Cassini–Huygens

The Cassini-Huygens Mission

(Artist concept of Cassini-Huygens Grand Finale ©NASA/JPL/Caltech)

The Cassini-Huygens mission is a flagship mission supported by the NASA, ESA and ASI space agencies.  The Cassini spacecraft was launched on October 15th, 1997 from Cape Canaveral and reached the Saturn planet on July, 1st 2004. This mission has been. The prime mission spanned from 2004 to 2007, followed by the Equinox mission from 2008 to 2010 and finally the Solstice mission from 2011 to 2017. The spacecraft finally ended in a voluntary plunge in Saturn atmosphere on September 15th, 2017 after thirteen years of data collection, both in-situ or by remote sensing. This is the heaviest scientific payload ever launched in the outer Solar System: twelve instruments dedicated to plasma and particles study, UV-to-Microwave remote sensing. Our Team has been involved as co-investigator or associate team members in the scientific analysis of the infrared spectrometer CIRS, the near-infrared spectrometer VIMS and the Radio Science- RSS Instruments to study the nature and evolution of Saturn’s rings, icy moons and Titan satellite.

CIRS VIMS RSS Radar

CIRS (Composite Infrared Spectrometer)

(Flight model of the CIRS Spectrometer before integration at NASA/GSFC © NASA)

The CIRS spectrometer was built to detect the thermal emission of planetary bodies at the distance of Saturn, which temperatures roughly ranges between 50 and 150 K. It is intended to explore the structure and dynamics of Saturn and Titan atmospheres, the diurnal and seasonal thermal cycles to explore the vertical structure of rings or to understand the nature of the sub-surface at few tens of cm in depth of the icy moons.

CIRS is the acronym for Composite InfraRed Spectrometer. This spectrometer is mounted with a 50-cm-large Cassegrain telescope and two Michelson interferometers moved by the same scan mechanism. One is lighting one single focal plane, FP1, equipped with thermopiles detectors covering the 17-1000 um wavelength domain, while the other has two focal planes quipped with 10-pixels-array detectors of HgCdTe in the 7-9 um (FP4) and 9-17 um (FP3). The highest spectral resolution is 0.5 cm-1, i.e ten times better than the previous spectrometer IRIS-Voyager that flew by Saturn in 1980 and 1981. Its sensitivity is 1000 to 10000 better. This instrument was built by a Consortium of laboratories including NASA/Goddard Space Flight Center, Observatoire de Paris, Service d’Astrophysique/CEA Saclay, QMW London and University of Oxford (Official Website at GSFC).

Related bibliography

• Flasar F. M. et al. (2004) Exploring the Saturn System in the Thermal Infrared: The Composite Infrared Spectrometer, Space Sci. Rev., 115, 169-297.
• Spilker, L., Ferrari, C., Cuzzi, J., Showalter, M., Pearl, J. and B. Wallis (2003) Saturn's rings in thermal infrared, in Surfaces and atmospheres of the outer planets, their satellites and ring systems, Review paper, Planet.Space.Sci., 51, 929-935.

VIMS (Visible and Infrared Mapping Spectrometer)

RSS (Radio Science Subsystem)

Radar

Cassini RADAR instrument operates in four different modes: i) SAR imager, ii) scatterometer, iii) radiometer and iv) altimeter. The SAR imager mode is the most useful for assessing surface features and morphologies as it provides images with the highest spatial resolution available on Titan’s surface around 300 m/pixel. The SAR mode is therefore mainly used for mapping Titan’s surface.

(Antenna beam configuration. At nadir, B3 is used for altimetry mode. Imaging is used during side-pointing geometry. B1-B2 and B4-B5 overlaps allow to derive topography © NASA/Stiles et al., 2009.)

Additionally, the PSS team developed with Telecom’ Paris a despeckling technique able to reduce the speckle noise that hinders small features. The data set is available on Zenodo: doi.org/10.5281/zenodo.528545.

Thanks to these enhanced data, the team also developed in collaboration with LATMOS and Bordeaux Observatory an inversion method for assessing the terrains properties such as surface roughness, relative permittivity and volume scattering of the subsurface of the largest Saturn’s moon. In some rare cases, the SAR mode is also used by the team for deriving digital topography model from stereo-like technique initially developed by the USGS.

The PSS team therefore uses these high level products for assessing the landscape evolution of Titan, by focusing on the interaction between the bedforms such dune fields and the current climate at the equatorial region, the weathering and erosion processes that sculpt these exotic landscapes as well as the hydrocarbon lakes at high latitudes.