Exam 3 Review

Venus rotates backward and Uranus and Pluto spin about an axis tipped nearly on its side. Based on what you learned about the motion of small bodies in the solar system and the surfaces of the planets, what might be the cause of these strange rotations?

Collisions were frequent in the early solar system, so it is not unlikely that these strange rotations are due to collisions of these planets with significantly large objects during their formation or subsequent evolution.

In which atmospheric layer are almost all water-based clouds formed?

Troposphere

Explain how an objects weight changes if the mass of a body changes and if the mass and/or the size of the planet changes

Tutoring

Venus and Earth are nearly the same size and distance from the Sun. What are the main differences in the geology of the two planets? What might be some of the reasons for these differences?

Venus and Earth are similar in having geology driven by mantle convection currents, which have brought hot lava near the surface and generate volcanic eruptions. These convection currents also placed stress on the crust and produced widespread tectonic features on both planets. Both have mountains, mountain ranges, and valleys. However, Venus also has unique features such as the coronae, and Earth has unique features such as the deep ocean trenches. Like Earth's surface, the surface of Venus is relatively young by solar system standards, less than a billion years. However, the geology of Earth is dominated by plate tectonics, whereas there is no indication of plate motions on Venus. Instead, Venus has "blob tectonics," where the rising of hot material from within plays a dominant role in sculpting its surface. In addition to the absence of plate tectonics, Venus is also different from Earth in having a much lower level of erosion, presumably because there is no precipitation and surface wind speeds are very low.

Newton's three laws of motion

- 1st states that every object will continue to be in a state of rest or move at a constant speed in a straight line unless it is compelled to change by an outside force. - 2nd states that the change of motion of a body is proportional to and in the direction of the force acting on it. f=ma. -3rd states that for every action there is an equal and opposite reaction (or: the mutual actions of two bodies upon each other are always equal and act in opposite directions)

Kepler's three laws

- 1st states that the orbits of all planets are ellipses. - 2nd states that the straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time. -3rd states that the square of a planet's orbital period is directly proportional to the cube of the semimajor axis of its orbit.

Ellipse

- A closed curve for which the sum of the distances from any point on the ellipse to two points inside (called the foci) is always the same. - Quantities: eccentricity, focus points, major axis, semimajor axis.

Describe the main driver of tectonic activity on Earth

- The Earth mantle is plastic and allows for (slow) convection currents due to the temperature difference between the top and bottom. - Convection results in Earthquakes: Sudden release of tension built up at plate boundaries. - Convection impacts volcanic activity: A volcano is a rupture in the crust of Earth near a plate boundary, that allows hot lava, volcanic ash, and gases to escape from below the surface. - Outer core convection has a magnetic field.

Compare the atmospheres of the terrestrial planets (pressure, composition)

- All of these bodies have solid rock surfaces, with common tectonic features, although the exact appearance depends on the planet's gravity, internal heat, and atmosphere. - Mercury: No atmosphere due to low gravity and the fact that the Sun blows it away. - Venus: Densest atmosphere, but it is thin compared to the size of the planet and the size of the giant's atmospheres. Consists of carbon dioxide (96%), 3.5 nitrogen, and small amounts of argon and oxygen. Pressure is 95 bars. - Earth: 78% nitrogen, 21% oxygen, 1% argon, traces of water vapor (H2O), carbon dioxide. Pressure is around 1 bar. - Mars: Average surface pressure at 0.007 bar, less than 1% of Earth. Composed of 95% of carbon dioxide, 3% nitrogen, and 2% argon. Thin.

Describe two ways to date planetary surfaces

- Date surfaces by counting craters. Density and superposition help you count.

Describe what factors determine the temperature of a planet

- Distance from Sun - Surface reflectivity (albedo) - Presence of atmosphere and atmospheric composition. Some gases can absorb far-infrared emitted by the surface.

Describe the best hypothesis we have for the formation of the Moon

- Giant Impact Hypothesis says that Earth was hit by large chunks of material orbiting in the inner solar system at the time terrestrial planets were forming. Material was ejected from the Earth. This material then condensed into the Moon.

Describe the components of Earth's interior and explain how scientists determined its structure

- Has been measured by Earthquakes. Transmission of seismic waves. These waves spread through the interior of Earth. - Mantle: The largest part of solid Earth. Consists of silicate. Plastic, and allows for (slow) convection currents due to the temperature difference between the top and bottom. - Core: Metallic, dense, larger than Mercury. The outer core is liquid, inner is solid. Contains iron, nickel, and sulfur, all compressed to a very high density. The inner core is solid due to high pressure at the center.

Explain how earthquakes can help us to describe (model) the Earth's interior

- If we know the arrival time from its origin, we can calculate the speed. By measuring earthquake arrival times, we can model the Earth's interior

Describe the common tectonic and impact features on these, planets and explain how they differ

- Mercury: Heavily cratered (old) with impact basins, but no large uplift. Has the highest scarps (Fault lines due to shrinking). - Venus: Venus is still tectonically active (more than 1400 pancake shaped volcanos), has a young surface (200 million years). We don't know whether it has global plate tectonics. - Earth: Younger surfaces indicating tectonic activity resurfacing them and planet that has global plate tectonics (moving plates). Shows tectonic ridges, where the crust stretched, and new surface formed. - Mars: Has the largest volcanos in the solar system due to its lack of global plate tectonics, the height difference between Venus and Earth volcanos is probably due to lava quality and high atmospheric pressure. Tectonic ridge is called Valles Marineris.

Describe how did the Earth atmosphere changed since its formation

- Temperature of Earth is increasing due to more GHGs.

Explain the reason for the tides on Earth, and how it affects the evolution of the system

- The Moon's gravitational pull generates something called the tidal force. The tidal force causes Earth—and its water—to bulge out on the side closest to the Moon and the side farthest from the Moon. - The change between wet and dry sequences might have helped the evolution of life.

Describe the physical process behind the greenhouse effect

- The gases keep infrared radiation from rapidly escaping into space, resulting an in an increase in temperature.

List at least three of the evidences for plate tectonics

- The matching outline Of the continents -Identical fossils on continents that are separate today -New seafloor -Satellite measurements of the plates' velocity

Explain what do we mean by planetary dynamo and describe what conditions are necessary to create a magnetic field for a planet

- The planetary dynamo is the physical process responsible for the Earth magnetic field. - In the liquid, conductive outer core the convection currents create magnetic field, which become aligned due to the Coriolis force (Earth rotation).

What is the difference between a differentiated body and an undifferentiated body, and how might that influence a body's ability to retain heat for the age of the solar system?

A differentiated body is one that has been heated to the point where it is liquid, and heavier, denser materials sink to the center of the planet, and the lighter elements rise to the outer layer. The concentration of materials helps to retain heat in the interior of a planet. Undifferentiated bodies were never heated enough for the elements to separate; they cool quickly and are typically smaller in size.

What is a dust devil? Would you expect to feel more of a breeze from a dust devil on Mars or on Earth? Explain.

A dust devil is a strong, tightly formed local whirlwind, which can move along a planet's surface. They can arise on Earth or on Mars, but because the martian atmosphere is so thin, you would feel much less breeze from a martian dust devil than from one on Earth.

Explain briefly how the following phenomena happen on Earth, relating your answers to the theory of plate tectonics A. earthquakes B. continental drift C. mountain building D. volcanic eruptions E. creation of the Hawaiian island chain

A. Tectonic plates can crash together (pull apart, burrow under another, slide alongside each other, jam together) causing part of Earth's crust to move and quake. B. Tectonic plates can slowly separate the crust, which could cause a continent to be detached from its parent body of land C. Tectonic plates jam against another, forcing the crust upwards along with deep rock being pushed above the surface. The great pressure from the plates essentially causes the Earth to buckle. D. Volcanoes are found at mid ocean ridges (mountain ranges formed at Earth's mantle at plate boundaries) and along subduction zones E. Hawaiian Island Chain came from "hot spots" where heat is rising from the mantle, it feeds volcanoes, and as plates shifted a chain of volcanoes formed.

As friction with our atmosphere causes a satellite to spiral inward, closer to Earth, its orbital speed increases. Why?

According to Kepler's third law, P^2=a^3, where a is the semimajor axis (essentially the distance from the center of Earth in our case). If the satellite spirals in (because of air friction), a decreases and, hence, so does P. Note that P = 2πa/V,, or V µ1/a0.5.Thus, a decrease in a means an increase in V.

Two asteroids begin to gravitationally attract one another. If one asteroid has twice the mass of the other, which one experiences the greater force? Which one experiences the greater acceleration?

According to Newton's Second Law, mass is inversely related to acceleration. This means the smaller one will have the greater acceleration. Since Newton's law of gravity says the force is proportional to the product of the two masses, both masses experience the same force.

One of the primary scientific objectives of the Apollo program was the return of lunar material. Why was this so important? What can be learned from samples? Are they still of value now?

Astronomy involves inferring the nature of celestial objects by observing and analyzing the light from them. In general, all we can do is look, not touch. Lunar science is quite different in this respect. Bringing back material from the Moon allows us to experiment directly on it. We can use radioactive dating methods on Moon rocks to determine the age of the Moon. From the composition of the lunar material, we can learn more about lunar chemistry and what this tells us about the Moon's origins. These findings provide clues to the origin and evolution of the Moon (and Earth too.) Having actual material from the Moon is a great step beyond merely observing its surface from Earth or orbiting spacecraft.

Why are we concerned about the increases in CO2 and other gases that cause the greenhouse effect in Earth's atmosphere? What steps can we take in the future to reduce the levels of CO2 in our atmosphere? What factors stand in the way of taking the steps you suggest? (You may include technological, economic, and political factors in your answer.)

CO2, methane, and water vapor are greenhouse gases; that is, they contribute to the greenhouse effect that raises the temperature of the lower atmosphere and surface of Earth. Increased amounts of greenhouse gases in the atmosphere produce global warming, shifting climatic zones, raising sea level as polar ice melts, and leading to desertification of temperate (and perhaps some tropical) regions. This is a difficult situation for policymakers. It is virtually impossible to stop the increase in atmospheric CO2 unless we cease essentially all use of fossil fuels. The less we burn off fossil fuels, the slower will be the global warming. These changes will have an impact on the world economy that could easily exceed a trillion dollars per year.

Frozen water exists on the lunar surface primarily in which location? Why?

Frozen water exists primarily in deep craters on the Moon's south pole. Parts of these craters are permanently in shadow and therefore do not receive enough energy from the Sun to evaporate the ice and escape into space.

Contrast the mountains on Mars and Venus with those on Earth and the Moon.

Earth and Venus have extensive mountains of both a volcanic and tectonic origin. On Earth, the biggest mountains are oceanic volcanoes (such as the ones in Hawaii) and continental tectonic features. On Venus, the tectonic Maxwell Mountains are substantially larger than the tallest volcanoes. On Mars, all the large mountains are volcanoes, and on the Moon, the rings of mountains were produced by impacts. The maximum height of mountains on a planet is governed by the surface gravity of that planet (so, gµM/R2 ). The bigger the planet, the smaller the mountains (because if a mountain were larger, it could not support itself at its base). Since Mars is smaller than Earth and Venus, it can support taller mountains. By this argument, the Moon could have higher mountains than any of the other terrestrial planets. But the mountains on the Moon were formed by impacts, and such impacts simply do not make huge mountains. Another factor is that Earth's mountains wear down relatively quickly over geologic timescales, and Venus doesn't suffer from quite the levels of erosion that Earth does.

One source of information about Mars has been the analysis of meteorites from Mars. Since no samples from Mars have ever been returned to Earth from any of the missions we sent there, how do we know these meteorites are from Mars? What information have they revealed about Mars?

Gas trapped in bubbles in the meteorites matches what we know of the martian atmosphere. Most of the martian meteorites are volcanic basalts; most of them are also relatively young—about 1.3 billion years old. We know from details of their composition that they are not from Earth or the Moon. There was no volcanic activity on the Moon to form them as recently as 1.3 billon years ago. It would be very difficult for ejecta from impacts on Venus to escape through its thick atmosphere. By the process of elimination, the only reasonable origin seems to be Mars, where the Tharsis volcanoes were active at that time.

Compare the density, weight, mass, and volume of a pound of gold to a pound of iron on the surface of Earth.

Gold is denser than iron, both have the same weight (a pound each), both have the same mass, but iron has a greater volume than gold.

How does the mass of an astronaut change when she travels from Earth to the Moon? How does her weight change?

Her mass does not change because that measures the amount of "stuff" that makes up her body. Her weight will decrease because that is a measure of the amount of gravitational force she is experiencing; on the Moon, her weight would be about 1/6 what it is on Earth.

If there is gravity where the International Space Station (ISS) is located above Earth, why doesn't the space station get pulled back down to Earth?

If the space station were not moving, it would do just that, but when the space station was first assembled at a certain height above Earth, it was provided an appropriate speed for that height in a direction parallel to the surface of Earth. As such, instead of falling toward Earth, it is continuously falling around Earth. Since friction with Earth's atmosphere slows down the ISS, it requires occasional upward pushes, or boosts, to stay in orbit.

How do impacts by comets and asteroids influence Earth's geology, its atmosphere, and the evolution of life?

Impacts by comets and asteroids can create large explosions and propel dust and debris into the atmosphere, potentially causing mass extinction events such as the one that included the extinction of the dinosaurs. Early life on Earth had to survive the high temperatures and subsequent loss of sunlight that resulted from such impacts. And, as life evolved, species had to survive occasional local and global catastrophes

Newton's law of universal gravitation

Newton's law of gravity states that there is an always attracting force between two bodies that have a mass. The force is proportional to the product of masses and inversely proportional to the square of the distance between their center of masses. If the first body attracts a second one, the second will also attract the first one with a force of equal magnitude and opposite direction, that is, the attraction is mutual.

Why is there so much more carbon dioxide in the atmosphere of Venus than in that of Earth? Why so much more carbon dioxide than on Mars?

On Earth, much of the carbon dioxide originally in the atmosphere dissolved in the ocean water and is now found in sea sediments. Venus has no such sink for its carbon dioxide. Mars is smaller than Earth and Venus, and so the escape velocity for carbon dioxide on Mars is smaller than on Venus, both now and in the past.

We believe that Venus, Earth, and Mars all started with a significant supply of water. Explain where that water is now for each planet.

On Earth, the water is still in the oceans and ice fields. Mars, which has significantly less gravity than Earth or Venus, gradually lost much of its original atmosphere. As the pressure decreased, liquid water could no longer remain liquid and either froze as temperatures dropped or evaporated. In the upper atmosphere, with no ozone layer, ultraviolet radiation from the Sun tore apart the molecular bonds of H2O and the lighter hydrogen was lost to space. The water that was left is frozen, in the polar caps, and (mostly) deeply buried in permafrost. On Venus, which began hotter since it was closer to the Sun and got hotter because of the greenhouse effect, water quickly became water vapor. This was lost into space when ultra-violet broke the water into H and O and lighter elements escaped from the top of the atmosphere.

Why is a decrease in Earth's ozone harmful to life?

Ozone blocks harmful UV rates, a decrease means those rays would not be blocked and would make it to Earth's surface.

What are the advantages of using radar imaging rather than ordinary cameras to study the topography of Venus? What are the relative advantages of these two approaches to mapping Earth or Mars?

Radar (radio waves) can penetrate Venus' planetary cloud cover, whereas visible light or infrared radiation can't. One can image the surface topography and also map the surface elevations of Venus using radar. Such work has been done from Earth, using the Arecibo Radio Telescope, and also from orbit about Venus by the Magellan spacecraft. The same technique is used to map the surface of Earth for areas that are generally shrouded in clouds (such as New Guinea and the Philippines). There is no great advantage to mapping Mars using radar, as we can get a pretty good idea of the martian surface topography from visible-light photographs, although radar (and now laser) mapping from orbit has been a great help in determining absolute altitudes of features on Mars.

What is the composition of the polar caps on Mars?

Seasonal ice caps are made up of dry ice, or crystals of frozen carbon dioxide; the northern residual cap is water ice, whereas the southern permanent ice cap is made predominantly of water ice with a covering of carbon dioxide ice.

What is the composition of the Moon, and how does it compare to the composition of Earth? Of Mercury?

The Moon is principally composed of silicate rocks, whereas Earth has more metals and volatile compounds. Earth has an iron core, but the Moon does not. Earth has liquid water in its surface layer, but the Moon does not. Mercury contains substantially more metals than the Moon, with a significant iron-nickel core.

Why does the Moon not have an atmosphere?

The Moon's mass, and therefore its gravitational force, is not large enough to retain gases and volatile compounds. Therefore, any gases released on the Moon quickly escape into space.

At the end of the section on the lunar surface, your authors say that lunar night and day each last about two Earth weeks. After looking over the information in Earth, Moon, and Sky and this chapter about the motions of the Moon, can you explain why?

The Moon's synchronous rotation means that it orbits Earth in the same time that it spins on its axis, in a period of roughly 29 days. To simplify matters, let us assume that during any 29-day period, we can neglect Earth's motion around the Sun. Then the Sun will remain in the same direction as seen from the Moon during such a 29-day period. This means that, as the Moon turns, a point on the Moon will face toward the Sun for half the time and away from the Sun for half the time. Thus, the lunar day and night each last about 2 weeks. Visitors need ways to keep cool during the days and keep hot during the nights.

The Moon has too little iron, Mercury too much. How can both of these anomalies be the result of giant impacts? Explain how the same process can yield such apparently contradictory results.

The effect of a giant impact in both cases is to separate the mantle material from the iron-rich core. The Moon is made from ejecta from a giant impact between Earth and a mini-planet, and is thus mostly mantle material. Mercury is made of the core material that is left behind after a giant impact, and therefore is enriched in iron.

What does a planet need in order to retain an atmosphere? How does an atmosphere affect the surface of a planet and the ability of life to exist?

The gravity of a planet helps to determine whether an atmosphere can be retained. Mars has a shallow atmosphere compared to Earth, but it is also only 1/3 the size of Earth. Venus and Earth are about the same size and both have atmospheres. A dense atmosphere insulates the surface of a planet so that more heat is retained; however, the composition of the atmosphere is also important. Certain gases lead to a greenhouse effect, allowing the planet to be warmer than you would expect from its position around the Sun. Life as we know it requires temperatures andpressures at which water is liquid.

What is the source of Earth's magnetic field?

The movement of Earth's liquid metallic core

The lunar highlands have about ten times more craters in a given area than do the maria. Does this mean that the highlands are 10 times older? Explain your reasoning.

The number of craters is proportional to the age only if the cratering rate has not varied over time. If the rate were higher in the past (cratering events were more frequent), then less time would be required to accumulate many craters. Since we know from radioactive dating of lunar samples that the Moon is only 4.5 billion years old, whereas the mare lava surfaces are typically 3.5 billion years old, it is not possible that the cratering rates have remained constant. This is the reasoning that leads us to the idea of an early heavy bombardment of the Moon. However, note that this reasoning requires that we have independent ages from lunar samples. Before the Apollo expeditions, some scientists hadactually estimated that the highlands were about 10 times older than the maria.

Why are the lunar mountains smoothly rounded rather than having sharp, pointed peaks (as they were almost always depicted in science-fiction illustrations and films before the first lunar landings)?

The primary reason why the lunar mountains are smoothly rounded is that there has been no water/ice erosion on the Moon as there has been on Earth. This type of erosion tends to undercut rocks and produce sharp, pointed peaks.

What do our current ideas about the origins of the Moon and Mercury have in common? How do they differ?

The similarities are mainly those of appearance: both suffered frequent and sometimes massive impacts early in their histories, with heavily cratered surfaces visible on each body. Mercury has much more iron than the Moon, so early on, Mercury must have lost most of its rocky mantle, probably due to impacts. At some point, probably due to internal cooling, Mercury shrank enough to create long "wrinkles" and scarps in the crust; such scarps are not seen on the Moon.

If identical spacecraft were orbiting Mars and Earth at identical radii (distances), which spacecraft would be moving faster? Why?

The spacecraft moving around Earth would be moving faster. Because Earth has a greater mass, it has a greater gravitational pull on the spacecraft; so for a similar orbit, the one orbiting Earth has to be moving faster to keep from being pulled to the ground.

Near the martian equator, temperatures at the same spot can vary from an average of -135 °C at night to an average of 30 °C during the day. How can you explain such a wide difference in temperature compared to that on Earth?

The thin martian atmosphere does not shield the surface from sunlight during the day and does not retain heat to keep the surface warm at night. Therefore, the surface is exposed to extreme temperatures relative to those on Earth.

In what way is the high surface temperature of Venus relevant to concerns about global warming on Earth today?

Venus' high temperature is the result of a runaway greenhouse effect. Venus' atmosphere is mostly carbon dioxide, which is a greenhouse gas. Human activities on Earth are slowly increasing the amount of carbon dioxide in our atmosphere. Increased amounts of this greenhouse gas are leading, climate experts agree, to a global warming effect on our planet. Most of the hottest annual temperatures ever recorded for Earth have occurred within the past 10 years. Although carbon dioxide (and other greenhouse gases) are still a very small part of Earth's atmosphere, Venus is a long-range example and warning of what might happen if these trends on Earth continue into the future.

Evil space aliens drop you and your fellow astronomy student 1 km apart out in space, very far from any star or planet. Discuss the effects of gravity on each of you.

We would move toward one another via our mutual gravitational attraction. Using Newton's second law, f=ma, the person with less mass will accelerate faster.

A body moves in a perfectly circular path at constant speed. Are there forces acting in such a system? How do you know?

Yes, there is a force pulling toward the center of the circle. According to Newton's first law, there must a force present to keep the object moving in a circle rather than a straight line.