The Moon

“Magnificent Desolation”…Buzz Aldrin

! Studies of lunar rocks show that the moon originally had a molten surface. As this so-called magma ocean cooled, intense volcanism continued for about 900 million years. An early volcanic eruption is shown here. Copyright William K. Hartmann

Lava on the Moon

Surface Features, Origin" Circular craters

� Holes made where high-speed objects hit� Raised rims made by piling up of surrounding

rock due to pressure of impact� Central peaks due to rebound of compressed rock

under the impact point" Highlands formed soon after birth of Moon

� Iron and heavy materials sank down� Lighter, less dense rock came to the surface� Bombarded by objects (space debris) that were

then abundant in a young solar system

Activity on the Moon"Regularly occurring, weak moonquakes

detected by seismometers left by Apollo flights"Major moonquakes are Richter 0.5 – 1.5"Most occur about 700 km deep, at the boundary

between the plastic asthenosphere and solid lithosphere

"Impacts: 80 – 150 meteoroids per year; masses ranging from 100 g to 1000 kg

Atmosphere and Water"No atmosphere. Lunar gravity is too weak to hold any

gases"Escape speed - 2.4 km/s"Most gas molecules move at much higher speeds even

at low temperatures and, therefore, escape"Very hot days: 130° C (266° F)"Very cold nights: –180° C (–292° F)"Some water ice detected in polar regions...

Current Science, Lunar Prospector Mission

"How did the Earth-Moon system form?

"How did the Moon evolve? "What is the impact history of

the Moon's crust? "What constitutes the lunar

atmosphere? "What can the Moon tell us

about the history of the Sun and other planets in the Solar System?

Lunar Prospector with the Trans-Lunar Injection (TLI) stageLaunched Jan 6, 1998

Impact: 09:52:02 GMT on July 31 1999

Water on the Moon•Neutron spectroscopy used to look for water on the Moon•Neutrons are subatomic particles that are continually ejected from the lunar soil by cosmic rays•Coincident dips in medium-energy neutrons at both lunar poles (see arrows) are definitive signatures for water •Total amount of water on the Moon could be anywhere from 10 million to 6 billion metric tons (2.6 to 26 billion

Clementine Mission

One of the major scientific goals of the Clementine mission was to map the Moon in 11 different wavelengths in the visible and near-infrared parts of the spectrum. The filter colors of theClementine cameras were carefully chosen to differentiate types of lunar surface material.

(http://www.nrl.navy.mil/cle mentine/ cle movies/cle movies_index.html)

SELENE: Japanese moon orbiter mission.

" It will be launched in 2003."The major objectives of the

mission are to obtain scientific data on lunar origins and evolution, and to develop the technology for future lunar exploration.

"The SELENE spacecraft consists of a lunar orbiter and a relay satellite around the moon.

"After a year-long remote-sensing mission, the propulsion module of the orbiter will separate for soft-landing testing.

Structure of the Moon"Very low density (3.3 grams/cc) suggests that

rock predominates, and there is very little iron"Surface covered by a thin blanket of pulverized

rock; the regolith"Regolith match the location: basaltic in the maria;

anorthositic in highlands"Crust: 65 km thick on near side;

150 km on the far side

Structure of the Moon, Continued

"Solid mantle (lithosphere); � about 800 km thick

"Semi-solid, plastic “outer core” (asthenosphere)

"There is no magnetic field on the Moon. Study of rocks shows that a weak magnetic field existed when the rocks formed. � No liquid core

"Solid iron core; under 700 km in diameter

Orbit and Motions of the Moon

"Orbits the Earth in 27.322 days"Elliptical orbit; mean center-to-center distance

384,400 km"Minimum distance 363,300 km"Maximum distance 405,500 km"Rotation (sidereal) period: 27.322 days"Synchronous rotation; same face to Earth"New Moon-to-New Moon (synodic) period:

29.531 days

Synodic Period

“With Respect to some Other Body”

Peculiarities of Lunar Orbit"Orbital plane tilted ~ 5° with respect to the

ecliptic (the plane of Earth’s orbit about the Sun)"Orbital plane tilted with respect to Earth’s equator"Orbital plane also tilted with respect to Moon’s

equator"Generally, Moon is higher in the winter sky;

lower in the summer

How Moon Formed, Currently Accepted Theory

Collision Ejection Theory"A young Earth (or even proto-Earth) was hit

by a large, Mars-sized asteroid (mass ≈ 10% of Earth mass)

"Glancing collision; tore off material from the surface region.

"Gravity collected ejected matter into Moon by , and orbited Earth due to initial angular momentum

"Differentiation had left Earth’s outer regions devoid of iron.

Collision Ejection Theory Continued

"Orbiting debris rained down on the young Moon, creating the craters seen in the highlands.

"Accounts for the orbital plane of the Moon being close to the ecliptic.

"May have been responsible for the tilt of Earth’s equator to the ecliptic. (Mercury and Venus do not have such tilts)

The idea in a Nutshell! “At the time Earth

formed 4.5 billion years ago, other smaller planetary bodies were also growing. One of these hit earth late in Earth's growth process, blowing out rocky debris. A fraction of that debris went into orbit around the Earth and aggregated into the moon.”See http://www.psi.edu/projects/moon/moon.html