Ch. 09: Homework

The majority of asteroids exist in the asteroid belt between Jupiter and Mars. Why would that be the case? The are two main possibilities: There used to be a planet there that was destroyed in a giant impact, or the planetesimals there were somehow prevented from forming a planet in the first place. To figure out which of these is correct, we can look at spectra to determine the composition of the asteroids themselves and study actual samples of asteroids that fell to Earth—that is, meteorites. The figure below explains the difference between the types of asteroids and meteorites. Based on the figure, which asteroid types would be more common if they were the result of a shattered planet?At least 75% of asteroids are primordial C-type. What does this imply about how the asteroid belt was formed?

A and B A.M-type B.S-type

Only larger objects have strong enough self-gravity to force themselves into a spherical shape. The first asteroid discovered, Ceres, is round and was originally classified as a planet. However, it is no longer considered a planet because many other smaller objects were found to exist within its orbit in the asteroid belt. Pluto was discovered later and was classified as a planet. It's larger than Ceres, is made of ice and rock, and is significantly farther from the Sun than the asteroids. Is it scientifically justifiable to classify Pluto as a planet, but not Ceres? Comparing Pluto to the other planets may answer this. Based on the information and the figure above, select all of the observed planetary properties that do not describe Pluto.

A and D A.Planets all have elliptical orbits that are nearly circular and lie close to the same plane. D.Planets in the inner Solar System are small and rocky, while planets in the outer Solar System are giants made mostly of hydrogen and helium.

Io's noncircular orbit causes it to bulge toward Jupiter in different ways throughout its orbit, creating friction in its interior that heats it to melting. Earth's Moon also has a noncircular orbit and experiences differential gravitational tidal forces from the Earth. This figure shows the relative sizes of the major moons in the Solar System. Considering what you know of the formation of objects in the inner versus outer Solar System, and given the information in the figure, which of these statements are factors in the Moon's lack of geological activity compared to Io?

B and E B.The Moon is made of material that has a higher melting point. E.Jupiter is much more massive than the Earth.

At least 75% of asteroids are primordial C-type. What does this imply about how the asteroid belt was formed?

C. It was formed mostly from pieces of planetesimals that were prevented from getting large enough to differentiate, but it also contains some pieces of objects that were large enough to differentiate and were later shattered.

Due to the mutual synchronous rotation of Pluto and Charon, choose the statement below that best describes what an observer on Pluto would see when looking toward Charon.

C. The observer would always see the same side of Charon, which would appear to hang motionlessly in the same spot in the sky all the time.

-passage- Compare Pluto's axial tilt to the axial tilts of the terrestrial planets (Table 6.1) and the giant planets (Table 8.1). Which planet will have seasons most similar to Pluto?

C. Uranus

On rare occasions, comets have been seen orbiting the Sun. These are planetesimals made of rock and ice that become visible to us when their ice sublimates at the closest approach to the Sun, making them glow brightly and grow tails. Where do they come from? We can answer that question by studying the orbits of the comets that pass close enough to us that we can observe them. We see two distinct types of orbits: short-period and long-period comets. Watch the following AstroTour animation, and choose the answer below that most likely follows from your observations.

D. Short-period comets come from some location near the ecliptic plane of the Solar System, and long-period comets come from farther away, with random directions in a spherical distribution around the Sun.

-passage- Compare the densities of these dwarf planets with the densities of the terrestrial planets (Table 6.1) and the giant planets (Table 8.1). From this comparison, what can you determine about the compositions of these dwarf planets?

D. The dwarf planets appear to be made of a mixture of rock and ice.

A chunk of iron weighing a few kilograms flies into the inner Solar System, is captured by Earth's gravity, enters the atmosphere burning brightly, and lands on solid ground. Three different names apply to the different stages of its journey. Place them in order from first to last.

Fist stage to Last stage: 1) Meteoroid 2) Meteor 3) Meteorite

Sort the meteorites by their likely origin in either a differentiated or undifferentiated body.

differentiated (3): - Turquoise spotty - light grey - plain tan Undifferentiated (1): - yellow dots and circles

Rank these hypothetical moons from oldest to youngest based on their cratering. You can assume the moons have never been volcanically active.

oldest to youngest: 1) a moon completely covered in craters, old and new 2) a moon partially covered with craters 3) a moon with very few craters

Indicate the correct motion of a comet as it orbits the Sun.

start at top and go down the line: A. Moving toward the Sun, less fast C. Moving toward the Sun, faster E. Moving fastest D. Moving away from the Sun, faster B. Moving away from the Sun, less fast

Identify the main parts of a comet in these two images.

Top to Bottom: C. Ion tail A. Dust tail D. Coma B. Nucleus

-article- Philae was able to collect and send data for 60 hours before it went silent. What powered the lander during that time?

A. reserve batteries

During the formation of the Solar System, smaller particles in the solar nebula combined to form planetesimals, some of which provided the building blocks for planets. The majority of planetesimals did not become planets, however, and some of them remain in the Solar System today as debris left over from the time of planet formation. Asteroids are a special class of planetesimals that orbit around the Sun. Study the distribution of known asteroids shown in this figure, and choose all of the statements below that match your observations.

A, E, and G A.Some asteroids cross Earth's orbit as they orbit around the Sun. E.There are clumps of asteroids that exist at particular spots in Jupiter's orbit. G.The majority of asteroids exist in a region between Jupiter and Mars.

Pluto's moon Charon is half the size of Pluto, making it the largest known moon in the Solar System when compared to the size of its planet. Tidal forces of Earth on the Moon have caused the Moon to be in synchronous rotation with the Earth, so the same side of the Moon always faces us. The same has happened to Charon due to the tidal forces of Pluto, but due to its large size, Charon has had the same effect on Pluto. Thus, they are in synchronous rotation with each other. If an observer on Pluto and another observer on Charon are standing motionlessly in the positions indicated in the above figure, choose the figure below that demonstrates where the observers will be in relation to each other after Charon has passed through one quarter of its orbit around Pluto.

A. green observer: GO faces down blue observer: BO faced up

What determines an asteroid's shape? Compare the images of asteroids below and choose the answer that best fits your observations.

A. Asteroids have a range of sizes, with the largest being spherical and the smaller ones irregular in shape.

What is the most likely reason for the different levels of geological activity between the Galilean moons?

A. Moons farther away from Jupiter experience weaker tidal heating.

-article- Why were scientists hopeful that they could regain communications with Philae during perihelion?

A. Since perihelion is the part of the orbit closest to the Sun, the solar panels may have produced sufficient power.

Comets that visit the inner Solar System were kicked there from the Kuiper Belt or Oort Cloud by gravitational close encounters with other objects. Pluto travels through the inner edge of the Kuiper Belt. As Ceres is just a large asteroid, could Pluto be just a large Kuiper Belt comet nucleus? Which of the following properties of Pluto would best help answer this question?

A. composition

-article- Rosetta took 10 years to travel from Earth to 67P. Imagine that you were sending a similar spacecraft to a comet. Make a sketch of the orbit of Earth and the orbit of your target comet. Indicate on your sketch the movements of both Earth and the comet during the time your spacecraft was traveling. What are some things that you need to know in order to make the spacecraft and the comet arrive in the same place at precisely the same time?

B, C, E, and F B.the exact speed of the spacecraft at each point in its orbit C.the exact orbital path of the spacecraft E.the exact speed of the comet at each point in its orbit F.the exact orbital path of the comet

-passage- Compare the masses of these dwarf planets with the mass of the Moon. Are these dwarf planets more or less massive than the Moon?

B. The dwarf planets are less massive than the Moon.

-passage- Add a row to your table for the orbital inclination of these dwarf planets. How does orbital inclination change as the orbital radius grows larger?

B. The orbital inclination increases as orbital radius increases.

Spectra and density calculations show that Pluto is mostly rock and ice, just like comets. Most Kuiper Belt objects are very small and distant, which makes them difficult to detect. So it was not until 2005 that Eris was discovered, and Eris is a Kuiper Belt object that is larger than Pluto. More objects large enough to be round have been found, and it is currently estimated that there are 100 to 200 more in the Kuiper Belt, and even more beyond that. This picture shows the largest Trans-Neptunian objects, whose orbits cross Neptune's. Considering these discoveries in a scientific manner, what does this imply about our classification of Pluto as a planet?

B. There is no scientifically satisfying way to answer this question: we need a better definition of a planet that has some physical meaning behind it.

-passage- Compare the orbital velocity of the dwarf planets as listed in Figure 9.32. How does the orbital velocity change as the orbital radius grows larger? Use concepts from Chapter 2 (that is, Kepler's laws) to explain this trend.

D. The orbital velocity decreases as the orbital radius increases.

Identify Triton, Pluto, and Charon.

Left to Right: A, C, B A. Orbits in the opposite direction of its gravitational companion's spin C. Was recently reclassified from planet to dwarf planet B. Is named after the mythological ferryman who takes souls across the river

Identify the major moons of Uranus.

Left to Right: C, E, A, B, D C. Miranda E. Ariel A. Umbriel B. Titania D. Oberon

Identify the major moons of Saturn. (Scroll down to see all answer options.)

Left to Right: F, G, A, E, B, D, C F. Mimas G. Enceladus A. Tethys E. Dione B. Rhea D. Titan C. Iapetus

In 2006, shortly after the discovery of Eris, the International Astronomical Union settled on a physically meaningful definition of a planet: an object that orbits around the Sun, is large enough to be spherical, and has cleared the neighborhood around it of other objects orbiting the Sun. An object that meets the first two criteria, but not the last, was given the new classification of dwarf planet. Sort the objects below according to how they are classified under these new definitions.

Planet: - Earth - Saturn Dwarf Planet: - Ceres - Pluto - Eris Not planet or dwarf - Eros - Io

Rank the parts of a comet by size, from smallest to largest.

Smallest to Larger 1) Nucleus 2) Coma 3) Tail

Identify these larger and prototypical asteroids in the Solar System (the orbits of these asteroids have the various colors).

Yellow: A. Aten Pink: B. Ceres Blue: C. Apollo Purple: D. Achilles Green: E. Sylvia Orange: F. Amor

The diagram shows a cross section of a planetesimal. Identify the types of asteroids that could result from the fragmentation of different parts of such a body.

center: A. M-type asteroid outer: B. S-type asteroid

Rank the Galilean moons of Jupiter in order of amount of geological activity, from greatest to least.

most activity to least activity C. Io A. Europa B. Ganymede D. Callisto

Order the moons of Jupiter from nearest the planet to farthest.

nearest to farthest: C. Io A. Europa B. Ganymede D. Callisto

Identify the following major moons of Jupiter.

left to right: C. Io A. Europa B. Ganymede D. Callisto

All of Jupiter's moons experience tidal heating from Jupiter, and they show signs of recent geological activity because of it. Based on their appearance, rank the four Galilean moons in order from the most recently geologically active to the least.

most active to least active: 1) Io 2) Europa 3) Ganymede 4) Callisto