A Guaranteed Time Programme with the Herschel Space Observatory



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Science Objectives

HssO main goal is producing a unified picture of the origin and evolution of water in the Solar System objects. The observations proposed in the HssO Program will result in a comprehensive set of sensitive and well-calibrated spectra of water, its isotopologues, and chemically related species in Solar System objects. Our immediate science objective is extracting vertical profiles and isotopic ratios in individual objects. This will be performed using sophisticated radiative transfer and retrieval models that have been developed by the members of the team.  Afterwards, the derived vertical profiles and mixing ratios will be compared with predictions of circulation/chemistry transport and photochemical models. In addition to these inter-connected objectives, serendipitous searches will enhance our knowledge of the composition of planetary and cometary atmospheres. Last but not least, we will carry a comparison of water abundance and isotopic ratio in Solar System objects with those with the Inter Stellar Medium (ISM), in collaboration with the WISH KP.

The scientific objectives of the HssO investigation can be separated into three groups:

bulletOuter planets, Titan, and Enceladus


bulletDetermine vertical deuterium to hydrogen (D/H) profiles in the Martian atmosphere (nearly an order of magnitude higher accuracy than the current best estimate). This constrains the water reservour, Jeans escape, and isotopic fractionation as a function of altitude and season.
bulletConfirm the non-terrestial reported values for water isotopes ratios 18O/16O and 17O/16O by measuring both the CO and the H2O isotopes.

Measure of the vertical distribution of H2O along with CO, O2, H2O2 and temperature of the lower and middle atmosphere of Mars for constraining models.This will help to better understand the aeronomie of Mars, and more precisely, the water cycle.

bullet Detect minor species (example OH, NO, etc.) in the Mars atmosphere.

Caractherize the variable hygropause level between 10 km and 50 km.


The detection of the H2O 556.935 GHz line of Mars by Odin (From Biver et al. 2005)

 The vertical profiles derived from the Mars-CMT.

Outer planets, Titan and Enceladus


Determine the origin of the water external sources on giant planets and Titan.

bulletImprove the accuracy of the water abundances

Determine the vertical profiles


Search for latitudinal variability of H2O on Jupiter and Saturn from rough mapping.


Search for temporal variability of all the above parameters. If variations are found, we will search for correlations with the position of the planets with respect to the major cometary trails.

bulletMonitor the continuum flux of Titan and Enceladus  and search for a hot-temperature component to better characterize Water-driven cryo-volcanism. 


Synthetic spectra of Neptune in the SPIRE (left) and PACS ranges, showing the expected signatures. Credits: HssO.
"Cassini" discovered organic molecules en much bigger concentrations as expected. Credits: NASA / JPL


Comets: 103P/Hartley 2,  22P/Kopff, 81P/Wild 2, 144P/Kushida,

29P/Schwassmann-Wachmann, and a Target of Opportunity comet.


Observe several water lines on cometary atmospheres. This will provide insights into the excitation of this molecule and optical depth effects. Observations of H3O+ will constrainn the excitation by ionic collisions. This will lead us to more realistic models of the thermodynamics of the atmosphere.


Obtain full spectral scans with PACS and SPIRE. This will provide us with the simultaneous measurement of a number of water lines, the serendipitous observations of other volatiles, and the determination of the comet spectral energy distribution (SED). Observations of the thermal emission of the dust is a powerful tool for studying the mineralogy (the PACS spectral range is well adapted for searches for hydrated silicates). In the broader framework of the formation of planetary systems, cometary dust observation will provide important clues for interpretation of the evolution of dusty disks around young stars and should be a key tool for interpretation of Herschel observations of circumstellar media.


Observe HDO and H2O to determine D/H in cometary water. This will provide further constraints for evolutionary Solar Nebula models.

The 110-101 H2O line at 557 GHz by Odin in comet C/2001 A2 (LINEAR) on 2.2 July 2001 (full line). Figure from Bockelee-Morvar & Crovisier 2001).


Synthetic spectra for HIFI and SPIRE for a comet at rh=Δ= 1 AU.Credits: HssO.

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This homepage was created by Miriam Rengel. If you have any inquire about this site contact  rengel@mps.mpg.de
Last update: 09 de Abril de 2008.