THE 8 PLANETS
NEXT STOP: SATURN!
Poor Saturn is neither the largest nor the most massive. But this planet may be most eccentric— memorable in its appearance and properties. Named after the Titan of Time, Saturn was the Roman king of the Titans and father of Jupiter. Saturn is the least dense planet, even less dense than water! How does this happen? Saturn is only 1/8 the density of Earth, but with its large volume, is over 95 times more massive than Earth. Comprising mainly of the lightest element, hydrogen, Saturn is very “light” for its size. Saturn’s mass is 95 times that of Earth, but its volume is 764 times that of Earth. Since density = mass/ volume, Saturn’s large volume and relatively small mass equates to a very small density (0.687). So, if you build an enormous bathtub and fill it with H2O, Saturn would bobble around on the surface like a rubber duckie! In contrast to Jupiter’s myriad of colorful bands and zones, Saturn’s upper atmosphere of mainly ammonia crystals gives the planet a bland yellow-brown coloration. Once every 30 years, Saturn exhibits ephemeral storms on its banded surface, one known as the Great White Spot. At its North Pole, Saturn has a weird hexagon-shaped storm that may be a novel aurora or a wave pattern. Underneath that banal surface, winds reach up to 1,100 mph, faster than those on Jupiter! Unlike its ever-changing gaseous layers, Saturn’s core may be solid iron, nickel, and rock. Reaching up to 11,700 °C at the core, Saturn radiates 2.5 times more energy than received from the Sun by the Kelvin-Helmholtz mechanism of slow gravitational compression and the “raining out” of droplets of helium in its interior. Accumulating into a helium shell surrounding the core, the helium droplets release heat by friction passing though low density hydrogen. Layers of metallic hydrogen (deep), liquid hydrogen and liquid helium (intermediate), and hydrogen gas (outer) blanket the core. Electrical currents within the metallic hydrogen caused Saturn’s weak magnetic field to form. Effective at deflecting solar wind particles, Saturn’s magnetosphere also produces aurorae. Saturn has magnificent, highly reflective ice rings, perfectly visible with a telescope. All gas giants have rings, but with nine main continuous rings, three discontinuous arcs if ice particles, rock debris, and dust, Saturn and its rings are truly inseparable. In 1655, Christiaan Huygens suggested Saturn was surrounded by a ring. Since then, astronomers have named the main rings from A to G. The Cassini Division is a large gap between rings A and B, and the Roche Division is a gap between rings A and F. Some moons, like Pan and Prometheus, are shepherd moons that prevent Saturn’s rings from expanding.
Saturn has the second most number of moons with 62. Inhabit Saturn’s rings, Saturn’s moons range from the hundreds of “moonlets” to its largest natural satellite Titan. Of its 62 known moons, Saturn has 53 with actual names, 13 with diameters larger than 50 km, 7 with hydrostatic equilibrium due to planetary mass, dense rings, and complex orbits of their own, 24 regular satellites (prograde orbits not greatly inclined) named after Titans and Titanesses, and 38 irregular satellites with farther orbits and high inclination orbits and named after Inuit, Norse, and Gallic mythological characters. There can be no objective boundary for the classification of Saturn’s moons, for Saturn’s rings contain objects from the microscopic to the largest object Titan.
The most prominent is Titan. Larger than Mercury, Titan is the only moon to retain a substantial atmosphere. Titan produces white convective clouds in cold nitrogen and methane atmosphere. Its surface is relatively young with few impact craters, dark regions of frozen hydrocarbons, flow channels, volcanoes, and sand of frozen water or hydrocarbons. The only moon with large bodies of methane/ ethane lakes, Titan, like Ganymede and Europa (Jupiter’s moons) may have a subsurface ocean of water and ammonia. The largest lake on Titan, Kraken Mare, is larger than the Caspian Sea.
BRIEF TAKES ON OTHER PROMINENT MOONS
MIMAS: smallest and least massive of inner round moons, large impact crater called Herschel, no known geologic activity
ENCELADUS: one of the smallest of Saturn’s spherical moons, smallest known body geologically active, diverse surface that includes ancient heavily cratered terrain and younger smoother areas, south pole unusually warm and emits jets of water vapor and dust that replenishes material in Saturn’s E Ring and is the main source of ions in Saturn’s magnetosphere, may have liquid water under south pole, pure ice and high reflective surface
TETHYS: third largest inner moon, large impact crater called Odysseus, cast canyon system called Ithaca Chasma, composed of mainly water ice with little rock
DIONE: second largest inner moon, heavily cratered old terrain, extensive system of troughs and lineaments named “wispy terrain” indicates tectonic activity
RHEA: second largest moon, only moon that has rings, two large impact basins called Tirawa and Inktomi (“The Splat”), a young crater which has butterfly-shaped bright rays, geologically dead
HYPERION: closest moon to Titan (when Titan makes four revolutions, Hyperion makes three), very irregular shape, sponge-like tan-colored icy surface, numerous impact craters, no well-defined poles or equator (chaotic rotation) which makes its rotational behavior unpredictable
IAPETUS: third largest moon, most distant large moon, greatest orbital inclination (orbits at a greater altitude, at 14.72°), one hemisphere is pitch-black (Iapetus’s leading hemisphere collides with dust and ice particles as it rotates, darkening its surface) and the other is bright as snow
MISSIONS: Cassini-Huygens, Pioneer 11, Voyager
- Order in Solar System: #6
- Number of Moons: 62
- Orbital Period: 29.5 years
- Rotational Period: 10.5 hours
- Mass: 5.6846 x 10^26 kg (95.152 Earths)
- Volume: 8.2713 x 10 ^14 km³ (763.59 Earths)
- Radius: 60,268 km (9.4492 Earths)
- Surface Area: 4.27 x 10^10 km² (83.703 Earths)
- Density: 0.687 g/cm³ (less than water!)
- Eccentricity of Orbit: 0.056
- Surface Temperature (Average): 134 K
- Escape Velocity: 35.5 km/s
- Apparent Magnitude: +1.47 to -0.24
On December 3, 2012, the planets Mercury, Venus, and Saturn will align with the Giza Pyramids in Egypt. This will be the first planetary/pyramid alignment in 2,737 years! Now, the three Giza pyramids are also in perfect alignment with the three stars of Orion’s belt. In 1983, Robert Bauval proposed this Orion correlation theory and published this idea in Discussions in Egyptology in 1989. The Giza pyramids were built in the 3rd millennium B.C. The alignment is very curious. Could the Egyptians have built the Giza pyramids that way on purpose?
- Eccentricity of Orbit: measures the ellipticity of orbit (ranges 0-1, with 0 as spherical and 1 as very elliptical)
- Density: mass per unit volume; mass in grams and volume in cubic centimeters
- Oblateness: measures how much the middle section of the planet bulges
- Surface Gravity: the larger the surface gravity, the thicker the atmosphere as gravity pulls in more gases
- Albedo: measures the fraction of light reflected compared to the amount of light received from the Sun; the higher the albedo, the more reflective the surface
- Escape Velocity: minimum speed or velocity needed to escape the planet’s gravitational pull
- Rotation: most planets rotate in counter-clockwise direction (prograde); others rotate in the clockwise direction (retrograde)
- Rotational period is shortest for gaseous planets and longest for Venus
- Roche Limit: about two and a half times the radius of the planet; within the Roche Limit, matter cannot accretes to form moons because the tidal force of the planet tears matter apart to form rings
Giant Planets: Giant planets have lighter elements such as hydrogen and helium in their atmospheres. They have stronger gravity and are at larger distances from the Sun. Jupiter, Saturn, and Neptune are stormy with great spots of lasting storms and belts and zones. However, Uranus is comparatively bland and uniform. All giant planets are home to convection, or hot gases rising and cold gases falling.
Terrestrial Planets: Terrestrial planets have heavier elements such as carbon, oxygen, and nitrogen. Mercury is most heavily cratered while Earth is least cratered. Larger terrestrial planets have plate tectonics. Earth has a sizable magnetic fields that can protect it from solar wind particles and Van Allen Belts. Earth has the “Goldilocks phenomenon,” or the right conditions for the development of life.
“The Planets” page under “The Solar System” is now complete. The outer planets, Jupiter, Saturn, Uranus, and Neptune, have been added with brief summaries and pictures. Enjoy! See the page here.