The Moon

What We See

Where We’ve Been

The Big Features

Oceanus (ocean)Maria (Mare) (sea)Craters

Highlands – bright, cratered regionsLowlands/Maria – dark, flat regions

Other Features

Mountains

Valleys

Librations

The result of (a) wobbling of the Moon’s axis toward/away from earth(b) Relative motion of the observer as Earth rotates(c) Non-circularity of moon’s orbit (change in size)

What’s it made of?

I…am…IRON MOON

Ti abundance(blue = lots, orange/purple = less)

But…no dipolar magnetic field. The moon’s weak B field comes from magnetic minerals.

The Real Dark Side of the Moon

Note which side the maria are on.Why only that side?

•Anorthosite: igneous rock rich in Ti, Fe•Basalt: fine-grained igneous rock caused by cooling magma

Mascons

Water?

Chandrayaan-1(water in blue)

Lunar Prospector measures neutrons from H

1996: Clementine indicates ice in deep craters1998: Lunar Prospector indicates ice1998: LP crashed into surface; no water seen2009: Moon Mineral Mapper aboard Chandrayaan-1 detects water

LCROSS• Launched with LRO in 2008• Atlas-Centaur rocket impactor

targeted Cabeus crater• Impactor (2305

kg/10,000mph) produced ejecta plume

• LCROSS probe flew through the plume and crashed, relaying data

• Data indicate 5% of plume mass was water

Where did the moon come from?

• 4 theories– Fission (moon broke off from earth)– Sisterhood/Co-accretion (formed at the

same time)– Capture (moon formed somewhere else but

drifted by and ended up in the Earth’s gravitational field)

– Giant Impactor (something hit the earth and the resulting material formed the moon)

Which one is right?

1. Fissiona. Composition of E and M are similar, but not that

similar.

b. Not enough mass in the Pacific Basin to account for the moon.

2. Sisterhood/Co-accretiona. See #1 about composition.

b. E and M should be the same age; M is younger.

Which one is right?3. Capture

a. E and M are too similar for the moon to have formed elsewhere

b. Angular momentum of the E/M system isn’t right for the moon having flown in and stopped

4. Giant Impactora. Given a Mars-sized impactor,

mass is rightb. Volatile metals and lack of water

on the moon indicate high temperatures in the past.

c. Simulations show it’s viable (angular momentum OK)

d. Lower density of moon, lack of iron are consistent with violent impact

Whack-a-Moon

t=0

t=24h

•Eventually, the cloud becomes a disk and then a moon.•The impactor core becomes the moon’s core•Intense heat is consistent with lack of volatiles and lack of similarity to the earth.