Planets 411

Explain the reasoning behind Callisto's appearance.

-The ridges resemble the ripples made as a stone hits water, but on Callisto they probably resulted from a cataclysmic impact with a meteorite. -Callisto froze before plate tectonic or other activity could start.

Give the basic information of the planet Venus.

-very dry, arid place -Venus's atmosphere is much more massive than our own, and it extends to a much greater height above the planet's surface -The surface pressure on Venus is about 90 times the pressure at sea level on Earth -high surface temperature (730 K) -main component of its atmosphere is carbon dioxide, almost all the remaining 3.5% is nitrogen

A meteor shower is caused by what?

Earth running through the debris of an old comet littering its orbit.

List the terrestrial planets from highest to lowest density

Earth, Mercury, Venus, Mars

What is the Roche limit?

The closest distance from the center of a planet that a satellite can approach without being pulled apart by the planet's gravitational field.

True or False: The source of Europa's energy is the external force of Jupiter's gravity.

True. As on Io, the ultimate source of the energy that keeps the ocean liquid and also drives the internal motion leading to the cracks in the icy surface is Jupiter's gravity.

Describe the characteristics of the Galilean moons of Jupiter.

-Io and Europa have large, iron-rich cores surrounded by thick mantles of generally rocky composition -Europa has a water/ice outer shell -Ganymede and Callisto are less dense overall; low-density materials, such as water ice, may account for as much as half their total mass -Ganymede has a relatively small metallic core topped by a rocky mantle and a thick icy outer shell -Callisto seems to be a largely undifferentiated mixture of rock and ice

Describe the magnetic fields of the terrestrial planets

-Mercury's weak magnetic field seems to be a fossil remnant from the time when the planet's iron core solidified. -Venus does not have a detectable magnetic field even though, like Earth, it probably has a molten core. -Mars rotates rapidly, but has a very weak magnetic field, implying that its core is nonmetallic, nonliquid, or both.

Give the basic information of the planet Neptune.

-Neptune was discovered after mathematical calculations of Uranus's slightly non-Keplerian orbit revealed the presence of an eighth planet. -Although Neptune lies farther from the Sun, its internal heat means that its upper atmosphere is actually slightly warmer than that of Uranus. -Fairly strong magnetic field and substantial magnetosphere -The atmospheres of Uranus and Neptune are very similar in composition to that of Jupiter—the most abundant gas is molecular hydrogen (84 percent), followed by helium (about 14 percent) and methane, which is more abundant on Neptune (about 3 percent) than on Uranus (2 percent). -blue color -Great Dark Spot is found here -The interior pressures of Uranus and Neptune are sufficiently low that hydrogen stays in its molecular form all the way into the planets' cores.

Give the basic information of the planet Saturn.

-Saturn orbits at almost twice Jupiter's distance from the Sun, making it considerably fainter (as seen from Earth) than either Jupiter or Mars -Saturn's electrically conducting interior and rapid rotation also produce a strong magnetic field and an extensive magnetosphere (but is only 1/20 of Jupiter's) -The planet's banded atmosphere is somewhat similar to Jupiter's, but Saturn's atmospheric bands are much less distinct -internal heating source -the planet with the rings -Because of its lower mass, Saturn has a less extreme core temperature, density, and pressure than Jupiter -Saturn's overall atmospheric temperature is a little lower because of its greater distance from the Sun -As on Jupiter, the troposphere contains clouds arranged in three distinct layers, composed (in order of increasing depth) of ammonia ice, ammonium hydrosulfide ice, and water ice -weaker gravity (due to 3 very thick cloud layers, thicker than each counterpart on Jupiter)

Describe the similarities between Uranus and Neptune (the two outermost planets)

-The atmospheres of Uranus and Neptune are very similar in composition to that of Jupiter—the most abundant gas is molecular hydrogen (84 percent), followed by helium (about 14 percent) and methane, which is more abundant on Neptune (about 3 percent) than on Uranus (2 percent). -The blue color of the outer jovian planets is the result of their relatively high percentages of methane. (absorbs red light)

What are the similarities between the jovian planets?

-The large masses and radii and relatively low average densities -Hydrogen and helium make up most of the mass of Jupiter and Saturn and about half the mass of Uranus and Neptune. -The abundance of hydrogen and helium on these worlds is a consequence of the strong jovian gravity -None of the jovian planets has a solid surface of any kind. Their gaseous atmospheres just become hotter and denser with depth because of the pressure of the overlying layers, eventually becoming liquid in the interior. -At the heart of each jovian planet lies a dense, compact core more massive than Earth. -All four jovian worlds have strong magnetic fields and emit radiation at radio wavelengths.

Give the basic information of the planet Uranus

-William Herschel discovered Uranus in 1781 -blue color -Uranus is just barely visible to the naked eye, under the best possible observing conditions. -Fairly strong magnetic field and substantial magnetosphere -The interior pressures of Uranus and Neptune are sufficiently low that hydrogen stays in its molecular form all the way into the planets' cores.

Describe Saturn's moon, Titan.

-a thick, uniform haze layer, in some ways similar to the smog found over many cities on Earth, envelops the moon -Titan's atmosphere is thicker and denser than Earth's and is certainly more substantial than that of any other moon. -atmosphere is composed mostly of nitrogen (more than 98 percent), with methane and trace amounts of other gases making up the rest -surface temperature is a frigid 94 K -the moon's surface is geologically active: methane rain, snow, and fog and ethane rivers and oceans -low mass (a little less than twice that of Earth's Moon) and hence low surface gravity (one-seventh of Earth's) -atmospheric pressure at ground level is 60 percent greater than that on Earth -weaker gravitational pull

Give the basic information of the planet Mars.

-atmosphere is quite thin and composed primarily of carbon dioxide -atmospheric pressure is only about 1/150 the pressure of Earth's atmosphere at sea level -atmosphere is 95.3 percent carbon dioxide, 2.7 percent nitrogen, and 1.6 percent argon, plus small amounts of oxygen, carbon monoxide, and water vapor - cool surface temperature (average surface temperatures on Mars are about 70 K cooler than on Earth)

Describe the basic information of the 12 medium-sized jovian moons.

-bodies having radii between about 200 and 800 km -Their densities suggest that all 12 are composed largely of rock and water ice -All move on nearly circular paths and are tidally locked by their parent planet's gravity, and so have permanently "leading" and "trailing" faces. -Most of these moons have old, heavily cratered surfaces, with no evidence for extensive geological activity.

Give the basic information of the planet Mercury.

-high surface temperature (up to 700 K at noon on the equator) -low mass (only 4.5 times the mass of the Moon)

Give the basic information of the planet Jupiter.

-largest planet in the solar system -overall reddish coloration and the alternating light and dark bands paralleling its equator -Great Red Spot is found here -the strongest planetary magnetic field in the solar system -internal heating source -The most abundant gas in Jupiter's atmosphere is hydrogen (roughly 86 percent of all molecules), followed by helium (nearly 14 percent). Small amounts of atmospheric methane, ammonia, and water vapor are also found. -both the temperature and the pressure of Jupiter's atmosphere increase with depth -of particular importance for Jupiter's magnetic field, this metallic hydrogen is an excellent conductor of electricity -Jupiter has many moons that vary greatly in size and other properties. There are four large Galilean moons (named after Galileo Galilei, who discovered them)

Describe Neptune's large moon, Triton.

-smallest of the seven large moons in the solar system -was captured from the Kuiper belt, probably not too long ago -4.5 billion kilometers from the Sun and possessing an icy surface that reflects much of the solar radiation reaching it -temperature of just 37 K -tall/high nitrogen geysers found here -extremely thin nitrogen atmosphere and a solid, frozen surface probably composed primarily of water ice -lack of cratering, indicating that surface activity has obliterated the evidence of most impacts

Describe the five medium-sized moons of Uranus and the single medium-sized moon of Neptune

All six moons are heavily cratered, and most show no clear evidence of any present or past geological activity.

What is odd about the rotation period of Venus?

An unexpectedly sluggish 243-day rotation period. Furthermore, Venus's spin was found to be retrograde—that is, opposite that of Earth and most other solar system objects and in the direction opposite Venus's orbital motion.

What does the surface of Callisto look like?

Callisto is in many ways similar in appearance to Ganymede, although Callisto is more heavily cratered and has few fault lines. Callisto's most obvious feature is a huge series of concentric ridges surrounding two large basins.

Describe the Great Dark Spot on Neptune.

Comparable in size to Earth, the Spot was located some 20° south of the planet's equator—quite similar to the Great Red Spot on Jupiter.

What is a prominent feature of Mercury's surface?

Craters. There are also extensive intercrater plains between the larger craters. These plains are the oldest visible parts of the planet's surface. They formed just under 4 billion years ago. In addition, Mercury has numerous smooth plains, akin to the lunar maria, where lava has filled depressions produced by large meteoritic impacts.

True or False: Europa has a strong magnetic field.

False. Europa has a weak magnetic field that constantly changes strength and direction.

True or False: Io has geological activity similar to Earth and works off of its internal heat.

False. It should be long dead, like our Moon, its internal heat lost to space billions of years ago. Instead, the source of Io's energy is external—Jupiter's gravity. Because Io orbits very close to Jupiter, the planet's huge gravitational field produces strong tidal forces on the moon, resulting in a large (100 m) tidal bulge.

True or False: Jupiter's moons increase in density the further they get from the planet.

False. Their densities decrease with increasing distance from Jupiter in a manner very reminiscent of the falloff in density of the terrestrial planets with increasing distance from the Sun.

True or False: there was never water on Mars

False. There is clear evidence that water once existed in great quantity on Mars.

Tru or False: Because of their low masses, the hydrogen and helium aren't condensed as much. Thus, Uranus and Neptune are less dense than Saturn.

False. the average densities of Uranus and Neptune are actually greater than the density of Saturn and similar to that of Jupiter. Astronomers interpret this to mean that Uranus and Neptune each have Earth-sized cores some 10 times more massive than our planet, with compositions similar to the cores of Jupiter and Saturn.

List Saturn's 6 medium-sized satellite bodies.

Iapetus, Mimas, Enceladus, Tethys, Dione, Rhea

Explain the Roche limit using Saturn as an example.

If our hypothetical moon is held together by its own gravity, and if its average density is similar to that of the parent planet (both reasonably good assumptions for Saturn's larger moons), then the Roche limit is approximately 2.4 times the radius of the planet. For example, in the case of Saturn (of radius 60,000 km), the Roche limit lies roughly 144,000 km from the planet's center—just outside the outer edge of the A ring. The rings of Saturn occupy the region inside Saturn's Roche limit.

List Jupiter's 4 Galilean moons in order going outward from the planet.

Io, Europa, Ganymede, Callisto

Describe the appearance of Saturn's moon Iapetus.

It has a distinctly "two-faced" appearance. Its leading hemisphere is very dark, while the other is very bright. In 2009 the Spitzer Space Telescope discovered a new, huge, diffuse ring more than 6 million kilometers from Saturn. Iapetus lies at the inner edge of this ring, and it causes the moon's asymmetric appearance.

Describe what we know about Saturn's rings.

It has rings ranging from A-E. From Earth, astronomers identified three rings, which they simply labeled A, B, and C. The A ring lies farthest from the planet and is separated from the inner B and C rings by a dark gap called the Cassini Division. A smaller gap, known as the Encke Gap, is found in the outer part of the A ring. Of the three main rings, the B ring is brightest, followed by the somewhat fainter A ring, and then by the almost translucent C ring. The additional rings listed in Table 8.3 cannot be seen.

What is prominent about Saturn's tiny ice-covered moon Enceladus?

It shows evidence of youthful terrain in the south where craters are mostly absent. The long blue "tiger stripe" streaks (about 1 km wide) are fractures in the ice through which gas escapes to form a thin but real atmosphere. It also has ongoing geological activity.

Which planet has the strongest planetary magnetic field in the solar system?

Jupiter

Which moon is the largest moon in the solar system?

Jupiter's Galilean moon, GANYMEDE, exceeds both the Earth's moon and the planet Mercury in size.

What is the most geologically active object in the entire solar system?

Jupiter's closest Galilean moon, Io. In mass and radius it is similar to Earth's Moon, but there the resemblance ends. It has ACTIVE VOLCANOES.

What is the source of energy for all the activity observed on Jupiter's Galilean moons?

Jupiter's gravitational field, via its tidal effect on the moons.

List some similarities and differences between Jupiter's belts and zones and weather systems on Earth.

Like weather systems on Earth, the belts and zones are regions of high and low pressure and are associated with convective motion. However, unlike storms on Earth, they wrap all the way around the planet because of Jupiter's rapid rotation. In addition, the clouds are arranged in three distinct layers, and the bright colors are the result of cloud chemistry unlike anything operating in Earth's atmosphere. Jupiter's spots are somewhat similar to hurricanes on Earth, but they are far larger and longer-lived.

Which planet has the greatest difference in surface temperature from day to night? What is the temperature range?

Mercury's 600 K temperature range is the largest of any planet or moon in the solar system

How has the Sun's gravity influenced Mercury's rotation?

Mercury's rotation rate is strongly influenced by the tidal effect of the Sun, which causes the planet to rotate exactly one and a half times for every one revolution around the Sun.

List the planets in order from the sun outward

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Which is the smallest of the seven large moons in the solar system?

Neptune's large moon, Triton, with about half the mass of the next smallest, Europa.

Are the volcanoes on Venus mainly associated with the movement of tectonic plates, as on Earth?

No. They are mainly shield volcanoes formed by lava upwelling through "hot spots" in the crust and are not associated with plate tectonics (which is not observed on Venus).

Compare 2 of Saturn's medium-sized bodies, Dione and Rhea.

Prior to Cassini's arrival, scientists thought that the light-colored wispy terrain on Saturn's Rhea and Dione was the result of events in the distant past, during which water was released from the moons' interiors and condensed on their surfaces. However, Cassini images reveal that the markings are in fact bright ice cliffs created by tectonic fractures, where stresses in the moons' icy interiors as they cooled and contracted caused the surface layers to crack and buckle.

Which planet is less dense than water and can actually "float"?

Saturn

How do scarps on Mercury differ from geological faults on Earth?

Scarps are thought to have been formed when the planet's iron core cooled and contracted, causing the crust to crack. Faults on Earth are the result of tectonic activity.

Why does Titan have a thick atmosphere when Ganymede and Callisto do not?

The answer lies largely in Titan's 94 K surface temperature, which is considerably lower than that of Jupiter's moons, making it easier for the moon to retain an atmosphere.

Compare Jupiter's belts and zones to the weather systems on Earth.

The belts and zones are Jupiter's equivalents of the familiar high- and low-pressure systems that control the weather on Earth. A major difference from Earth is that Jupiter's rapid differential rotation causes these systems to wrap all the way around the planet, instead of forming localized circulating storms as on our own world.

Why was Voyager 1 unable to photograph the surface of Titan? Why do we now have a much better understanding of the moon's surface?

The haze layers high in the moon's dense atmosphere are opaque to visible light. The Huygens probe landed on the surface, and Cassini's radar and infrared sensors can penetrate the haze.

Why do observations of a planet's magnetosphere allow astronomers to measure the rotation rate of the interior?

The magnetic field is generated by the motion of electrically conducting liquid in the deep interior and therefore presumably shares the rotation of that region of the planet.

Why do all the jovian planets have strong magnetic fields?

They all combine the two essential ingredients needed to operate a planetary dynamo: (1) rapid rotation, in all cases faster than Earth's rotation, and (2) conducting liquid interiors: metallic hydrogen in the cases of Jupiter and Saturn and "slushy" ice in the cases of Uranus and Neptune.

What surface property of the medium-sized moons tells us that the outer solar system was once a very violent place?

They are all very heavily cratered—a result of the heavy bombardment that marked the clearing of the comets from the outer solar system.

True or False: Jupiter's Galilean moon Europa is covered by an ocean of liquid water whose surface layers are frozen.

True

True or False: Neptune's large moon, Triton, was captured from the Kuiper Belt.

True

True or False: Triton is the only large jovian moon not to orbit in its parent planet's equatorial plane.

True, with an orbital inclination of about 20°

True or False: the jovian planets undergo differential rotation

True. Because the jovian planets have no solid surfaces to "tie down" the gas flow, different parts of their atmospheres can and do move at different speeds.

True or False: Ganymede has had tectonic motion much like Earth's in the past.

True. Ganymede has a system of grooves and ridges that may have resulted from tectonic motion, like mountain building and faulting at plate boundaries on Earth.

True or False: Titan's atmosphere seems to act like a gigantic chemical factory.

True. Powered by the energy of sunlight, it is undergoing a complex series of chemical reactions that ultimately result in the observed composition. The upper atmosphere is thick with smoggy haze, and the surface may be covered with hydrocarbon sediment that has settled from the clouds.

True or False: All four jovian worlds have planetary ring systems girdling their equators.

True. The properties and appearance of each planet's rings are intimately connected with the planet's small and medium-sized moons, with many of the inner jovian moons orbiting close to (or even within) the parent planet's rings.

Why are atmospheric features much less evident on Uranus than on the other jovian planets?

Uranus's low temperature means that the planet's clouds lie deeper in the atmosphere, making them harder to distinguish from Earth. (Only a few atmospheric features on Uranus; Few clouds exist in Uranus's cold upper atmosphere)

List the five medium-sized moons of Uranus and the single medium-sized moon of Neptune

Uranus: Oberon, Miranda, Ariel, Titania, Umbriel Neptune: Proteus

Describe 4 important differences between the atmospheres of Venus and Earth.

Venus's atmosphere is much more massive, hotter, and denser than that of Earth, and is composed almost entirely of carbon dioxide.

Describe the surface of Venus.

Venus's surface appears to be mostly smooth, resembling rolling plains with modest highlands and lowlands. Only two continent-sized features, called Ishtar Terra and Aphrodite Terra, adorn the landscape, and these contain mountains comparable in height to those on Earth. Volcanic activity appears to resurface the planet every few hundred million years. Many areas of Venus have volcanic features.

Which planet is the 3rd brightest object in the entire sky? The night sky?

Venus, Jupiter (after Venus)

Why is mathematical modeling essential to understanding the interior structures of the jovian planets?

We have no direct observations of the interiors of these worlds. Everything we know is derived from theoretical models of their interiors, coupled with observations of their masses, radii, and surface properties.

Do all the jovian planets have moon systems? If so, how many each?

Yes. All four jovian planets have extensive moon systems—Jupiter has at least 67 natural satellites orbiting it, Saturn has 62, Uranus 27, and Neptune 14.

Where is the asteroid belt found?

between the orbits of Mars and Jupiter

Where is the Kuiper belt found?

beyond the orbit of Neptune

Where is the Oort Cloud found?

beyond the orbit of Neptune

What is the main component in Venus's atmosphere?

carbon dioxide

We use (blank) to measure the geological structures thousands of miles beneath the surface of the Earth and Moon.

earthquakes and moonquakes

Do jovian planets have faster or slower rotation speeds and thus shorter or longer days than terrestrial planets?

faster rotations, shorter days

Is Earth's moon more or less dense than Earth?

much less dense

Does Mercury have an atmosphere?

no

The 4 planets closest to the sun are (blank) as opposed to the farther 4 which are (blank)

terrestrial, jovian

What is Mercury's most prominent global feature?

the Caloris Basin

What was the old rotation period of Mercury (what we originally thought) and what is it now?

the rotation period of Mercury is not 88 days, as had previously been thought, but just under 59 days—in fact, exactly two-thirds of Mercury's year

Does Venus have an atmosphere?

yes