologues in planetary and cometary atmospheres. The nature of cometary activity and the thermodynamics of cometary comae will be investigated by studying water excitation in a sample of comets. The D/H ratio, the key parameter for constraining the origin and evolution of Solar System species, will be measured for the first time in a Jupiter-family comet. A comparison with existing and new measurements of D/H in Oort-cloud comets will constrain the composition of pre-solar cometary grains and possibly the dynamics of the protosolar nebula. New measurements of D/H in Giant Planets, similarly constraining the composition of proto-planetary ices, will be obtained. The D/H and other isotopic ratios, diagnostic of Mars' atmosphere evolution, will be accurately measured in H 2 O and CO. The role of water vapour in Mars' atmospheric chemistry will be studied by monitoring vertical profiles of H 2 O and HDO and by searching for several other species (and CO and H 2 O isotopes). A detailed study of the source of water in the upper atmosphere of the Giant Planets and Titan will be performed. By monitoring the water abundance, vertical profile, and input fluxes in the various objects, and when possible with the help of mapping observations, we will discriminate between the possible sources of water in the Outer Planets (interplanetary dust particles, cometary impacts, and local sources). In addition to these inter-connected objectives, serendipitous searches may further enhance our knowledge of the composition of planetary and cometary atmospheres. For further details see:

Direct detection of the Enceladus water torus withHerschel

“…2), including in addition the 2 02 −1 11 (987 GHz), 3 12 -3 03 (1097 GHz), 1 11 -0 00 (1113 GHz), and 2 12 -1 01 (1670 GHz) H 2 O lines, were obtained on June 24, 2010 (β = +2 • ) in the framework of the "HssO" key program (Hartogh et al 2009). Since the HIFI beam at 1670 GHz (HPBW ∼ 12.6 ) partially resolves Saturn's ∼16.5 disk, a crude fivepoint map (center, east, west, north, south) was also obtained in that line.…”

Ammonia and other parent molecules in comet 10P/Tempel 2 fromHerschel/HIFI and ground-based radio observations

“…Comet 10P was also observed in 2010 with the Herschel Space Observatory (Pilbratt et al 2010) using HIFI (de Graauw et al 2010), within the framework of the Water and related chemistry in the Solar System (HssO) project (Hartogh et al 2009). Several water rotational lines were observed and mapped from 15 June to 29 July 2010 (Szutowicz et al 2011 and in prep.).…”

First detection of hydrogen isocyanide (HNC) in Titan’s atmosphere

“…Observations of Titan were performed on June 14 and December 31, 2010, as part of the Herschel guaranteed time key program "Water and related chemistry in the Solar System" (HssO, see Hartogh et al 2009). We used the HIFI heterodyne receiver in band 1a (covering the 480-560 GHz spectral region), with two orthogonal polarizations (H and V) simultaneously.…”