What are the main characteristics of our solar system?
four small planets close to the Sun and four large planets far from the Sun
The formation of terrestrial-type planets around a star is most likely to have occurred by what process?
accretion, or slow accumulation of smaller particles by mutual gravitational attraction
The average density of the large, outer planets is
close to the density of water.
What fraction of the mass of Earth is made up of the elements hydrogen and helium?
much less than 1%
At what point in time do we say that the protosun became the Sun?
when thermonuclear fusion reactions began at its center
Most of the mass of the universe—98%—is in the form of
hydrogen and helium
The region at the farthest limits of the solar system in which a large number of objects composed of rock and ice circle the Sun in a roughly spherical region is called the
Oort comet cloud
The average density of a planet is
its total mass divided by its total volume
Which planets do not have any natural satellites?
Mercury and Venus
The planet with the greatest mean density is
How do we measure the mass of an extrasolar planet?
We use Newton's law of gravity, using the measured distance of the planet from its star and the planet's gravitational pull on the star
What is the basic difference between comets and asteroids?
Comets are mostly composed of ices, whereas asteroids are mainly composed of rocks
In our solar system, which of the following planets is not a member of the terrestrial group?
Which of the following characteristics is not typical of our planetary system?
The physical size of most of the planets is about the same
Pluto is a 2:3 resonance orbit with Neptune. What does this mean?
During the time Neptune orbits the Sun three times, Pluto orbits it twice
Fusion is the process by which
elements are transformed into heavier elements by nuclear reactions.
The largest of the terrestrial planets is
The asteroid belt exists between the orbits of which planets?
Mars and Jupiter
The smallest planet in our solar system is
A curious fact about the structure of the planet Jupiter, compared with the structure of Earth, is that it has
much greater mass but much lower average density
At the present time, the discoveries of how many extrasolar planets have been confirmed?
Viewed from a position above the north pole of the Sun, the direction of the motion of the planets in their orbits is
What is surprising about the extrasolar planets that have so far been discovered?
Many of the extrasolar planets are giant planets like Jupiter, orbiting at distances characteristic of terrestrial planets like Earth, where giant planets cannot form
What is the Kuiper belt?
relatively flat distribution of objects in the plane of the ecliptic, extending from around the orbit of Pluto out to about 50 AU from the Sun
Accretion is the process by which
dust grains and ice crystals coalesce to form planetesimals