Module 6: The Moon

The Moon's elliptical orbit around Earth has a period of _____ days, the same as the time for one rotation.

27.3

Today astronomers have a good understanding of how the Solar System formed. The planets began to form about_____ billion years ago, with the smaller bodies cooling first. The solar system was born in an interstellar _____, and enormous rotating aggregate of gas and dust. The cloud was made mostly of _____ gas (71 percent) and _____ (27 percent), with tiny traces of other elements and tiny interstellar _____ of dust. The rotating interstellar cloud began to collapse and flatten into a rotating disk with most of the mass concentrated in the _____. The disk, called the solar _____, was about _____ AU in diameter and perhaps _____ AU thick.

A. 4.6 B. cloud C. hydrogen D. helium E. grains F. center G. nebula H. 200 I. 10

In addition to the eight terrestrial and Jovian planets, there are several other bodies that orbit the Sun. The largest of these is _____, and the second largest is Pluto . They, along with several similar smaller bodies, are unlike the eight planets. They are all small in size and are composed of ice and rock. They have odd orbits that are non-circular and are highly tilted with respect to the other planets. Such as object is called a _____ planet, defined as an object that orbits the Sun, is massive enough that its gravity compresses it into an approximately spherical shape, but has not swept its orbital region clear of other objects that add up to a mass comparable to its own mass.

A. Eris B. Pluto C. dwarf

Not all planetesimals in the solar nebula went on to become planets. _____ is the largest planet. Its gravity kept the region between it and _____ so stirred up that most planetesimals there never formed a large planet. These rocky or metallic objects, called _____ , are not spherical and are far smaller than planetary bodies. (The one exception is Ceres, which is large enough to be classified as a _____ planet.) This region, now referred to as the _____ belt, contains many planetesimals that remain from this early time. Beyond Neptune, extending to perhaps 50 AU from the Sun, is a region called the Kuiper belt. It looks similar to the asteroid belt, but the objects here are made mostly of ice. The outermost parts of the protoplanetary disk had planetesimals that were too sparsely distributed for large planets to grow. Icy planetesimals in the outer Solar System remain today as _____ and are about 10 kilometers across. More than 10^12 of these icy bodies orbit the Sun in the _____ cloud, which may extend 100,000 AU from the Sun. These are relatively pristine samples of the material from which our planetary system formed.

A. Jupiter B. Mars C. asteroids D. dwarf E. asteroid F. Kuiper G. comet nuclei H. Oort

The outer, Jovian planets are, from closest to farthest from the Sun, _____, _____, _____, and ____. They are _____, gaseous, and _____ dense, with no true surface and a deep hydrogen-rich atmosphere. They are relatively far from the Sun, so their surface temperatures are _____. They also have _____ moons. Jupiter and Saturn have a composition very similar to that of the Sun, and the inner planets would have a similar composition if we were to _____ the Sun's hydrogen and helium and other gases that condense only at low temperatures.

A. Jupiter B. Saturn C. Uranus D. Neptune E. large F. less G. colder H. numerous I. remove

According to the violent-birth hypothesis of the Moon's origin, the Moon formed from debris blasted out of the young Earth by the impact of a _____ -sized object. As the debris by this collision cooled, its _____ drew it together into what we now see as the Moon. Because Earth was already differentiated (the dense iron and nickel had already sunk to Earth's core) when this large impact happened, only surface rock was blasted out of Earth, leaving our planet's iron ____ intact. This explains the Moon's _____ overall density (3.3 g/cm^3) compared to Earth's density.

A. Mars B. gravity C. core D. low

The inner, terrestrial planets are, from closest to farthest from the Sun, ____, _____, _____, and _____. They are _____, rocky, and ______ dense, with a solid surface and a relatively thin or no atmosphere. They are relatively close to the Sun, so their surface temperatures are _____. They also have very few moons.

A. Mercury B. Venus C. Earth D. Mars E. small F. more G. hotter H. very few

The Moon lacks a significant atmosphere for two reasons. It's interior is too _____ to cause volcanic activity, which was an important source of Earth's atmosphere. The Moon's gravity is too _____ to retain gas for long. The Moon's escape velocity is only about one fourth that of Earth's.

A. cool B. weak

The eight planets of our Solar System orbit the Sun in approximately circular orbits, all lying in nearly the same plane. The planets travel around the Sun in the same direction-they are orbiting the Sun ____, as seen from above Earth's North Pole. Each planet also spins on its rotation axis- they are spinning _____, as seen from above Earth's North Pole. Also, the tilt of each planet's rotation axis relative to the plane of its orbit is not far from the perpendicular. Two exceptions are Venus (whose rotation axis is tilted by 177.4 degrees, so its rotates clockwise) and _____ (whose rotation axis is tilted by 97.9 degrees).

A. counterclockwise B. counterclockwise C. Venus D. Uranus

As of May 2016, astronomers have discovered the presence of 1964 confirmed ____ orbiting stars other than the Sun. Most of the exoplanets were discovered by the _____ spacecraft. This orbiting observatory continuously monitored the brightness of 170,000 stars in a small, distant patch of the Milky Way. Astronomers then used the transit method to search for exoplanets that orbit these stars. Currently the best two candidates for a "twin Earth" (an Earth-like planet that orbits a Sun-like star) orbit a star that's a smaller and bit cooler than ours but are within that star's _____ zone (a region at the right distance from the star to allow water to remain liquid, which is considered essential for a planet to support life). The two exoplanets are located 1,200 light-years away in a five-planet system orbiting a star called Kepler-62 in the constellation Lyra, and are called Kepler-62e and -62f. Kepler-62e orbits on the inner edge of the habitable zone and is roughly 60 percent larger than Earth. Kepler-62f is only 40 percent larger than Earth, making it the exoplanet closest to the size of our planet known in the habitable zone of another star. Because of their sizes and orbits, these two exoplanets are likely either rocky—like Earth—or watery. They are by far the best candidates for habitability of any exoplanet found so far.

A. exoplanets B. Kepler C. habitable

As the planetesimals struck the growing planets, their impact released _____ energy that heated both the planetesimal and the planet. Vast amounts of heat were released as mountain-size mass of rock plummeted onto a planet. This heat, in combination with radioactive heating, melted the planets and allowed matter with high density (such as iron) to sink to their _____, and matter with lower density (such as silicate rock) to float to their _____.

A. gravitational B. cores C. surfaces

Some features of the Moon and its orbit are odd. Unlike all other large moons in the solar system, our Moon has an orbit with a _____ tilt with respect to its planet's equator. Compared to all other large moons in the solar system, our Moon is exceptionally _____ in size compared to its planet. These oddities suggest that our Moon formed _____ _____ the moons of the other planets.

A. large B. large C. differently from

Atmospheres were the _____ part of the planet-forming process. The outer planets probably captured most of their atmospheres directly from the solar nebula, and because the nebula was _____ in hydrogen and helium, so are their atmospheres The inner planets were not massive enough, and were too hot, to capture gas from the solar nebula, and are therefore _____ in hydrogen and helium. Venus, Earth, and Mars probably created their original atmospheres by _____ eruptions and by retaining gases from infalling comets and icy planetesimals that vaporized on impact. Small bodies, such as Mercury and our Moon, keep essentially no atmosphere at all because their _____ gravity means that their escape velocity is rather small , and atmospheric gases tend to escape easily from them.

A. last B. rich C. deficient D. volcanic E. weak F. small

Identify the following features on the near side of the Moon.

A. mare B. highlands C. craters D. rays

The ages of the rock returned by astronauts from the Moon reveal the history of its surface. Like Earth, the Moon is about 4.5 billion years old. However, the lunar ____ ("seas") are relatively recent features. They were formed after a time of violent impacts with massive asteroid-size objects which lasted from about 4.5 billion years ago to 3.8 billion years ago. The force of these impacts cracked the Moon's thin crust. About 3.8 billion years ago molten lava began to flow out from the Moon's interior. These lava flows lasted until about 3.1 billion years ago. By then the lava had covered the many craters that were on the surface at that time. Because few craters have been formed since then, there are relatively few craters in the smooth, dark _____ In general, is a surface with only a few craters is _____ than a surface with many craters. If a surface has a crater in it, the crater must be _____ than the surface.

A. maria B. lava C. maria D. younger E. younger

Apollo astronauts set up seismic detectors on the Moon, which showed that the Moon's interior is essentially inactive and has a simpler structure than Earth's. The Moon's surface is rock chunks and fine powder called _____ , tens of meters deep. Below this is the Moon's _____, about 100 km thick on average. Beneath the crust is a thick ____ of solid rock, going down about 1000 km. The Moon has a small _____ that may be partially molten and contains far _____ iron and nickel than Earth's. The Moon's interior is more solid than Earth's, indicating that the moon has cooled off _____ than Earth has. This is because the Moon is much _____ than Earth. In general, the smaller the world, the faster it cools off and the _____ internal heat it is likely to have retained.

A. regolith B. crust C. mantle D. core E. less F. faster G. smaller H. less

The Moon's gravity causes _____ in Earth's oceans. The force of gravity between two objects is _____ when the two objects are closer together. One the side of Earth facing the Moon, the ocean is closer to the Moon than the solid Earth is. The Moon's gravity pulls more _____ on the ocean than it does on Earth. The ocean is pulled up away from Earth, thus producing a tidal bulge. On the side of Earth away from the Moon, the solid Earth is closer to the Moon than the ocean is. The Moon's gravity pulls more _____ on Earth than it does on the ocean. Earth is pulled out from under the ocean, thus producing another tidal bulge.

A. tides B stronger C. strongly D. strongly

The photo shows crater Pytheas and the south-central Imbrium basin (part of Mare Ibrium). A highlands area is in the foreground (bottom half of the photo), including crater Copernicus. Are the following statements true or false? Crater Pytheas is younger than the Mare Ibrium. The Mare Ibrium is younger than the highlands area Crater Copernicus is younger than the highlands area From this photo alone we can't tell whether crater Copernicus is younger or older than the Mare Ibrium or crater Pytheas. .

A. true B. true C. true D. true

There are three ways of searching for extrasolar planets (planets that orbit stars other than the Sun). These planets are now called exoplanets. Match the description with the correct name of the method. As the star and the exoplanet orbit each other, they tug on each other with their gravity, resulting in a slight wobble in the star's position. Sometimes the star moves toward us and its spectral lines are blueshifted. Later in its orbit, the star moves away from us and its spectral lines are redshifted. (See Figure 8.18 in your text.) From measuring these Doppler shifts, astronomers can conclude that the star has a dim unseen companion that may be an exoplanet.

Doppler method

As Earth rotates, we are carried first into one bulge and then the next. We are carried through a bulge twice a day, so there are two high tides and _____ low tides per day. The Sun also creates tides on Earth, but the Sun's tidal force is only about ____ the Moon's. Earth's gravity also causes tides in the Moon's crust. The force of Earth's gravity on the Moon's tidal bulge cause and maintains the _____ rotations that keeps the same side of the Moon always facing the Earth.

E. two F. two G. one-half of H. synchronous

The solar nebula eventually condensed into _____ while the central bulge became the _____. The Sun heated the _____ part of the solar nebula, and the temperature in the disk from the Sun to almost the orbit of _____ never dropped low enough for water and other substances with similar condensation temperatures to condense there However, the heavier elements, like iron and silicates, could condense everywhere in the disk. The nebula thus became divided into two regions: an _____ zone of silicate-iron particles, and an _____ zone of similar particles on which ices also condensed. Small clumps of dust then clumped together to form larger objects called _____ (small planetlike bodies) a few kilometers across. The planetesimals near the Sun were made of rock and iron, while those far from the Sun were made of ices, rock and iron. The planetesimals _____ attracted each other to form the terrestrial and Jovian planets. Once a planet grew somewhat larger than Earth, it was able to attract and retain gas by its own _____, Jupiter, Saturn, Uranus, and Neptune may have begun as Earth-size bodies of ice and rock, but their gravitational attraction resulting in their becoming surrounded by the huge envelopes of hydrogen-rich gases that we see today.

J. planets K. Sun L. inner M. Jupiter O. inner P. outer Q. planetesimals R. gravitationally S. gravity

The gravitational field of an unseen planet bends light from a distant star in such a way that it causes the star to brighten temporarily while the planet is passing in front of it.

gravitational lensing method

We always see the same side of the Moon because the Moon rotates on its axis in the same amount of time it takes to orbit Earth. This is called _____ rotation.

synchronous

When an exoplanet passes in front of its parent star, the light from the star dims by a tiny amount.

transit method