Exam 23: The Earths Companions

Io is the most volcanically active body in the solar system at this time.

Large, smooth, dark areas visible on the Moon with the unaided eye are called _____.

Planetismals are small planet-like bodies in our solar system.

To measure vast distances in the solar system, astronomers use the ____, the Earth's average distance from the Sun.

The gravity of Jupiter, Saturn, Uranus, and Neptune resulted in their becoming surrounded by envelopes of nitrogen-rich gas.

The existence of huge channels that look like dry riverbeds on Mars is strong evidence that it ____.

The nebular hypothesis proposes that our solar system was born about 1 billion years ago.

The largest part of a(n) ______ is its long, glowing tail, a narrow column of dust that may extend for 100 million km.

______ dominate the topography of lunar highlands.

Astronomers estimate that our galaxy contains ______ stars.

Mars is named for the Roman god of war, presumably because of its distinct _____ color when seen in the sky.

______ is the planet that is most like the Earth in diameter and mass.

The Moon and Mercury lack ______.

Like most stars the sun is made mainly of hydrogen.

Venus's atmosphere has much more carbon dioxide than that of Earth and its greenhouse effect is much stronger.

The sun, its eight planets and their moons, together with smaller objects such as asteroids and comets, form the ____.

Comets are small solid bodies of rock or iron in the outer part of our solar system.

The absence of fold mountains and the presence of many _______ imply that Mars has been geologically quiet for billions of years

The moon formed from debris blasted out of Mars by an impact of an object about the size of Mercury.

As meteors enter the Earth's atmosphere, large numbers are slowed by air resistance and may reach the ground as smaller fragments called meteorites.