The evolution of planets and moons under an active star is a topic of highly interdisciplinary nature. Studies of Sun-like stars at various stages of their evolution imply that the early active Sun had a profound impact on the Earth-like planets. Solar EUV forcing affects the ionosphere and upper atmosphere of planets, while plasma (solar wind or planetary in nature) interacts with the planetary environment in a more complex way. There are reasons to believe that the combined solar EUV and solar wind forcing of the early Sun is responsible for significant losses of volatiles from the Earth-like planets, the nonmagnetized planets being particularly vulnerable for such a loss. Loss of water may affect a planet in an unpredictable and cataclysmic way, restricting the possibilities for emerging biological life.
The interaction of plasma with an unmagnetized planet is also a topic of interest from the standpoint of basic plasma physics. For instance, finite gyroradius effects can be studied on a planetary scale, providing unique opportunities for understanding fine structure plasma dynamics. Processes related to plasma instabilities and energy transport can be examined in a wide array of environments, allowing us to more fully understand how they operate. Thus the study of unmagnetized bodies involves time scales ranging from billions of years to milliseconds.
During the fifth Alfven conference our focus will be on the plasma interaction with unmagnetized planets and moons in the solar system: Venus, Mars, Moon, Titan, Io, and similar bodies. New findings from the analysis of data (e.g. Venus Express, Mars Express, Kaguya, Cassini, Chandrayaan-1, Galileo, and most recent Phobos-Grunt and Yinghuo-1) as well as recent progress in theory and modeling, make the theme of the conference timely. The objective will be to promote discussions leading to a better understanding of the physical processes that determine how weakly magnetized planets and moons evolve under an active Sun. Comparing phenomena from different, but similar, planets and moons will be emphasized to increase understanding of the general physics behind the plasma environment in plasma/planet interactions and to facilitate planning for future missions.
The fifth Alfven conference will specifically address the following science questions:
1. How is the plasma interaction region above nonmagnetized objects formed and maintained?
2. What is the coupling between the incident plasma and the ionosphere/upper atmosphere or the surface?
3. What are the main physical acceleration/energization processes leading to escape and mass-loss from nonmagnetized planets and how do they affect the volatile inventory over time?
4. How do models implement the physics and variability of the system, and do models agree with data?
5. What is the role of the "Sun in time" in the evolution of nonmagnetized planets/moons?