A Guaranteed Time Programme with the Herschel
main goal is producing a unified
picture of the origin and evolution of water in the Solar System objects. The observations proposed in the
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:
Outer planets, Titan, and Enceladus
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,
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
Synthetic spectra of Neptune in the SPIRE (left) and PACS
ranges, showing the expected signatures. Credits:
"Cassini" discovered organic moleculesen 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
cometspectral 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
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: