The Evolution of the EUV Sun through Time: Coronal Emission of the Young Sun and its Consequences on Early Planetary Atmospheres and Life

We present X-ray-EUV-UV observations of solar analogs with different ages that serve as proxies for the Sun during most of its main sequence lifetime. We are carrying out an in-depth study of the evolution of the transition region (TR) and corona of the Sun from its active youth through its distant terminal main sequence future. Observations primarily obtained with ASCA, ROSAT, EUVE, FUSE and IUE are part of this comprehensive study of the Sun in Time across the electromagnetic spectrum. For this program we have defined a homogeneous sample of single G0-5 V stars with well known rotation periods and ages. These stars cover ages from 130 Myr to 9 Gyr. We are studying the dynamics and energetics of the lower layers of the atmospheres of these solar like stars, and investigating the variations of magnetic related properties with age and rotation period. This program is central to the understanding of the evolution of magneto dynamic atmospheric phenomena, and the associated high energy emissions of the Sun and solar type stars. This study also focuses on the important question of the influence of the young Sun's strong XUV emissions on the developing planetary system - in particular on the photochemical and photoionization evolution (and possible erosion) of early planetary atmospheres and ionospheres. To this end, we are constructing spectral irradiance tables (from 1A -7500A) for the Sun at different ages. The results of this spectral irradiance study will be discussed. Also discussed will be possibilities of observing coronal mass ejections, flares, and winds and plasma outflows of young active suns with future EUV and other space missions.