  Solar Proton Events (SPEs) can cause abrupt and significant enhancements to
the Martian surface radiation dose. Observations of the impact of SPEs on the
Martian surface are available from satellites and surface detectors, but the
data set is very limited in time, and the energy range is limited in scope,
which makes it insufficient to estimate the impact of major events on the
Martian surface. On the other hand, long-term data of SPEs impacting the Earth
spanning a large energy range is widely available, and can be used to estimate
the impact of major events on Mars on long timescales. Herein, we take major
SPEs observed during the past several decades on Earth (1956 - 2014), along
with PAMELA observations (2006 - 2014) and use the GEANT4 Monte Carlo code to
calculate the Martian surface radiation dose. We study the contribution of
proton fluence and spectral shape of events on the surface radiation dose and
estimated the impact of possible major SPEs on the Martian surface in the
future. These results have major implications for the planned human exploration
of Mars. Overall we find that the radiation dose from extreme events can have a
significant impact on astronaut health, and in rare, worst case scenarios, the
estimated dose can even reach lethal levels.
