Visual and Infrared Mapping Spectrometer on the Cassini Spacecraft

Transcription

1 Visual and Infrared Mapping Spectrometer on the Cassini Spacecraft Credit: NASA / JPL Emily Pilinski University of Colorado at Boulder

2 Topics to Cover Introduction to the Instrument Instrument Requirements and Design Science Motivation Science Results Recommended Reading 2

3 VIMS Characteristics Mass (current best estimate) = kg Peak Operating Power (current best estimate) = W Average Operating Power (current best estimate) = W Peak Data Rate (current best estimate) = kilobits/sec Dimensions (approximate) = 78 cm x 76 cm x 55 cm 2-in-1 Instrument: VIMS-Visible, VIMS-Infrared trumentscassinivims/instcassinivimsdetails/ 3

4 VIMS-Infrared, VIMS-IR VIMS Infrared Mapper Built at JPL using heritage from Near Infrared Mapping Spectrometer (NIMS) that flew on Galileo to Jupiter Spectral Range microns 256 Channels, Field of View: 32 x 32 mrad 1-D InSb (Indium Antimonide) Detector captures spectrum of one point and time Whiskbroom scanning technique Thermally isolated from S/C Solar calibration port, LED calibration 4 [Brown, et al. 2004] & [Miller, et. al]

5 VIMS-Visible (VIMS-V) VIMS-Visible Built by Italian Collaborators Spectral Range microns 96 Channels, Field of View: 32 x 32 mrad Optical Head consists of scanning telescope and diffraction grating spectrometer Scanning telescope uses push-broom technique in down-track direction to generate a 3-d image cube with information as a function of wavelength, position, time 5 [Miller, et al.]

6 Operating in Tandem Mapping because mirror can be adjusted to acquire different areas of target Data from both optical systems combined before transmitting to Earth to maximize information content Not only VIMS-V and VIMS-IR that operate together, but also used with RADAR, ISS, and more. [Miller, et al.] 6

7 Condensed Science Objectives Flyby of Venus/Jupiter Titan Surface and atmospheric composition and interactions Identify volcanism, surface geology, geomorphology Winds and upper atmosphere dynamics from clouds Saturn Distribution and profiles of clouds, aerosols, variable gases Rings Map particle distribution and dynamics Characterize particle size and surface properties Icy Satellites Mineralogical compositions at surface Relate material to other icy satellites of other planets (Iapetus, Hyperion and Phoebe) 7 [Brown, et al. 2004] & [Miller, et. al]

8 Traceability Matrix: Titan-specific Example Surface Atmospheric Science Goal Science Objective Instrument/Obs. Requirements Composition and distribution of aerosols Studies of methane, ethane, and acetylene, and more at microbar and millibar levels using stellar occultation measurements. A1, A2, A4 Characterize atmospheric circulation and physics Determination of equipotential surfaces near the 1 mbar level. Determination of the 3-d solar flux deposition and constrain the surface solar energy flux over latitude, longitude and time. Determination of wind fields as revealed by movements of clouds and hazes A1, A2, A4 Determine vertical optical extinction profile of atmos. Determination of vertical aerosol distributions and associated microphysical and optical properties, over latitude/longitude and time. Studies of stratospheric aerosol distributions from stellar occultation measurements. A1-A4 Characterize Surface geology and geomorphology Composition determination at the wavelengths of near-infrared atmospheric windows in Titan s atmosphere (e.g. 0.95, 1.1, 1.3, 1.6, 2.0, 2.7 μm). Map composition as a function of longitude and latitude S1-S4 Identify Volcanism and Lightning Searches for signs of active volcanism and tectonism S1-S4, A5 [Brown, et al. 2004] & [Miller, et. al] September 13, 2011

9 Atmospheric Measurements Types Observation Type Spectral Resolution Spatial Resolution Distance Result A1 High High Within 25 object radii Used during closest approach combined for Feature Tracks. Both V & IR. A2 High Moderate Outside of 25 object radii Provides global mosaics. Uses both V & IR. A3 Not specified. Not specified. Not specified. Nightime thermal measurements of Saturn s atmospheric thermal profile. IR only A4 Not specified. Not specified. Not specified. Observations of weak emissions and hight altitudes. Obs. Integrated from IR only. A5 Full spectrum Not specified. Less than 10 Saturn radii. High-speed detection of lightening to determine altitude and total energy. 9 [Brown, et al. 2004] & [Miller, et. al]

10 Surface Measurements Types Observation Type Spectral Resolution Spatial Resolution Distance Result S1 High Low Far Away Baseline for future targets, performed shortly after SOI S2 High Modest (10-20 km) Approach Provides best coverage S3 High High Approach (Good coverage) Product of tradeoffs between S1/S2 S4 High High Closest Approach (Limited coverage) Ride along measurements when other instrument is prime, ex. ISS. Other measurement types not included in this summary are the modes for stellar occultations and ring observations. 10 [Brown, et al. 2004] & [Miller, et. al]

11 Selection of Spectral and Spatial Resolution Designed a robust instrument to adapt to many possible outcomes and discoveries Variation of targets size and distance: Rings, Icy Satellites, Titan, Saturn, Enceladus Atmospheric, ring dynamics on the scale of ~100 km Surface composition on the scale of ~10 km Variation of distance from the target, see orbital progression to the right Unknown constituents, designed to be robust to what they would find Credit: NASA / JPL

12 Spectrum Selection Example spectrum from Titan with methane atmospheric transmission bands highlighted in grey. Titan s atmospheric windows at 2.0, 2.7 and 5.0 mm are useful for surface composition studies 12 [McCord, et al. 2008]

13 Science Motivation: Titan Example Cassini Wide Angle Camera g/pia06230 Cassini VIMS-IR g/pia

14 Spectrum Usage Example 14 [Brown, et al. 2008]

15 Science Highlights: Titan s Lakes VIMs/RADAR have helped to peer through the haze to characterize the hydrocarbon lakes of Titan. Observations: Lakes appear to change with the season Smooth surfaces indicate no waves despite windy surface Composed of primarily methane and ethane and Contain sediments which could be helpful in reconstructing history of Titan 15 Credit: NASA/JPL/University of Arizona/DLR

16 Science Highlights: Rings Cryon Volcanism on Titan from RADAR/VIMS observations. VIMs confirmed the sources of the E-ring were the ice plumes from Enceladus 43_modest.jpg 16

17 Recommended Reading Global-scale surface spectral variations on Titan seen from Cassini/VIMS [Barnes, et. al 2007] The identification of liquid ethane in Titan s Ontario Lacus [Brown, et al. Nature 2008] The Visual and Infrared mapping spectrometer for Cassini [Miller, et al. unknown] Recommend websites if interested in more information on VIMs and Cassini:

18 Flyby Example MUg 18

19 References Barnes, et. al. Global-scale surface spectral variations on Titan seen from Cassini/VIMS, Icarus 186, , Brown, et al. The Cassini Visual and Infrared Mapping Spectrometer (VIMS) Investigation, Space Science Reviews, , Brown, et al. The identification of liquid ethane in Titan s Ontario Lacus, Nature, Vol. 454, , Miller, et al. The Visual and Infrared Mapping Spectrometer for Cassini, 19