Interiors

Lithosphere (solid surface, lithos = rock)

Earth has thinnest lithosphere.
The key ingredient is the size. Since Earth is the largest in size it is the most geologically active. Venus is a lot like the Earth geologically but it doesn’t have plate tectonics.
Mars is the in-between planet. It is dead geologically, volcanos are extinct. Lithosphere is thicker so it’s harder for anything interior to get to the exterior. It only recently died though.
Mercury and the Moon died geologically a long time ago. Their surfaces are similar, and they are the smallest. They carry the marks of every impact that landed on them for the past 4 billion years or so. This is because they do not renew their surfaces (like the Earth).

Mantle

Molten rock

Core (nickel and iron)

Mercury is way off with its core in comparison with the other planets. Its core is way too big for its size. Explanation: it must have been much larger at one time and it had a collision that deteriorated a lot of the exterior.
The core affects the planet’s magnetic field. Earth has the strongest magnetic field.

Surface

Mercury and the Moon look a lot alike, old surfaces with many craters.
The moon has marias, smooth surfaces, that are younger than the crater areas.
The moon also has canyons called rilles
When Mercury was cooling the core might have shrunk a little bit, heating up the planet, and the outer parts wrinke, creating long cliffs. The Moon never did this because its core was too small to really affect the surface.
Mercury - There isn’t a real atmosphere but the solar winds vaporize sodium (and something else) sending them floating above the surface.
Mars – Virtually no craters. There is evidence that there was fast-moving liquid on the surface, probably water.

Interior is hot. Space is cold. Hot flows towards cold. A planet has to continue to expend energy to keep its temperature up. If it stops it cools (and leads to death?)

So we talk about what heated up a planet in the first place, how it keeps the heat, and how it’s transferred.

Accretion – how planets form. Small particles stick to each other, growing to the size of a kilometer. Then there are planetessimals that group to each other, and then form protoplanets, etc?

Heating by accretion – two lumps collide together and they shatter. This died billions of years ago.

Heating by differentiation – a planet the size of Earth that is molten. Gravity drives frictional processes. Heavy metals sink to the center. Conversion of gravitational potential energy to kinetic energy to thermal energy. This died shortly after heating by accretion.

Even though there isn’t a lot of radioactive material on Earth, there is some in Earth’s core. This leads to heating by radioactivity. This still happens still today.

Modes of energy transport:

Conduction – basketball handed to the next person toward the “surface”. Atoms “jostle” heat down the line.

Convection – material physically moves to pass heat to the surface.

Radiation – matter throws out photons out into space.

Where do these occur? Conduction occurs in the core, convection occurs in the mantle, and radiation happens from the surface. All of these work to transfer heat from the hot place to the cool place. It has to do with efficiency in these places. Because of the pressure and density conduction is most efficient in the core. So on and so forth.

Why did Mercury cool off faster than the Earth? It has to do with size.

Surface Area / Volume.

Surface Area dictates cooling. The volume has to do with the heating.

Pudding crust example – move it to smaller plates to cool. If you leave it in the pot it will never cool.

The rate of cooling/heating grows to 1/r. The bigger the planet the less efficiently it will cool.

4/03/09

What changes a planet’s surface?

1 - Impact cratering

2 – Volcanism- hole in the crust

3 - Tectonic activity- shifting, sliding of surface plates

4 - Erosion (a.k.a. gradation)- by wind, water, etc.

Mercury

It is so small it is geographically dead. Smaller than Earth but larger then the Moon
How do you know? The craters mean the surface is old. They are left from the heavy bombardment from debris during the formation of the solar system. (Earth resurfaces itself every 250 million years.) Mercury’s crust is so thick that even if something was going on underneath it wouldn’t make its way to the surface.
Mercury also has cliffs. They look like cracks in pictures. Remember Mercury’s core is way too big for the size of the planet; it was thought to have been hit by a heavy impact that blew off much of the outer crust, leaving it much to thin for its large center. As the core cooled, it shrank, affecting the surface crust. It makes it crack and buckle causing these massive cliffs.
Visited by Messenger on a flyby mission a year ago; before that not visited since the 1970s

Mars

It is more interesting geologically than Mercury.
It is also geologically dead. But it is clear Mars was alive much longer than Mercury, about 3-4 billion years, and died about 1 billion years ago.
There are very few craters on one side (lots on the other). But even those are worn down, weathered perhaps.
There is also a huge canyon called Valles Marineris. It is a clear tectonic feature. It is so large it could span the entire width of the US. It is huge cliffs from tectonic activity.
There are also massive volcanoes, much larger than Earth’s volcanoes. They look a little like craters. The largest volcano in the Solar System is Olympus Mons (and it is on Mars). It is 25 miles high. It has been dead about 2 billion years

Why does Mars have the largest volcanoes in the Solar System? Take Earth for example. If there was something 25 miles high on Earth, the difference in the force from top to bottom would be greater than the tensile strength of what’s holding it up. Over time the force of gravity will destroy it to a pile of rubble not more than 10 miles high. But the difference on Mars is that the rock making up Olympus Mons is strong enough to resist gravity – so it is still standing.

One side of Mars has lots of volcanoes and so it has fewer craters because the volcanoes were resurfacing the area around them- NEWER SIDE. The other side has many craters so that surface is OLDER than the other side’s surface.
It has an atmosphere, but it’s not very big. It’s only a fraction of the density of Earth’s atmosphere (We’ll discuss more in later chapters.)
Mars shows evidence of having had running water at one point. A picture of one Rover’s tire tracks shows ice. Four days later another picture shows that some of it evaporated. But the air pressure is too low on Mars now so water cannot exist as a liquid there now. More evidence of water- canals where water clearly ran through canyons; also areas in lower elevation there are areas of sediment deposited by running water. Clearly there was a time where Mars had a thick enough atmosphere for water to have existed. (We will discuss reasons why it thinned later.)
“Face” on Mars- actually an area of high elevation

Venus

To see Venus well you have to take ultraviolet pictures and even then you see only thick clouds. You never see the surface.

Radar imaging – a radar satellite orbits Venus and bounces radar waves off the surface. It comes back with two bits of information:
(1) height of the surface (measured using the time it takes the radar wave to come back), and
(2) the smoothness of the surface (measured using a pulse with a certain frequency - wider return frequencies indicate rough surfaces).

Venus also has craters (not many) but they are very worn down – indicating that it is still geologically active.
Venus has a very cracked surface- craters have been eroded and edges smoothed
It also still has active volcanoes.
Pancake domes- Not exactly a volcano because there’s no hole; where lava rose beneath crust but never broke through the surface