ASTR 103 TAMU CONCEPT QUIZ EXAM 4

Which of the following correctly lists two key pieces of evidence that, together, indicate that we should expect human activity to cause global warming?

*(1) Carbon dioxide tends to make planets warmer than they would be otherwise; (2) measurements demonstrate that human activity is raising the carbon dioxide concentration in the atmosphere.*

In general, which type of planet would you expect to cause the largest Doppler shift in the spectrum of its star?

*A massive planet that is close to its star* -Doppler shifts measure velocity, and the star will move faster if it experiences a greater gravitational tug from its planet. A massive, close-in planet will cause the strongest gravitational tug.

Which of the following best describes how the greenhouse effect works?

*A planet's surface absorbs visible sunlight and returns this absorbed energy to space as infrared light. Greenhouse gases slow the escape of this infrared radiation, which thereby heats the lower atmosphere.* -This is the basic mechanism of the greenhouse effect, and it explains why more greenhouse gases mean more warming.

What cools off faster?

*A tiny terrestrial planet*

Why are smaller terrestrial bodies such as Mercury or the Moon "geologically dead"?

*A. They cool off faster than Earth did.* B. They were hit by fewer meteorites C. They are made of different material than Earth.

Jupiter's moons, Io,Europa, and Ganymede have tidal heating because?

*A. an orbital resonance keeps their orbits elliptical* B. they are the closest moons to Jupiter C. they are the largest moons in the solar system

To detect extrasolar planet by means of the Doppler shift, you look for a periodic shift of the spectrum lines

*A. of the star the planet is orbiting* B. of the planet C. of the star and the planet

Which of the following is not a piece of evidence supporting the idea that Europa may have a subsurface ocean?

*Astronomers have detected small lakes of liquid water on Europa's surface.* -There is no evidence of liquid water on Europa's surface, and even if liquid water emerged the cold temperatures would ensure that it would quickly freeze.

Which of the following gases is not a significant ingredient of the jovian planet atmospheres?

*Carbon dioxide* -Carbon dioxide is important in the terrestrial planet atmospheres, but not in the jovian planet atmospheres.

Suppose you are using the Doppler method to look for planets around another star. What must you do?

*Compare many spectra of the star taken over a period of many months or years.* -We look for Doppler shifts in the star's spectrum that, over time, shift back and forth to indicate the influence of an orbiting planet.

Many scientists suspect that Venus has a stronger and thicker lithosphere than Earth. If this is true, which of the following could explain it?

*The high surface temperature that has "baked out" all the liquid water from Venus's crust and mantle* -Without water, the rock would be stronger and the lithosphere could become thicker.

Which of the following will allow you to learn something about a transiting planet's atmospheric composition?

*Compare spectra obtained before and during an eclipse.* -The spectrum before the eclipse is that of the star and planet combined. The spectrum during eclipse, when the planet is behind its star, is that of the star alone. The difference between the two spectra therefore represents the planet's spectrum, from which we learn about atmospheric composition.

Suppose Earth were to cool down a little. How would the carbon dioxide cycle tend to restore temperatures to normal?

*Cooler temperatures lead to slower formation of carbonate minerals in the ocean, so carbon dioxide released by volcanism builds up in the atmosphere and strengthens the greenhouse effect.*

Which of the following best describes the geological histories of the Moon and Mercury?

*Early in their histories, they suffered many impacts and experienced some volcanism and tectonics, but they now have little geological activity at all.*

Why does Earth have so little carbon dioxide in its atmosphere compared to Venus?

*Earth has just as much carbon dioxide as Venus, but most of it is locked up in carbonate rocks rather than being free in the atmosphere.* -The carbon dioxide became locked up like this on Earth after it dissolved in water and combined with minerals to make carbonate rock. This does not occur on Venus because there is no liquid water.

When we see a meteor shower, it means that _________.

*Earth is crossing the orbit of a comet* -The meteor shower is caused by particles that have been shed by the comet along its orbit.

Which of the following is not a piece of evidence supporting the idea that an impact caused the mass extinction that occurred 65 million years ago?

*Fossilized dinosaur bones contain fragments of rock from the impact.*

Why didn't a planet form where the asteroid belt is now located?

*Gravitational tugs from Jupiter prevented material from collecting together to form a planet.* -Early in the solar system's history there should have been plenty of material to form a planet here, but Jupiter's gravity prevented it. Over time, most of this material has left this region (crashing to other planets or ejected from solar system), leaving the asteroid belt of today with much less mass than would be needed to form a planet.

When is the soonest we are likely to have moderate-resolution images and spectra of Earthlike planets around other stars?

*In a decade or two, through space observatories now in the early planning stages.* -Scientists have numerous ideas about how they might obtain such images and spectra, but budgetary limitations mean that little work is being done in these areas right now.

All the following statements are true. Which one is most important in explaining the tremendous tidal heating that occurs on Io?

*Io orbits Jupiter on an elliptical orbit, due to orbital resonances with other satellites.* -On an elliptical orbit, tides vary and flex Io's shape.

From the viewpoint of an alien astronomer, how does Jupiter affect observations of our Sun?

*It causes the Sun to move in a small ellipse with an orbital period of about 12 years.* -Jupiter exerts a gravitational tug on the Sun, causing the Sun to move around their mutual center of mass with the same orbital period as Jupiter.

Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury every 125 years. What can we conclude?

*It has been on its current orbit for only a very short time compared to the age of our solar system.* -Comets cannot survive more than a couple hundred passages through the inner solar system because they lose mass with each pass. So this comet cannot have been on its current orbit for more than a few tens of thousands of years.

Which of the following statements best describes the size of the largest asteroid, Ceres?

*It is a little less than half the diameter of our Moon.* - This size is large enough for Ceres to qualify as a dwarf planet.

What is Pluto's moon Charon thought to have in common with our own Moon?

*It probably formed as a result of a giant impact.* -That seems to be the most likely explanation for Charon's relatively large size in comparison to Pluto, and the giant impact may also explain the two smaller moons of Pluto.

Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different?

*It would have only one tail instead of two.* -There would be no plasma tail without the solar wind. The dust tail would still be present, since it responds to radiation pressure rather than the solar wind.

What would happen to Jupiter if we could somehow double its mass?

*Its density would increase but its diameter would barely change.*

Which of the following best explains why many jovian moons have been more geologically active than the Moon or Mercury?

*Jovian moons are made mostly of ice that can melt or deform at lower temperatures than can the rock and metal that make up the Moon and Mercury.* -right answer feedback: That is why icy worlds need far less internal heat for geological activity than rocky worlds.

Which of the following is most unlikely to be found on Titan?

*Lakes of liquid water in the warmer equatorial regions* -Titan's surface temperature is never anywhere close to being warm enough for liquid water, even at its equator.

All the following statements about Mars are true. Which one might have led to a significant loss of atmospheric gas to space?

*Mars lost any global magnetic field that it may once have had.* -This allowed the solar wind to strip atmospheric gas into space.

Recent evidence suggests that Mars once had a global magnetic field. Assuming this is true, which of the following could explain why Mars today lacks a global magnetic field like that of Earth?

*Mars's interior has cooled so much its molten core layer no longer undergoes convection.* -Convection of the molten core is required for a global magnetic field.

Suppose that large jovian planets had never formed in our solar system. Which of the following would most likely be true?

*Neither the asteroid belt nor Oort cloud would exist.* -Jupiter's gravity is responsible for the existence of the asteroid belt, and the Oort cloud is thought to consist of comets ejected from the region of the jovian planets by their gravity. So without the jovian planets, neither the asteroid belt nor the Oort cloud would be likely to exist.

Suppose we had a device that allowed us to see Earth's interior. If we looked at a typical region of the mantle, what would we see happening?

*Not much; on human time scales, the mantle looks like solid rock.* -The mantle is solid. Mantle convection is the slow flow of this solid rock, but it occurs too slowly to notice on human time scales. (The cycling time for rock from the bottom to the top of the mantle is about 100 million years.)

Based on everything you have learned about the formation of our solar system, which of the following statements is probably not true?

*Only a tiny percentage of stars are surrounded by spinning disks of gas during their formation.* -Spinning disks are a natural consequence of how we think stars form, which is one reason we expect planets to be quite common; the fact that we have now discovered thousands of extrasolar planets lends further support to the idea that disks and planets should both be common.

Which of the following objects are probably not located in the same general region of the solar system in which they originally formed?

*Oort cloud comets* -Oort cloud comets probably formed between the jovian planets are were kicked out to their current large distances from the Sun.

Assuming that our ideas about how "hot Jupiters" ended up on their current orbits are correct, why didn't our own solar system end up with any hot Jupiters?

*Our solar nebula must have been blown into space shortly after the formation of the jovian planets.* -This would prevent much inward migration from occurring.

According to our theory of solar system formation, why did Uranus and Neptune end up to be much less massive than Jupiter and Saturn?

*Particles in the solar nebula were more spread out at greater distances, so that accretion took longer and there was less time to pull in gas before the solar wind cleared the nebula.*

Based on discoveries to date, which of the following conclusions is justified?

*Planetary systems are common and planets similar in size to Earth are also common.* -The statistics of extrasolar planets known to date strongly support these conclusions.

What are the two geological features that appear to set Earth apart from other terrestrial worlds in our solar system?

*Plate tectonics and a high level of erosion* -Neither of these features appears to exist on any other terrestrial world in our solar system.

Which two factors are critical to the existence of the carbon dioxide (CO2) cycle on Earth?

*Plate tectonics and liquid water oceans* -right answer feedback: Carbon dioxide dissolves in the oceans and becomes incorporated into carbonate rock; plate tectonics recycles the carbonate rock into the mantle, where it melts and releases its gas back to the atmosphere.

Why won't Pluto collide with Neptune?

*Pluto orbits the Sun exactly 2 times for every 3 Neptune orbits.* -This stable orbital resonance means that Pluto and Neptune never come close together.

The choices that follow describe four hypothetical planets. Which one would you expect to have the most features of erosion? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.)

*Size: same as Venus. Distance from Sun: same as Mars. Rotation rate: once every 25 hours.* -This planet is large enough to have had outgassing make an atmosphere and rotates fast enough to drive winds.

The choices that follow describe four hypothetical planets. Which one's surface would you expect to be most crowded with impact craters? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.)

*Size: same as the Moon. Distance from Sun: same as Mars. Rotation rate: once every 10 days.* -The smallest size means the least geological activity to have erased past impact craters, so lots of craters would still be present.

The choices that follow describe four hypothetical planets. Which one would you expect to have the hottest interior? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.)

*Size: twice as big as Earth. Distance from Sun: same as Mercury. Rotation rate: once every 6 months.* -right answer feedback: Largest size means the highest interior temperature.

Which of the following is a real piece of evidence pointing to recent geological activity on Pluto?

*Surface regions that suggest glacial movement of frozen ices of nitrogen and methane.* -Apparently, Pluto has enough internal heat to drive flows of these ices, which exist in solid form only at very low temperatures.

Uranus and Neptune have methane clouds but Jupiter and Saturn do not. Which factor explains why?

*Temperatures on Jupiter and Saturn are too high for methane to condense.* -But methane can condense on Uranus and Neptune because they are farther from the Sun and hence colder.

What makes us think that Mars must once have had an atmosphere that was warmer and had higher surface pressure?

*The atmosphere is too cold and thin for liquid water today, yet we see evidence that water flowed on the surface in the past.* - If water really did flow, the atmospheric conditions must have been different.

Why are there fewer large impact craters on the Earth's seafloor than on the continents?

*The crust on seafloors is younger than on continents, so it has had less time in which to suffer impacts.* -Seafloor crust is continually recycled, so that the seafloor is nearly everywhere younger than about 200 million years. Therefore evidence of any earlier impacts has been erased as the seafloor crust was recycled.

When you see the bright flash of a meteor, what are you actually seeing?

*The glow from a pea-sized particle and the surrounding air as the particle burns up in our atmosphere* -In other words, you do not see the particle itself, but only the effects it has on the surrounding air as it burns up.

Which of the following best why we see horizontal "stripes" in photographs of Jupiter and Saturn?

*The light stripes are regions of high clouds, and the dark stripes are regions where we can see down to deeper, darker clouds.* -And the reason these stripes stretch all the way around these planets is the strong Coriolis force that comes from the planets' rapid rotation.

Most of the Moon's surface is densely covered with craters, but we find relatively few craters within the lunar maria. What can we conclude?

*The maria formed after the heavy bombardment ended.* - They contain few craters because they formed after most impacts had occurred.

Which of the following general statements about Earth's atmosphere is not true?

*The nitrogen and oxygen in Earth's atmosphere keep the surface pleasantly warm.* -Only greenhouse gases influence surface temperature, and neither oxygen nor nitrogen is a greenhouse gas.

You observe a star very similar to our own Sun in size and mass. This star moves very slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet?

*The planet must be closer to the star than Earth is to the Sun.* -According to Kepler's third law, a planet with a shorter orbital period must be closer to the star, assuming the star has the same mass as the Sun.

According to current understanding, which of the following is required for a planet to have rings?

*The planet must have many small moons that orbit relatively close to the planet in its equatorial plane.* -Ring particles come from small and large impacts on these small moons.

Why is the radiation so intense in the region that traces Io's orbit around Jupiter (the Io torus)?

*The region is full of gases that become ionized after they are released from volcanoes on Io.* -right answer feedback: Io's low gravity allows these gases to escape.

Which statement about Saturn's rings is not true?

*The rings must look much the same today as they did shortly after Saturn formed.* -Ring particles cannot last long compared to the age of the solar system, so the rings much change their appearance with time.

In science fiction movies, spaceships are often shown dodging through large numbers of closely spaced, boulder-size objects. Which of the following real things in our solar system would look most like such science fiction dangers?

*The rings of Saturn* -The rings consist of countless small particles ranging in size from dust grains to city blocks, so it would be quite a challenge to dodge them.

Why does Jupiter have three distinct layers of clouds?

*The three layers represent clouds made of gases that condense at different temperatures.* -The three cloud layers are ammonia, ammonium hydrosulfide, and water. Each of these gases condenses at a different temperature and hence at a different altitude in Jupiter's atmosphere.

Current evidence suggests that some massive jovian planets orbit at very close orbital distances to their stars. How do we think these planets ended up on these close orbits?

*These planets migrated inward after being born on orbits much farther from their stars.* -We still think that jovian planets must form in cold, outer regions of their star systems, which is why the idea of migration was first proposed. Although work is still preliminary, models suggest that this type of migration is indeed likely.

Jupiter and the other jovian planets are sometimes called "gas giants." In what sense is this term misleading?

*They actually contain relatively little material in a gaseous state.* -Much more of their mass is liquid, metallic, or in strange high-pressure states that we don't naturally find on Earth.

Which of the following best describes why scientists seek to identify even very small asteroids that could potentially hit Earth?

*To try to prevent an impact that might destroy a town or city.* -The hope is that if we can first identify potential threats, then we can find a way to divert their paths before they hit Earth.

Why do astronomers believe that Triton is a captured moon?

*Triton orbits Neptune in a direction opposite that of Neptune's rotation.* -This "backward" orbit is a tell-tale sign of a captured moon.

Which of the following best explain what we think happened to outgassed water vapor on Venus?

*Ultraviolet light split the water molecules, and the hydrogen then escaped to space.* -This did not occur on Earth, because the temperatures allowed the water vapor to condense into liquid water and rain down to the surface.

Which jovian planet should have the most extreme seasonal changes?

*Uranus* -Its large axis tilt gives it seasons that each last about ¼ of its 84-year orbit.

All the following statements about Venus are true. Which one offers evidence of a global repaving about a billion years ago?

*Venus has relatively few impact craters and these craters are distributed fairly evenly over the entire planet.* -This suggests that older impact craters were covered over everywhere on the planet.

To date, we've found very few planets orbiting their stars at distances comparable to the distances of the jovian planets in our solar system. Why do astronomers think this is the case?

*We have not yet been searching for planets at such distances for a long enough time.* -Remember that we must observe at least something close to one complete orbit—and preferably more—before we can be confident of an extrasolar planet discovery. Jupiter takes 12 years to orbit the Sun, and Neptune takes 165 years, so we would need observations over similarly long period to detect planets in these types of orbits around other stars.

Suppose you find a meteorite made almost entirely of metal. According to current science, which of the following statements must be true?

*Your meteorite is a fragment from the core of a large asteroid that shattered in a collision.* -Only a large asteroid would have undergone differentiation to make a metal core, so this must be the source of the meteorite.

The reason that small planets tend to lose interior heat faster than larger planets is essentially the same as the reason that _________.

*a large baked potato takes longer to cool than a small baked potato* -A smaller object has proportionally more surface area through which to lose its interior heat.

Suppose a planet is discovered by the Doppler method and is then discovered to have transits. In that case, we can determine all the following about the planet except ______________.

*its rotation period* -We do not get any direct information about rotation period. (However, if the planet is very close to its star, we can sometimes conclude that it has synchronous rotation, in which case the rotation period and orbital period are the same.)

Which two factors are most important to the existence of plate tectonics on Earth?

*mantle convection and a thin lithosphere* -Mantle convection helps move the plates, and the plates probably exist because the lithosphere was thin enough to break into these plates.

The cores of the terrestrial worlds are made mostly of metal because ______.

*metals sunk to the centers a long time ago when the interiors were molten throughout* -the sinking was part of the process called differentiation

If we could put all the asteroids together, their total mass would be _________.

*much less than the mass of any terrestrial planet* -There may once have been enough material in the asteroid belt to assemble another terrestrial planet, but there is no longer enough today.

The transit method allows us in principle to find planets around __________.

*only a small fraction of stars that have planets* -We can see transits only if the planetary orbits are nearly precisely edge-on as viewed from Earth, which means that most planetary systems cannot be detected through transits. The Kepler mission overcame this limitation by studying a large number of stars (about 150,000).

Gaps in the asteroid belt (often called Kirkwood gaps) are caused by ______.

*orbital resonances with Jupiter* -Asteroids with orbital periods that are simple fractions (such as ½, 1/3, ¼) of Jupiter's period receive repeated tugs with each orbit, and these tugs tend to nudge them out of those orbits, clearing a gap.

Suppose that Earth's atmosphere had no greenhouse gases. Then Earth's average surface temperature would be ________.

*well below the freezing point of water* -Without the greenhouse effect, Earth's average temperature would be about -16°C, which is well below freezing (0°C). Thanks to the greenhouse effect, the actual global average temperature is about 15°C.

How does Io get heated by Jupiter?

A. Auroras B. Infrared light *C. Jupiter pulls harder on one side than the other* D. Volcanoes

Suppose you found a star with the same mass as the Sun moving back and forth with a period of 16 months. What could you conclude?

A. It has a planet orbiting at less than 1 AU. *B. It has a planet orbiting at greater than 1 AU.* C. It has a planet orbiting at exactly 1 AU. D. It has a planet, but we do not have enough information to know its orbital distance

Jupiter is about three times as massive as Saturn, but only slightly larger. Why?

A. It is made of stronger material. B. It is made of weaker material. *C. Adding mass increases gravity and compresses gases.* D. Because they are made of different gases. E. None of the above.

How is Pluto different than the other objects in the Kuiper belt?

A. It's orbit is unlike the orbits of other Kuiper belt objects. B. It has moons, unlike other Kuiper belt objects. C. It is larger than all the other Kuiper belt objects *D. None of the above*

Why are some small Jovian planet moons geologically active?

A. They have large amount of radioactive material. B. Impact cratering melted the interior. *C. Ice is able to deform at lower temperatures* D. All of the above

How does the composition of Uranus and Neptune compare to the composition of Jupiter and Saturn?

A. Uranus and Neptune have compositions very similar to Jupiter and Saturn B. Uranus and Neptune are mostly rocky whereas Jupiter and Saturn are mostly hydrogen and helium. C. Uranus and Neptune are mostly hydrogen and helium whereas Jupiter and Saturn are mostly hydrogen compounds. *D. Uranus and Neptune are mostly hydrogen compounds whereas Jupiter and Saturn are mostly hydrogen and helium.*

When New Horizons arrived at Pluto, it found ?

A. a dead, rocky world B. a dead, icy world C. an active, rocky world *D. an active, icy world*

Which of the following is not evidence that has been found for liquid water on Mars's surface in the past?

A. the presence of small spheres called "blueberries" that form near salty water environments B. layered deposits similar to sedimentary rocks C. ancient riverbeds *D. none of the above (all are evidence of past water)* E. all of the above (none are evidence of past water

What is the structure of Jupiter like?

A.Rocky core, thin atmosphere B. Gaseous throughout *C. Gaseous on the outside, then liquid hydrogen, more dense metallic hydrogen,rocky/icy/metallic core* D. Gaseous on the outside, then liquid hydrogen, then helium, then the other elements

What is the main reason that Venus is warmer than Earth?

A.Venus is closer to the sun than Earth B.Venus has a higher reflectivity than Earth C. Venus has a lower reflectivity than Earth *D. The greenhouse effect is much stronger on Venus than on Earth.*