10. Saturn: lord of the rings
- Saturn has the lowest
mass density of any planet in the solar system, low enough for the planet to
float on water, and this means that Saturn is primarily composed of the
lightest element hydrogen.
- Saturnís rapid rotation
has pushed its lightweight material out in the planetís middle, creating the
most pronounced equatorial bulge of any planet.
- Saturn is just a great
big liquid drop, covered by a thin atmosphere of gas, slightly smaller than
Jupiter and less than a third of its mass.
- Liquid hydrogen is
compressed inside Saturnís depths to form an electrically conducting, liquefied
- There is no solid surface
anywhere inside Saturn, though it might have a core of melted ice and molten
rock that is about ten times as massive as the Earth.
- Saturn radiates almost twice as
much energy as it receives from the Sun, and most of the planetís excess heat
is generated by helium raining down into its liquid metallic hydrogen core.
- Saturnís rings are completely
detached from the planet and separated from each other.
- The rings of Saturn are not
solid, but instead composed of innumerable small water-ice particles and larger
chunks of water ice.
- The icy constituents of Saturnís main A, B and C rings are
as big as hailstones, snowballs and even icebergs; there are more smaller ones,
but the big kind supply most of the ring mass.
The total mass of the rings of Saturn is comparable to that of its medium-sized
satellite Mimas, which is 396 kilometers across.
- Saturn has a retinue of diffuse,
tenuous, and nearly transparent rings, designated the D, E, F and G rings, that
are most likely composed of microscopic ice crystals, smaller than snowflakes
and about the size of the dust in your room.
- Two small moons confine the edges
of Saturnís narrow F ring and shepherd the ring particles between them.
- The icy material in the prominent
rings of Saturn has been marshaled into thousands of individual ringlets,
resembling ripples on a pond, but with circular, oval and even spiral shapes.
- Gravitational interaction with
nearby, external satellites can sculpt Saturnís ring material into numerous
ringlets and produce waves in it.
Small moons embedded within Saturnís rings can sweep out gaps, keeping them
open and also sharpening their edges.
The gaps within Saturnís rings are not completely empty; the Cassini Division
contains about 100 ringlets.
- Enigmatic dark spokes stretch radially across Saturnís
rings, moving at constant speed regardless of distance from the planet, in
apparent violation of the laws of gravity.
- Saturnís dark ring spokes consist of
microscopic dust-sized particles that may become electrically charged and
levitated above the larger ring particles. They might then be swept around
Saturn by its rotating magnetic fields.
- Planetary rings lie closer to a
planet than its large satellites, within the Roche limit where the planetís
tidal forces will rip a large satellite to pieces and prevent small bodies from
coalescing to form a larger moon.
- The rings of Saturn could have
formed when a moon was pulled toward the planet by tidal forces and eventually
- Small moons embedded in the rings
of Saturn might sustain them.
- Saturnís relatively small moon
Enceladus emits jets of ice particles, powdery snow, water vapor and organic
compounds, which vent from warm fissures, known as tiger stripes, in the moonís
south polar crust.
- The active jets on Enceladus
suggest that tidal effects may make the moon hot inside. The tiger-stripe
fractures could rub against each other, creating heat, or open to expose
explosive ice to the vacuum of space. The interior ice might be melted into
underground seas of liquid water containing organic chemical elements.
- Saturnís largest moon, Titan, is
a planet-sized world with a substantial atmosphere whose surface pressure is
about 1.5 times the air pressure at sea level on Earth.
- Titanís atmosphere is composed of
98.4 percent molecular nitrogen, nearly 1.6 percent methane, and trace amounts
of other hydrocarbons; so nitrogen molecules are the main constituents of
Titanís atmosphere, as they are in the Earthís air.
- Hazy smog, composed of complex
organic molecules, envelops Titanís atmosphere and hides its surface from view.
- The Huygens Probe touched down on the surface of Titan on 14 January
2005, detecting methane rainfall and dark narrow riverbeds on the way down.
The probe landed at equatorial latitudes, on a damp, moist riverbed littered
with pebbles that were apparently rounded by flowing liquid.
- Radar pulses from the Cassini spacecraft in orbit about Saturn
have seen through the haze that shrouds Titan, revealing long, deep meandering
channels on Titanís surface, which resemble terrestrial rivers but are
attributed to flowing methane or ethane rather than water.
- The Cassini radar instrument has imaged dark, flat, smooth places with
shore-like boundaries. They have been attributed to large lakes of liquid
methane and ethane, and the spectral signatures of liquid ethane have been
detected in at least one of them.
- Seasonal variations might account
for the fact that there are now about 20 more lakes at high northern latitudes
on Titan than high southern ones. Clouds may rain methane during winter in the
north, when southern lakes are evaporating in the local summer.
Vast dunes accumulate near Titanís equator, shaped by strong winds blowing east
to west. Unlike Earthís sand dunes, Titanís dunes are thought to be composed
of organic material that has rained down from its smoggy skies.
- The dunes and lakes on Titan may
contain hundreds of times more hydrocarbons than all the oil and gas reserves
- Saturn has six mid-sized icy
moons that retain impact craters dating back to their early history; some of
them exhibit signs of internal activity and ice volcanism. Impacting objects
almost broke the moons Mimas and Tethys apart.
- A number of unique small,
irregularly shaped moons revolve around Saturn with remarkable orbits. The
co-orbital moons have almost identical orbits, the Lagrangian moons share their
orbit with a larger satellite, and the shepherd moons confine the edges of
- Saturnís mid-sized moon Hyperion
is so light that it must be about half filled with empty spaces, and it tumbles
chaotically along its orbit with no definite rotation period or orientation in
- The enigmatic moon Phoebe moves
around Saturn in the opposite, retrograde direction to the planetís other
mid-sized satellites. Phoebe has sharp-edged craters and a varying brightness
that suggest thin dark surface deposits overlying bright water ice.
- An enormous, exceptionally
distant, wide and diffuse ring of Saturn is apparently replenished by
micrometeorite impacts with Phoebe; the ejected material might also move in
toward Saturn, striking the next innermost moon Iapetus and accounting for the
dark side of its two-faced surface.
Copyright 2010, Professor Kenneth R. Lang, Tufts University