Astronomy #2 (ch.8)

The most probable time sequence for the solar system's formation was that the

Sun contracted first as a gas ball, and the planets and moons formed shortly afterward by accretion and condensation.

According to modern theories, one significant difference between the formation of the terrestrial and Jovian planets is that

both formed by accretion of planetesimals, but the Jovian planets became massive enough to attract gas onto them directly from the solar nebula.

The most probable theory for the solar system's formation is

gas and dust clouds condensed to form the Sun, while planets formed later within a nebular disk.

The most common elements in the universe are

hydrogen, smaller quantities of helium, and very small quantities of heavier elements.

The birthplace of the Sun and planets (and of other stars and maybe their planets) is thought to have been

in cool gas and dust clouds.

The environment where the Jovian planets initially formed contained all the following ingredients except one. Which was the exception?

liquids (water and ammonia)

Radioactive decay in an atom occurs because the

nucleus contains a mix of neutrons and protons that is not stable.

Together, hydrogen and helium account for what percentage of the total mass of all matter in the universe?

98%

In order to employ the radioactive age-dating technique on a sample of rock, it is necessary to know all of the following except one. Which is the exception?

the mass of the rock when it was formed

The temperature began to rise at the center of the solar nebula because

the nebula was contracting, increasing the speed of motion of the atoms.

The ages of meteorites have been found through radioactive dating. One major difficulty with this technique is that

the original abundances of the elements are not precisely known.

What is the process of chemical differentiation?

the sinking of heavy material to the center of a planet or other object and the rising of lighter material toward the surface

The protosun became a full-fledged star when

thermonuclear fusion reactions began at its center.

At the present time, how many extrasolar planets have had confirmed discoveries?

thousands

Each of the following is a technique used to discover exoplanets except one. What is the exception?

ultraviolet excess

The most common ices in the early solar nebula were

water ice, methane, and ammonia.

The timescale over which material in the solar nebula accreted to form planets was about

100 million years.

Our solar system seems to have formed about how long ago?

5 billion years

How has the present mix of chemical elements in the universe been produced?

H and some He were formed in the Big Bang, while the heavier elements have been slowly formed in the centers of stars over the life of the universe.

What is surprising about the planet orbiting the star 51 Pegasi?

It has a mass almost as large as Jupiter, but its orbital radius is smaller than that of Mercury.

When dealing with radioactive decay of materials, we often read about the age of a particular rock. What is meant by the age of a rock?

It is the time since the rock was formed and the elements within the rock were isolated with definite abundance ratios.

What type of search technique has discovered the largest number of planets around the stars other than the Sun?

Looking for tiny variations in the star's radial velocity, caused by the gravitational pull of one or more planets orbiting the star.

A theory of the origin of the solar system must take into account all important general properties of the planets. These include three of the four properties listed below. Which one is not an important general property of the planets?

The magnetic fields of the planets are produced by a variety of mechanisms.

In describing the early solar system we discuss solids and vapors but no liquids. Why do we believe liquids were absent?

The pressure in the solar nebula was too low to permit liquids to exist.

A proplyd is

a protoplanetary disk, such as is observed around some stars in the Orion nebula, for example.

The Oort cloud is

a spherical solar system halo of icy objects far beyond the orbit of Pluto.

Astrometry is the very precise measurement of

a star's position in the sky (e.g., to measure its motion).

The steps in the process of formation of the large, outer planets were

accretion of planetesimals to form a core, followed by gravitational capture of hydrogen and helium gas.

The manner in which the terrestrial planets formed was

accretion of solid planetesimals containing mostly rocky material.

The age of the solar system has been dated rather precisely to 4.56 billion years. What method was used to determine this number?

determining the age of meteorites by radioactive dating

Suppose you were to go back in time and explore the early solar nebula (during the formation of the solar system). If you were to travel outward from the protosun, the first solid material you would encounter would be

dust-sized grains of iron and rocky material.

If a large cloud of gas and dust is initially rotating, and it begins to contract without losing any mass, it will rotate

faster.

Most of the elements beyond H and He in the periodic table in our Sun and solar system probably originated

from fusion reactions in the centers of earlier stars.

What name is given to the concentration of mass that formed at the center of the solar nebula, eventually becoming the Sun?

protosun

The most probable process for the formation or acquisition of the Sun's planets is

relatively slow growth of smaller objects by collisions and mutual gravitational attraction.

What process heated the early solar nebula as it slowly condensed toward a central protosun?

release of heat by collisions of particles as they gain kinetic energy in falling toward the center of the nebula

Which of the following types of material has the highest condensation temperature in the planetary system?

rocks and dust grains

The three common substances believed to have been important in planet formation are

rocks, ices, and gas.

The process of accretion in planetary formation is the

slow accumulation of solid particles by gravity and collision into larger, solid objects.

What are chondrules?

small, glassy spherical pebbles contained in most meteorites

The reason most of the terrestrial planets have dense, iron cores is because

terrestrial planets were initially molten or partially molten, and the iron sank to the center.