Numerous exoplanets with masses ranging from Earth to Neptune and radii larger than Earth have been found recently through observations. These planets possess atmospheres that range in mass fractions from 1% to 30%, reflecting the diversity of atmospheric mass fractions. Such diversities are supposed to be caused by differences in the formation processes or evolution. Here we consider giant impacts onto planets causing atmosphere losses in the later stage of their formation. We perform smoothed particle hydrodynamic simulations to study the impact-induced atmosphere loss of young super-Earths with 10%-30% of atmospheric mass fractions. We find that the kinetic energy of the escaping atmosphere is almost proportional to the sum of the kinetic impact energy and self-gravitational energy released from the merged core. We derive the relationship between the kinetic energy and the escaping atmosphere mass. The giant impact events for planets of comparable masses are required in the final stage of the popular scenario of rocky planet formation. However, we show it results in a significant loss of the atmosphere. This latter fact severely constrains the formation scenario because many rocky planets with substantial atmospheres are observed. Those planets should have avoided the giant impact event unless the mechanism for gaining atmosphere after the giant collision is identified.
[Poster PDF File]