Jupiter – key facts Largest and most massive planet in the Solar System: ~ 11 Earth radii and 318 Earth masses Composed primarily of H and He, but enriched in heavy elements compared to the Sun. Bulk composiFon: 71% H; 24% He; 5% heavier elements Rotates in just less than 10 hrs. Emits twice as much energy as it receives from the Sun – thermal energy generated by slow gravitaonal contracFon is radiated into space Internal heat and rapid rotaon combine to generate a turbulent atmospheric flow that stretches into eastward and westward directed winds called jets (c.f. the jet stream on Earth) Zones and belts represent different alFtudes in atmosphere (IR image on right) Jupiter – key facts Largest and most massive planet in the Solar System: ~ 11 Earth radii and 318 Earth masses Composed primarily of H and He, but enriched in heavy elements compared to the Sun. Bulk composiFon: 71% H; 24% He; 5% heavier elements Rotates in just less than 10 hrs. Emits twice as much energy as it receives from the Sun – thermal energy generated by slow gravitaonal contracFon is radiated into space Internal heat and rapid rotaon combine to generate a turbulent atmospheric flow that stretches into eastward and westward directed winds called jets (c.f. the jet stream on Earth) Zones and belts represent different alFtudes in atmosphere. Jupiter’s internal structure appears to consist of a rock+ice core lying at its centre with mass ~ 10 Earth masses. Central temperatures are ~ 20,000 K On top of this lies a mantle composed mainly of “metallic hydrogen” – a state of hydrogen that exists under extremely high pressures (> 106 atmospheres) in which it behaves as a liquid and the electrons are stripped off atoms making it electrically conducFng On top of this lies an layer of molecular hydrogen (+ helium and molecules such as ammonia). The rapid rotaon of Jupiter combined with the electrically conducFng metallic hydrogen give rise to a powerful magneFc field – 20 Fmes stronger at the surface of Jupiter than the Earth’s field is at the surface of the Earth. Jupiter has a reFnue of 67 confirmed moons: the 4 galilean satellites and a collecFon of much smaller objects (called irregular satellites) many of which appear to be captured asteroids/comets in inclined, eccentric and oden retrograde orbits Io – the closest of the galilean satellites. Volcanically acFve due to internal heang caused by Fdal flexing by Jupiter’s gravitaonal field because of Io’s eccentric orbit. Mean density suggests it is largely made of rock. Europa – in a 2:1 orbital resonance with Io caused by Jupiter’s Fdes expanding the orbits of the galilean satellites. Mean density suggests Europa composed largely of rocky material. Images and spectroscopy indicate a smooth surface made of water ice. Lack of craters suggests regular resurfacing by a liquid ocean lying ~100 km below the ice crust. Further evidence for subsurface ocean is provided by Europa’s magneFc field which requires the presence of an electrically conducFng fluid. Ganymede – the largest and most massive satellite in the solar system. In a 2:1 resonance with Europa. Mean density suggests this satellite is largely icy, but with an iron and rocky core. Surface shows different ages suggesFng that a semi-liquid mantle may exist under the icy crust Callisto – the most distantly orbiFng of the galilean satellites. Mean density suggests that Callisto is largely icy. Its highly cratered surface indicates that it is an ancient surface, not subject to renewal by erupFons from an interior mantle. The galilean satellites are believed to have formed in a disc of gas and rocks that surrounded the young Jupiter, just like the planets formed around the Sun. Saturn – key facts The second largest and most massive planet in the solar system: approximately 100 Earth masses or ~1/3 of Jupiter’s mass Similar bulk composiFon to Jupiter, but significant deficiency of He in atmosphere - suggesFng that He is “raining out” of the atmosphere. This also leads to Saturn radiang more heat than it receives from the Sun. The spin period is ~ 10 hrs. Rapid rotaon combined with internal heat generates turbulence and jets. Bands and zones are present but less disFnct than on Jupiter because of hazes high in Saturn’s atmosphere. Hosts an impressive ring system and a large collecFon of satellites (62 confirmed in total): 1 large moon, 6 moderate sized moons, and a large collecFon of small irregular satellites. Titan is only moon in solar system with significant atmosphere. Saturn – key facts The second largest and most massive planet in the solar system: approximately 100 Earth masses or ~1/3 of Jupiter’s mass Similar bulk composiFon to Jupiter, but significant deficiency of He in atmosphere - suggesFng that He is “raining out” of the atmosphere. This also leads to Saturn radiang more heat than it receives from the Sun. The spin period is ~ 10 hrs. Rapid rotaon combined with internal heat generates turbulence and jets. Bands and zones are present but less disFnct than on Jupiter because of hazes high in Saturn’s atmosphere. Hosts an impressive ring system and a large collecFon of satellites (62 confirmed in total): 1 large moon, 6 moderate sized moons, and a large collecFon of small irregular satellites. Titan is only moon in solar system with significant atmosphere. Saturn’s interior is similar to that of Jupiter: a rock+ice core surrounded by a mantle of electrically conducFng liquid metallic hydrogen, on top of which sits an envelope of molecular hydrogen. The existence of a metallic hydrogen layer combined with the rapid rotaon leads to generaon of a magneFc field whose strength at Saturn’s surface is about 3% of Jupiter’s. Saturn’s rings are composed of small icy parFcles ranging in size from 1 cm to 5 m, with the most abundant being ~ 10 cm. A small telescope from Earth allows the more massive A and B rings to be observed, along with the Cassini division. Observaon of the lower density D, C, F, G and E rings require either larger telescopes or in situ space cra such as Voyager or Cassini. Saturn’s rings are highly structured due to the gravitaonal influence of embedded moons and more distantly orbiFng satellites. The Cassini division is a gap between the B and A rings that coincides with a 2:1 orbital resonance with the satellite Mimas. The gap is created because material located there has a conjuncFon with Mimas every two orbits, leading to regular gravitaonal perturbaons that remove parFcles from locaons in the vicinity of the 2:1 resonance. The Keeler gap is formed and maintained by a small embedded satellite Daphnis. Wave-like features are observed at the edges of the gap induced by the gravitaonal perturbaons due to Daphnis. These perturbaons create and maintain the gap through a process of angular momentum and energy exchange between the parFcles in the ring and the satellite. ParFcles orbiFng interior to Daphnis orbit faster and are tugged back by the satellite’s gravity as they overtake it. They lose angular momentum and move onto orbits slightly closer to Saturn. The opposite happens to parFcles that orbit outside Daphnis, and they move onto orbits slightly further from Saturn, creang the gap. Collisions between ring parFcles have the effect of trying to close the gap, so a balance is maintained between satellite perturbaons on the ring material and collisional spreading of the ring parFcles. A pair of satellites can also act to shepherd and maintain a narrow ring. Saturn’s F-ring is shepherded by a pair of satellites that orbit interior (Prometheus) and exterior (Pandora) to the ring. Saturn has 6 medium sized regular satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus) and one large satellite (Titan – the 2nd largest satellite in the solar system). All of these regular satellites are located outside of the so-called Roche zone where the Fdal forces of Saturn would disrupt a body held together by its own gravity. The rings lie inside of the Roche zone. Enceladus is an icy moon with clearly defined linear surface features that appear to be the source of cryo- volcanic acFvity. Geysers of ice parFcles and water vapour are acFve in the regions covered by blue stripes. The ice parFcles act as the source of the E-ring. The presence of these geysers indicates a heat source – most likely Fdal damping by Saturn of Enceladus’ orbital eccentricity that is maintained by its gravitaonal interacFon with Dione with which it shares a 2:1 resonance, similar to the Jovian satellites. Titan is the only moon in the solar system with a dense atmosphere. The atmosphere extends ~ 200 km from Titan’s surface, and is composed primarily of nitrogen with a mixture of organic compounds such as methane (CH4) and ethane (C2H6). The image to the right is a composite of visible and IR images taken by the Cassini spacecra. Temperatures near Titan’s surface (~95 K) allow methane and ethane to exist in vapour, liquid or solid phases. Exploraon of Titan by the Huygens probe in 2005 demonstrated the existence of river channels caused by liquid ethane and methane on the surface which falls as rain from the atmosphere. The surface was imaged by the probe showing the landing site to be strewn with ice boulders. Uranus – key facts Uranus is the inner-most of the ice-giant planets and has a featureless surface. The most unusual fact about Uranus is that its rotaon axis is Flted by ~98o relave to its orbital angular momentum vector – this is assumed to arise because Uranus experienced a giant impact with a smaller planetary body shortly aer formaon.