Atmospheric interactions of planetary bodies with the solar wind

Orbiting spacecraft about Venus have revealed a partially penetrable boundary sheath with induced fields limiting solar wind effects on the atmosphere structure and evolution. Mars differs structurally, the explanation awaiting an orbiter mission such as the European Space Agency is considering. In weak comets gyro-radii exceed other scale lengths, while in active comets the gas and solar plasma couple over the largest scale, boundary sheaths being unimportant - As occurred during early rapid-outgassing phases of Venus and Mars.