as101 lesson 10

Mercury

Terrestrial planet

Mercury orbital properties

Closest planet to Sun; average distance about 0.39 AU; eccentric orbit; no seasons because axial tilt ~0°

Mercury geology

Heavily cratered, large iron core, Caloris Basin, old volcanism, geologically dead

Mercury atmosphere

Extremely thin; mainly atoms like He, Na, O from surface bombardment

Mercury magnetic field

Present but weak; about 1% of Earth’s

Mercury exploration

Mariner 10 flybys; MESSENGER orbiter and surface study

Venus

Terrestrial planet

Venus orbital properties

0.72 AU from Sun; nearly circular orbit; very slow retrograde rotation; no real seasons

Venus geology

Volcanic plains, highlands, little/no plate tectonics, probable past/possible recent volcanism

Venus atmosphere

Very dense; mostly CO2; pressure about 90 times Earth’s; sulfuric acid clouds

Venus greenhouse effect

Runaway greenhouse causes hottest surface of any planet

Venus magnetic field

No significant global magnetic field

Venus exploration

Mariner 2, Venera landers, Pioneer Venus, Magellan radar mapping, Venus Express

Earth

Terrestrial planet

Earth orbital properties

1 AU from Sun; nearly circular orbit; 23.5° tilt causes seasons

Earth geology

Active plate tectonics, volcanism, erosion, differentiated interior

Earth atmosphere

Mostly N2 and O2; liquid water present; ozone layer present

Earth magnetic field

Strong magnetosphere protects from solar wind

How Earth’s core is studied

Seismic waves from earthquakes

Earth lesson: global warming

Human-added greenhouse gases increase warming risk

Earth lesson: ozone depletion

CFCs destroy ozone, increasing harmful UV exposure

Earth lesson: mass extinction

Impacts and human activity can cause major species loss

Moon origin

Most accepted theory is giant impact hypothesis

Moon characteristics

Large relative to Earth, no substantial atmosphere, geologically dead, tidally locked

Moon surface

Highlands, maria, many impact craters, little/no erosion, no plate tectonics

Moon water ice

Detected near polar regions in permanently shadowed areas

Moon atmosphere

Virtually none

Moon missions significance

Apollo returned rock samples; orbital/lander missions mapped surface, age, composition, and confirmed polar ice

Why Moon matters

Helps explain Earth’s history, impacts, and early solar syst