2009 Annual Science Report
VPL at University of Washington Reporting | JUL 2008 – AUG 2009
Hydrodynamic Escape From Planetary Atmospheres
We use computer models to simulate the behavior of the upper atmospheres of different planets (Earth, Venus, Mars, Earth-like exoplanets, etc.) during their early evolutionary stages. Young stars produce more flares and other stellar activity than older stars, and the young Sun emitted a greater amount of energetic photons than it does today, which heated the upper atmospheres of the planets. This atmospheric heating led to fast atmosphere escape, which probably controlled the atmospheric composition of early planets. The atmospheric composition on early Earth provides critical constraints on the origin and early evolution of life on this planet. The atmospheric composition of other planets provide important constraints on their habitability.
The research objective of this project is to develop a state-of-the-art numerical model to investigate atmospheric escape from the early terrestrial planets. Atmospheric escape is one of the key processes that control atmospheric composition, which is critical to the origin and early evolution of life. Atmospheric escape also to a large degree defines the habitable zone, and research in this area is applicable to understanding habitability in other planetary systems. Our recent study on the stability of early Martian atmosphere also impacts the habitability of and presence of life on the planet during its early evolution stages.
We have further developed the 1-D, multi-component, hydrodynamic thermosphere-ionosphere model. We successfully expanded an energetic electron production / transport model (the GLOW model) to include major gases in planetary atmospheres other than those in the present Earth, coupled the hydrodynamic thermosphere-ionosphere model with the GLOW model. The coupled model was validated against the thermosphere-ionosphere of present Venus and Mars.
The validated model was then used to investigate the stability of CO2 atmospheres of early Noachian Mars and super Earths in the habitable zones of M-stars. Its application to the atmospheric stability of early Noachian Mars was published in GRL in January 2009 (Tian et al., 2009). In that paper we argue that early Noachian Mars was probably not as warm and wet as some people have proposed because of the strong solar XUV radiation and the subsequent fast atmosphere escape as a result of the expansion of the thermosphere and ionosphere. The application of the model to the atmosphere stability of super Earths in the HZ of M-stars was accepted to ApJ in August 2009 (Tian et al., 2009). In this paper we propose that super Earths should be capable of maintaining their CO2 inventory despite the strong XUV radiation from their low mass parent stars.
PROJECT INVESTIGATORS:Feng Tian
PROJECT MEMBERS:James Kasting
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Sources of prebiotic materials and catalysts