When
3:30 p.m., April 12, 2011
Where
Kuiper Space Sciences 308
Robert E. Johnson is the scheduled speaker. Dr. Johnson is the John Lloyd Newcomb Professor of Engineering Physics, University of Virginia Astronomy Department and Department of Materials Science and Engineering.
“Molecular Kinetic Modeling of Atmospheric Escape: Pluto and Titanâ€
Abstract:
Our understanding of the evolution of planetary atmospheres is being enormously enhanced by spacecraft data on objects in the outer solar system and telescopic observation of exoplanets. Cassini is orbiting in Saturn’s system, New Horizon is on its way to the Pluto-Charon system, and the MAVEN mission to study escape from Mars will be launched soon. Surprisingly, the large amount of Cassini data on the thick atmosphere of the moon Titan, instead of re-enforcing our understanding of escape, led to rates that differed by orders of magnitude. This disagreement was due to a lack of a detailed description of how escape changes in character from evaporation on a molecule by molecule basis (Jeans escape) to an organized flow (hydrodynamic escape) a process of considerable interest for the early stages of the evolution of a planet’s atmosphere and for exoplanets orbiting close to their parent star. Therefore, we carried out extensive molecular kinetic simulations of atmospheric escape and found that the transition from Jeans to hydrodynamic escape occurs over a surprisingly narrow range of the Jeans parameter which is the ratio of the gravitational energy to the thermal energy of the molecules. The results of these simulations will be described as well as applications of a molecular kinetic model to escape from Titan and a fluid/ kinetic hybrid model to escape from Pluto.
“Molecular Kinetic Modeling of Atmospheric Escape: Pluto and Titanâ€
Abstract:
Our understanding of the evolution of planetary atmospheres is being enormously enhanced by spacecraft data on objects in the outer solar system and telescopic observation of exoplanets. Cassini is orbiting in Saturn’s system, New Horizon is on its way to the Pluto-Charon system, and the MAVEN mission to study escape from Mars will be launched soon. Surprisingly, the large amount of Cassini data on the thick atmosphere of the moon Titan, instead of re-enforcing our understanding of escape, led to rates that differed by orders of magnitude. This disagreement was due to a lack of a detailed description of how escape changes in character from evaporation on a molecule by molecule basis (Jeans escape) to an organized flow (hydrodynamic escape) a process of considerable interest for the early stages of the evolution of a planet’s atmosphere and for exoplanets orbiting close to their parent star. Therefore, we carried out extensive molecular kinetic simulations of atmospheric escape and found that the transition from Jeans to hydrodynamic escape occurs over a surprisingly narrow range of the Jeans parameter which is the ratio of the gravitational energy to the thermal energy of the molecules. The results of these simulations will be described as well as applications of a molecular kinetic model to escape from Titan and a fluid/ kinetic hybrid model to escape from Pluto.