Cassini ISS. The Imaging Science Subsystem. (The Cameras)

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1 Cassini ISS The Imaging Science Subsystem (The Cameras)

2 "We are the eyes of Cassini, our cameras capture all the dramatic sights and vistas there are to see around Saturn. And through their imagery, they convey a sense of adventure, a sense of 'being there,' that we could otherwise only imagine. (Dr. Carolyn Porco, Cassini Imaging Team leader and director of the Cassini Imaging Central Laboratory for OPerationS (CICLOPS), Space Science Institute, Boulder, quoted on the Cassini ISS web site.)

3 Same mosaic of images, using only visible light. Cassini discovered two new rings! The Janus/Epimetheus ring. The Pallene Ring Moon made rings coincident with orbits of Janus/Epimetheus and Pallene. WAC, Sept , visible light, from 2.2 million km.

4 Giovanni Domenico Cassini ( )

5 Giovanni Domenico Cassini ( ) The Original Imaging Science Subsystem

6 Giovanni Domenico Cassini ( ) The Original Imaging Science Subsystem Saturn, 1676

7 The Imaging Science Subsystem Science Objectives To map the 3-D structure and motions within the Saturn/Titan atmospheres. To study the composition, distribution, and physical properties of clouds and aerosols. To investigate scattering, absorption, and solar heating within the S/T atmospheres. To search for evidence of lightning, aurorae, airglow, and planetary oscillations. To study the gravitational interactions between the rings and Saturn's satellites. To determine the rate and nature of energy and momentum transfer within the rings. To determine ring thickness and sizes, composition, and physical nature of ring particles. To map the surfaces of the satellites (including Titan) to study their geological histories. To determine the nature and composition of the icy satellite surface materials. To determine the rotation states of the icy satellites.

8 The Imaging Science Subsystem Science Objectives To map the 3-D structure and motions within the Saturn/Titan atmospheres. To study the composition, distribution, and physical properties of clouds and aerosols. To investigate scattering, absorption, and solar heating within the S/T atmospheres. To search for evidence of lightning, aurorae, airglow, and planetary oscillations. To study the gravitational interactions between the rings and Saturn's satellites. To determine the rate and nature of energy and momentum transfer within the rings. To determine ring thickness and sizes, composition, and physical nature of ring particles. To map the surfaces of the satellites (including Titan) to study their geological histories. To determine the nature and composition of the icy satellite surface materials. To determine the rotation states of the icy satellites. Instrument Requirements Duel Focal Length: A Narrow Angle Camera (NAC) for high resolution images. Should have as long a focal length as practically possible, and a Wide Angle Camera (WAC) for context and broad spatial coverage, with a FOV 6 to 8 times larger than the NAC. Broad and identical spectral range in both cameras, from 1100nm to 200nm (compared to nm on Voyager and nm on Galileo). Improved filter wheel design (over the 8 filter Voyager and Galileo design), to increase the spectral range.

9 The Imaging Science Subsystem Science Objectives To map the 3-D structure and motions within the Saturn/Titan atmospheres. To study the composition, distribution, and physical properties of clouds and aerosols. To investigate scattering, absorption, and solar heating within the S/T atmospheres. To search for evidence of lightning, aurorae, airglow, and planetary oscillations. To study the gravitational interactions between the rings and Saturn's satellites. To determine the rate and nature of energy and momentum transfer within the rings. To determine ring thickness and sizes, composition, and physical nature of ring particles. To map the surfaces of the satellites (including Titan) to study their geological histories. To determine the nature and composition of the icy satellite surface materials. To determine the rotation states of the icy satellites. Instrument Requirements Duel Focal Length: A Narrow Angle Camera (NAC) for high resolution images. Should have as long a focal length as practically possible, and a Wide Angle Camera (WAC) for context and broad spatial coverage, with a FOV 6 to 8 times larger than the NAC. Broad and identical spectral range in both cameras, from 1100nm to 200nm (compared to nm on Voyager and nm on Galileo). Improved filter wheel design (over the 8 filter Voyager and Galileo design), to increase the spectral range. End Result: Narrow Angle Camera with 2 m focal length telescope and 2 wheel filter system. 24 filters 200 nm nm. Wide Angle Camera with 0.3 m focal length and 14 filters abandoned due to complexity, weight and cost: Replaced with spare Voyager era camera, 0.2 m focal length. 2 wheel filter system with 18 filters 380 nm nm.

10 The Imaging Science Subsystem Two Cameras, 1024 x 1024 CCD arrays (1 Mega Pixel). Thermally isolated and cooled to -90 ºC. Narrow Angle Camera (NAC): 6 micro radians per pixel. 0.35º field of view. Focal Length 2000 mm. 24 filters. Wide Angle Camera (WAC): 60 micro radians per pixel. 3.5º field of view. Focal Length 200 mm. 18 filters.

11 Narrow Angle Camera (NAC) Reflector, 95cm x 40cm x 33cm. Focal Length ± 0.07 mm. Spectral range nm. Limiting magnitude ~ 14. Thermally isolated from mounting kg. F/N FOV mrad. 12 x 2 filter wheels. CCD Filter Computer Reflecting Telescope Saturn

12 Wide Angle Camera (WAC) Refractor, 55cm x 35cm x 33cm. Focal Length ± 0.02 mm. Spectral range nm. Limiting magnitude ~ Not thermally isolated kg. F/N 3.5. FOV mrad. 9 x 2 filter wheels. Computer CCD Filter Refracting Telescope Saturn

To map the 3-D structure and motions within the Saturn/Titan atmospheres... Saturn s Aurora Borealis. Photographed in black and white, but given orange false colour.

13 To map the 3-D structure and motions within the Saturn/Titan atmospheres... Saturn s Aurora Borealis. Photographed in black and white, but given orange false colour. Actual colour of Saturn s aurora is unknown. 1,200 km high sheets, tallest aurora in the solar system! 472 NAC images over 81- hour period. Oct , visible light. Huge storm in Saturn s northern hemisphere. Image taken Dec. 24, 2010, storm had a latitudinal extent of 10,000 km, and was still active as of July Possibly connection to seasonal changes, Saturn s rings cast a shadow over the winter hemisphere. Nearly true colour WAC image. Dec. 24, 2010, visible light, from 1.9 million km.

To study the composition, distribution, and physical properties of clouds and aerosols... South polar vortex, revealing vigorous convective storms.

NAC, polarised visible and infrared filters. July 14 2008, from 392,000 km.

14 To study the composition, distribution, and physical properties of clouds and aerosols... South polar vortex, revealing vigorous convective storms. Similar in structure to hurricane on Earth, but locked to pole. Detailed close up, reprojected as if from above pole. NAC, polarised visible and infrared filters. July , from 392,000 km. Filters chosen so that methane gas is transparent, allowing a view deeper into atmosphere. Methane band filters show convective cells do not reach base of stratosphere, as they do on Earth. Oblique angle image, showing shadows. NAC, polarised infrared filters. July , from 778,000 km.

Methane clouds reflect more light than ground surface.

15 To investigate scattering, absorption, and solar heating within the S/T atmospheres... Equatorial storm clouds on Titan. Methane clouds reflect more light than ground surface. Passing of Saturn equinox in August 2009 has resulted in storms moving up from southern regions. NAC image, near-infrared filter + visible filter. Oct , from 2.1 million km.

16 To search for evidence of lightning, aurorae, airglow, and planetary oscillations... Saturn s Aurora Borealis. Photographed in black and white, but given orange false colour. Actual colour of Saturn s aurora is unknown. 1,200 km high sheets, tallest aurora in the solar system! 472 NAC images over 81- hour period. Oct , visible light.

17 To study the gravitational interactions between the rings and Saturn's satellites... Shepherd moon Prometheus (86 km) stretching streamers out of the F ring. Followed by Pandora (81 km), orbiting outside the F ring. NAC images, April , visible light, 1.2 million km.

Division contains many darker rings of contaminated ice. NAC, red, green and blue filters. Sep. 29 2006, from 1.8 million km.

18 To determine ring thickness and sizes, composition, and physical nature of ring particles... True colour image of rings, centred on Cassini Division looking towards unlit side. Division contains many darker rings of contaminated ice. NAC, red, green and blue filters. Sep , from 1.8 million km. Side on image of rings, plus crescent of Enceladus. Sunlight reflects of southern side of rings and brightens Saturn s southern hemisphere. WAC, polarised infrared light. Nov , from 1.7 million km.

19 To map the surfaces of the satellites (including Titan) to study their geological histories... Map of Mimas. Composite image produced from photos taken until July Resolution 216 m per pixel.

20 To determine the nature and composition of the icy satellite surface materials... Herschel Crater, Mimas. Dark markings at bottom of crater walls: Icy materials evaporate into space Impurities left to slide down crater wall. Relative lack of craters on Herschel floor. Examining Herschel Crater on Mimas. Composite of 7 NAC images and 1 WAC image (note reduced resolution in South), Feb , visible light, from 19,000 km.

21 References Porco, C.C., West, R.A., Squyres, S., McEwen, A., Thomas, P.C., Murray, C.D., DelGenio, J.A., Ingersoll, A.P., Johnson, T.V., Neukum, G., Veverka, J., Dones, L., Brahic, A., Burns, J.A., Haemmerle, V., Knowles, B., Dawson, D., Roatsch, Th., Beurle, K., and Owen, W., 2004, Cassini Imaging Science: Instrument Characteristics and Anticipated Scientific Investigations at Saturn, Space Science Review 115, Engineering Technical Write Up cassiniorbiterinstruments/instrumentscassiniiss/instcassiniissdetails/ Images, animations and descriptions available at the website of Cassini Imaging Central Laboratory for Observations: and at saturn.jpl.nasa.gov/photos/.

Saturn and Planetary Rings 4/5/07

Saturn and Planetary Rings 4/5/07 Saturn and Planetary Rings Announcements Reading Assignment Chapter 15 5 th homework due next Thursday, April 12 (currently posted on the website). Reminder about term paper due April 17. There will be