Answers

ConceptChecks

ConceptCheck 4-1: Our solar system contains only one star, the Sun. The other stars are far, far away.

ConceptCheck 4-2: Mars is classified as an inner planet, even though it is farther from the Sun than is Earth. This is because the Earthlike planets all orbit very close to the Sun (within 2 AU), while the outer planets (Jupiter, Saturn, Uranus, and Neptune) all lie much farther (more than 5 AU) from the Sun.

ConceptCheck 4-3: If a planet’s overall density is the same as the density of rocks at its surface, one can infer that the rocks deep in its core must be the same density as the rocks found at its surface.

ConceptCheck 4-4: Table 4-2 lists four moons having diameters greater than 3476 km: Io, Ganymede, Callisto, and Titan.

ConceptCheck 4-5: Before sunlight is reflected off a planet, the incoming sunlight must interact with the chemical elements in the planet’s atmosphere, altering it in predictable and important ways that allow astronomers to make inferences about what chemical elements are present in the planet’s atmosphere.

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ConceptCheck 4-6: The spectrum of a solid surface shows broad features whereas the spectrum observed from light passing through a gas shows sharp, definite spectral lines.

ConceptCheck 4-7: Jupiterlike planets are composed of mostly gases and ices of hydrogen and helium, which would normally not seem to be able to combine together to form a planet very close to a hot star. One plausible explanation for recently discovered Jupiterlike planets that are found orbiting nearby stars in the high-temperature region is that these planets formed far from the star and somehow moved to an orbit close to the star after the planet formed.

ConceptCheck 4-8: Ceres has a diameter of about 900 km. This is about the same size as a large U.S. state, such as the length of California.

ConceptCheck 4-9: Because broad categories overlap due to the history of how and when objects were first discovered, Pluto is classified as a dwarf planet, a Kuiper-belt object, and a trans-Neptunian object; it is not, however, an asteroid.

ConceptCheck 4-10: Whereas the Kuiper belt lies in the same plane as Earth’s orbit around the Sun, the Oort cloud is a spherical distribution of comets that completely surrounds the solar system. If a comet has an orbit that is considerably different from that of the flat plane of the solar system, it most likely originated in the spherical Oort cloud that exists in all directions around our solar system.

ConceptCheck 4-11: The chemical element of carbon that makes up much of our human bodies and the living plants all around us and the very oxygen atoms we breathe was made inside a star that no longer exists.

ConceptCheck 4-12: To be correct, the nebular hypothesis must explain why all the planets orbit the Sun in the same direction and in nearly the same plane. This arrangement is unlikely to have arisen purely by chance.

ConceptCheck 4-13: The closest a large, Jupiterlike planet composed primarily of hydrogen and helium could form would be much farther away in a much hotter solar nebula.

ConceptCheck 4-14: Called chemical differentiation, denser, iron-rich materials migrated to the centers of the planets while the less dense, silicon-rich minerals float to the outside surface before the initially molten planet solidified in the early solar system.

ConceptCheck 4-15: Neptune and Uranus are more than twice as far from the Sun than Saturn, and in the early solar nebula, there would have been far too little material for them to collect and build a planet.

ConceptCheck 4-16: Jets from the Sun, a T Tauri wind, and accretion onto the planets are the processes that characterize the final stages of solar system evolution.

ConceptCheck 4-17: An extrasolar planet with an orbit that causes a star to wobble side to side will not exhibit any Doppler-shifted spectra as seen from Earth because the star will not be moving alternatively toward and away from Earth, and therefore the radial velocity method will fail to detect such an orbiting extrasolar planet.

CalculationChecks

CalculationCheck 4-1: The shape of a planet’s orbit is given by the value of its eccentricity. The closer this value is to zero, the closer the orbit’s shape is to that of a perfect circle. According to Table 4-1, the orbit of Venus has the eccentricity closest to zero (0.007), making it the most circlelike of all planetary orbits.

CalculationCheck 4-2: If we divide Saturn’s 120,536-km diameter up into Earth’s 12,756-km diameter, we find that 120,536 km ÷ 12,756 km = 9.449, so about 9½ Earths would fit across Saturn’s diameter.

CalculationCheck 4-3: The asteroid belt is located between Mars and Jupiter at about 3 AU from the Sun, whereas the much larger Kuiper belt is beyond the orbit of Neptune and is located between about 30 AU and 50 AU from the Sun.

CalculationCheck 4-4: The brightness versus time graph in Figure 4-19a shows the transit lasting 3 hours. If the star was half the present size, it would take half the time, or 1½ hours.

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