Our Planetary System - Jovian Planets
Our solar system has only 2 important objects Ė Sun and Jupiter. Jupiter is so much more massive than anything else in the solar system (other than the Sun), the rest of the planets and other items are just debris. Also, with the moons of Jupiter the way they are, itís like a mini solar system within the solar system.
Differential rotation = I go this way, you go that way. The bands on Jupiter show this with some going easterly and some westerly.
The flattening of Jupiter requires that there is a relatively small (compared with the size of Jupiter), dense core at its center.
Galileo showed that even very deep in the atmosphere, Jupiter has winds that move very fast. This is thought to be due to heating from the planet, not the Sun. Galileo also showed us about the four main moons, including that Ganymede has a weak magnetic field, meaning it has a slushy liquid water under its surface.
The Great Red Spot is a giant hurricane that has raged for over 300 years on Jupiter. Nobodyís really sure of what the energy is thatís formed it, but it appears to be caught between two of the bands, which keep convection turning the hurricane, and keeping it in a steady position.
Jupiter has a very high escape velocity. Because of this, the original atmosphere and hydrogen have not been able to escape.
Jupiterís current source of energy cannot be radioactive (the numbers are too low), nor nuclear fusion (core is not hot enough). Itís thought to be the slow escape of gravitational energy released during the planetís formation.
Because of theoretical modeling based on mass, density, rotation, temperature and composition, it is believed that Jupiter gets denser and denser the deeper you go. Eventually, the hydrogen gets so dense that it becomes a liquid. This conductive liquid area of the planet would also account for the gigantic magnetic field.
Jupiter and its moons are like a mini solar system. The rocky moons form closest to the planet, with the less dense, icy objects further away.
The surface of Europa is water ice, with cracking and motion. The cracking and motion suggest that below the ice is liquid water. Tidal flows crack the ice, and allow water to flow up, which then freezes.
Ganymede is not as heavily cratered as Callisto. Just as cratering caused the Earthís moon to have maria come up to the surface, the same pattern happened with Ganymede, but Ganymede had water not lava.
The Galilean moons closest to Jupiter show less cratering than those further away. The reason is not due to location, but rather activity. Io shows almost know cratering, and the same for Europa (although there is a little more). Ganymede has a lot of cratering, and Callisto even more so.
Europa shows evidence of having liquid water beneath its surface. Also, the moon has a weak magnetic field, indicating that the water is salty. This would be strong indication that thereís a possibility of life under the icy surface of Europa.
Discovery of life on Europa would make it more likely that there are other planets with life on them.
Of the Galilean moons, Europa has more water than on Earth. Water is also on Ganymede (the largest moon in the solar system), and in Callipso. Water is very common among the Jupiter moons.
Jupiter has no solid surface.
Storms in Jupiterís atmosphere are generally much longer lived than storms on Earth.
Helium does not play an important role in producing the colors in Jupiterís atmosphere. Itís convection of the bands that cause the light colored zones and dark colored belts.
Jupiter is noticeably flattened due to its rapid rotation.
Jupiter emits more energy than it receives from the Sun.
Although often referred to as a gaseous planet, Jupiter is mostly liquid in its interior.
Because of Jupiterís strong tidal force (not magnetic field), the Galilean satellites rotate synchronously with their orbits around the planet.
Io is not the only moon in the solar system with active volcanoes.
Scientists speculate that Europa may have liquid water below its frozen surface
Ganymede shows evidence of ancient plate tectonics.
Compared with Earthís orbit, the orbit of Jupiter is approximately 5 times larger.
Compared with Earthís density, the density of Jupiter is much less.
According to Figure 11.7 (ďJupiterís AtmosphereĒ), if ammonia and ammonium hydrosulfide ice were transparent to visible light, Jupiter would appear bluish.
Jupiterís rocky core is larger than Earth.
Ioís surface appears very smooth because it is continually resurfaced by volcanic activity.
The Galilean moons of Jupiter are sometimes described as a miniature inner solar system because the moonsí densities decrease with increasing distance from Jupiter.
Ring crossing is where the rings disappear because we are looking at them head on. The next time that this will happen is this year, in 2010. The last time it happened was in 1996.
Saturnís clouds are thicker, and there are fewer holes and gaps to see past the top layer. Therefore, we rarely get to see the colorful levels below as we do on Jupiter.
Saturnís shape is oblong due to the flattening from the rotation. Because the degree of flattening is less than a planet made entirely of hydrogen and helium alone, astronomers believe Saturn has a rocky core that is perhaps twice the mass of Jupiterís.
Saturnís atmosphere is roughly 200 km compared to Jupiterís of 80 km. Saturnís is much thicker. This is due to Saturn having a weaker gravity than Jupiter. Jupiterís is more compressed.
Jupiter consists of about 13.8% helium. Saturn, however, has only about 7.4%. Saturn is deficient in helium compared to Jupiter.
Galileo first saw Saturnís rings in 1610, but didnít realize what they were. Huygens in 1655 was the first to realize that they were rings.
If a satellite got too close to Saturn, within the Roche limit, it would be ripped apart by tidal forces.
There are two thoughts on the formation of the rings: left over material from Saturnís creation, or a satellite got too close and broke up. All the activity observed in the ring indicate that it must be relatively young, no more than 50 million years old. Itís too young to be left over material, so it must be material from a moon.
Mimas (the death star moon) is close to the rings, and its resonant interaction with ring particles causes the Cassini division.
Titan has a very thick atmosphere. Because of this, when Voyager flew by, it was unable to see through the haze layer to the surface.
Titan is just a little smaller than Ganymede. It is large like the Galilean moons. Titan has an atmosphere, unlike the Galilean moons. As with the Galilean moons, it most likely has a rocky core surrounded by a thick mantle of water ice.
Itís believed Titan has a thick atmosphere while other large moons do not due to the distance it is from the Sun. Since itís further away, it formed where it was cooler. This allows for more water ice to absorb methane and ammonia. As a result, Titan had more methane and ammonia gas than Ganymede and Callisto.
Enceladus shows no sign of impact craters, which means that theyíve been erased by water. It is covered by fine crystals of pure ice, which reflect almost 100% of the sunlight falling on it.
Co-orbital satellites share an orbit. They orbit at different distances, but at some point, they switch tracks with the one that was on the outside moving to the inside track, and the one that was on the inside moving to the outside track.
Hyperion has a chaotic rotation. Because of this, the sun would almost never rise in the same place, and wouldnít set opposite it either. It could be possible for the sun to rise, and then set in the exact same spot. As with the moon, Saturn would be swinging around in the sky all over the place.
Saturn has an icy/rocky core.
As with Jupiter, Saturn has many storms including the long lived dragon storm.
Relative to Jupiterís atmosphere, Saturnís atmosphere is deficient in helium.
All of the gas giants (Jupiter, Saturn, Uranus and Neptune) have rings.
The composition of Saturnís ring particles is predominantly water ice.
Although Saturnís ring system is tens of thousands of kilometers wide, it is only a few tens of meters thick.
Saturnís rings exist because they lie within the planetís Roche limit.
Two small shepherd satellites are responsible for the unusually complex form of Saturnís F ring.
Titanís surface is obscured by thick ammonia haze and methane clouds.
Astronomers do not think Titan is covered with water. It does have methane lakes, however.
The next time Saturnís rings will appear roughly edge-on as seen from Earth will be around 2010.
The winds on Saturn are fastest at the equator.
Saturnís icy-rocky core is roughly 10 times more massive than planet Earth.
The atmospheric pressure at the surface of Titan is about one-and-a-half times greater than the atmospheric pressure at Earthís surface.
A tidally locked moon of Saturn always presents the same face to the planet.
The moons Telesto and Calypso, orbiting at the Lagrangian points of Saturn and the moon Tethys always stay the same distance apart.
Uranus and Neptune
William Herschel discovered Uranus by accident while mapping faint stars.
The orbit of Uranus did not fit any models. Therefore, it was determined that there must be another planet affecting the orbit.
After realizing that there must be another planet affecting Uranusís orbit, mathematicians determined the new planetís mass and orbit. Galle then found the planet within a few degrees of the calculated location.
Nobody really knows why Uranus is spinning on itís side. Therefore, most astronomers think it must have been hit by something big.
Neptune has an internal heat source. Because of this, itís slightly warmer than Uranus. This makes the upper atmosphere warmer. This, along with less haze, makes it easier to see into Neptune than Uranus.
The magnetic fields of Uranus and Neptune are about a hundred times stronger than Earthís.
A day on Titania would be either really cold or really really cold. It orbits Uranus in the same skewed equatorial plane. Therefore, half of the Uranus year it has the north pole toward the Sun, and the other half of the year, the south pole is pointed toward the Sun.
Miranda has a wide range of surface terrains. It appears to have been catastrophically broken up many times, and gravity pulled the pieces back together in a chaotic way.
Neptuneís moon system does not have a regular moon system (no moons on roughly circular, equatorial, prograde orbits) as the other Jovian worlds do. Because of this, itís believed the moons are actually captured bodies rather than moons that formed at the time the planet did.
Since Triton has a retrograde orbit, it is spiraling into Neptune. Eventually, it will get within the Roche limit and be torn apart, creating a new ring around the planet.
Uranusís rings were discovered by stellar occulation as the rings passed in front of a bright star, momentarily dimming the star.
Neptuneís rings were discovered by Voyager 2.
Shepherd satellites and small inner satellites play a part in the appearance of Uranusís rings.
Neptune is only surrounded by five rings that are dark, and extremely thin. They have clumping which causes ďholesĒ in the rings.
Uranus was the first planet discovered in over 2000 years. Itís doubtful that there will be another planet discovered in our solar system, but we are finding exo-planets. We probably wonít see one in our own solar system, because all of the large bodies have been found. Everything else is about the size of Pluto, and itís not worthy of being a planet according to some geocentric (self-centered) astronomers who canít accept that Pluto rocks.
Since its discovery, Uranus has completed just two-and-a-half orbits of the Sun.
During the northern summer of Uranus, an observer near the north pole would observe the Sun high and almost stationary in the sky.
Uranusís rotation axis is almost parallel to the plane of the ecliptic.
Voyager 2 observed nitrogen geysers on the surface of Neptuneís moon Triton.
The magnetic fields of both Uranus and Neptune are highly tilted relative to their rotation axes and significantly offset from the planetsí centers.
Tritonís orbit is unusual because it is retrograde.
Neptune was discovered due to its gravitational effect on Uranus.
The radius of Uranus was determined accurately by observing the planet pass in front of a background star during the late 1970s.
Triton is smaller than Earthís Mass.
Neptune does not have the most extensive ring system in the solar system. That goes to Saturn
The discovery of new planets mostly requires the patient use of improving technology.
Uranus was discovered about the same time as the U.S. Declaration of Independence.
Compared with Uranus, the planet Neptune is roughly the same size.
The five largest moons of Uranus all orbit directly above the planetís equator.
Moons that show few craters probably have warm interiors.
A gas giant planet orbiting a distant star would be expected to have evidence for hydrogen in its spectrum.
The solar system object most similar to Neptune is Uranus.