When the NASA Rover Curiosity landed on Mars, it carried
with it a radiation meter to assess the dose of ionizing radiation on the
surface of the Red Planet. Since there
is so much interest in launching human missions to Mars, the greatest known
risk was thought to be radiation exposure from cosmic rays. Unlike earth, Mars has a fractional atmosphere
and equally insignificant natural magnetic shield to buffer and push the high
energy – high mass cosmic radiation away from human contact. But after more than a year on the surface of
Mars watching the radiation meter daily – here is what Curiosity has reported –
and it is not good news at all for would be Martian explorers:
The rover discovered that the ‘natural’ background radiation
exposure on Mars (almost entirely- 95% - from high energy cosmic rays) was on
the order of 0.67 millisieverts per day.
Let me put that in perspective.
On the earth – with its very effective cosmic ray shield of a thick
atmosphere and the magnetosphere protects us from this natural cosmic
environment endless bombardment of ionizing radiation. Thus, for the average human at the average spot
on earth, we routinely receive on the order of 0.007 millisieverts per day of
background radiation – a difference of almost 100 times less! Here are some other comparisons. One day on Mars would be the equivalent of receiving
33 chest x-rays per day, or on average, one whole body CAT scan every 5
days. The Martian astronaut would be
receiving 244 times the allowed radiation dose from all nuclear power sources
for the public and 60 times the maximum dosage allowed for professional nuclear
power plant workers. And at that rate,
the astronaut would be receiving in a single one year nearly twice the current allowable
lifetime dose for career NASA astronauts – and the minimal Mars mission is
estimated at three years for a cumulative over-dose of six times the current career
radiation exposure. Further – during the
time of measurement, the sun was unusually quiet and did not add its typical
solar induced dose to the picture, which only inevitably adds to the bleak
picture.
What is the solution?
I believe it is ‘relatively simple’: increase the transit speed and thereby reduce
the transit time and future Martian explorers and settlers will all inevitably
live under the Martian surface where they can be effectively and safely shielded
from the hazardous environment on the surface.
PS. The same is true
for lunar explorers as well as practically everywhere outside of low earth
orbit.
