The following statements summarize and describe many of the key terms and concepts presented in the chapter.
- The planets can be arranged into two groups: the terrestrial
(Earth-like) planets (Mercury, Venus, Earth, and Mars) and the
Jovian (Jupiter-like) planets (Jupiter, Saturn, Uranus, and
Neptune). Pluto is not included in either group. When compared to the Jovian planets,
the terrestrial planets are smaller, more dense, contain proportionally more rocky material,
have slower rates of rotation, and lower escape velocities.
- The lunar surface exhibits several types of features. Most craters were
produced by the impact of rapidly moving interplanetary debris (meteoroids).
Bright, densely cratered highlands (terrae) make up most of the
lunar surface. The dark, fairly smooth lowlands are called maria (singular,
mare). Maria basins are enormous impact craters that have been flooded with
layer upon layer of very fluid basaltic lava. All lunar terrains are mantled with a
soil-like layer of gray unconsolidated debris, called lunar regolith, which
has been derived from a few billion years of meteoric bombardment. Much is still unknown
about the Moon's origin. One hypothesis suggests that a giant asteroid collided with Earth
to produce the Moon. Scientists conclude that the lunar surface evolved in four
phases: (1) the original crust; (2) lunar highlands; (3)
maria basins; and (4) youthful rayed craters.
- Mercury is a small, dense planet that has no atmosphere and exhibits
the greatest temperature extremes of any planet. Venus, the brightest planet
in the sky, has a thick, heavy atmosphere composed of 97 percent carbon dioxide, a surface
of relatively subdued plains and inactive volcanic features, a surface atmospheric pressure
90 times that of Earth's, and surface temperatures of 475°C (900°F).
Mars, the Red Planet, has a carbon dioxide atmosphere only 1 percent as dense
as Earth's, extensive dust storms, numerous inactive volcanoes, many large canyons, and
several valleys of debatable origin exhibiting drainage patterns similar to stream valleys
on Earth. Jupiter, the largest planet, rotates rapidly, has a banded
appearance caused by huge convection currents driven by the planet's interior heat, a
Great Red Spot that varies in size, a thin ring system, and at least 16 moons
(one of the moons, Io, is a volcanically active body). Saturn is best known
for its system of rings. It also has a dynamic atmosphere with winds up to 930 miles per
hour and storms similar to Jupiter's Great Red Spot. Uranus and
Neptune are often called the twins because of similar structure and
composition. A unique feature of Uranus is the fact that it rotates on its side. Neptune has
white, cirruslike clouds above its main cloud deck and an Earth-size Great Dark
Spot, assumed to be a large rotating storm similar to Jupiter's Great Red Spot.
Pluto is a small frozen world with one moon (Charon). Pluto's noticeably
elongated orbit causes it to occasionally travel inside the orbit of Neptune, but with no
chance of collision.
- The minor members of the solar system include the asteroids,
comets, and meteoroids. Most asteroids lie between the orbits of
Mars and Jupiter. No conclusive evidence has been found to explain their origin. Comets are
made of frozen gases (water, ammonia, methane, carbon dioxide, and carbon monoxide) with
small pieces of rocky and metallic material. Many travel in very elongated orbits that carry
them beyond Pluto, and little is known about their origin. Meteoroids, small solid particles
that travel through interplanetary space, become meteors when they enter
Earth's atmosphere and vaporize with a flash of light. Meteor showers occur
when Earth encounters a swarm of meteoroids, probably material lost by a comet.
Meteorites are the remains of meteoroids found on Earth. The three types
of meteorites (classified by their composition) are (1) irons, (2)
stony, and (3) stony-irons. One rare kind of meteorite, called a
carbonaceous chondrite, was found to contain amino acids and other organic
compounds.
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