Review: the giant planets and their moons

Comparing the planets These can be divided into two groups: terrestrial and Jovian The differences are obvious in Mass, Radius, and Average Density

Early Solar System Temperatures Differentiation in the early solar system caused most of the lighter material to condense out near Jupiter and Saturn

Jupiter Most of what we have learned about the Jovian planets has come from spacecraft. Voyager I and II Galileo spacecraft and probe Cassini spacecraft and the Huygens probe

Gravitational “Slingshots” are used for missions to the outer planets, to save energy or to allow heavier payloads.

Gravitational “Slingshots” were very successful in the Voyager missions to all four Jovians.

Jupiter’s Interior

Jupiter’s Atmosphere We know some things about the upper layers of Jupiter’s atmosphere from the probe that was carried by the Galileo spacecraft. It survived until it was about 150 km below what we call the “surface” of Jupiter.

Jupiter’s atmosphere has very obvious bands

Jupiter’s Convection Jupiter radiates about twice as much heat as it absorbs from the Sun, so the extra heat is coming from the interior. This creates Jupiter’s weather as the heat moves up from the interior.

Jupiter’s Red Spot is a very long-lived storm We first observed Jupiter’s Great Red Spot over 300 years ago

Jupiter’s Brown Oval was a temporary feature All jovian planets have differential rotation of their atmospheres. So the rotation depends on the latitude.

The Pioneer 10 spacecraft studied the magnetic fields All the Jovian planets have extensive magnetic fields Jupiter’s extends well past the orbit of Saturn!

Aurorae on Jupiter Aurorae have been seen on both Jupiter and Saturn. These are caused by the solar wind interacting with the magnetic field of the planet.

A Cometary Impact on Jupiter was seen in 1994.

Shoemaker-Levy 9 Comet Impact with Jupiter Tidal forces from Jupiter caused this comet to break up into a row of smaller objects. Then on a later orbit the fragments hit the atmosphere of Jupiter in 1994.

Shoemaker-Levy 9 Comet - Fragment G hit Jupiter. The impact left a huge dark mark in the atmosphere.

Moons of the solar system: 3 categories: 7 large (each is distinctive) 12 medium-size many small (most are captured)

Io Europa Ganymede Callisto Galilean Moons of Jupiter, shown in relative size. Two are similar in size to our Moon; two are similar in size to Mercury. Io Europa Ganymede Callisto

Galilean Moon Orbits

Galilean Moon interiors are quite distinct from each other

Io is the most volcanic object in the solar system, due to tidal forces between Io, Europa, and Jupiter

Io Notice the large ring of volcanic ejecta around a volcano

Io A volcanic plume is seen on the left limb. The plume is about 150 km high.

Io A volcanic eruption is seen in a caldera.

Europa, with an enhanced image on the right. A thick layer of ice covers the entire surface. An ocean under this layer might support life.

Ganymede is the largest moon in the solar system

Ganymede has an icy surface with cracks similar to those seen on Europa and other moons. The surface is older, darker, and has more craters.

Callisto has an even older and darker surface.

Jupiter’s Red Spot compared to the sizes of the four Galilean moons (in a photomontage)

Saturn Cassini is currently in orbit around Saturn and is continually sending back more data about Saturn and its moons.

Comparison of Saturn with Earth and Earth-Moon distance

Saturn’s atmosphere is similar to Jupiter’s Saturn’s atmosphere is similar to Jupiter’s. Although we sent a probe into Jupiter’s atmosphere, we are just guessing about Saturn. (Cassini data will be coming out soon.)

Uranus and Neptune Just one spacecraft (Voyager II) visited Uranus and Neptune. Both planets get their bluish color from methane in their atmospheres.

Uranus’s seasons are extreme due to its tilt

Jovian interiors Uranus and Neptune are sometimes called the “ice giants” because they have larger amounts of water ice, ammonia, and methane.

Jovian magnetic fields Uranus’ and Neptune’s magnetic fields have strange orientations, and are not at all aligned with the rotation of the planet. Saturn’s magnetic field is perfectly aligned.

Planetary Rings Rings around planets are important to understand because they allow us to test theories about the formation of the solar system. The early solar system was a disk-shaped nebula around a protostar, and it very likely had some of the features that we see today in the rings of the Jovian planets. The capture of ring material by shepherd moons, or the clearing of gaps in the rings, are critically important to the accretion process that formed large objects in the solar system nebula.

Saturn over four years of observation.

The Roche Limit is the radius at which a moon will fragment into pieces due to the tidal force and form the fragments that make up a ring.

Jovian Ring Systems are inside the Roche limit

Saturn’s rings, first quarter of full image.

Saturn’s rings, second quarter of full image.

Saturn’s rings, third quarter of full image.

Saturn’s rings, fourth quarter of full image.

Shepherd moons control the dynamics of parts of the ring.

The Encke gap in the rings, showing a twisted thin ring in the gap.

The Encke gap in the rings of Saturn The Encke gap in the rings of Saturn. Notice the spiral structure on the inner edge.

A shepherd moon causes waves in the edges of the Keeler gap in the rings of Saturn.

Jupiter’s faint rings were seen again in 2007 by the New Horizons spacecraft on it way to Pluto.

Rings of Uranus top picture shows detail of the outermost ring

Two shepherd moons were seen in one photo taken by the Voyager II spacecraft as it went by Uranus.

Neptune’s faint rings were seen in one photo from Voyager II.

The significance of Rings Rings around planets are important to understand because they allow us to test theories about the formation of the solar system. The early solar system was a disk-shaped nebula around a protostar, and it very likely had some of the features that we see today in the rings of the Jovian planets. (It was probably much thinner than the artists drawings!) The capture of ring material by shepherd moons, or the clearing of gaps in the rings, are critically important to the accretion process that formed large objects in the solar system nebula.

On Nov. 5, 2014, the ALMA observatory (in Chile) announced that they had obtained an image of a protoplanetary disk around a distant star. See the ALMA website for details (link)