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Joel Schwartz Northwestern Physics & Astronomy May 13 th, 2013 Voyager 1 Image. Saturn. Nov 1980. LPI. 3 May 2013.

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Presentation on theme: "Joel Schwartz Northwestern Physics & Astronomy May 13 th, 2013 Voyager 1 Image. Saturn. Nov 1980. LPI. 3 May 2013."— Presentation transcript:

1 Joel Schwartz Northwestern Physics & Astronomy May 13 th, 2013 Voyager 1 Image. Saturn. Nov LPI. 3 May 2013.

2 Moons of Solar System. NASA SSE. 3 May 2013.

3 Discovery  All three satellites were first observed by Giovanni Cassini.  Iapetus: October 25 th, 1671  Rhea: December 23 rd, 1672  Tethys: March 21 st, 1684  These moons & Dione were originally called Sidera Lodoicea (The Stars of Louis) by Cassini, after Louis XIV.

4 Orbital Locations Orbital Diagram of Saturn Moons U. Cincinnati Physics- Gas Giants. 4 May 2013.

5 Etymology  Associated with siblings of Kronos, as suggested by John Herschel.  Tethys: Sister of Kronos & wife of Oceanus. Linked to rivers & water.  Rhea: Wife/Sister of Kronos. Referred to as the “Mother of the Gods.”  Iapetus: Brother to Kronos; father of Atlas & Prometheus. Considered the “Father of the Human Race” by the ancient Greeks.

6 Greek Titans Greek Titans (Various). Wikipedia. 4 May 2013

7 Previous/Current Space Missions  Pioneer 11: August-September 1979  Voyager 1: November 1980 (no Iapetus flyby)  Voyager 2: August 1981  Cassini-Huygens: July 2004 & onward  Initial images by Voyager 1 & 2, then more detailed photography by Cassini- Huygens.

8 Tethys (Saturn III)  Radius: 531.1km  Density: 985 kg/m^3  Vis. Geo. Albedo: 0.8  Semimajor Axis: 294.7k km  Period: days (tidally locked)  Inclination: 1.88° Cassini Image. Tethys. National Space Science Data Center. 4 May 2013.

9 Tethys (cont.)  Heavily cratered, but not to the extent of Rhea.  Largely water-ice with small amounts of rock.  Gravitationally holds Telesto & Calypso.  Quite noticeable is Odysseus Crater, prominent in the Western Hemisphere. Cassini Image. Tethys with Odysseus Crater. NASA SSE. 4 May 2013

10 Tethys (cont.)  Has a high visual geometric albedo.  Is bombarded by water-ice particles from geysers on Enceladus.  Has the Ithaca Chasma running roughly from the north to south pole. Voyager 2 Image. Tethys with Ithaca Chasma. 26 Aug NSSDC. 4 May 2013.

11 Composite Spectroscopy Data A Pair of Pac-Men. 26 Nov NASA SSE. 4 May 2013.

12 Rhea (Saturn V)  Radius: 763.8km  Density: 1240 kg/m^3  Vis. Geo. Albedo: 0.7  Semimajor Axis: k km  Period: days (tidally locked)  Inclination: 0.35° Cassini Image. Portrait of a Lady. 10 Mar NASA SSE. 4 May 2013.

13 Rhea (cont.)  Cold body with tenuous atmosphere; similar to Tethys.  Density suggests ¾ water-ice, ¼ rock, and homogeneous.  Due to distance from Saturn, Rhea does not receive significant tidal heating effects. Voyager 1 Image. Rhea Mosaic. Nov NSSDC. 3 May 2013.

14 Rhea (cont.)  Large amount of craters, which can be subdivided into two regions:  Heavy cratered bright terrain with diameters above 40km.  Polar & equatorial areas with smaller diameter craters.  “Wispy” subsidence fractures also present. Voyager 1 Image. Rhea, Enhanced. 12 Nov NSSDC. 4 May 2013.

15 False-Color Imaging  Saturn-facing view of Rhea from 35,000km.  Demonstrates hemispherical color and albedo differences.  Reddish hues near poles identify composition changes (multiple explanations). Cassini Image. False-Color Rhea. 2 Mar NSSDC. 4 May 2013.

16 Iapetus (Saturn VIII)  Radius: 734.5km  Density: 1090 kg/m^3  Vis. Geo. Albedo: 0.05 to 0.5  Semimajor Axis: k km  Period: days (tidally locked)  Inclination: 14.72° Voyager 2 Image. Iapetus. Aug NASA SSE. 3 May 2013.

17 Iapetus (cont.)  Similar to Tethys, density suggests composition of mostly water-ice.  Overall shape is not ellipsoidal, but rather “walnut.”  Has two recognizable features: ridge at equator & dual albedo. Cassini Image. Iapetus, Equatorial Ridge. NSSDC. 4 May 2013.

18 Iapetus (cont.)  Although 3 rd largest moon of Saturn, Iapetus orbits much further out than Titan.  Inclination is highest of all regular satellites, giving best view of Saturn’s rings.  Pattern of craters follows albedo: heavy in bright region, less elsewhere (Turgis seen here.) Cassini Image. Iapetus, Engelier Crater. NSSDC. 3 May 2013.

19 Equatorial Ridge  Around equator, Iapetus has a chain of ~20km mountains.  These break up on side facing away from Saturn into the bright Voyager Mountains.  Multiple proposed theories for ridge. Cassini Image. Voyager Mountains. 10 Sep NASA SSE. 4 May 2013.

20 Two-Tone Albedo Cassini Image. Global View of Dichotomy. 27 Dec NASA SSE. 4 May 2013.

21 Future Mission Prospects  Tethys, Rhea, & Iapetus are all devoid of many life-harboring properties.  Furthermore, there are other bodies in the Solar System which should have preferential scientific importance.  Marginally, Iapetus does have unique albedo & ridge features.  Even still, the prospect for future missions is understandably low.


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