Astro 210 Exam 2 Practice Problems

# Astro 210 Exam 2 Practice Problems - Hour Exam 2 Review...

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Hour Exam 2: Review Questions Plausible questions: either from old exams, or at right level for this exam As discussed in class, planets in the solar system have many characteristics in common and also many diFerences. These shed light on the process of planet formation. Give one example of a feature that is common to both terrestrial and jovian planets, and re±ects information about the formation of the solar system. Brie±y describe how our current theories for the formation of the solar system account for this similarity. 1

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Exoplanets of roughly Jupiter-size masses have been found with surprisingly short orbital periods. Consider a planet with Jupiter’s mass M = 2 × 10 27 kg, radius R = 7 × 10 7 m, albedo A = 0 . 5, and composition. The planet orbits a star with the same mass, radius, and temperature as the Sun; the orbital period is P = 3 . 65 days = 0 . 01 yr (a) Assume the planet is slowly rotating, and Fnd the daytime temperature of the planet. Express your answer in Kelvin. (b) Assume your answer to part (a) was T = 1600 K (which would be wrong!). ±or a Jovian-type atmosphere, would the most abundant species be evaporated? Justify your answer with the appropriate calculation. 2
a 3 AU = P 2 , or a = 10 2 / 3 AU = 0.046 AU. The usual temperature formula for this a and A = 0 . 5 gives T = 332[(1 A ) /a 2 AU ] 1 / 4 K = 1300 K (1) (b) We need to compare escape speed and thermal speed for the dominant atmospheric species, molecular hydrogen: m (H 2 ) = 2 m p . We have v esc = r 2 GM R = 62 km / s (2) and v rms = r 3 kT m = r 3 kT 2 m p = 4 . 4 km / s (3) and thus we have v esc v rms = 14 > 6 (4) and so the hydrogen atmosphere survives. 3

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## This note was uploaded on 10/06/2011 for the course ASTRO 210 taught by Professor Fields during the Spring '08 term at University of Illinois, Urbana Champaign.

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Astro 210 Exam 2 Practice Problems - Hour Exam 2 Review...

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