Introduction to the Solar System

Jupiter: 16 moons
4 small ones just outside the rings
4 Galilean satellites
8 outer, loosely bound satellites
Saturn: 18 moons
Uranus: 15 moons
Neptune: 7 moons
But these are the moons we've collected in our list, due to telescopic observations and Voyager 1 and 2. Could easily be more

Amalthea
Discovered in 1892 by telescope
Cratered lump 270 x 155 km
Orange, due to sulfur volcanism of Io
One of the 4 small moons that continually crash into each other to produce Jupiter ring particles
BOARD: Jupiter, ring, 2 small moons, Galilean moons, 8 outer moons retrograde
We see all these fantastic places that our robot spacecraft have gone to
We hear about how, at 35,000 mph, they take 13 years to get to Neptune
We know that Voyager skimmed over Neptune like a bug 1/4 inch off a basketball, 2 billion miles away
We heard that targeting Triton was like sinking a putt from here to Antarctica
With all these little moons wildly orbiting around their planets, there must have been an incredible resourcefulness and ingenuity in the Voyager mission plan
Appears to be an incredible triumph of deterministic, omniscient science.
With Newtonian physics we have this almost incomprehensible power to make Nature do our bidding
I sometimes wonder a little at the arrogance this engenders and the limitations that are inherent in our power
These achievements seem so incredible that I think it makes people totally in awe of the knowledge and power of science. It's magic.
But because of this, science is really a potentially dangerous force in modern society (as any magic is)
Shouldn't we look carefully at the limitations of our abilities, to keep all this in a human perspective?
When you dig a little into the actual process of planetary space exploration, as the videos I've showed do, you can see it also as a human endeavor
You see the scientists frowning and laughing, rejoicing and struggling
Amalthea is a tiny moon of Jupiter, the size of New Jersey, orbiting between Io and the rings
It's hard to see in a telescope
The truth is, we weren't certain where it would be
So we depended on Voyager's navigational images on approach to Jupiter to spot it
We couldn't get very close, but we figured out where to point the cameras and here's what we saw
SL: Elongated moon, longest part always points toward Jupiter due to tides

Most of Saturn's moons are heavily cratered, like Ganymede and Callisto
They are brighter and seen to have icier surfaces
Because of the condensation sequence (both solar system and Saturn), we expect these moons to have more ice than rock or carbonaceous material
They are lower in density than the Galilean moons of Jupiter
And they are brighter because they have more ice
BOARD: Saturn, ring, 6 small moons, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Iapetus, Phoebe
Small moons break up to feed the rings (all discovered by Voyager)
Mid sized moons all discovered with Earth telescopes
All about 1/2 the size of our Moon
They are all tidally locked -- they keep the same face towards Saturn, just like the Moon does with the Earth
After the midsize ones is giant Titan, which we have talked about
A kind of Bode's rule is followed by the moons. Each one is twice as far away from Saturn as the one closer in
Because they have cratered surfaces, the surfaces are old, we suspect they have not had much volcanism or tectonism.
But there has been some

Analogous to Jupiter's Galilean moons
Mimas 390 km
Enceladus 502 km
Tethys 1048 km
Dione 1120 km
Rhea 1530 km

The Death Star
Huge impact made a crater big enough to almost break it apart
Remember the rule -- Impactor was 1/10 the size of the crater
But it hit at 40 x faster than a speeding bullet

Has the most evidence of geological activity of all the Saturnian satellites
Somewhere in between Europa and Ganymede in activity
Sort of a geological missing link
Europa has a smooth, cracked ice surface
Ganymede has huge fissures from ice volcanism where the lava was slush
With Enceladus we see old and young surfaces and a global system of cracks
To me, this system of ice cracks looks something like what we see in the Venus highlands (rock volcanism)
But on Enceladus, we see ice-slush rift zones that have frozen
We can see how the surface has split and slush has erupted onto the surface
Craters are split by this process
The water froze onto the surface and obliterated craters
But Enceladus is too small for internal heating
So tidal forces of Saturn probably caused the internal heating

Also like Enceladus but with more crates and less ice volcanism
Can see evidence of one canyon-like rift
And some parts of the surface look older than others, indicating that there may have been several eras of volcanism

Bright streaks on the surface -- may be streaks of snow
Varied terrains with differing crater densities
Again, probably due to several different eras of volcanism
Most distinguishing feature -- trailing hemisphere has dark and bright areas
For moons in synchronous orbit, there are 4 distinct faces
Facing hemisphere -- always towards the planet
Leading hemisphere -- always pointing forward in orbit
Anti - planet hemisphere -- always away from planet
Can you imagine living here -- Saturn may cover the sky on the one hemisphere, but from this side, we wouldn't even know Saturn existed!
Trailing hemisphere -- always following in the orbit

Largest of the Saturn satellites except for mighty Titan
Large enough to have had internal heat driving geological (ice) processes
White streaks may be frost, exuded from fractures that criss-cross the moon
Evidence of tectonism along with volcanism

Extremely irregularly shaped
Instead of spinning, it tumbles around chaotically
may be the result of an off center hit by a large meteorite relatively recently

One side is very black, and the other is very white
One face is always pointing towards Saturn
Leading hemisphere is black
Trailing hemisphere is white
The difference is so pronounced that it was seen in telescopes in the 1600s
Observers could only see Iapetus when it was on one side of Saturn
BOARD Dark hemisphere facing , can't see Saturn Bright, hemisphere facing, can see
Black stuff is black dust around Saturn smacking onto the leading side
'Like bugs splatting on the windshield' Lovely imagery by Hartmann

Small, outer moon of Saturn that orbits backwards (retrograde orbit)
A captured moon
Not bright and icy -- very dark
Same black color as other interplanetary objects (comets)
Probably a carbonaceous surface

Moons orbit around the equator -- so we see them face on
Only the 5 largest moons could be seen from Earth
Voyager discovered many new moons around Uranus and Neptune
Before Voyager, we knew of 5 Uranus moons, and they were named after characters in Shakespeare's Midsummer Night's Dream
There weren't enough characters after discovering the new moons, so they were named after characters in other Shakespeare plays and in a poem by Alexander Pope
Voyager got its best pictures of the 5 large moons that we already new, and so the mission planned to image them
BOARD Uranus, rings, Puck, Miranda, Ariel, Umbriel, Titania, Oberon

Very small moon discovered by Voyager
many smaller moons inside Puck's orbit
Probably part of a larger body that was struck 3.5 By ago
many of the inner moons may be younger collisional fragments
Very dark and carbonaceous

Miranda was a big surprise
Incredibly tortured moon
Very small, so we expected very little geological activity
But it is the most highly fractured moon of all, with enormous ice cliffs and immense systems of grooves
16,000 foot sheer ice cliff on a tiny, cold moon
It was probably smashed into bits that re-coagulated

Has 20 km deep canyon that formed from ice lava oozing up from the interior
Youngest and most geologically active of Uranus' moons

Very dark and carbonaceous
Old cratered surface
One bright crater on the equator (on edge of moon from Voyager's perspective)

With Titan, Triton and Titania, these names get confusing
Largest of Uranus' moons
Prominent fault valleys go a long way around the moon
Also has a very large crater, like Mimas
But not quite big enough to disrupt the moon
Looks a lot like one of the 5 big moons of Saturn

Ancient, heavily cratered surface
Impacts have bright rays of crater ejecta like the moon
Probably made of ice and frost, rather than ejecta glass like the moon
Dark patches inside the craters are probably from dust-ladened ice lava

Only 2 moons were known from telescopes (Large Triton, and Nereid)
Voyager discovered 5 more
Like Uranus, the 5 new ones orbit close to the planet, on the outskirts of the rings
BOARD: Neptune, rings, 4 close in moons, proteus, Triton, Nereid

Dark, with an enormous crater
Almost certainly was broken up from an impact
Crater is too large to have left it intact

One of the solar system's great moons, easy to see in telescope
We will discuss it along with Pluto and the Kuiper belt next lecture
Orbits Neptune in the wrong direction -- retrograde orbit

Discovered in 1949 with telescopes as they rapidly got better
Very elliptical orbit
Just on the edge of Neptune's gravitational sphere of influence
We think Triton and Nereid are captured moons (comet like)

VIDEO: NEPTUNE'S COLD FURY, NOVA (Second half)

6/28/96