Astronomy Chapter 8
Why did the solar nebula heat up as it collapsed?
As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy.
How massive would Earth have been if it had accreted hydrogen compounds in addition to rock and metal? Assume the same proportion of the ingredients as listed in the table. Materials in the Solar Nebula Hydrogen and Helium Gas hydrogen, helium do not condense in nebula 98% Hydrogen Compounds water (H2O), methane (CH4), ammonia (NH3) <150 K 1.4% Rock various minerals 500-1300 K 0.4% Metals iron, nickel, aluminum 100-1600 K 0.2% Express your answer using two significant figures
MicyEarth/MrealEarth = 3.3
According to our theory of solar system formation, why do we find some exceptions to the general rules and patterns of the planets?
Most of the exceptions are the result of giant impacts.
Within the frost line, planetesimals were composed entirely of rock and outside the frost line planetesimals were composed entirely of ice.
False
The materials that made up the solar nebula can be categorized into the four general types as follows. Rank these materials from left to right based on their abundance in the solar nebula, from highest to lowest.
Hydrogen and Helium Gas Hydrogen Compounds Rock Metals
According to the nebular theory, how did the Kuiper belt form?
It is made of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet.
What is the significance of this image? Image https://media.pearsoncmg.com/aw/aw_bennett_tcp_8/img/8_04b_CO_Figure.jpg
It shows an actual disk of material orbiting another star, providing strong evidence the planets really do form in such disks.
The materials that made up the solar nebula can be categorized into these four general types. Rank these materials from left to right based on the temperature at which each would condense into a solid, from highest to lowest. Note: For a substance that does not condense at all, rank it as very low temperature.
Metals Rock Hydrogen Compounds Hydrogen and Helium Gas
What happened during the accretion phase of the early solar system?
Particles grew by colliding and sticking together.
What can you conclude from studying this graph? Graph http://media.pearsoncmg.com/aw/aw_bennett_tecp_3/images/06_010_VQ.jpg
Potassium-40 has a half-life of 1.25 billion years.
________________ allows us to determine the age of a solid rock.
Radiometric dating
What do meteorites reveal about the solar system?
They reveal that the age of the solar system is approximately 4.6 billion years.
Which of the following is the origin of almost all the large moons around the jovian planets?
They were formed by condensation and accretion in a disk of gas around the planet.
Earth's atmosphere resulted from the impact of icy planetesimals that originated in the outer regions of the Solar System.
True
Some radioactive isotopes found in meteorites suggest that the solar system may have been formed shortly after a supernova occurred nearby.
True
The more massive planets in the solar system tend to be less dense than the lower mass planets.
True
We have direct evidence from ALMA that supports nebular theory.
True
The nebular theory of the formation of the solar system successfully predicts all but one of the following. Which one does the theory not predict?
the equal number of terrestrial and jovian planets
What is being shown in the zoom-out box of this painting? Painting http://media.pearsoncmg.com/aw/aw_bennett_tcp_5_mu/vq/08_07_VQ.jpg
the formation of a jovian planet
What percentage of the solar nebula's mass consisted of rocky material?
0.4 percent
Suppose you find a rock that contains some potassium-40 (half-life of 1.3 billion years). You measure the amount and determine that there are 5 grams of potassium-40 in the rock. By measuring the amount of its decay product (argon-40) present in the rock, you realize that there must have been 40 grams of potassium-40 when the rock solidified. How old is the rock?
3.9 billion years
You find a rock 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, whereas 1/3 remains in the rock. Based on this graph, about how old is the rock? Graph http://media.pearsoncmg.com/aw/aw_bennett_tecp_3/images/06_010_VQ.jpg
2 billion years
What percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium?
2 percent
This diagram represents the solar nebula early in its history and shows the location of the frost line. Suppose you discover an object that is made of metal, rock, and ice. In which region of the solar system did it form? Diagram http://media.pearsoncmg.com/aw/aw_bennett_tecp_3/images/06_09_VQ.jpg
4
The age of our solar system is approximately
4.6 billion years.
What percentage of the solar nebula's mass consisted of hydrogen and helium gases?
98 percent
All the planets in the solar system rotate in the same direction as they orbit the Sun.
False
As you've learned from Part B, hydrogen and helium gas never condense under conditions found in the solar nebula. The remaining three categories of material in the solar nebula are shown again here. Rank these materials from left to right based on the distance from the Sun at which they could condense into a solid in the solar nebula, from farthest to closest.
Hydrogen Compounds Rock Metals
Why are the inner planets made of denser materials than the outer planets?
In the inner part of the nebula only metals and rocks were able to condense because of the high temperatures, whereas hydrogen compounds, although more abundant, were only able to condense in the cooler outer regions.
This painting shows an object colliding with Earth. What is thought to have happened as a result of this collision? Painting https://media.pearsoncmg.com/aw/aw_bennett_tcp_8/img/8_12_Figure.jpg
It blasted away debris that then accreted in Earth orbit to form the Moon.
Why did the solar nebula flatten into a disk?
It flattened as a natural consequence of collisions between particles in the spinning nebula, changing random motions into more orderly ones.
What is the leading hypothesis for the origin of the Moon?
It formed from the material ejected from Earth in a giant impact.
According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?
It got hotter, its rate of rotation increased, and it flattened into a disk.
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 would Earth's mass be, if it had been possible to capture hydrogen and helium gas in the proportion listed in the table? Express your answer using two significant figures.
MgaseousEarth/MrealEarth = 170
Which of the following is not evidence supporting the giant impact theory for the formation of the Moon?
Scientists have found several meteorites that appear to be the remains of the object that caused the giant impact.
According to our theory of solar system formation, why does the Sun rotate slowly today?
The Sun once rotated much faster, but it lost angular momentum due to internal friction. The Sun once rotated much faster, but it transferred angular momentum to charged particles caught in its magnetic field and then blew the particles away with its strong solar wind.
According to the nebular theory, what are asteroids and comets?
They are leftover planetesimals that never accreted into planets.
Where did the elements heavier than hydrogen and helium come from?
They were produced inside stars.
As viewed from above Earth's North Pole, all of the planets orbit the Sun in the same (counterclockwise) direction.
True
Based on our theory of how our own solar system formed, we would expect that other solar systems would be quite common.
True
Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass?
You'll have 0.25 kilogram of the radioactive substance remaining.
Jovian Planets Details
accreted from icy planetesimals ejected icy planetesimals that are now Oort cloud comets formed in regions cold enough for water to freeze large moons formed in surrounding disks of material formed in a region of the solar system with lower orbital speeds
Terrestrial Planets Details
accreted from planetesimals of rock and metal surfaces dramatically altered during the heavy bombardment
Mars was formed by the _____________ of smaller objects.
accretion
What does this photo show? Photo http://media.pearsoncmg.com/aw/aw_bennett_tcp_5_mu/vq/08_01_VQ.jpg
an interstellar cloud that will ultimately give birth to thousands of star systems
Based on our current theory of Earth's formation, the water we drink comes from
comets that impacted Earth.
Ice can form from a gas through the process of ________________
condensation.
Hydrogen compounds in the solar system can condense into ices only beyond the____________
frost line.
The first few hundred million years of the solar system's history were the time of the ___________________, during which Earth suffered many large impacts.
heavy bombardment
Which of the following types of material can condense into what we call ice at low temperatures?
hydrogen compounds
Which of the following lists the ingredients of the solar nebula from highest to lowest percentage of mass of the nebula?
light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metal
What kind of material in the solar nebula could remain solid at temperatures as high as 1,500 K, such as existed in the inner regions of the nebula?
metals
In essence, the nebular theory holds that _________.
our solar system formed from the collapse of an interstellar cloud of gas and dust
What was the frost line of the solar system?
the distance from the Sun where temperatures were low enough for hydrogen compounds to condense into ices, between the present-day orbits of Mars and Jupiter
Our Moon was most likely formed by a collision between Earth and a Mars-sized_________
planetesimal.
The heavy bombardment phase of the solar system lasted
several hundreds of millions of years.
Our solar system was created by the gravitational collapse of the__________
solar nebula.
The era of planet formation ended when the remaining hydrogen and helium gas of the solar nebula was swept into interstellar space by the ____________
solar wind.
At first, the Sun's present-day rotation seems to contradict the prediction of the nebular theory because
the theory predicts that the Sun should have been rotating fast when it formed, but the actual rotation is fairly slow.
The orbital speed of the solar nebula at Pluto's average distance from the Sun is about 5 km/sec. When the solar nebula was about 10000 AU in radius, how fast would the same material have orbited? (Remember that when the cloud was larger, motions were more random, so we can calculate only the average.) Use the law of conservation of angular momentum (see Section Conservation Laws in Astronomy).
v≈20m/s
Observations of young stars (as well as theory) tell us that when the Sun was young the solar wind
was stronger than it is today.
What is the most likely reason that there are no giant planets beyond Neptune?
By the time planetesimals grew to a large enough mass to hold onto an atmosphere, the solar nebula had been blown away.
The Moon probably formed at the same time that Earth formed, rather like the formation of a double planet.
False
Impacts were extremely common in the young solar system but no longer occur today.
False
Nebular theory predicts that other solar systems that formed in the same way should also have 8 planets.
False
Process of Science: We cannot test the nebular theory for the formation of the Solar System in a rigorous scientific way because the Sun and planets formed in the distant past.
False
According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane?
The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk.
This photo shows a slice of a meteorite. What is its significance? Photo http://media.pearsoncmg.com/aw/aw_bennett_tcp_5_mu/vq/08_06_VQ.jpg
The shiny metal flakes embedded in rock are just what we expect if condensation really occurred as the nebular theory predicts.
Which of the following are relatively unchanged fragments from the early period of planet building in the solar system?
all of the above
This sequence of paintings shows how a large gas cloud can collapse to become a much smaller, spinning disk of gas. What law explains why cloud spins faster as it shrinks in size? Paintings http://media.pearsoncmg.com/aw/aw_bennett_tecp_3/images/06_07_08_VQ.jpg
the law of conservation of angular momentum
This sequence of paintings shows how a large gas cloud can collapse to become a much smaller, spinning disk of gas. What law explains why the center of the cloud becomes so much hotter as the cloud shrinks in size? Paintings http://media.pearsoncmg.com/aw/aw_bennett_tecp_3/images/06_07_08_VQ.jpg
the law of conservation of energy
The age of the solar system can be established by radioactive dating of
the oldest meteorites.
Which of the following puzzles in the solar system cannot be explained by a giant impact event?
the orbit of Triton in the opposite direction to Neptune's rotation
