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Q1. Alternative fates of Venus. a) The escape velocity from Venus' surface is ~10¹ m/s, but in hydrodynamic escape models, both bulk and thermal velocities are <<10¹ m/s out to very large distances from the planet (example below). Explain qualitatively how gas might escape from the planet without ever exceeding Venus' surface escape velocity.

Q1. Alternative fates of Venus. a) The escape velocity from Venus' surface is ~10¹ m/s, but in hydrodynamic escape models, both bulk and thermal velocities are <<10¹ m/s out to very large distances from the planet (example below). Explain qualitatively how gas might escape from the planet without ever exceeding Venus' surface escape velocity.

Applications and Investigations in Earth Science (9th Edition)
Applications and Investigations in Earth Science (9th Edition)
9th Edition
ISBN:9780134746241
Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Chapter1: The Study Of Minerals
Section: Chapter Questions
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Q1. Alternative fates of Venus. a) The escape velocity from Venus' surface is ~10 m/s, but in hydrodynamic escape models, both bulk and thermal velocities are <<10¹ m/s out to very large distances from the planet (example below). Explain qualitatively how gas might escape from the planet without ever exceeding Venus' surface escape velocity. 106 105 104 BULK VELOCITY (CM S') - 10² 10³ 10 D 10² 10³3 E 104 ALTITUDE (KM) FIG. 6. Bulk velocities for the numerical solutions. from Watson et al. Icarus 1981 105 b) We have seen that the basic equations for hydrodynamic escape have supersonic and sub-sonic solutions. Suppose that Venus was embedded in a gaseous nebula (e.g. during solar system formation). Explain, with reference to the basic equations for hydrodynamic escape as discussed in lecture, how this would affect the physical validity of the supersonic and/or sub-sonic solutions. c) In the case of Venus, a runaway greenhouse is believed to have been followed by loss of almost all water from the planet. State and explain two circumstances under which a long-lived runaway greenhouse might not cause loss of much water from the planet.
Transcribed Image Text:Q1. Alternative fates of Venus. a) The escape velocity from Venus' surface is ~10 m/s, but in hydrodynamic escape models, both bulk and thermal velocities are <<10¹ m/s out to very large distances from the planet (example below). Explain qualitatively how gas might escape from the planet without ever exceeding Venus' surface escape velocity. 106 105 104 BULK VELOCITY (CM S') - 10² 10³ 10 D 10² 10³3 E 104 ALTITUDE (KM) FIG. 6. Bulk velocities for the numerical solutions. from Watson et al. Icarus 1981 105 b) We have seen that the basic equations for hydrodynamic escape have supersonic and sub-sonic solutions. Suppose that Venus was embedded in a gaseous nebula (e.g. during solar system formation). Explain, with reference to the basic equations for hydrodynamic escape as discussed in lecture, how this would affect the physical validity of the supersonic and/or sub-sonic solutions. c) In the case of Venus, a runaway greenhouse is believed to have been followed by loss of almost all water from the planet. State and explain two circumstances under which a long-lived runaway greenhouse might not cause loss of much water from the planet.
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