Solar System Planets: The Earth + Moon

I. Moon- Atmosphere- Surface/Geological Features/Moon Rocks- Interior- Origin

II. Mercury- Basic Facts- Exploration- Cratering

The Moon has no atmosphere• allows us to see the surface with fine detail

• escape speed is too low on the Moon- all gas molecules can escape!

• no atmospheric pressure means that water can not exist in liquid form

- only in solid or vapor

• temperature variations – extreme!- day T = 403 K = 266 F- night T = 93 K = -292 F- day/night are each 2 weeks long!

• no weathering of the surface by water, storm

• no protection from high energy solar particles, cosmic rays

Lunar Geological Features

1.Craters• ~30,000 visible with small telescopes from Earth• millions visible from lunar orbiting satellites• origin: interplanetary debris

• sizes: largest 100’s kmacross a result of fastmoving impact rocksof only a few km’s across!

• large craters oftenproduce “central peak”craters

Clavius Craterdiameter = 232 kmdepth of 16,000 feet

2. Lunar “Maria” - dark, smooth regions • first thought to actually be wet areas (before we knew Moon had no atmosphere)• now believed to be smoother, younger (fewer craters) surfaces• idea is that impacts created large basin and then lava flowed over surface • relatively ‘low’ compared to highlands on moon; 2-5 km below other parts• rough mountain ranges surrounding ‘maria’ suggest large impact originally• evidence for ‘flows’ (lava?) along the smooth maria

Lunar Geological Features

3. Lunar Highlands• most of moon (85%) is actually covered with lighter, higher land: Highlands• predominantly on the side of the Moon facing away from Earth• roughly cratered, but no smooth lava flow ‘maria’ regions• crust must be thicker in the highland areas

Lunar Geological Features

Cratering: Age of Moon’s Surface

• can use cratering patterns to determine AGE of surface

• no atmosphere to protectbombardment; no erosion bywind/water OLD surface(as old as ~3 billion years)

• Earth’s surface only a few100 Myrs old (geological activity has re-surfaced planet)

• highlands have many more craters; maria have fewercraters highlands ‘older’

The smaller the planet, the less internal heat(geology) it willhave; less geologicalactivity on surface

A Brief History of Lunar Exploration

• 1959: Soviet Lunas 1, 2, 3 orbited around Moon

• 1960’s: US Ranger - flyby mission- first space pictures- many TV cameras

• 1966-67: Lunar Orbiter- 5 orbiting spacecraft- full coverage of pictures

• 1966-68: Lunar Surveyor- surveying for landing sites - testing the “soil” (sink?)

Highlights from Apollo 11 missionlaunch: July 16th 1969arrival at Moon: July 20th 1969first humans to land on the Moon

Neil Armstrong“Buzz” AldrinMichael Collins

Command Module (CM):“Columbia”

On July 20, 1969, after a four day trip, the Apollo astronauts arrived at the Moon. This photo of Earthrise over the lunar horizon is one of the most famous images returned from the space program, although even the astronauts themselves cannot remember who actually took it.

First steps on the Moon• July 20th 1969

- Neil Armstrong- “Buzz” Aldrin

Touchdown of Moon astronauts near the coast of Hawaii on July 26th 1969

Lunar Exploration: Apollo Missions• Apollo 1-10: pre-landing missions (Apollo 1 module fire killed 3 astronauts while being tested)

• Apollo 11-17 landed (except Apollo 13, which had an explosion and returned to Earth) 12 different astronauts walked on the Moon during 1969-1972

• Principal Scientific results of the Apollo missions:

1. The Moon is ancient and still preserves an early history (the first billion years) that must be common to all terrestrial planets.

2. The youngest Moon rocks are virtually as old as the oldest Earth rocks. The earliest processes and events that probably affected both planetary bodies can now only be found on the Moon.

3. Early in its history, the Moon was melted to great depths to form a "magma ocean." The lunar highlands contain the remnants of early, low density rocks that floated to the surface of the magma ocean.

4. The Moon is not a primordial object; it is an evolved terrestrial planet with internal zoning similar to that of Earth.

5. The Moon is lifeless; it contains no living organisms, fossils, or native organic compounds

Recent Lunar Exploration

• 1994: Clementine- UV, IR, visible cameras- possible water ice at poles- radio waves reflected off ice

• 1998: Lunar Prospector- also found evidence for ice- crashed near pole in 1999

• Currently: Smart 1 Probe- European satellite- ion propulsion (several months!)- will search for water at poles

Moon Rocks: Sampling the Surface of the Moon

• surface material: “regolith” – pulverized by constant impacts

• ~2500 samples brought backby astronauts; ~850 lbs total!!

• all rocks are IGNEOUS (i.e., from molten processes)

• totally dry rocks (no water)

• all rocks older than 3 Byr

Moonquakes: Studying the Moon’s Interior

Seismometer placed on Moon by lunar astronauts

• ~ 3000 quakes/year

• much lower intensitythan Earth: 0.5-1.5 Richter

• indicate that Moon’s interior is more rigid thanEarth’s (some ‘plasticity’)

Moon’s interior structure

• iron-rich core like Earth• asthenosphere layer: somewhat pliable “plastic” layer• solid layer just below surface – no plate tectonics• smaller planet than Earth – less internal energy, less geological activity!• moon probably had a weak magnetic field early in history

- core is now solid, so no current is generated

crust is thicker on non-Earth facing side

Color-coded images illustrate surface geography

Clementine data• blue – lowland marias

• red - highlands

Galileo data – flyby in 1989• blue – lowland marias

• red - highlands

Theories for Origin of Moon• Fission: originally part of Earth but torn free

– Problem: would have fallen back or been flung into space, not into orbit.

– Fails to explain why lunar chemistry differs from Earth's

• Co-Creation: formed in its present orbit – can not explain why lunar chemistry differs from Earth's

• Capture: formed as a separate planet but captured by Earth – Conditions for successful capture very stringent

• Impact: formed from Mega-Impact of Mars-sized planet – Computer modeling suggests SS forms 100 or so small

planets, then collide to make larger objects– can explain differences in chemistry: – impact occurred after chemical differentiation in Earth; therefore,

not as much iron was part of the Moon– high temperatures during impact would have vaporized the

volatile and water vapor in rocks– Currently favored model

Computer Simulation of Formation of Moon

• Moon may have formed by a Mars-sized object impact on Earth

• Some of the materialdoes not fall backonto the Earth, butforms a satelliteof Earth