Programación

A Guaranteed Time Programme with the Herschel Space Observatory

Mission

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:

	Mars
	Outer planets, Titan, and Enceladus
	Comets

Determine 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.

	Confirm 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.

	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.

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

Improve 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.

Monitor 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

	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 r_h=Δ= 1 AU.Credits: HssO.