ISP 205 - Astronomy Gary D. Westfall1Lecture 10 The Moon The Moon has 1/80 the mass of the Earth and 1/6 its gravity The Moon has no atmosphere because.

1ISP 205 - Astronomy Gary D. Westfall Lecture 10

The MoonThe Moon• The Moon has 1/80 the mass of the Earth and 1/6 its

gravity

• The Moon has no atmosphere because of its low gravity

• The density of the moon is 3.3 g/cm3 compared with Earth’s 5.5 g/cm3

• The Moon rotates on its axis every 27.3 days which is exactly equal to the time it takes to orbit Earth

• Views of the moon from Redshift


Exploration of the MoonExploration of the Moon• The Russian Luna 9 was the first spacecraft to land on the Moon in 1966• On July 20, 1969, Neil Armstrong stepped out on the surface of the Moon• 9 Apollo missions were flown (list given in Table 8.2)

3 did not land and 6 landed on the surface• The last mission was flown in December, 1972

Here is Jack Schmidt during Apollo 17

• Here is the lunar module from Apollo 17 leaving the surface of the moon


Top 10 Discoveries from ApolloTop 10 Discoveries from Apollo• The Moon is not a primordial object; it is an evolved

terrestrial planet with internal zoning similar to that of Earth.

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

• 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.

• The Moon and Earth are genetically related and formed from different proportions of a common reservoir of materials.

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


Top 10 Discoveries from Apollo, cont.Top 10 Discoveries from Apollo, cont.• All Moon rocks originated through high-temperature processes

with little or no involvement with water. They are roughly divisible into three types: basalts, anorthosites, and breccias.

• 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.

• The lunar magma ocean was followed by a series of huge asteroid impacts that created basins which were later filled by lava flows.

• The Moon is slightly asymmetrical in bulk form, possibly as a consequence of its evolution under Earth's gravitational influence. Its crust is thicker on the far side, while most volcanic basins -- and unusual mass concentrations -- occur on the near side.

• The surface of the Moon is covered by a rubble pile of rock fragments and dust, called the lunar regolith, that contains a unique radiation history of the Sun which is of importance to understanding climate changes on Earth.


Composition of MoonComposition of Moon• The Moon is made of lighter silicate rock• The Moon has no iron core like Earth• The Moon has no current seismic activity• The moon has no magnetic field• The Moon has no volatile materials• It is as if the Moon were composed of the same basic

materials as the Earth’s crust with the volatile material and the core metals missing


General Appearance of the MoonGeneral Appearance of the Moon• To the naked eye, the Moon has seas and

continents Craters are not visible Features are named for seas

Maria are younger Dark, round plains much less cratered

Sea of Tranquility, Sea of Clouds, etc. Continents or plains are not named

Highlands are older Low density rock formed early, severe cratering

• Since the invention of the telescope, craters have been observed and named


Impact CratersImpact Craters• The moon provides an important benchmark for

understanding the history of the solar system

• The Moon preserves the history of the solar system through its uneroded record of impact craters

• The observed craters on the moon were once thought to be volcanic in origin

• Now the craters are understood to be all from the impact of meteors

Terrestrial Volcano

Lunar Impact Crater


The Cratering ProcessThe Cratering Process• Any object striking moon

does so at least escape velocity (2.4 km/h or 5400 mi/h)

• This impact creates an explosion the produces a round crater


Using Crater CountsUsing Crater Counts• We can use the number of impact craters on the Moon’s

surface to estimate its age• By looking at the current population of asteroids and

comets one can deduce that 1 km crater produced every 200,000 years 10 km crater produced every million years 1 or 2 100 km craters produced every billion years

• This calculation gives 3.3 to 3.8 billions years for the age of the Moon

Compares well with radioactive dating

• There is evidence that the cratering rate was much higher just after the formation of the solar system 4.5 billion years ago

Highlands have 10 times more craters than maria


Deducing Information from CratersDeducing Information from Craters• If a crater forms on top

of another crater, that crater is newer

• Looking at the edges of a crater one can say Old craters have smoother

edges from meteor erosion Young craters have sharp

edges

Ptolemaeus Crater taken by Apollo 16


Theories for the Origin of the MoonTheories for the Origin of the Moon• Theories for the origin of the Moon fall into

three categories The fission theory

The Moon was once part of the Earth but separated early in its history

The sister theory The Moon formed at the same time as the Earth but

independently The capture theory

The Moon was formed elsewhere in the solar system and later captured by Earth


Evidence Against These TheoriesEvidence Against These Theories• The fission theory

Modern calculations show that fission cannot occur Recently discovered chemical differences rule out this

theory

• The sister theory Moon should have much larger iron core like Earth

• The capture theory A body can only be captured into orbit if there is a

mechanism to slow the body - there is none Orbit would be very elliptical - it is circular


The Giant Impact TheoryThe Giant Impact Theory• Moon was created by collision of Earth with an

object about 1/10 the size of Earth

• The Mars-like object might have stuck the Earth and ejected a large chuck of the crust into orbit around the Earth that formed the Moon Explains lack of volatiles and chemical composition


The Planet MercuryThe Planet Mercury• Mercury is the closest planet to the Sun

• Mercury orbits the Sun in 88 days

• Mercury has an eccentric orbit (e = 0.206) with a semimajor axis of 58 million km (0.39 AU)

• The plane of Mercury’s orbit is tilted 7 degrees from the ecliptic

• Interactive Solar System


Mercury’s Strange RotationMercury’s Strange Rotation• Mercury was once thought to rotate once per orbit

• Radar observations showed that Mercury does not keep one face toward the Sun Takes 59 days to rotate on it axis Takes 88 days to orbit Sun


Viewing Mercury in the SkyViewing Mercury in the Sky• Position of Mercury in the sky at 6 pm, Oct. 3 looking SW

• Mercury Sky View.RS3


Composition and StructureComposition and Structure• Mercury’s mass is 1/18 that of the Earth

2nd smallest

• Mercury’s diameter is 4880 km 2nd smallest

• Mercury’s density is 5.4 g/cm3

2nd densest

• Mercury is thought to consist of an iron-nickel core surrounded by a silicate crust Core is roughly the size of the Moon Probably molten because Mercury has a magnetic field


The Surface of MercuryThe Surface of Mercury• Mercury strongly resembles the Moon in

appearance• Mercury is covered with thousands of craters

and larger basins up to 1300 km in diameter• Some of the brighter craters are rayed

• Mercury’s basins resemble the Moon’s maria

• There is no evidence of plate tectonics on Mercury

• Long scarps are visible cutting across craters


Fly-by of MercuryFly-by of Mercury• Here is a series of photos of Mercury shot by

Mariner 10

QuickTime™ and aSorenson Video decompressorare needed to see this picture.


Origin of MercuryOrigin of Mercury• The problem with understanding the origin of

Mercury is the opposite of understanding the origin of the Moon

• Mercury has too little silicates and too much iron

• Mercury may have suffered a catastrophe early in its history that tore away a fraction of its mantle

• Both the Moon and Mercury have strange compositions that tell astronomers that the early solar system was chaotic

ISP 205 - Astronomy Gary D. Westfall1Lecture 10 The Moon The Moon has 1/80 the mass of the Earth and 1/6 its gravity The Moon has no atmosphere because.

Documents

moon slide

youngest moon rocks

astronomy gary

earth views

redshift slide

oldest earth rocks

lunar magma ocean

apollo missions