The young Sun was more active than in the present. It rotated faster, it emitted higher X-ray and EUV radiation, and it was more active magnetically. Therefore, the interplanetary space, the solar wind, and the heliosphere, were very different as well as, they are dictated by the state of the Sun itself. Understanding the space environment of the early solar system is necessary if we want to understand the formation and evolution of the solar system and the planets, including the Earth.
One particular topic I study is the role and state of cosmic rays in the early solar system. Cosmic rays are highly energetic particles that are coming from outside of the solar system and zoom through it due to their high energies. However, their transport is modulated by the solar and interplanetary magnetic field that can push them away from the inner parts of the solar system (that is why they are anti-correlated with the number of sunspots over the solar cycle). Cosmic rays are important as they can ionized the protoplanetary disk at which planets are formed. They also impact the Earth as they help to produce complex molecules, they create genetic mutations and impact the rate of speciation, they trigger lightning, and they have general impact on the atmosphere.
