astronomy chapter 7

the sun is made of ____ H and ____ He

74% and 24%

the big bang formed….

H, He, and Li

where were most heavier elements formed

insides stars through nuclear fusion and dring stellar explosions

what is nuclear fusion

the process of combining lighter atomic nuclei to form heavier nuclei

what is a supernova

a powerful explosion that occurs when certain massive stars reach the end of their lives

what happens to element released by dying stars?

they spread into space and can become part of new stars and planets

how old is the solar system

~4.6 billion years old

what is radiometric dating

a method of determining age by measuring radioactive decay

what is a half life?

the time required for half of a radioactive substance to decay

what condition must a rock meet for accurate radiometric dating?

it must remain unaltered since it solidfied

where were the oldest rocks found

on the moon

how can crater counts estimate a surfaces age?

older surfaces generally have more impact craters

what is a solar nebula

an interstellar cloud of gas and dust from which the solar system formed

how cold was the solar nebula

~7-20 kelvin

how large was the solar nebula

~2,000-20,000 AU across

what probably happened near the solar nebula to start its collapse

a cataclysmic event compressed the cloud under pressure

what caused the nebula to keep collapsing once it started

its own gravity pulled the matter inward

what formed at the center of the collapsing nebula

the protosun

how did the protosun gain mass

more matter built up on it as the nebula collapsed

what happened to the protosuns density as it grew

its density increased

what happened to the protosuns temp. as it contracted

its temp. increased

what was the first light emitted by the protosun before nuclear fusion?

blackbody radiation, produced as the protosun heated up

what is angular momentum

a measure of rotational motion around an axis

what is conservation of angular momentum?

angular momentum stays constant in an isolated system

what happened to the solar nebulas rotation speed as it shrank?

its rotation speed increased as its size decreased

why did the solar nebula form a disk shape?

rotation caused the gas and dust to flatten into a disk

what formed at the center of the rotating nebula

a hotter,denser, more rapidly rotating central region

what is a protoplantary disk

a disk of gas and dust around a young star where planets can form

what did models predict about early planet forming systems

they would form a disk and bulge shape

what happens to gas and dust in a protoplanetary disk

they collide and clump together gradually forming larger pieces

what are planetesimals

large clumps that attract smaller pieces through gravity

why are planetesimal important

they act as seeds that grow into planets

what happened as the protosuns central temperature rose?

ice and cold molecules near the protosun melted

what pushed light particles outward from the protosun?

radiatino from the protosun pushed hydrogen and helium outward

what is the snow line (frost line)

the boundary beyond which gases and ices could remain solid and frozen

where was the snow line located in the early solar system

about 3 Au from the sun between mars and jupiter

why are planets closet to the sun rocky and low in gas

high temperatures near the sun prevented ices and gases from remaining there

what happened when the suns core reached critcal temp. and pressure?

hydrogen fusion began in the core

when did the sun being hydrogen fusion?

about 500 million years after the collapse began

what does nuclear fusion in the sun produce?

large amounts of energy, including energetic photons

what happened when photons moved outward from the suns core

the increased radiation disturbed the remaining gas in the protoplanetary disk

how did the suns birth affect planet formation

the increased radiation and solar activity caused planet formation to cease

How many planets orbit the Sun in the same direction that Earth does?

all

In essence, the nebular theory holds that _______.

our solar system formed from the collapse of an interstellar cloud of gas and dust

Where would you expect terrestrial planets to form in the solar nebula?

anywhere between 0.3AU and the frost line

The jovian planets are thought to have formed as gravity drew hydrogen and

helium gas around planetesimals made of _______

rocks, metals, and ices

What do we mean by the frost line when we discuss the formation of planets in the solar nebula?

It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense

What is the 'giant impact hypothesis' for the origin of the Moon

The Moon formed from material blasted out of Earth's mantle and crust by the impact of a Mars-size object

You find a meteorite containing radioactive potassium-40 and its decay product argon-40. You assume that all the argon-40 was made from radioactive decay of potassium-40. The rock now has twice as much argon-40 as potassium-40; that is, 2/3 of the original potassium-40 has decayed into argon-40 while 1/3 remains in the rock. Based on the graph of the previous question, about how old is the rock?

2 billion years

According to modern scientific dating techniques, approximately how old is the solar system?

4.5 billion years

In the same evolutionary sequence of a collapsing gas cloud shown in the previous question, what law explains why the center of the cloud becomes so much hotter as the cloud shrinks in size?

The law of conservation of energy

Which of the following best explains why we can rule out the idea that planets are usually formed by near-collisions between stars?

Stellar near-collisions are far too rare to explain all the planets now known to orbit nearby stars

According to our modern science, which of the following best explains why the vast majority of the mass of our solar system consists of hydrogen and helium gas?

Hydrogen and helium are the most common elements throughout the universe, because they were the only elements present when the universe was young

According to our present theory of solar system formation, which of the following statements about the growth of terrestrial and jovian planets is NOT true?

The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal

What is the primary basis upon which we divide the ingredients of the solar nebula into four categories (hydrogen/helium; hydrogen compound; rock; metal)?

The temperatures at which various materials will condense from gaseous form to solid form

Many meteorites appear to have formed very early in the solar system's history. How do these meteorites support our theory about how the terrestrial planets formed?

The meteorites appearance and composition is just what we'd expect if metal and rock condensed and accreted as our theory suggests

According to present understanding, which of the following statements about the solar wind is not true?

It is even stronger today than it was when the Sun was young

According to our present theory of solar system formation, how did Earth end up with enough water to make oceans?

The water was brought to the forming Earth by planetesimals that accreted beyond the orbit of Mars

What is the primary reason that astronomers suspect that some jovian moons were captured into their current orbits?

Some moons have orbits that are 'backwards' (compared to their planet's rotation) or highly inclined to their planet's equator

Why are terrestrial planets denser than jovian planets?

Only dense materials could condense in the inner solar nebula

The region of our solar system between Mercury and Mars has very few asteroids, while the region between Mars and Jupiter has many asteroids. Based on what you have learned, what is the most likely explanation for the lack of asteroids between Mercury and Mars?

There were very few planetary leftovers in this region, because most of the solid material was accreted by the terrestrial planets as the planets formed

According to modern science, what was the approximate chemical composition of the solar nebula?

98 percent hydrogen and helium, 2 percent everything else

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from?

They were produced by stars that lived and died before our solar system was born

What do we mean by accretion in the context of planet formation?

The growth of planetesimals from smaller solid particles that collided and stuck together

What do we mean by the period of heavy bombardment in the context of the history of our solar system?

The first few hundred million years after the planets formed, which is when most impact craters were formed.