Unit 2
In which atmospheric layer are almost all water-based clouds formed?
Troposphere
Basalt
igneous rock produced by the cooling of lava; makes up most of Earth's oceanic crust and is found on other planets that have experienced extensive volcanic activity
The far side of the Moon is
Dark for two weeks a month
Titan is a natural satellite of
Saturn
Troposphere
The lowest layer of Earth's atmosphere
seismic waves
vibrations that travel through Earth carrying the energy released during an earthquake
Fault
(geology) a crack in the earth's crust resulting from the displacement of one side with respect to the other
The mean distance of the Earth from the Sun in astronomical units is
1
How many of Jupiter's moons did Galileo discover?
4
The heavy bombardment phase of the solar system formation appears to have been over by
4 billion years
The ages of rocks taken from the lunar highlands have typical ages of
4.0 to 4.2 billion years ago
The solar system is about
4.5 billion years old
About how long does it take Uranus to orbit the sun once?
84 earth years
Summary 9.3
A century ago, Grove Gilbert suggested that the lunar craters were caused by impacts, but the cratering process was not well understood until more recently. High-speed impacts produce explosions and excavate craters 10 to 15 times the size of the impactor with raised rims, ejecta blankets, and often central peaks. Cratering rates have been roughly constant for the past 3 billion years but earlier were much greater. Crater counts can be used to derive approximate ages for geological features on the Moon and other worlds with solid surfaces.
Photosynthesis
A complex sequence of chemical reactions through which some living things can use sunlightto manufacture products that store energy (such as carbohydrates), releasing oxygen as a by product
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 shooting star?
A dust particle hitting Earth
Greenhouse gas
A gas in the atmosphere that absorbs and emits radiation
Ozone
A heavy molecule of oxygen that contains 3 atoms
Explain how high-speed impacts form circular craters. How can this explanation account for the various characteristic features of impact craters?
A high-speed projectile will penetrate somewhat into the surface of the larger body before stopping. This abrupt loss of energy is transferred into a shock wave and heat that fractures and vaporizes some of the rock. It is this rapid heating and explosion that throws debris out of the impact site. The explosion tends to send energy in all directions, generating a circular crater. There is a rebound effect from the shock wave that will fill in the crater a little and flatten the floor, sometimes creating a central peak. Some of the debris ejected during the explosion will also fall back into the crater, the rest will be distributed outward from the impact site and make the ringed mountains that surround each crater. These are the characteristic features of impact craters.
How do the planets discovered so far around other stars differ from those in our own solar system? List at least two ways.
A much greater variety of planets has been found around other stars than exists in our solar system. Large Jupiter-sized planets ("hot Jupiters") have been found orbiting close to their stars, which challenges our simple view of planetary system formation. There are also super-Earths and mini-Neptunes, planets intermediate in size between the terrestrial and jovian planets in our solar system. And a number of exoplanets have eccentric orbits, unlike the planets of the solar system.
Volcano
A place where material from a planets mantle erupts to the surface
Terrestrial planet
Any of the planets Mercury, Venus, Earth, or Mars; sometimes the Moon is included in the list
14.3 Summary
A viable theory of solar system formation must take into account motion constraints, chemical constraints, and age constraints. Meteorites, comets, and asteroids are survivors of the solar nebula out of which the solar system formed. This nebula was the result of the collapse of an interstellar cloud of gas and dust, which contracted (conserving its angular momentum) to form our star, the Sun, surrounded by a thin, spinning disk of dust and vapor. Condensation in the disk led to the formation of planetesimals, which became the building blocks of the planets. Accretion of infalling materials heated the planets, leading to their differentiation. The giant planets were also able to attract and hold gas from the solar nebula. After a few million years of violent impacts, most of the debris was swept up or ejected, leaving only the asteroids and cometary remnants surviving to the present.
14.5 Summary
After their common beginning, each of the planets evolved on its own path. Different possible outcomes are illustrated by comparison of the terrestrial planets (Earth, Venus, Mars, Mercury, and the Moon). All are rocky, differentiated objects. The level of geological activity is proportional to mass: greatest for Earth and Venus, less for Mars, and absent for the Moon and Mercury. However, tides from another nearby world can also generate heat to drive geological activity, as shown by Io, Europa, and Enceladus. Pluto is also active, to the surprise of planetary scientists. On the surfaces of solid worlds, mountains can result from impacts, volcanism, or uplift. Whatever their origin, higher mountains can be supported on smaller planets that have less surface gravity. The atmospheres of the terrestrial planets may have acquired volatile materials from comet impacts. The Moon and Mercury lost their atmospheres; most volatiles on Mars are frozen due to its greater distance from the Sun and its thinner atmosphere; and Venus retained CO2 but lost H2O when it developed a massive greenhouse effect. Only Earth still has liquid water on its surface and hence can support life
Which moon is completely tidally locked, in a 1:1 spin-orbit resonance with its planet?
All of the above
Why do meteors in a meteor shower appear to come from just one point in the sky?
All the meteors in a meteor shower typically come from the same comet, which is in a periodic orbit around the Sun. The loosened dust from the comet follows the path of the parent body. As Earth intersects the debris along the comet's orbit, it plows into this material. Since the dust particles are all moving together in space before they encounter Earth, if you trace back the streak of each meteor, its path will appear to diverge from one place in the sky called the radiant.
The features of Mercury are named in honor of famous people in which fields of endeavor?
Artists, writers, composers, and other contributors to the arts and humanities.
Why is it difficult to drop a probe like Galileo? How did engineers solve this problem?
Aside from having to engineer the craft to survive the magnetosphere of Jupiter, the high speeds involved would guarantee that the probe would burn up on entering the atmosphere. The problem was solved using a heat shield in front of the spacecraft to absorb the heat. After the probe had slowed down, the heat shield was jettisoned and the parachute was deployed, further slowing the probe.
How do asteroids and comets differ?
Asteroids are composed primarily of rock and metal and reside in the inner part of the solar system. Comets are typically icy objects that come from the outer and become visible as they approach the sun ice sublimates, asteroids have greater densities
How did our exploration of the Moon differ from that of Mercury (and the other planets)?
Because of its proximity to Earth, we have been able to send manned missions to the Moon and return lunar material to Earth for study. Robotic missions have also been used to explore the lunar surface. All other solar system objects—planets, asteroids, and comets—have been studied only by telescope and/or robotic missions. No humans have visited them.
We think the "frost line" during the times when the solar system was forming was
Between Mars and Jupiter's orbit
How are Triton and Pluto similar?
Both Triton and Pluto are very cold worlds in the outer reaches of the solar system. They are similar in size (between 2000 and 3000 km) and similar in density, and thus similar in the proportion of rock and ice that makes them up. Both have a thin atmosphere of nitrogen, which freezes and sublimates depending on the temperature. Both have irregular or unusual orbits, with Triton moving in a retrograde orbit (unique for a larger-size moon) and Pluto in a tilted, highly elliptical orbit. Astronomers think that Triton may be a captured moon from the realm of trans-neptunian dwarf planets like Pluto.
What changed in our understanding of the Moon and Moon-Earth system as a result of humans landing on the Moon's surface?
By landing on the surface of the moon, we were able to collect surface samples and then use radiocarbon dating techniques to determine the age of the Moon. We were able to conclude that the moon is dead geologically.
Compare the geology of Callisto, Ganymede, and Titan.
Callisto is an ice-covered moon whose inner materials have never fully differentiated into different-density layers. It has no inner or outer activity and is basically geologically dead. Ganymede has a central rocky core and shows signs of tectonic activity, including regions of young surface terrain and long cracks in the crust. Titan has similar mass, size, and composition to Callisto and Ganymede, but has an active geology of liquid hydrocarbons on the surface, evaporation into the atmosphere, and rain back onto the surface.
The biggest known asteroid
Ceres
Why is the shape of the magnetosphere not spherical like the shape of Earth?
Charged particles from the Sun moving at high velocities interact with the magnetic field, compressing it in the direction of the Sun and elongating the field away from the Sun.
Why is Mars red?
Chemical reactions between surface rock and atmospheric oxygen literally rusted the surface.
How do terrestrial and giant planets differ?
Closer to the sun, smaller, higher densities, silicates and metals. Giants have lower densities, far from sun, larger, no solid surface, more moons
What is the composition of clouds on Mars?
Clouds on Mars are of three types: dust clouds; water-ice, like those on Earth; and clouds of frozen carbon dioxide crystals (dry ice).
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.
With which one of the following astronomical objects are meteor showers associated
Comets
What is comparative planetology and why is it useful to astronauts?
Comparative planetology is the study of how planets work and evolve by comparing them and the processes that have influenced their development. This method allows us to learn about the origin and evolution of the entire solar system, instead of each planet as a discrete object in space.
If Earth was to be hit by an extraterrestrial object, where in the solar system could it come from and how would we know its source region?
Earth could be hit by any of the small bodies in the solar system , most likely a comet or a near-earth asteroid. We can tell the difference based on the orbit of its approach to Earth (If we found it in advance) and by its composition-whether it is primarily rocky or icy.
Why are there so many craters on the Moon and so few on Earth?
Earth is geologically active while the moon is geologically dead
8.1 Summary
Earth is the prototype terrestrial planet. Its interior composition and structure are probed using seismic waves. Such studies reveal that Earth has a metal core and a silicate mantle. The outer layer, or crust, consists primarily of oceanic basalt and continental granite. A global magnetic field, generated in the core, produces Earth's magnetosphere, which can trap charged atomic particles.
Compare the current atmospheres of Earth, Venus, and Mars in terms of composition, thickness (and pressure at the surface), and the greenhouse effect.
Earth's atmosphere is about 4/5 nitrogen and 1/5 oxygen; Venus' atmosphere is mostly carbon dioxide, with a pressure about 90 times higher than Earth; Mars' atmosphere is also mostly carbon dioxide, with a pressure only about one hundredth that of Earth. Venus has had an ongoing runaway greenhouse effect, leading to extraordinarily high surface temperatures. Earth is presently seeing the greenhouse effect increase with higher levels of carbon dioxide in the atmosphere. Mars has had a "runaway refrigerator" effect leading to a thinner atmosphere and colder temperatures over time.
10.6 Summary
Earth, Venus, and Mars have diverged in their evolution from what may have been similar beginnings. We need to understand why if we are to protect the environment of Earth.
8.5 Summary
Earth, like the Moon and other planets, has been influenced by the impacts of cosmic debris, including such recent examples as Meteor Crater and the Tunguska explosion. Larger past impacts are implicated in some mass extinctions, including the large impact 65 million years ago at the end of the Cretaceous period that wiped out the dinosaurs and many other species. Today, astronomers are working to predict the next impact in advance, while other scientists are coming to grips with the effect of impacts on the evolution and diversity of life on Earth.
How and why is Earth's moon different from the larger moons of the giant planets?
Earths moon is not geologically active compared to the other moons and it is close to the sun so it is rocky
The angular distance between a planet and the Sun, as viewed from the Earth, is called
Elongation
In which domain of living things do you find humankind?
Eukarya
The earth has impact craters
False
A planet is said to be at aphelion when it is
Farthest from the Sun
Why are some planets and moons more geologically active than others?
First of all, a world needs to be solid to have geological activity. Among the terrestrial planets, geological activity depends to a large degree on the size of the planet and resulting internal heat; larger planets are better able to retain their primordial heat or to keep the heat from the decay of radioactive materials inside them. The Moon and Mercury, being small, are now geologically dead. Mars, Earth, and Venus all exhibit volcanism, but less for Mars as it has cooled more due to its smaller size. Some of the moons of the outer planets are geologically active due to heat caused by structural flexing in the large gravitational fields of the giant planets. How this internal activity manifests on the surface also depends on the composition of the object.
What are the main atmospheric heat sources of each of the giant planets?
For Jupiter, Saturn, and Neptune, both sunlight and internal sources provide energy to the atmosphere. Uranus has no or very little internal heat, so it gets its energy from the Sun. Jupiter has the largest internal energy source, about the same as the total solar energy absorbed by Jupiter. Most of the internal energy of Jupiter is primordial heat, left over from the formation of the planet 4.5 billon years ago. Saturn has an internal energy source about half as large as Jupiter's; since its mass is only about one quarter as great, this means that it is producing twice as much energy per unit mass of material as does Jupiter. The source of this energy is the separation of helium from hydrogen in Saturn's interior. In the liquid hydrogen mantle, the heavier helium forms droplets that sink toward the core, releasing gravitational energy. In effect, Saturn is still differentiating—letting lighter material rise and heavier material fall. Uranus and Neptune are different. Neptune has a small internal energy source, while Uranus does not emit a measurable amount of internal heat.
Compare the atmospheric circulation (weather) of the four giant planets.
For both Jupiter and Saturn, convection from their internal heat sources mixes the atmosphere and promotes cloud formation. Their rapid rotation spreads out these cloud features into parallel bands that circle the planets at all latitudes. For Uranus, the circulation is also equatorial and the wind speeds are high. Since there is no convection to mix the gases and create many clouds, Uranus' atmosphere is smeared out and rather featureless. Neptune's wind speeds are much higher than its rotational speed, so the atmosphere smears out into parallel bands like Jupiter and Saturn.
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.
The gas giants are mostly
Gas
What differences did Grove K. Gilbert note between volcanic craters on Earth and lunar craters?
He found that Earth volcanoes have small, deep craters on mountaintops, whereas lunar craters are larger, have different shapes than volcanic craters and are mountain-rimmed and circular with floors generally below the level of the surrounding plains.
Most of Jupiter's mass is in
Hydrogen
What evidence do we have that there was running (liquid) water on Mars in the past? What evidence is there for water coming out of the ground even today?
Images from orbiting spacecraft of runoff channels and outflow channels all show evidence of formation by running water. Several dry basins contain minerals that only form with water and indicate extensive lakes in the past. In 2015, some dark streaks (recurring slope lineae or "gullies") that got longer over the course of several days showed spectra of hydrated salts, and may be evidence of saltwater on Mars today.
A "geologically old" surface is characterized by
Impact craters
Explain the role of impacts in planetary evolution, including both giant impacts and more modest ones.
Impacts in early planet formation led to heating of the protoplanets, allowing for differentiation of materials and outgassing of lighter elements. Later, larger impacts probably led to some of the unusual characteristics of planets, such as formation of the Moon around Earth, Mercury's consisting of mostly core material and not as large a mantle or crust as the other planets, and the slow, retrograde rotation of Venus. Later impacts led to craters on all the solid worlds and to the deposition of volatile substances on worlds in the inner solar system that lacked them. Such impacts contributed to changes in the early planetary atmospheres.
Explain the energy source that powers the volcanoes of Io.
Io is close enough to Jupiter (and caught between Jupiter and the large moons on the other side of Io) to experience significant tidal heating, where the moon alternately stretches and relaxes in its elliptical orbit about the planet. This generates enough heat to produce molten silicate lava that erupts as volcanoes.
The large Venusian volcano Maxwell Montes dominates the topography on the northern continent of
Ishtar
Why doesn't the moon fall down?
It is falling but it is also moving sideways
Which planet has the strongest magnetic field, and hence the largest magnetosphere? What is its source?
Jupiter has the largest magnetosphere. The large, rapidly spinning, liquid-metallic hydrogen above the core is the source of its magnetic field.
11.2 Summary
Jupiter is 318 times more massive than Earth. Saturn is about 25% as massive as Jupiter, and Uranus and Neptune are only 5% as massive. All four have deep atmospheres and opaque clouds, and all rotate quickly with periods from 10 to 17 hours. Jupiter and Saturn have extensive mantles of liquid hydrogen. Uranus and Neptune are depleted in hydrogen and helium relative to Jupiter and Saturn (and the Sun). Each giant planet has a core of "ice" and "rock" of about 10 Earth masses. Jupiter, Saturn, and Neptune have major internal heat sources, obtaining as much (or more) energy from their interiors as by radiation from the Sun. Uranus has no measurable internal heat. Jupiter has the strongest magnetic field and largest magnetosphere of any planet, first discovered by radio astronomers from observations of synchrotron radiation.
12.2 Summary
Jupiter's largest moons are Ganymede and Callisto, both low-density objects that are composed of more than half water ice. Callisto has an ancient cratered surface, while Ganymede shows evidence of extensive tectonic and volcanic activity, persisting until perhaps a billion years ago. Io and Europa are denser and smaller, each about the size of our Moon. Io is the most volcanically active object in the solar system. Various lines of evidence indicate that Europa has a global ocean of liquid water under a thick ice crust. Many scientists think that Europa may offer the most favorable environment in the solar system to search for life.
Mantle
Largest layer of the earth
What are the dark areas on the Moon that form the "face" we can see with the naked eye?
Lava-filled basins
8.4 Summary
Life originated on Earth at a time when the atmosphere lacked O2 and consisted mostly of CO2. Later, photosynthesis gave rise to free oxygen and ozone. Modern genomic analysis lets us see how the wide diversity of species on the planet are related to each other. CO2 and methane in the atmosphere heat the surface through the greenhouse effect; today, increasing amounts of atmospheric CO2 are leading to the global warming of our planet.
Saturn's rings are
Many solid, icy chunks
One of the largest volcanoes in our solar system — if not the largest — is Olympus Mons. This volcano is located on
Mars
Explain the runaway refrigerator effect and the role it may have played in the evolution of Mars.
Martian gravity is not strong enough to hold a gaseous atmosphere over a long period of time, so the atmosphere would have gotten thinner as gas escaped. This would lead to lower temperatures, and more gas would have frozen and deposited out of the atmosphere, lowering temperatures still further. The thinner atmosphere and colder temperatures would lead to the loss of most water from the planet, except for water ice, permafrost ground deposits, and perhaps underground saltwater.
Describe the basic internal structure of Mercury
Mercury is one of the densest of the planets, at 5.4 g/cm3. It has an enormous iron-nickel core nearly 3500 km in diameter, which is encased in a rocky/silicate crust about 700 km deep. The metallic core, representing nearly 60% of the planet's total mass, produces a weak magnetic field.
Summary 9.5
Mercury is the nearest planet to the Sun and the fastest moving. Mercury is similar to the Moon in having a heavily cratered surface and no atmosphere, but it differs in having a very large metal core. Early in its evolution, it apparently lost part of its silicate mantle, probably due to one or more giant impacts. Long scarps on its surface testify to a global compression of Mercury's crust during the past 4 billion years.
In what ways are meteorites different from meteors? What is the probable origin of each?
Meteorites are large enough to withstand the violent passage through Earth's atmosphere, whereas meteors burn up from the heat of friction. Meteors typically come from comets that have passed through the solar system; their solid material is freed when the ice is vaporized by the heat of the Sun. Most meteorites, on the other hand, are from asteroids or from debris kicked up on the Moon or Mars during an impact.
14.2 Summary
Meteorites are the debris from space (mostly asteroid fragments) that survive to reach the surface of Earth. Meteorites are called finds or falls according to how they are discovered; the most productive source today is the Antarctic ice cap. Meteorites are classified as irons, stony-irons, or stones accordingly to their composition. Most stones are primitive objects, dated to the origin of the solar system 4.5 billion years ago. The most primitive are the carbonaceous meteorites, such as Murchison and Allende. These can contain a number of organic (carbon- rich) molecules.
What is the difference between a meteor and a meteorite?
Meteors are falling bodies burning in the atmosphere, meteorites are those that have reached the ground.
A friend of yours who has not taken astronomy sees a meteor shower (she calls it a bunch of shooting stars). The next day she confides in you that she was concerned that the stars in the Big Dipper (her favorite star pattern) might be the next ones to go. How would you put her mind at ease?
Meteors do not come from stars but from pieces of comets or asteroids that have broken off or been set free, and that enter Earth's atmosphere. Meteors are small solid objects of stone or metal, whereas stars are huge balls of hot gas and are trillions of miles away. You could also point out that meteor showers like the one she saw occur annually and yet no one has reported stars missing after any of them. The constellations (star patterns) have been observed since humans have had written history, with no reports of any disappearing.
How are comets related to meteor showers?
Most meteor showers originate with particular comets that pass through the inner solar system and lose some of their solid material, which then goes into orbit along the comet's path. Showers happen whenever Earth in its orbit passes through the path of the comet and its debris.
10.4
Most of what we know about Mars is derived from spacecraft: highly successful orbiters, landers, and rovers. We have also been able to study a few martian rocks that reached Earth as meteorites. Mars has heavily cratered highlands in its southern hemisphere, but younger, lower volcanic plains over much of its northern half. The Tharsis bulge, as big as North America, includes several huge volcanoes; Olympus Mons is more than 20 kilometers high and 500 kilometers in diameter. The Valles Marineris canyons are tectonic features widened by erosion. Early landers revealed only barren, windswept plains, but later missions have visited places with more geological (and scenic) variety. Landing sites have been selected in part to search for evidence of past water.
Summary 9.1
Most of what we know about the Moon derives from the Apollo program, including 400 kilograms of lunar samples still being intensively studied. The Moon has one-eightieth the mass of Earth and is severely depleted in both metals and volatile materials. It is made almost entirely of silicates like those in Earth's mantle and crust. However, more recent spacecraft have found evidence of a small amount of water near the lunar poles, most likely deposited by comet and asteroid impacts.
Which of the gas giants has the largest icy/rocky core compared to its overall size?
Neptune has the largest core, extending out to about 20,000 km from the center of the planet.
Do all planetary systems look the same as our own?
No. Among the thousands of other planetary systems we have observed so far, systems have evolved along different evolutionary paths. Some have gas giant planets much closer to the Sun, for example.
How was the Mars Odyssey spacecraft able to detect water on Mars without landing on it?
Odyssey used a gamma-ray spectrometer to detect hydrogen below the martian surface. Analysis of the signals indicated that the hydrogen was probably from water molecules in ice frozen below the surface.
7.1 Overview of Our Planetary System
Our solar system currently consists of the Sun, eight planets, five dwarf planets, nearly 200 known moons, and a host of smaller objects. The planets can be divided into two groups: the inner terrestrial planets and the outer giant planets. Pluto, Eris, Haumea, and Makemake do not fit into either category; as icy dwarf planets, they exist in an ice realm on the fringes of the main planetary system. The giant planets are composed mostly of liquids and gases. Smaller members of the solar system include asteroids (including the dwarf planet Ceres), which are rocky and metallic objects found mostly between Mars and Jupiter; comets, which are made mostly of frozen gases and generally orbit far from the Sun; and countless smaller grains of cosmic dust. When a meteor survives its passage through our atmosphere and falls to Earth, we call it a meteorite.
Why do the giant planets and their moons have compositions different from those of the terrestrial planets?
Planets formed initially through the accretion of solid materials in the solar nebula. Due to the temperature in the interior of the solar system, the only substances capable of condensing there were rocks and metals. Any volatile materials could not condense so close to the heat of the early Sun. In the outer solar system, rock, metal, and hydrogen compounds (ices) were all solids and, as a result, there was much more material to form planets. The protoplanets that formed were large enough to also capture H and He gas and grow much, much larger and become the giant planets.
List at least three major differences between Pluto and the terrestrial planets.
Pluto is much smaller than all the terrestrial planets (and even smaller than many of the big moons of the giant planets). Its composition is ice and rock as opposed to the composition of rock and metal of the terrestrial planets. Pluto's orbit is highly elliptical and inclined to the plane of the ecliptic as opposed to the circular orbits near the plane of the ecliptic for the terrestrial planets. Pluto has a thin and variable atmosphere of nitrogen, while three of the terrestrial planets have much thicker and warmer permanent atmospheres. (Nitrogen dominates Earth's atmosphere, while carbon dioxide dominates the atmospheres of Venus and Mars. Mercury has only a very thin "temporary" atmosphere, borrowed from the solar wind.) Pluto is but one object of many (including some of the same size as Pluto) in the Kuiper Belt, whereas each of the terrestrial planets dominates the mass in their respective orbits.
How was Pluto discovered? Why did it take so long to find it?
Pluto was discovered at Lowell Observatory by a young, relatively untrained Clyde Tombaugh, from comparisons of photographs taken several days apart that showed the relative motion of Pluto against a background of stars. Pluto was difficult to find because of its small size and great distance from Earth. Although Percival Lowell had suggested that Pluto could be found by its effects on the orbits of other outer planets such as Uranus and Neptune, in fact a planet with so little mass could not be pinpointed by its gravitational effects. It was just luck that Pluto was found where Tombaugh had been told to search.
What do we mean by primitive material? How can we tell if a meteorite is primitive?
Primitive material was formed in the early stage of the solar system, before planets cooled off enough to differentiate elements of different density. It was not subject to great heat or pressure after it formed. We can identify primitive meteorites by their composition; primitive meteorites are usually undifferentiated stones, with some metallic grains mixed in. Some primitive meteorites are darker, carbonaceous stones.
Describe how we use radioactive elements and their decay products to find the age of a rock sample.
Radioactive element decay in a systematic way. The half life measures the amount of time it takes half of the sample to decay. The world melts and this time measured does not reflect the age of the world it comes from.
7.4 Origin of the Solar System
Regularities among the planets have led astronomers to hypothesize that the Sun and the planets formed together in a giant, spinning cloud of gas and dust called the solar nebula. Astronomical observations show tantalizingly similar circumstellar disks around other stars. Within the solar nebula, material first coalesced into planetesimals; many of these gathered together to make the planets and moons. The remainder can still be seen as comets and asteroids. Probably all planetary systems have formed in similar ways, but many exoplanet systems have evolved along quite different paths, as we will see in Cosmic Samples and the Origin of the Solar System.
12.5 summary
Rings are composed of vast numbers of individual particles orbiting so close to a planet that its gravitational forces could have broken larger pieces apart or kept small pieces from gathering together. Saturn's rings are broad, flat, and nearly continuous, except for a handful of gaps. The particles are mostly water ice, with typical dimensions of a few centimeters. One Saturn moon, Enceladus, is today erupting geysers of water to maintain the tenuous E Ring, which is composed of very small ice crystals. The rings of Uranus are narrow ribbons separated by wide gaps and contain much less mass. Neptune's rings are similar but contain even less material. Much of the complex structure of the rings is due to waves and resonances induced by moons within the rings or orbiting outside them. The origin and age of each of these ring systems is still a mystery.
sedimentary rock
Rock formed by the deposition and cementing of fine grains of material, such as pieces of igneous rock or the shells of living things
Igneous rock
Rock produced by cooling from molten state
metamorphic rock
Rock produced by physical and chemical alteration without melting from high temp and pressure
12.3 summary
Saturn's moon Titan has an atmosphere that is thicker than that of Earth. There are lakes and rivers of liquid hydrocarbons, and evidence of a cycle of evaporation, condensation, and return to the surface that is similar to the water cycle on Earth (but with liquid methane and ethane). The Cassini-Huygens lander set down on Titan and showed a scene with boulders, made of water ice, frozen harder than rock. Neptune's cold moon Triton has a very thin atmosphere and nitrogen gas geysers.
12.4 summary
Saturn's moon Titan has an atmosphere that is thicker than that of Earth. There are lakes and rivers of liquid hydrocarbons, and evidence of a cycle of evaporation, condensation, and return to the surface that is similar to the water cycle on Earth (but with liquid methane and ethane). The Cassini-Huygens lander set down on Titan and showed a scene with boulders, made of water ice, frozen harder than rock. Neptune's cold moon Triton has a very thin atmosphere and nitrogen gas geysers.
Describe and compare the rings of Saturn and Uranus, including their possible origins.
Saturn's rings form a wide and complex system, consisting mostly of particles and pieces of ice, and are highly visible. They may have formed from one or more moons that broke up due to a collision, or are left over from early debris that never coalesced into a moon. The rings of Uranus are thin and hard to see, consisting mostly of chunks of carbon and hydrocarbons with very little reflectivity. They may also have formed from the breakup of a small moon due to a collision. They may be kept thin by the presence of shepherd moons.
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 are the seasons like on Jupiter?
Since Jupiter's spin axis is only tilted about 3° from the perpendicular, it does not experience seasons at all.
Where would you look for some original planetesimals left over from the formation of our solar system?
Small asteroids, kuiper belt objects, small moons that havent been heated, these things have not been altered much since the creation of the solar system so they can tell us about the structure of the past
Jupiter's magnetic field is
Strong and generated inside a metallic hydrogen zone
8.2 Summary
Terrestrial rocks can be classified as igneous, sedimentary, or metamorphic. A fourth type, primitive rock, is not found on Earth. Our planet's geology is dominated by plate tectonics, in which crustal plates move slowly in response to mantle convection. The surface expression of plate tectonics includes continental drift, recycling of the ocean floor, mountain building, rift zones, subduction zones, faults, earthquakes, and volcanic eruptions of lava from the interior.
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.
Summary 9.2
The Moon, like Earth, was formed about 4.5 billion year ago. The Moon's heavily cratered highlands are made of rocks more than 4 billion years old. The darker volcanic plains of the maria were erupted primarily between 3.3 and 3.8 billion years ago. Generally, the surface is dominated by impacts, including continuing small impacts that produce its fine-grained soil.
7.3 Dating Planetary Surfaces
The ages of the surfaces of objects in the solar system can be estimated by counting craters: on a given world, a more heavily cratered region will generally be older than one that is less cratered. We can also use samples of rocks with radioactive elements in them to obtain the time since the layer in which the rock formed last solidified. The half-life of a radioactive element is the time it takes for half the sample to decay; we determine how many half-lives have passed by how much of a sample remains the radioactive element and how much has become the decay product. In this way, we have estimated the age of the Moon and Earth to be roughly 4.5 billion years.
8.3 Summary
The atmosphere has a surface pressure of 1 bar and is composed primarily of N2 and O2, plus such important trace gases as H2O, CO2, and O3. Its structure consists of the troposphere, stratosphere, mesosphere, and ionosphere. Changing the composition of the atmosphere also influences the temperature. Atmospheric circulation (weather) is driven by seasonally changing deposition of sunlight. Many longer term climate variations, such as the ice ages, are related to changes in the planet's orbit and axial tilt.
10.3 Summary
The atmosphere of Venus is 96% CO2. Thick clouds at altitudes of 30 to 60 kilometers are made of sulfuric acid, and a CO2 greenhouse effect maintains the high surface temperature. Venus presumably reached its current state from more earthlike initial conditions as a result of a runaway greenhouse effect, which included the loss of large quantities of water.
greenhouse effect
The blanketing (absorption) of infrared radiation near the surface of a planet. Example is CO2
The Hubble Space Telescope images of Pluto in 2002 showed a bright spot and some darker areas around it. Now that we have the close-up New Horizons images, what did the large bright region on Pluto turn out to be?
The bright spot turned out to be what has been nicknamed Sputnik Planum (the Sputnik Plains). It appears to be a bowl or sea of frozen and perhaps liquid nitrogen, much brighter and younger (no craters visible) than the darker highlands of Pluto.
Core
The central part of the earth below the mantle
Solar nebula
The cloud of gas and dust from which the solar system formed
What are the visible clouds on the four giant planets composed of, and why are they different from each other?
The clouds of Jupiter and Saturn are primarily crystals of frozen ammonia. On Uranus and Neptune, the clouds are composed of methane. The temperatures of these worlds dictate the cloud composition. For Jupiter and Saturn, the temperatures keep methane in a gaseous state, while on Uranus and Neptune, the colder temperatures allow the methane to freeze and condense into clouds.
On a Mars photograph, you see a crater. The crater floor is flat, and appears to be sediment washed in by water. Which occurred first in time?
The crater impact
How do storms on Jupiter differ from storm systems on Earth?
The cyclonic storm features on Jupiter are regions of high pressure, whereas storms on Earth, such as hurricanes, are low-pressure areas.
What are the principal features of the Moon observable with the unaided eye?
The dark maria, the lighter highlands, and a few large craters such as Tycho are visible. The contrast between the light and dark of these features is sometimes called "the man in the Moon."
The mountains on the Moon were formed by what process?
The long, semi-circular mountain ranges that border the maria are debris ejected from the massive impacts that formed these basins, piled up at the edge of the bowl dug out by the explosion that resulted from the impact. The central peak mountains in large craters are due to rebound from the sudden removal of overlying rock.
14.4 Summary
The first planet circling a distant solar-type star was announced in 1995. Twenty years later, thousands of exoplanets have been identified, including planets with sizes and masses between Earth's and Neptune's, which we don't have in our own solar system. A few percent of exoplanet systems have "hot Jupiters," massive planets that orbit close to their stars, and many exoplanets are also in eccentric orbits. These two characteristics are fundamentally different from the attributes of gas giant planets in our own solar system and suggest that giant planets can migrate inward from their place of formation where it is cold enough for ice to form. Current data indicate that small (terrestrial type) rocky planets are common in our Galaxy; indeed, there must be tens of billions of such earthlike planets.
Summarize the four main hypotheses for the origin of the Moon.
The fission hypothesis suggests that the Moon was once part of Earth but separated early in their history. The sister hypothesis proposes that the Moon formed together with, but independent of, Earth. In the capture hypothesis, the Moon formed elsewhere in the solar system and was later captured by Earth. The newer giant impact hypothesis suggests that a Mars-sized object grazed Earth, ejecting material from both Earth and itself—material that condensed to form the Moon.
11.3 Summary
The four giant planets have generally similar atmospheres, composed mostly of hydrogen and helium. Their atmospheres contain small quantities of methane and ammonia gas, both of which also condense to form clouds. Deeper (invisible) cloud layers consist of water and possibly ammonium hydrosulfide (Jupiter and Saturn) and hydrogen sulfide (Neptune). In the upper atmospheres, hydrocarbons and other trace compounds are produced by photochemistry. We do not know exactly what causes the colors in the clouds of Jupiter. Atmospheric motions on the giant planets are dominated by east-west circulation. Jupiter displays the most active cloud patterns, with Neptune second. Saturn is generally bland, in spite of its extremely high wind speeds, and Uranus is featureless (perhaps due to its lack of an internal heat source). Large storms (oval-shaped high- pressure systems such as the Great Red Spot on Jupiter and the Great Dark Spot on Neptune) can be found in some of the planet atmospheres.
12.1 Summary
The four jovian planets are accompanied by impressive systems of moons and rings. Nearly 200 moons have been discovered in the outer solar system. Of the four ring systems, Saturn's is the largest and is composed primarily of water ice; in contrast, Uranus and Neptune have narrow rings of dark material, and Jupiter has a tenuous ring of dust.
7.2 Composition and Structure of Planets
The giant planets have dense cores roughly 10 times the mass of Earth, surrounded by layers of hydrogen and helium. The terrestrial planets consist mostly of rocks and metals. They were once molten, which allowed theirstructures to differentiate (that is, their denser materials sank to the center). The Moon resembles the terrestrial planets in composition, but most of the other moons—which orbit the giant planets—have larger quantities of frozen ice within them. In general, worlds closer to the Sun have higher surface temperatures. The surfaces of terrestrial planets have been modified by impacts from space and by varying degrees of geological activity.
Which types of planets have the most moons? Where did these moons likely originate?
The giant planets have the most moons, especially Jupiter and Saturn. Many of them are thought to have been captured from the small-body population during the formation of the solar system
accretion
The gradual accumulation of mass as by a planet forming from colliding particles in the solar nebula
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 and pressures at which water is liquid.
What is the thickest interior layer of Earth? The thinnest?
The mantle is the thickest region at about 2900 km. The crust is the thinnest, ranging from about 6 to 70 km deep.
Describe the interior heat source of Saturn.
The mantle of Saturn is still differentiating: The heavier helium is sinking, displacing the lighter hydrogen, which then rises. The "falling" of the helium releases gravitational energy, which heats the interior.
What are the maria composed of? Is this material found elsewhere in the solar system?
The maria are composed chiefly of basalt. Basalts are also found on Earth, Venus, Mars—and to a much lesser extent—Mercury.
Describe the current atmosphere on Mars. What evidence suggests that it must have been different in the past?
The martian atmosphere consists mostly of carbon dioxide, but is very thin, less than 1% of Earth's atmosphere. However, the strong evidence of water on Mars in the past that our missions have found means that the atmosphere must have been thicker and warmer, or water would have evaporated away very quickly.
10.5 Summary
The martian atmosphere has a surface pressure of less than 0.01 bar and is 95% CO2. It has dust clouds, water clouds, and carbon dioxide (dry ice) clouds. Liquid water on the surface is not possible today, but there is subsurface permafrost at high latitudes. Seasonal polar caps are made of dry ice; 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. Evidence of a very different climate in the past is found in water erosion features: both runoff channels and outflow channels, the latter carved by catastrophic floods. Our rovers, exploring ancient lakebeds and places where sedimentary rock has formed, have found evidence for extensive surface water in the past. Even more exciting are the gullies that seem to show the presence of flowing salty water on the surface today, hinting at near-surface aquifers. The Viking landers searched for martian life in 1976, with negative results, but life might have flourished long ago. We have found evidence of water on Mars, but following the water has not yet led us to life on that planet.
What are the moons of the outer planets made of, and how is their composition different from that of our Moon?
The moons of the outer planets consist of a mixture of ice and rock, whereas our Moon is just rock.
plate tectonics
The motion of segments or plates of the outer layer of a planet over the underlying mantle
11.1 summary
The outer solar system contains the four giant planets: Jupiter, Saturn, Uranus, and Neptune. The gas giants Jupiter and Saturn have overall compositions similar to that of the Sun. These planets have been explored by the Pioneer, Voyager, Galileo, and Cassini spacecraft. Voyager 2, perhaps the most successful of all space-science missions, explored Jupiter (1979), Saturn (1981), Uranus (1986), and Neptune (1989)—a grand tour of the giant planets—and these flybys have been the only explorations to date of the ice giants Uranus and Neptune. The Galileo and Cassini missions were long-lived orbiters, and each also deployed an entry probe, one into Jupiter and one into Saturn's moon Titan.
List some reasons that the study of the planets has progressed more in the past few decades than any other branch of astronomy
The planets are relatively close to Earth, and technology has been developed that has allowed us to send spacecraft to all of the major planets and many other small worlds. Space missions to these bodies will allow us to make close observations that we cannot obtain from the earth's surface, of from telescopes in orbit around earth. Spacecraft that land on other planets allow us to make measurements of rocks and the lower atmosphere, and spacecraft that orbit other planets allow us to study surface geology.
Why were the rings of Uranus not observed directly from telescopes on the ground on Earth? How were they discovered?
The rings of Uranus consist of dark, coal-like particles in narrow bands, making them almost impossible to see from Earth. They were discovered using a flying infrared telescope during the occultation of a star as Uranus passed in front of it. The light from the star dimmed several times before it was blocked by the disk of Uranus and afterward, indicating the presence of several distinct rings.
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.
What was the solar nebula like? Why did the Sun form at its center?
The solar nebula was a huge cloud of material made up of gas and dust. The sun formed at the center due to gravitational forces, caused that material to stick together, and once the mass and density increased sufficiently, nuclear fusion caused a star to form: the sun.
Describe the solar nebula, and outline the sequence of events within the nebula that gave rise to the planetesimals
The solar nebula was initially a cloud of dust and gas that began to rotate around its center due to conservation of angular momentum as it contracted by gravitational attraction. The central region of the nebula became a star, while the outer regions flattened and made a rotating disk. Things near the center remained hot, while farther out in the disk things cooled off. Grains or droplets of material condensed (heavier solid materials could survive the heat in the inner parts, but volatile materials (droplets or ices) could survive only farther out. Closer in, particles began to cool and form compounds, including rock and metal grains that grew larger by gravitational impacts and mergers. Farther out, the droplets and icy pieces were able to grow. Accretion of these larger pieces (rock or ice) formed planetesimals.
Most of the mass in the solar system is contained in
The sun
What is the evidence for a liquid water ocean on Europa, and why is this interesting to scientists searching for extraterrestrial life?
The surface of Europa features jagged blocks of ice that seem to have rotated and collided with one another, which would not likely happen on a solid moon. Long, straight cracks in the crust are also more likely to happen over a liquid subsurface layer than a solid one. Also, a weak magnetic field implies the presence of a liquid layer below the surface. This is interesting for searchers of extraterrestrial life because liquid water is essential for life as we know it, and life seems to exist in most places on Earth where liquid water is found. For example, life is found near vents on the deep ocean floor where chemical energy from hot springs can serve as a source of energy.
Why are there so many impact craters on our neighbor world, the Moon, and so few on Earth?
The tectonic plates on Earth are constantly rebuilding the crust, so when an impact happens the crater is covered by new crust being formed via the movement of the tectonic plates. Earth is the only planet with these plates, so on the moon when there's an impact there's no way for the crater to be covered.
Explain our ideas about why the terrestrial planets are rocky and have less gas than the giant planets
The terrestrial planets and the gas planets are thought to have formed under different conditions. The inner planets are made of elements that can survive the heat of the Sun; gases would have evaporated. The giant planets are far enough away that gases could accumulate around the planet cores and remain there for the age of the solar system.
Summary 9.4
The three standard hypotheses for the origin of the Moon were the fission hypothesis, the sister hypothesis, and the capture hypothesis. All have problems, and they have been supplanted by the giant impact hypothesis, which ascribes the origin of the Moon to the impact of a Mars-sized projectile with Earth 4.5 billion years ago. The debris from the impact made a ring around Earth which condensed and formed the Moon.
Explain the evidence for a period of heavy bombardment on the Moon about 4 billion years ago.
There are about 10 times more craters on the highlands than on a similar area of maria. The radioactive dating of highland samples shows that they are only slightly older than the maria, about 4.2 billion years versus 3.8 billion years. If the impact rate was constant over the Moon's history, the highlands would be least 10 times older than the maria, or about 38 billion years old. That's older than the age of the universe. Thus, the impact rate must not have been constant, and been at a much higher rate earlier than 3.8 billion years ago.
What are the main challenges involved in sending probes to the giant planets?
There are many challenges, mainly the huge distances that require many years of flight time. The spacecraft must be reliable and robust to survive the journey. The low temperatures of space require onboard heating so the components don't freeze. The light levels are too low for solar panels to provide enough energy, requiring onboard power systems. Transmitters must be powerful enough to communicate with Earth over the vast distances of space. A somewhat more advanced answer might also include: at low light levels, photographs require longer exposures; however, fast-moving spacecraft will change position during these times and smear the image unless the arm with the camera moves backward at the same rate that the spacecraft moves forward.
Summarize the origin and evolution of the atmospheres of Venus, Earth, and Mars.
These atmospheres were produced by gas escaping from the interior of the planet, and the deposit of volatile materials by the impacts of chunks from farther out in the solar system (such as comets). How well a planet retained its atmosphere depends on its mass (gravity); since Mars has lower mass than Venus and Earth, it lost more of its atmosphere over time. We think all three planets started with similar atmospheres of carbon dioxide, ammonia, and methane. The reducing (hydrogen-bearing) molecules were broken up by ultraviolet radiation from the Sun, with hydrogen escaping into space. On Venus, large amounts of carbon dioxide produced a runaway greenhouse effect, leading to the thick, hot atmosphere observed today. On Mars, temperatures fell as more of the atmosphere was lost and the greenhouse effect of the carbon dioxide could no longer keep the warmth in; cold temperatures froze water on the surface and out of the atmosphere, leading to the present thin atmosphere of mostly carbon dioxide. On Earth, a mild greenhouse effect and the presence of liquid water that could absorb carbon dioxide led to an atmosphere of mostly nitrogen and to conditions that could lead to the development of life. Free oxygen was added to Earth's atmosphere when plants evolved, and gave off oxygen as a byproduct of photosynthesis.
What characteristics do the worlds in our solar system have in common that lead astronomers to believe that they all formed from the same "mother cloud" (solar nebula)?
They generally rotate and revolve in the same direction and their orbits lie roughly in the same plane. The chemical makeup of the giant planets is similar to the sun.
Neptune is closest in size to which planet?
Uranus
The planet Neptune was found by studying the deviations in another planets orbit. Which other planet was discovered in this fashion?
Uranus
10.2 Summary
Venus has been mapped by radar, especially with the Magellan spacecraft. Its crust consists of 75% lowland lava plains, numerous volcanic features, and many large coronae, which are the expression of subsurface volcanism. The planet has been modified by widespread tectonics driven by mantle convection, forming complex patterns of ridges and cracks and building high continental regions such as Ishtar. The surface is extraordinarily inhospitable, with pressure of 90 bars and temperature of 730 K, but several Russian Venera landers investigated it successfully
Describe two anomalous features of the rotation of Venus and what might account for them.
Venus has retrograde rotation about its axis, opposite to the direction of spin of most other planets; also, its rotational period is longer than any other planet's. It is in fact longer than its orbital period, so its day is longer than its year. Astronomers think Venus suffered a collision with another large body during the formation period of the solar system, changing its rotational motion in both these ways.
14.1 Summary
When a fragment of interplanetary dust strikes Earth's atmosphere, it burns up to create a meteor. Streams of dust particles traveling through space together produce meteor showers, in which we see meteors diverging from a spot in the sky called the radiant of the shower. Many meteor showers recur each year and are associated with particular comets that have left dust behind as they come close to the Sun and their ices evaporate (or have broken up into smaller pieces).
List several ways that Venus, Earth, and Mars are similar, and several ways they are different.
Venus, Earth, and Mars are similar in that they consist of rock and metal for the most part; they are terrestrial planets, closer in to the Sun than the jovian planets; all have atmospheres (although they are of different constituents and with different pressures); all have volcanic activity on their surfaces; and all have or have had some kind of greenhouse effect change their surface temperatures. The three planets are different in many ways, among them: their size (Mars is significantly smaller); their atmospheres (Mars and Venus is dominated by CO2, while Earth's is dominated by nitrogen (and has a significant amount of oxygen); the presence or absence of liquid water on their surfaces today; the major way that their surfaces undergo large-scale changes (plate tectonics on Earth, blob tectonics on Venus, impacts and wind action on Mars); whether they are now or have been in the past suitable for life.
10.1 Summary
Venus, the nearest planet, is a great disappointment through the telescope because of its impenetrable cloud cover. Mars is more tantalizing, with dark markings and polar caps. Early in the twentieth century, it was widely believed that the "canals" of Mars indicated intelligent life there. Mars has only 11% the mass of Earth, but Venus is nearly our twin in size and mass. Mars rotates in 24 hours and has seasons like Earth; Venus has a retrograde rotation period of 243 days. Both planets have been extensively explored by spacecraft.
Explain why visual observation of the gas giants is not sufficient to determine their rotation periods, and what evidence was used to deduce the correct periods.
What is seen visually on each of these worlds is the upper atmosphere, with winds and storms that do not necessarily move at the same rate as the planet as a whole. Radio observations revealed the existence of magnetic fields originating in the cores of these planets. The rotation periods are determined from the fact that the magnetic fields rotate at the same velocity as the interiors.
How was the rotation rate of Mercury determined?
With the use of radar. Radar beams were directed to Mercury and the reflected beams showed the tell-tale signs of Doppler broadening. The measured degree of this frequency broadening provided an exact value for the rotation rate of Mercury.
Bar
a force of 100,000 Newtons acting on a surface area of 1 square meter; the average pressure of Earth's atmosphere at sea level is 1.013 bars
iron meteorites
a meteorite composed mainly of iron-nickel alloy
stony meteorite
a meteorite composed mostly of stony material, either primitive or differentiated
Exoplanet
a planet that orbits a star outside the solar system
The Van Allen belts are
charged particles trapped in the earth's magnetic field
Photochemistry
chemical changes caused by electromagnetic radiation
Meteorite
a portion of a meteor that survives passage through an atmosphere and strikes the ground
Comet
a small body of icy and dusty matter that revolves about the Sun; when a comet comes near the Sun, some of its material vaporizes, forming a large head of tenuous gas and often a tail
Meteor
a small piece of solid matter that enters Earth's atmosphere and burns up, popularly called a shooting star because it is seen as a small flash of light
meteor
a small piece of solid matter that enters Earth's atmosphere and burns up, popularly called a shooting star because it is seen as a small flash of lightning
Asteroid
a stony or metallic object orbiting the Sun that is smaller than a major planet but that shows no evidence of an atmosphere or of other types of activity associated with comets
stony-iron meteorites
a type of differentiated meteorite that is a blend of nickel-iron and silicate materials
Granite
a type of igneous silicate rock that makes up most of Earth's continental crust
Resonance
an orbital condition in which one object is subject to periodic gravitational perturbations by another, most commonly arising when two objects orbiting a third have periods of revolution that are simple multiples or fractions of each other
Giant planet
any of the planets Jupiter, Saturn, Uranus, and Neptune in our solar system, or planets of roughly that mass and composition in other planetary systems
Time=
distance/speed
Tectonic
geological features that result from stresses and pressures in the crust of a planet; tectonic forces can lead to earthquakes and motion of the crust
Differentiation
gravitational separation of materials of different density into layers in the interior of a planet or moon
Rift zone
in geology, a place where the crust is being torn apart by internal forces generally associated with the injection of new material from the mantle and with the slow separation of tectonic plates
Most of Uranus and Neptune (except for the outer bits) is in which phase?
liquid
meteor shower
many meteors appearing to radiate from one point in the sky; produced when Earth passes through a cometary dust stream
A spring tide happens at lunar phase
new
Planetesimal
objects, from tens to hundreds of kilometers in diameter, that formed in the solar nebula as an intermediate step between tiny grains and the larger planetary objects we see today; the comets and some asteroids may be leftover planetesimals
Radioactivity
process by which certain kinds of atomic nuclei decay naturally, with the spontaneous emission of subatomic particles and gamma rays
synchrotron radiation
radiation emitted when charged particles spiral rapidly in a magnetic field
Primitive rock
rock that has not experienced great heat or pressure and therefore remains representative of the original condensed materials from the solar nebula
What causes the gas tail of a comet to always point away from the Sun?
solar wind
Mare
the Latin word used to refer to the lunar "seas"
Tidal heating
the heating of a planet or moon's interior by variable tidal forces caused by changing gravitational pull from a nearby planet or moon
Stratosphere
the layer of the earth's atmosphere above the troposphere, extending to about 32 miles (50 km) above the earth's surface (the lower boundary of the mesosphere).
Highlands
the lighter, heavily cratered regions of the Moon, which are generally several kilometers higher than the maria
Convection
the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.
Crust
the outer layer of a planet
runaway greenhouse effect
the process by which the greenhouse effect, rather than remaining stable or being lessened through intervention, continues to grow at an increasing rate
Magnetosphere
the region around a planet in which its intrinsic magnetic field dominates the interplanetary field carried by the solar wind; hence, the region within which charged particles can be trapped by the planetary magnetic field
Subduction
the sideways and downward movement of the edge of a plate of the earth's crust into the mantle beneath another plate.
mass extinction
the sudden disappearance in the fossil record of a large number of species of life, to be replaced by fossils of new species in subsequent layers; mass extinctions are indicators of catastrophic changes in the environment, such as might be produced by a large impact on Earth
Half-life
the time required for half of the radioactive atoms in a sample to disintegrate
Where do planets get their light?
they reflect sunlight
Which gas is the most effective "greenhouse gas" in the earth's atmosphere as it exists now, averaged over time and area?
water vapor
Describe the seasons on the planet Uranus.
we know the planet is "on its side." Each pole experiences a 21-year sunlit "summer" and later a 21-year dark "winter." For the other half of the "Uranus year," the equator receives the light of the Sun and each hemisphere experiences what we would call a normal "day." In all, each pole experiences 42 years of light and 42 years of dark during its 84-year-long orbit.