Protecting Future Mars Colonies From Solar Radiation: An Early Warning System

We all know that space can be a dangerous place. Many safety measures are put in place by space agency scientists so astronaut’s lives are protected and mission success can be assured. Generally, some degree of certainty can be insured in near Earth orbit, protecting astronauts onboard the International Space Station and Shuttle missions, as most activities go on within the Earth’s protective magnetosphere. But in the future, when we establish a colony on the Moon and Mars, how will human life be protected from the ravages of solar radiation? In the case of Mars, this will be of special interest as should something go wrong, colonists will be by themselves…

Solar energy is essential to life on Earth. Without it, we wouldn’t be here. In space, this friendly source of energy suddenly becomes our enemy. Highly energetic particles in the form of ions (i.e. atoms of solar elements stripped of most of their electrons) are generated by the Sun and ejected into space during periods of intense solar activity. These intense periods of solar activity are known as “solar maxima”, occurring approximately every 11 years as a part of the solar cycle. Although we can predict the periods of the solar cycle, we cannot predict when the Sun might launch a devastating solar flare or increase its solar wind output. Astronauts caught in a solar “ion storm” will receive high doses of radiation, putting them at risk of short term radiation poisoning and long term health problems.

Astronauts in Earth orbit are comparatively protected from the worst of the solar radiation as the energetic ions will be deflected by the Earth’s strong magnetic field. But future manned missions to Mars are at an obvious risk as Mars does not have a significant magnetic field and has a very tenuous atmosphere. So what can be done for our future colonists?

Research is afoot to protect long-haul travel through space (i.e. the six month transit between the Earth and Mars), but colonies will need to be warned about the onset of a solar storm should a long-term Mars base be established. Taking the lead from the recent real-time early warning system established with the Solar and Heliospheric Observatory (SOHO), sitting in the Earth-Sun First Lagrangian Point, 1.5 million km away from the Earth in direct line of sight of the Sun, the concept of an early warning system for Mars could be (inexpensively) set up.

Like Earth, Mars has its own Lagrangian points with the Sun. Currently there are no man-made satellites in L_{1 (Mars)} or L_{2 (Mars)} orbit, but it is conceivable that these islands of gravitational stability may be used to greatly benefit future Mars colonies.

The SOHO mission receives the signal that solar ions are approaching Earth an hour before atmospheric impact. This not only provides excellent diagnostic data, but also gives advanced warning to companies and organizations that the Earth is 60 minutes away from experiencing an increase in solar radiation. Emergency procedures can be enacted accordingly, possibly saving delicate satellites and astronauts.

A simple, cost effective probe may be inserted into the Mars-Sun L₁ point. This probe needn’t be as sophisticated as SOHO, it just needs to monitor the flux of energetic particles travelling toward Mars. Akin to a “flag” system on a patrolled beach (red for “dangerous”, no swimming. Green for “safe”, water is safe), Mars settlers could have advanced warning of an incoming flood of ions from the Sun. If constantly measured by a particle detector on the probe at the L₁ point, various stages of danger levels may be used to indicate to settlers unprotected on the surface of what severity of risk they are in. Surface “walkabouts” may be tightly restricted by such a system.

The Mars L₁ time-lag problem
The distance between Earth’s L₁ point and the planet is approximately 1.5 million km. This provides information on the solar wind particles approximately 1 hour before they are received on Earth. Mars is a less massive planet than the Earth; therefore, Mars’ L₁ point will be closer to the planet than the Earth’s.

Reaching a logical conclusion, assuming solar particles are travelling at the same velocity in near-Mars orbit as with near-Earth orbit, a Mars early warning system of the design outlined above will be less effective than the terrestrial version. So, how much time will the Mars early warning system provide to colonists from detection (at L₁) to impact (at Mars’ surface)?

Using the equation from Lagrangian point calculations:

where r is the distance of L₁ from Mars, R is the distance between the bodies and M_M and M_S are the masses of Mars and the Sun respectively.

Using R = 2.28 × 10¹¹ meters, M_M = 6.4191×10²³ kg and M_S = 1.98892×10³⁰ kg, we arrive at a value of 1.08 million km, 72% of the distance of Earth’s 1.5 million km.

Now, keeping the assumption that it will approximately take solar ions 60 minutes to travel 1.5 million km (from Earth’s L₁ point to Earth), the time from L₁ to Mars’ surface = 60 × 72% = 43.2 minutes.

Although 43 minutes is less than the warning time Earth-based solar wind probes are able to provide, this is not a great reduction in lag time, and would still greatly benefit the humans unprotected from solar radiation on the surface of Mars.

References:
Article adapted from my conceptual article written for Marspedia.org: Early Warning System (Solar Radiation).