Chapter 8: Moons, Rings, and Plutoids

Titan

largest moon of Saturn; has extremely dense N2 atmosphere with oceans of methane and ethane; atmospheric pressure about one-and-a-half times greater than that of Earth's surface, might rain liquid CH4, liquid H2O below the surface, gravity comparable to our Moon

Sedna

most distant object detected in our Solar System

planet

1. Orbits a star (page 352 reads "Sun") 2. Is massive enough that the own gravity makes it approximately spherical 3. Has "cleared the neighborhood" around its orbit

4 Galilean Moons

Io, Europa, Ganymede, Callisto

Galilean moons

Io, Europa, Ganymede, Callisto

7 large moons in our Solar System

Moon, Io, Europa, Ganymede, Callisto, Titan, Triton

plutoid

a dwarf planet orbiting beyond Neptune

Cassini Division

a relatively empty gap in Saturn's ring system; discovered in 1675 by Giovanni Cassini; it's now known to contain a number of thing ringlets

Encke Gap

a small gap in Saturn's A ring

D ring

collection of very faint, thin rings, extending from the inner edge of the C ring down nearly to the cloud tops of Saturn; this regions contains so few particles that it is completely invisible from Earth

Pluto

dwarf planet discovered in 1930; thought to be the explanation fro the irregularities of Uranus and Neptune's orbits, but it turned out there wee no irregularities; slightly bigger than our moon; very eccentric orbit; weak atmosphere: nitrogen and carbon monoxide, has 5 moons; floating "hills" of water ice in sea of frozen nitrogen

F ring

faint narrow outer ring of Saturn, discovered by Pioneer 11 in 1979; the F ring lies just inside the Roche limit of Saturn and was found by Voyager 1 to be made up of several ring strands apparently braided together

tidal heating

forced orbital eccentricity

Ganymede

largest moon of the Solar System; moon of Jupiter; larger than Mercury; radioactive heating, surface is a mix of rock (dark regions) and water ice (lighter regions); magnetic field: there might be a layer of salty water

Triton

largest natural satellite of Neptune; retrograde orbit; thin nitrogen atmosphere; frozen lakes, volcanically active

Kuiper Belt

located in the outskirts of our Solar System; water ice and volatile chemical compounds

New Horizons

mission to Pluto and the Kuiper belt; launched in 2006; closest approach on July 14, 2015; currently beyond Pluto

Callisto

moon of Jupiter; surface is mostly rocky but also has much water water ice; many craters so the surface is inactive; no tectonic activity so interior is cold; the most cratered object in the Solar System, no weather

Charon

moon of Pluto, discovered in 1976, big compared to it; mountains, canyons, different coloration; canyon-like structure; same face of Pluto always faces it

Io

most active body in our Solar System; covered in active super hot volcanoes, "anchovy pizza", youngest surface in the Solar System

ringlets

narrow region in Saturn's planetary ring system where the density of ring particles is high; Voyager discovered that the rings visible from Earth are actually composed of tens of thousands of these

Miranda

nearly destroyed, enormous canyons (12 times deeper than Grand Canyon)

plutinos

objects orbiting at the same orbit as Pluto

Roche limit

often called the tidal stability limit, this gives the distance from a planet at which the tidal force (due to the planet) between adjacent objects exceeds their mutual attraction; objects within this limit are unlikely to accumulate into larger objects; the rings of Saturn occupy this region within Saturn's limit

C ring

one of three Saturnian rings visible from Earth; it lies closest to the planet and is relatively thin compared to the other 2

B ring

one of three Saturnian rings visible from Earth; it's the brightest of of the three and lies just past the Cassini Division

A ring

one of three Saturnian rings visible from Earth; it's the farthest from the planet and is separated from the B ring by the Cassini Division

shepherd satellites

satellite whose gravitational effect on a ring helps preserve the ring's shape; orbit near the outer edges of the rings or within the gaps; examples are two satellites of Saturn, Prometheus and Pandora, whose orbits lie on either side of the F ring

Europa

second moon out from Jupiter, covered entirely by water ice that is several km thick; 3x more water than earth; has salt water below its surface; potential for indigenous life

E ring

second outermost ring of Saturn that is extremely wide

Dactyl

smallest moon in the Solar System, orbits asteroid Ida

stellar occultation

the dimming of starlight produced when a solar system object such as a planet, moon, or ring passes directly in front of a star

radiation darkening

the effect of chemical reactions that result when high-energy particles strike the icy surfaces of objects in the outer solar system; the reactions lead to a build of a dark layer of material

tectonic fractures

where stresses in the moon's icy interiors as they cooled and contacted caused the surface layers to crack and buckle (Dione - one of Saturn's moons)