Man must rise above Earth, to the top of the atmosphere and beyond; for only then will he fully understand the world in which he lives. Socrates

The Earth and Other Planets

Science 2201

Chapter 16

“morning stars”& wanderers

Geocentric Solar System

Heliocentric Model

Solar System

Figure 16-1

Most of the mass in the solar system is in the Sun, and most of the rest is in the Jovian planets. (Distances in this figure are not to scale.)

The Sun and its Planets

• Planets and moons tend to orbit about the sun in a counterclockwise direction

• Orbits of planets and their moons are in the same general plane

• Planets and moons tend to rotate on their axis in counterclockwise direction

Solar System

The Nebular Hypothesis

• theory for origin of solar system

• rotating nebula had formed gaseous rings which condensed into the planets and moons, with the nebula’s nucleus forming the sun p. 323

Figure 16-2

As the nebula that formed the solar system collapsed, it began to rotate and flatten into a disk. The stages in solar system formation include (a) a slowly rotating nebula, (b) a flattened disk with massive center, (c) planets in the process of birth represented as mass concentrations in the nebula, and (d) the solar system.

The Planets

Mercury (.39 au)

Small, rocky, airless world withan extreme climate!

• Mariner 10, did 3 flybys 1974-75• Years & Days: “fastest planet”

– Orbital period = 88 Earth days– Rotation period = 59 Earth days

• Planet of Extremes– Day temp’s exceed 800oF– Night temp’s drop to –280oF

• Surface:– Almost doubles as the moon. Mercury contains impact craters

ranging from ½ mile to one over 800 miles wide. Ridges and basins filled with cooled lava fill the picture.

Venus (.72 au)

A forbidding yet fascinating worldof scorching temp’s, rocky plains,& huge volcanoes.

• Data from 17 landing probes & 18 flybySpacecraft (Pioneer of ‘78 & Magellan of ’93)• An Out-of-Control Greenhouse Effect

– 30-mile thick atmosphere of CO2 generates surface pressure 100X Earth’s and traps heat, sustaining temp’s > 800oF.

• Slow and Backward Planet– Venus rotates very slowly, once every 243 Earth days– Venus orbits the sun every 225 Earth days, so on Venus, a day is

longer than a year!– Spins not from west to east, like the other planets, but from east

to west. Perhaps an asteroid collision set Venus on a backward rotation.

Earth (1 au)

The very special “third rock.”

Hospitable Home Planet• Vast oceans of liquid water and protective atmosphere

rich in oxygen.

• Orbits in stable, nearly circular path, so never too far or too close to the Sun

• One Moon—large by solar system standards—acts to stabilize Earth, preventing tilt from shifting wildly.

• Oceans of water absorb and transfer heat, regulating global temperatures.

• Precious envelope of air serves as a breathable, protective blanket.

Mars (1.52 au)

The red planet, our nearest neighbor.

• Observed by Mariner 9, ‘71, Viking ‘77,

And Pathfinder spacecraft of 1997

• An Unearthly World– Thin atmosphere (like Earth’s at 140,000 ft) of 95% CO2

– Elliptical orbit accentuates seasonal differences—temp range from –190oF to 62oF

– Dry, desolate surface, but tilted axis gives it polar ice caps

– 2 small moons: Deimos & Phobos—may be captured asteroids

– Olympus Mons – 13 mile high volcanoe the size of Arizona!

– Valles Marineris – system of canyons up to 4 miles deep forms an immense gash 2500 miles across.

Asteroids

Tens of thousands of small rocky bodies orbit the sun in a large area between Mars and Jupiter. (asteroids, or better, planetoids)

• Thought to be material that failed to become a planet during formation of solar system.

Asteroids

Rocks in space through which the Earth passes as it travels around the Sun.

• Meteors may be tiny grains of sand or may be very large.

• Billions enter Earth’s atmosphere each year, encounter friction some 50 miles overhead and burn white hot.

• If lands = meteorite.

Meteors

The Planets kidzone link