MERCURY

Q: Why are there so many craters?

Mercury

We see so many craters because:

• No atmosphere means no weather.

• No weather means no weathering and erosion.

We see so many craters because:

No plate tectonics to “recycle” the crust.

Why Mercury so hot?

Mercury is hot because:

• It is so close to the sun!

Energy reaching a planet from the sun

decreases rapidly with distance

INVERSE SQUARE LAW

(any property) varies inversely as the square of the distance from an object

1

d2

So….

With distance, same energy must be spread over larger and larger area

Mercury

Why are the day/night temps so different?

Temperatures are so extreme because there is no atmosphere :

• to block radiation from reaching the surface

• To prevent heat from leaving.

Venus• Q: Why is it so hot when it is

farther from sun than Mercury?

VENUS

Venus is so hot because:

• Its atmosphere traps heat and won’t let it out.

The Greenhouse Effect

Why DOES Venus have an atmosphere?

• OUTGASSING—gases are released by volcanic activity.

• And…

And…

• It has enough gravity to hang on to the gas.

Why does the earth’s atmosphere have so much oxygen?

Photosynthesis

Cyanobacteria began to oxygenate the earth

about 2.4 BYA

Where do we find the only life forms in the universe?

Is there life on MARS?

Uh, no.

Is there WATER on MARS?

YESPenetrating radar shows there is

lots of water frozen under the poles.

Was there ever surface water on MARS?

(maybe)There are erosional features that look as though made by

liquid.

On the other hand…

the atmospheric pressure is so low (0.01atm) that liquid water would boil

away.

Why is Jupiter “banded?”

1. Convection within atmosphere.

In a fluid, hot stuff rises, cool stuff sinks.

On our planet, warmer rises from the equator, sinks at the poles.

• If the earth did not rotate, all winds would blow north and south.

2. Rapid rotational speed (10 hours)

Compared to its axis, a planet is rotating faster at the equator than at the poles.

So, as air moves away from the poles…

It moves over a faster moving surface, and appears to curve to the right.

When air moves to the north from the equator,

• It curves to the right

The earth’s global wind belts, showing the Coriolis effect.

3. The Coriolis Effect.

Why does Jupiter have so many ‘moons” ?

MORE MASS, MORE GRAVITY.

What are the rings of Saturn?

Mostly ice crystals and carbon dust.

Size = few cm to few m

Only few hundred m thick.

How did Saturn’s rings form?

• Collisions among satellites due to complex gravitational “tides”

Why does Uranus “lie on its side?”

MASSIVE collision.

Why is Neptune blue?

• Methane in upper atmosphere absorbs red wavelengths, letting blue though.

Neptune’s moon Triton is unique because…

• It orbits backwards (retrograde)

• It is volcanically active.