Jupiter from ground Jupiter is one of the favorite objects of the backyard astronomer who watch the cloud bands and Great Red Spot which grace the planet. The 4 Galilean moons (and sometimes their shadows on the planet) provide endless amusement.
Jupiters magnetosphere Jupiter has an enormous dipole magnetic field. The "official" rotation rate of the planet is that of the dipole field, which can be easily determined from radio observations. The dipole field is presumably anchored deep inside the planet. The surface features we see (cloud spot, Great Red Spot) rotate with different periods!
Jupiter vs Earth size
Voyager movie This movie was derived from images over a period of about 40 days from one of the Voyager spacecraft as it appoached Jupiter. The movie shows one image each Jupiter rotation period. The different cloud bands show differential rotation, proving that the disk we see cannot be a solid surface.
Belts and zones
Giant planet interiors Read words at next image.
Giant Planet interiors Model of interior of 3 outer planets. (Note that the temperature that reads 8E4 for Saturn should read 0.8E4) These are very uncertain, but suggestive of the overall structure. There are many sources of uncertainties. One prime uncertainty is the equation of state (EOS) of hydrogen and helium at the temperatures and pressures that hold deep inside these planets. Above something like 1E6 atmospheres of pressure, hydrogen is thought to be in a "metallic" state, where the electrons are not bound to individual nuclei, but form an electron gas, similar to the behavior of electrons in an ordinary metal. We simply cannot make this stuff in a lab, except for fleeting moments of high pressure in a pressure gun (see 8 April).
The models are made as for a star- we take all the physics and observations and attempt to make a self-consistent model, or set of density, pressure, temperature, composition at a number of radii. In many ways, it is harder to make a model of Jupiter than a model of the Sun- although the Sun has the complication of fusion, it has a simpler EOS!
The "ionic ocean" or "ionic slush" region is a region thought to be hot ionized water with dissolved NH3 (ammonia) and probably lots of other molecules and ions. It is hot ( a few thousand K) and partially ionized.
The terms "gas" "ice" and "rock" are used in a compositional context, rather than a physical state context by planetary modelers (which drives most students- and me - crazy). "Rock" is everything that condenses at 500 K or higher- eg Mg, Fe, Si. "Ice" is stuff that condenses between 50 and 500 K, including C, CH4, NH3,H20, CO, CO2. "Gas" is H and He.
Jupiter atmospheric probe Part of the Galileo spacecraft detached from the main spacecraft and went on a suicide mission into Jupiter.
Moons of the Solar System Shown to scale are all the large and medium sized moons of the solar system, along with some of the smaller ones. Top row is our Moon, then 2 moons of Mars. Next row is Jupiter moons. Next is Saturns, then Uranus and Neptune. Finally, Charon, moon of Pluto. Since this slide was made, two additional moons of Pluto have been discovered.
Jupiter's 4 big moons Io, Europa, Ganymede and Callisto. (I eat green cheese)
Jupiter and Io
Io Io , the pizza moon. Io is the most volcanically active place in the solar system (per square kilometer). The surface is covered with sulfur and sulfur dioxide frost from the volcanoes. (The average surface temperature is cold- about 130 K).
The following images show some of the volcanic features on Io.
Io volcano Because Io has only a tenuous atmosphere, volcanic eruptions spray out like a symmetric lawn sprinkler (but one that can be 10s to 100s of km high!). On Earth, volcanic eruptions are disrupted by winds.
Io lava flow
Io's changing face Images taken some time (??) apart show extensive changes in surface of one region of Io.
Europa Europa's surface is the smoothest of any major body in the solar system. It is composed mainly of ice. Europa has a very tenuous (1E-12 Earths atmosphere) atmosphere composed primarily of oxygen (O2). This is preseumably derived from solar UV photons breaking apart H2O molecules on the surface and near-surface of the moon. There are few impact craters on Europa, indicating a "young" surface.
Europa ice rafts This image (showing a region about 45 km across) show what is interpreted as a region of recent ice flow, resulting in chaotic ice rafts (now frozen in place). How thick is the ice on Europa? That, my friend, is the big question. Estimates range from 1 km to 100's of km.
Model of Europa interior Not to be taken too seriously! (I know you won't!) Europa may have an iron core, rock mantle, liquid ocean, and ice shell.
Ocean or ice? What is below Europas outer ice shell? Some clues (magnetic field, surface cracks in ice) suggest a salty subsurface H20 ocean!
Saturn Move aside Sauron, this is the real Lord of the Rings! (All the giant planets have rings, but the others pale to insignificance compared to Saturn's). The rings are composed of particles of almost pure H20, ranging in size up to meters across. The rings may have been formed by the tidal disruption of an icy moon about 300 km across (a "medium sized" moon). The age of the rings are hotly debated. The brightness of the ice argues for a recent origin (so that there has not been time for dust to darken the ice) but the particles have frequent collisions, which would break off "fresh" surfaces even in ancient ice.
The rings are a truly amazing physical system. They are extremely thin for their huge size. There are ring gaps which have moons in them, and ring gaps that don't. Although gravity is the dominant physics, there are some aspects that cannot be explained with gravity (like the spokes).
Saturn's rings at opposition As Saturn orbits the Sun every 29 years, we see the rings from a continuously changing orientation. Every 15 years or so there is a "ring plane crossing" when we see the rings exactly edgeon. The rings are so thin they literally disappear. A PRC is a good time to search for small moons in amongst the ring particles. The next RPC will occur in September, when Saturn, unfortunately, will be close to the Sun in the sky.
See APOD 19 March 2009 for a related image I didn't show in class.
Saturn and Earth
Saturn as seen from Voyager Voyagers 1 and 2 provided spectacular images of the outer planets, but were only flyby missions, so could not provide continuing coverage. Later missions were dedicated to individual planets and provided much more detailed information- Galileo to Jupiter and Cassini- Huygens to Saturn.
Saturn as seen from Voyager Spacecraft can of course see planets and moons from angles impossible to see from Earth. At Saturn, the interplay of shadows of the rings on the planet and shadow of the planet on the rings provide for many visually stunning images.
Saturn from Cassini Wow! One of my favorite images of Saturn. Its on a poster outside my office.
Another awesome Saturn image
Rings backlit Wow! An image of the rings seen backlit by Sun, which is behind Saturn. Very faint tenuous rings and clouds of dust are seen. The little dot outside the main rings just inside one of the fuzzy rings (on left side of Saturn- at about 9:30 position) is- us. (See APOD 11 January 2009, titled "In the Shadow of Saturn" - I like that title)
Cassini Saturn tour This shows a sample plan for Cassini orbiting Saturn. Only about half the orbits are shown. (Not sure how actual tour has compared to this, but the number of orbits must be similar). A far cry from the Voyager days, when the spacecraft got one brief encounter as it whizzed by the planet on its way to the next ( If this is Tuesday, it must be Saturn)
Rings in visible light and by radio occultation
"Spokes" in the rings These features rotate with the magnetic field of Saturn, not with the rings, so must be some sort of non-gravitational effect.
Earth and Titan Titan is larger in volume than Mercury (but less massive). Here it is shown with clouds digitally removed. Some of the dark areas on Titan may be lakes of liquid hydrocarbons! (See APOD 7 Feb 2007 and 30 May 2007 for some images of that I didn't show in class)
Titan in visible light Titan is the only moon with a substantial atmosphere. The atmosphere, mostly made of nitrogen (N2) has a surface pressure 1.5 sea level pressure here on Earth. The coloring is perhaps from chemicals more complex than hydrocarbons, perhaps molecules called tholins. The atmosphere is almost opaque in visible light, and is sometimes referred to as "smoggy" (presumably not from SUVs). Titan has a bit of a "reverse greenhouse effect", as the atmosphere is more transmissive in the IR than in the visible, unlike the atmospheres of Earth, Venus, and Mars.
Surface of Titan The Huygens Titan lander dropped from Cassini took these awesome pictures of the surface of Titan. The "rocks" are probably frozen methane or ethane. (See 17 January 2005 APOD).
Neptune Earth Uranus to scale Neptune and Uranus are sometimes called the "ice giants". The word "ice" here is used in a compositional, rather than a physical state, context. "Ice" is most everything between H and He (the gases) and silicon and iron.
Neptune The blue color is due to methane absorbing most of red light and perhaps an unknown coloring agent.
Uranus and Earth
Uranus A milder blue than Neptune, but still colored by methane. Looks like not much is going on in its atmosphere.