Astronomy chapter 4

Redshift

Light shifted to longer wavelengths when an object moves away; used to measure planetary rotation

3-to-2 spin–orbit coupling

Mercury rotates 3 times for every 2 orbits

Retrograde rotation

Rotation opposite the direction of orbit (Venus)

Prograde rotation

Rotation in the same direction as orbit

Late Heavy Bombardment

Early period of intense impacts that formed many craters

Crater

Bowl-shaped depression from an impact

Scarp

Cliff formed when a planet’s crust shrinks

Convection

Heat transfer by moving material

Runaway greenhouse effect

Feedback loop where heating releases more greenhouse gases and traps more heat

Mercury orbit distance

0.387 AU

Mercury orbital period

88 Earth days

Mercury eccentricity

0.206

Mercury rotation period

59 Earth days

Mercury rotation direction

Prograde

Mercury diameter

4880 km

Mercury density

5430 kg/m³

Mercury temperature

Day 350°C, Night −170°C

Mercury surface age

Oldest of inner planets

Mercury core

Very large iron core

Mercury magnetic field

Weak but present

Mercury scarps

Cliffs from crust shrinking

Why Mercury has a large core

Giant planetesimal impact stripped mantle

Why Mercury’s dynamo is confusing

Planet is small but still has a magnetic field

Venus orbit distance

0.723 AU

Venus orbital period

225 Earth days

Venus eccentricity

0.01

Venus rotation period

243 Earth days

Venus rotation direction

Retrograde

Venus diameter

12,104 km

Venus density

5243 kg/m³

Venus temperature

460°C everywhere

Venus atmosphere

Thick carbon dioxide clouds

Venus surface age

Relatively young

Venus tectonics

Flake tectonics

Why Venus has few craters

Surface resurfaced by volcanism

Why Venus has no magnetic field

Slow rotation and no core convection

Evidence of volcanism on Venus

Few craters and lava flows

Why Venus has same temperature everywhere

Thick CO₂ atmosphere traps heat

Runaway greenhouse on Venus

Heat releases more CO₂, trapping more heat

Earth orbit distance

1 AU

Earth orbital period

365 Earth days

Earth eccentricity

0.02

Earth rotation period

23.9 hours

Earth rotation direction

Prograde

Earth diameter

12,756 km

Earth density

5515 kg/m³

Earth temperature range

60°C to −90°C

Earth atmosphere

Nitrogen and oxygen

Earth tectonics

Moving plate tectonics

Earth magnetic field

Strong

Why Earth supports life

Magnetic field and moderate climate

Earth surface water

Covers about 70%

Mars orbit distance

1.5 AU

Mars orbital period

687 Earth days

Mars eccentricity

0.09

Mars rotation period

24.6 hours

Mars rotation direction

Prograde

Mars diameter

6794 km

Mars density

3934 kg/m³

Mars temperature range

20°C to −140°C

Mars atmosphere

Thin carbon dioxide

Mars tectonics

Two crustal plates

Mars volcano

Largest shield volcano

Mars magnetic field

Lost

Why Mars lost atmosphere

Lost magnetic field

Evidence Mars was geologically active

Volcanoes and surface features

Evidence of water on Mars

River valleys, ice caps, minerals

Runaway icehouse on Mars

CO₂ freezes, cooling increases

Internal heat causes geology

Drives volcanism and tectonics

Magnetic field protects atmosphere

Shields from solar wind

Why dense elements are in cores

They sink during differentiation

Volcanoes create atmospheres

Release gases

Convection in cores

Creates magnetic fields

Convection in atmospheres

Causes winds

Cratering indicates age

More craters means older surface

Heavily cratered surface indicates

Geologically old

Planet with largest greenhouse effect

Venus

Planet with oldest surface

Mercury

Planet with two crustal plates

Mars

Planet with plate tectonics

Earth

Slowest rotating planet

Venus

Main gas in Mars atmosphere

Carbon dioxide

Correct orbital order

Mercury, Venus, Earth, Mars

Planet with Moon-like surface

Mercury

Planet with strongest magnetic field

Earth