When
3:30 p.m., Oct. 12, 2010
Where
Kuiper Space Sciences 308
Dr. Feng Tian (Research Associate at LASP, University of Colorado) is the scheduled speaker.
Host: Roger Yelle.
Planetary Upper Atmospheres under Strong XUV Radiation
Solar system terrestrial planets were exposed to strong (10~100 times present levels) soft X-ray and EUV (XUV) radiation from the young Sun for several hundred million years after their formation. Planetary upper atmospheres expanded to several planetary radii under such XUV radiation and fast escape of major atmosphere gases occurred. The radial outflow, as a result of fast atmosphere escape, effectively controlled the energy budget and planetary upper atmospheres could no longer remain in the traditional hydrostatic regime. Thus a new regime, the hydrodynamic regime, is proposed for planetary upper atmospheres under intensive XUV radiation. The critical EUV level, beyond which the planetary upper atmosphere enters the hydrodynamic regime, depends on the composition of the atmosphere. Such a fundamental phenomenon applies to both early solar system terrestrial planets, which are no longer directly observable, and exoplanets under strong XUV radiation such as hot Jupiters (already observed) and hot super Earths (future observations).
Atmosphere escape from planets under strong XUV radiation has important consequences not only on the atmospheres of solar system terrestrial planets, but also on the habitability of exoplanets; in particular those around low mass M-type stars. In this talk we will explore the hydrodynamic planetary upper atmospheres of early Earth, Mars, and super Earths in the habitable zones of low mass M-stars, focusing on the following topics: 1) hydrogen abundance early Earth atmosphere and its impact on the origin of life; 2) early Noachian Mars atmosphere stability and early Mars climate; 3) atmosphere stability of habitable super Earths around M-stars; and 4) Earth sourced nitrogen in lunar soil and its implication on the onset time of paleomagnetism and the rise of oxygen in the Earth's atmosphere.
Host: Roger Yelle.
Planetary Upper Atmospheres under Strong XUV Radiation
Solar system terrestrial planets were exposed to strong (10~100 times present levels) soft X-ray and EUV (XUV) radiation from the young Sun for several hundred million years after their formation. Planetary upper atmospheres expanded to several planetary radii under such XUV radiation and fast escape of major atmosphere gases occurred. The radial outflow, as a result of fast atmosphere escape, effectively controlled the energy budget and planetary upper atmospheres could no longer remain in the traditional hydrostatic regime. Thus a new regime, the hydrodynamic regime, is proposed for planetary upper atmospheres under intensive XUV radiation. The critical EUV level, beyond which the planetary upper atmosphere enters the hydrodynamic regime, depends on the composition of the atmosphere. Such a fundamental phenomenon applies to both early solar system terrestrial planets, which are no longer directly observable, and exoplanets under strong XUV radiation such as hot Jupiters (already observed) and hot super Earths (future observations).
Atmosphere escape from planets under strong XUV radiation has important consequences not only on the atmospheres of solar system terrestrial planets, but also on the habitability of exoplanets; in particular those around low mass M-type stars. In this talk we will explore the hydrodynamic planetary upper atmospheres of early Earth, Mars, and super Earths in the habitable zones of low mass M-stars, focusing on the following topics: 1) hydrogen abundance early Earth atmosphere and its impact on the origin of life; 2) early Noachian Mars atmosphere stability and early Mars climate; 3) atmosphere stability of habitable super Earths around M-stars; and 4) Earth sourced nitrogen in lunar soil and its implication on the onset time of paleomagnetism and the rise of oxygen in the Earth's atmosphere.