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Miller's Astronomy 1 lecture notes on Gas Giant Rings

Transcript of A1 12 Rings

  • 1.Rings of the Gas GiantsLACC 11.1, 11.4 Understand what conditions and processes shaped the gas giant planets ring systems: Roche limit, shepherding moons Know the following ring systems in some detail: Jupiter (dust from moons?), Saturn (recent break up of icy object?), Uranus (break up of a moon?), Neptune (unknown) Bright = icy and young, Dark = dusty and old An attempt to answer the big questions: what isout there? Are we alone?

2. Ring Systems http://www.jb.man.ac.uk/distance/strobel/solarsys/solsysb.htm 3. Ring Systems http://www.jb.man.ac.uk/distance/strobel/solarsys/solsysb.htm 4. Ring Systems Moons of Saturn: Moons of Jupiter: 1.Atlas 1.Metis 2.1980S27 2.Adrastea 3.1980S26 3.Amalthea 4.Janus 4.Thebe 5.Epimetheus 5.Io 6.Mimas 6.Europa 7.Enceladus 7.Ganymede 8.Telesto 8.Callisto 9.Tethys 9.Leda 10.Calypso 10.Himalia 11.Dione 11.Lysithea 12.1980S6 12.Elara 13.Rhea 13.Ananke 14.Titan 14.Carme 15.Hyperion 15.Pasiphae 16.Iapetus 16.Sinope 17.Phoebe http://www.astro.rug.nl/%7Eetolstoy/ACTUEELONDERZOEK/JAAR2000/moons/aoz.html 5. Jupiters Ring Jupiter's intricate, swirling ring system is formed by dust kicked up as interplanetary meteoroids smash into the giant planet's four small inner moons, according to... NASA's Galileo spacecraft.http://www2.jpl.nasa.gov/galileo/status980915.html http://pds.jpl.nasa.gov/planets/captions/jupiter/jupring.htm 6. Saturns RingsMost of the rings are only a few tens of metersthick with a total mass equivalent to a mediumsized moon. The rings are made out of particlesranging from microscopic dust to barnyard sizedboulders with perhaps a few kilometer-sizedobjects as well. ...the rings are composed mostlyof ice crystals with some impurities. Scientists once thought that the rings wereformed at the same time, as the planets whenthey coalescing out of swirling clouds ofinterstellar gas 4.8 billion years ago. Under thismodel, remnants of material within the Rochelimit could not condense and would becomerings. However, in recent years this idea seemsto be awed. The rings appear to be young,perhaps only hundreds of millions of years old.One of the clues to this theory is that the ringsare bright. As Saturn travels though space, therings accumulate dust particles that have beendarkened from solar radiation. If the rings wereold, they should appear dark. Another theorysuggests that perhaps a comet few too close toSaturn and tidal forces broke it into pieces....Perhaps one of Saturn's moons was struck byan asteroid smashing it into the bits and piecesthat form the rings. http://www.solarviews.com/eng/ http://pds.jpl.nasa.gov/planets/captions/saturn/2moons.htmsaturnrings.htm 7. Saturns Rings http://science.nasa.gov/headlines/y2002/12feb_rings.htm 8. Saturns Rings This image shows Saturn's rings and the shadow of nearby Mimas. They are now nearly edge-on toward the Sun, and long moon shadows drape across them. Scientists are now studying theclumpy, disturbed ring material, stretching up to two miles above the ring plane - contrasted with an estimated normal ringthickness of only six feethttp://www.dailymail.co.uk/sciencetech/article-1172205/Saturn-close-Sensational-cosmic-images-bring-ringed-planet-life.html 9. Saturns Rings:Shepherd Moons This composite of two images shows Pan, left, and Prometheus, right, in nearby rings. Pan is trailed by a series of edge waves in the outer boundary of the gap. Prometheus just touches the inner edge of Saturn's F ring, and is followed by a series of dark channels http://www.dailymail.co.uk/sciencetech/article-1172205/Saturn- close-Sensational-cosmic-images-bring-ringed-planet-life.html 10. Uranuss Ring(s)Radio measurements showedthe outermost ring, the epsilon,to be composed mostly of iceboulders several feet across.However, a very tenuousdistribution of ne dust alsoseems to be spread throughoutthe ring system. The particles that make up therings may be remnants of amoon that was broken by a high-velocity impact or torn up bygravitational effects.http://www.nineplanets.org/uranus.html http://pds.jpl.nasa.gov/planets/captions/neptune/neprings.htm 11. Shepherd Moons Shepherd moons work in pairs on the inner and outer edge of rings to gravitational push and pull (accelerate and de-accelerate) ring particles. The result is to conne the ring particles to within the shepherd moons orbits.http://pds.jpl.nasa.gov/planets/captions/neptune/neprings.htm 12. Neptunes (Rings) None of Neptunes rings were detected from scattering effects on Voyagers radio signal propagating through the rings, which indicates that they are nearly devoid of particles in the centimetre size range or larger. The fact that the rings were most visible in Voyager images when backlit by sunlight implies that they are largely populated by dust-sized particles, which scatter light forward much better than back toward the Sun and Earth.Their chemical makeup is not known, but, like the rings of Uranus, the surfaces of Neptunes ring particles (and possibly the particles in their entirety) may be composed of radiation-darkened methane ices. The present rings are narrow, and scientists have found it difcult to explain how the orbits of the known moons can effectively conne the natural radial spreading of the rings. This has led many to speculate that Neptunes present rings may be much younger than the planet itself, perhaps substantially less than a million years. The present ring system may be markedly different from any that existed a million years ago. It is even possible that the next spacecraft to visit Neptunes rings will nd a system greatly evolved from the one Voyager 2 imaged in 1989.http://www.britannica.com/EBchecked/topic/409330/Neptune/54304/The-ring-system 13. Rheas (Rings!? 6 March 08) http://planetary.org/news/2008/0306_A_Ringed_Moon_of_Saturn_Cassini.html 14. Ring Systems They are not stable; they evolve and change over time. Unless something replenishes them or keeps them from dissipating, they will not last longer than a few 100 millions years; one of Neptunes might not last a century. They generally form inside a planets Roche limit. Objects that come closer than this distance to a planet tend to be ripped apart by tidal forces. Since the gas giants have strong gravitational elds, they have strong tidal forces. Shepherding moons are moons that keep a ring system nice an tidy, by not letting material drift out of a ring and/ or into gaps.http://planetary.org/news/2008/0306_A_Ringed_Moon_of_Saturn_Cassini.html 15. HW Ch 11: Franknoi, Morrison, and Wolff, Voyages Through the Universe,3rd ed. Ch 11, pp. 263-264: 9. Ch 13: Image Analysis Quiz accessible from: http://www.brookscole.com/cgi-brookscole/course_products_bc.pl? d=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of next class period.Be working your Solar System project.