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The Cassini CIRS Instrument and Science during the Titan-A Encounter

The Cassini CIRS Instrument and Science during the Titan-A Encounter. Public Outreach Presentation JPL/Telecon - October 26th 2004 Conor Nixon (University of Maryland) on behalf of the CIRS Team. What is CIRS?. CIRS is the Composite Infrared Spectrometer :

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The Cassini CIRS Instrument and Science during the Titan-A Encounter

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  1. The Cassini CIRS Instrument and Science during the Titan-A Encounter Public Outreach Presentation JPL/Telecon - October 26th 2004 Conor Nixon (University of Maryland) on behalf of the CIRS Team

  2. What is CIRS? • CIRS is the Composite Infrared Spectrometer: • Composite: contains two Fourier Transform spectrometers. • Infrared: covers 7-17 microns in mid-infrared (IR), 17-1000 microns (1 mm) in the far-IR. • Spectrometer: rather than imaging (building a spatial picture), CIRS concentrates on achieving high spectral resolution: distinguishing different wavelengths of heat radiation. • CIRS was assembled at NASA GSFC, with hardware contributions from the UK, France and Germany.

  3. CIRS—> Where is CIRS?Location on the Cassini Spacecraft

  4. Cassini optical remote sensing instruments:(or why CIRS is the greatest!)

  5. What does CIRS do? • CIRS is a versatile instrument, which can be used to investigate many different aspects of the Saturn system: • Surfaces: CIRS can be used to help find out what the surfaces of the moons are composed of. • Atmospheres: CIRS will be used to investigate both the temperature structure and the composition of the atmospheres of Titan and Saturn. • Rings: CIRS spectra yield information on ring particle sizes, shapes and composition.

  6. Atmospheric Remote Sensing with CIRS • CIRS can observe planetary atmospheres in two distinct ‘geometries’: • The NADIR geometry looks through the atmosphere to the surface beneath (or deep atmosphere for Saturn). • The LIMB geometry is a grazing view through the atmosphere and back into space. • We’ll see how these views give us very different spectra, on the next couple of slides.

  7. CIRS vs IRIS: • CIRS is the successor to the IRIS spectrometer which flew on the Voyager spacecraft. • CIRS however is improved in almost every way: • more sensitive (better detectors); • higher spectral resolution (compare the ‘IRIS limb viewing’ right, to ‘CIRS limb viewing’)

  8. CIRS also covers a wider range of wavelengths than IRIS: CIRS ventures into the longer wavelength ‘sub-mm’ regime (up to 1 mm) whereas IRIS stopped at 50 microns (0.050 mm). • The figure (right) shows predicted CIRS spectra of Titan, in both the ‘nadir viewing’ (top) and ‘limb viewing’ (bottom) geometries. • Molecular signatures of water, carbon monoxide and hydrogen cyanide are identified.

  9. Titan’s atmosphere:   • A major goal for CIRS is to map the atmospheric temperature of Titan. • Using a mixture of limb and nadir viewing modes, CIRS can sense the temperatures from the top of the troposphere (0.15 bar) right up into the mesosphere (6x10-6 bar)

  10. T0,… T0, Ta, Tb,… Ta, Tb,… (Tb, T3-T5), T6,… T4,… T4,… Tb,... T4,… T4,… T6

  11. TA: Mid-IR Nadir Temperature Map

  12. Mid-IR Nadir Temperature Map (-22:00 to -16:45 hrs) • North-South scans at 10 rad/s with CIRS FP3/4 arrays, to cover the entire visible hemisphere centred on -14.5°S, 151°W. • Will sound temperatures at 4.0--0.4 mbar in the stratosphere via the 4 band of methane. • Spectral resolution of 3 cm-1 will yield 2 scale height vertical resolution (or better). • First look at the northern hemisphere, allowing stratospheric wind fields to be derived. • Will also map global variation of stronger hydrocarbons and nitriles (C2H2, C2H6, HCN, CH3D etc).

  13. Probe Health and Safety • The CIRS global temperature map will further serve to characterize the atmospheric temperature and wind field of Titan, which is poorly known at present. • All such information is of high value to the Huygens probe mission, the health and safety of which is dependent on correct altitude/pressure deployment of parachute(s), and hence on the atmospheric temperature field.

  14. TA: Far-IR Nadir Composition Integration

  15. Far-IR ‘Nadir’ Composition Integration(-15:30 to -11:30 hrs) • 4-hour integration at 30°S, 200°W on Titan (airmass ~1.5), with some time spent on space for calibration purposes. • CIRS highest (0.5 cm-1) spectral resolution. • Over the mission, spatial coverage will eventually provide global map of CH4, HCN, CO in stratosphere. • Will also build up S/N over time to search for new species in far-IR (17m to 1mm).

  16. CIRS Riders • CIRS will also ride-along during the VIMS (-11:30 to -5:00), ISS (-5:00 to -1:50) and UVIS (+5:30 to +8 hrs) PRIME observations, in a mixture of spectral resolution modes, to further supplement CIRS PRIME observation requests.

  17. END OF PRESENTATION(additional materials follow)

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