ConceptChecks
ConceptCheck 15-1: The solar system is filled with planets that have semimajor axes increasing from one to the next by about a factor between 1.4 and 2. The exception to this pattern is Jupiter, but the pattern would hold up if there was a planet where the asteroid belt currently exists.
ConceptCheck 15-2: Ceres is an asteroid and also a dwarf planet—large enough to pull itself into a sphere but unable to gravitationally clear out its surroundings.
ConceptCheck 15-3: Jupiter’s gravity prevented a planet from forming where the asteroid belt currently exists. The planet would have probably been about the size of Earth, but mass was ejected and all the mass in the asteroid belt today could only form a very small object 1500 km in diameter (less than the distance from Los Angeles to Chicago).
ConceptCheck 15-4: The Hayabusa mission returned samples of the asteroid Itokawa, where analysis on Earth showed a match to meteoritic dust.
ConceptCheck 15-5: The Dawn spacecraft was able to assess Vesta’s composition by measuring the infrared spectra of the asteroid’s surface. Analysis finds a match with about 6% of the meteorites found on Earth.
ConceptCheck 15-6: Iridium is common in asteroids, but rare in Earth’s rocks. A thick layer of iridium is found around the world dating back 65 million years, implying a massive impact at that time. More evidence comes from a massive impact event dated at 65 million years old near the Yucatán Peninsula.
ConceptCheck 15-7: If a nickel-iron sample cools too quickly, it will not contain a Widmanstätten pattern, which takes millions of years to form. This is not a feature that can be artificially produced on Earth.
ConceptCheck 15-8: The buildup of larger objects in the formation of the solar system involved heating (due to radioactivity and collisions) leading to alteration of their chemical composition. However, the carbonaceous chondrites do not show chemical alteration that would have occurred if they were heated. Therefore, this class of meteorites appears to contain some original unaltered material present in the early solar nebula.
ConceptCheck 15-9: The Deep Impact mission measured the density of Comet Tempel 1 and found it be significantly less dense than water—only 60%. Because the comet is mostly water (with smaller amounts of other material), the comet must be porous with empty spaces to have a density lower than water.
ConceptCheck 15-10: From Kepler’s third law, the longer the orbital period, the larger the semimajor axis of the orbit. The short-period comets already orbit beyond Neptune in the Kuiper belt, and the long-period comets require a collection of objects much farther out; this is called the Oort cloud.
CalculationChecks
CalculationCheck 15-1: 100 m. Since the crater is about 20 times larger than the fragment hitting Earth, the fragment is about (2000 m)/20 = 100 m across.
CalculationCheck 15-2: 5 km. (5 km/s) × (1 s) = 5 km.
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