ASTRONOMY 3: Introductory Astronomy: The Solar System

Winter 2012

Detailed case study: the basic properties of the Moon

a quarter the Earth size, one eighth the Earth mass

synchronous rotation (spin and orbital period = 27.3 days)

Near and far sides of the Moon have different crater density

Tidal effect (internal dissipation of distortion by the Earth)

Surface Features

cratered highland and dark maria

rilles (lava channels), domes, cones, and collapsed pits

ancient bombardment and later resurface

Craters' density as a function of their size: age determination

Lunar Sample Return

Regolith, lunar dust, pulverized by meteoritic bombardment

Maria is covered with volcanic basalt: no water, hydrated minerals, or volatile elements, 3.1-3.8 Gyr

Terrae is covered with breccia: a wide variety of rocks that have been broken apart, mixed, and fused together

Impact melts: distinct elemental signature of meteoritic material

age 3.8-4.0 Gyr => late bombardment or conclusion of impact episode

Some aluminum-rich iron-poor rocks are found in both Mare and Terrae => global magma ocean

The lunar interior

different crater densities between the near and far size of the Moon

Measure seismic waves set off by moon quakes and impacts

impact affects 2km to 10-20 km, crust=70km in mare and over 100 km in highlands, far size thicker than near side

Differentiation: heating due to radioactive decay and melting of the mantle

Hypotheses for Lunar Origin

co accretion: similar amount of iron and magnesium rich rocks but less volatile, cobalt, and nickel as Earth outer mantle

capture: ratios of ¹⁶O ¹⁷O ¹⁸O suggest Moon & Earth formed in the same region

fission: large but not enough angular momentum

giant impact: knock out Earth's outer mantle to form the Moon. But the Earth's orbit is nearly circular

Basic properties

closest planet from the Sun, eccentric orbit with 88 day period.

smallest terrestrial planet with a density of 5.43 g/cc

orbit-spin 3:2 resonance: due to the tidal effect of the Sun

Hot (740K) days and cold (90K) nights

Surface Features

highlands and lowland planes: possible ice near the poles

not many small craters: covered up by once molten rock

no volcanic features: lobes, domes, and cones, but material which filled Rudaki crater appears to be similar as the surrounding regions: volcanic outflow

signs of ancient volcanism and tectonic stress

Crater history: resurfacing and late bombardment

giant impact in the Caloris basin and its antipode: wave focusing

Iron core and small magnetic field

scraps: cooling contraction

condensed and cold interior: small size objects are more easily cooled

Basic properties

Transit of Venus: Cap Cooks' attempt to measure the size of the solar system

Similar mass and size as the Earth

Very slow rotator

Surface features: Impact craters

1000 modest size or large impact craters

no small craters: small meteorites are burned up in the thick atmosphere

compared with the lunar crater history: surface on Venus is young (500 million years)

uniform distribution: equilibrium or catastrophe?

shock wave damage of craters

Venus: Volcanos

common feature, isolated features like Hawaii islands, hot spots?

long drainages, lava domes, resurfacing, coronae

volcanic plains, shield volcanos, & stratovolcanos: determining factor: viscosity

Basic Tectonism

plateaus and lowlands, but no global linear features

Tectonic features are localized

Very slow erosion rate: no water or plate movement

cause: slow rotation, atmosphere, thin lithosphere, no water lubricant

heat loss through vertical mantle upwilling: conduction and convection

Lithosphere and hydrosphere

Diverse geology: volcanos, impact craters, and plates

Internal structure: inner and outer cores, mantle

Geodynamo and magnetic reversal

Historic Interests

Canals on Mars: life on Mars?

Mariners' missions: craters and moon like

Viking landers: exotic chemistry

Path finder: Martian sample, early Martian conditions were Earth like

Global surveyor: fine structure map

Present surface properties:

Dry and cold. Polar caps. Global dust storms

young features on one and old features on the other hemisphere.

continuous volcanism: huge volcanos, extensive faults

local and regional tectonics

floods of enormous magnitude near the polar caps

Gross properties:

Radius, 3,396 km about half that of Earth

Mass: about 0.1 that of the Earth, interior is cool more easily

spin period is about 24 hours

cool temperature: 273 K in the summer.

Findings of Mars explorations

Rock samples:

wide range in silicon's abundance: signs for differentiation

fine sand: weathering products and mixing by dust storm

Highlands and plane dichotomy

craters on highlands: older than 3.8 Gy.

Mars crater more degrade than the lunar craters: erosion

branching valleys are common on Mars

smooth area between the craters

ejecta form thin sheets similar to splash in a mud pond

Volcanos:

Biggest in the solar system: a thick lithosphere

faults

stacks of sedimentary formation

Water flooding

Channels and valley networks

catastrophic release of water pool

sudden eruption of ground water.