Missions to Mars Shouldn’t Exceed Four Years Due to Radiation Risks, Scientists Say

Missions to Mars Shouldn’t Exceed Four Years Due to Radiation Risks, Scientists Say
Conceptual image showing a crewed mission on the Martian surface. (Image: NASA)

An international collaboration of scientists say it’s safe for astronauts to fly to Mars and back, provided the length of the mission does not exceed four years and that crewed flights to the Red Planet coincide with a well-known solar cycle.

Space can kill you in all sorts of different ways, with particle radiation being among the most serious hazards. Small doses of ionising radiation aren’t the problem — it’s the long-term exposure that’ll get you. The deleterious effects of particle radiation are cumulative, leading to health conditions such as cancer, a damaged nervous system, cataracts, radiation sickness, and reproductive issues that can influence the health of offspring.

These risks are of obvious relevance when it comes to planning of a crewed trip to Mars, as NASA is doing right now. The current plan is to send American astronauts to the Red Planet in just 12 years, so it’s important that NASA understands the ways in which it can protect its crew.

Indeed, once in space, the astronauts won’t have Earth’s magnetosphere to protect them. Even with shielding, the crew will be exposed to solar energetic particles and galactic cosmic rays, the latter of which is particularly harmful to human health.

Artist's conception of a crewed mission to Mars, including habitats on the surface.  (Image: NASA) Artist’s conception of a crewed mission to Mars, including habitats on the surface. (Image: NASA)

An international team of scientists recently investigated this topic to learn if a round-trip mission to Mars might be too dangerous for humans and if the timing of such missions could offset potential risks. Researchers from UCLA, MIT, GFZ Potsdam, and the Skolkovo Institute of Science and Technology in Moscow were involved in the study, which now appears in the science journal Space Weather.

They made their calculations by referencing models of particle radiation inside our solar system and models of how this radiation might impact human health and the state of a spacecraft. Results showed that a potential mission to the Red Planet should not exceed four years and that, “while space radiation imposes strict limitations and presents technological difficulties for the human mission to Mars, such a mission is still viable,” write the researchers in their study.

A key finding has to do with the timing of the mission. The scientists recommend that flights to Mars leave during the Sun’s solar maximum, when solar activity is at its peak (December 2019 marked the previous solar minimum — the start of the current solar cycle — with the next solar maximum predicted for July 2025). The solar maximum might seem like the worst possible time of departure, but galactic cosmic rays — the most dangerous of the energetic particles — get deflected during periods of enhanced solar activity. And indeed, galactic cosmic rays are at their lowest between six and 12 months following peak solar activity, according to a UCLA press release.

This is good news, as average flights to Mars are around nine months. A return trip after about two years at Mars seems totally doable. This would include time spent on the Martian surface, which isn’t protected by a magnetosphere. Missions to Mars lasting more than four years will require protective measures, such as better shielding, underground habitats, and possibly even biological interventions.

The next best windows for the shortest flights to Mars will appear in 2030 and again in 2050, with both departure dates corresponding to periods of solar maximum, according to the research. Interestingly, “for the previous solar cycle, the smallest effective dose would have been accumulated for a flight starting in 2000, during solar max,” write the scientists.

Another key finding of the study has to do with the thickness of the spacecraft’s protective shielding. The researchers found that thick shielding would protect the crew — but only to a point. Beyond a certain threshold of thickness, the shielding would only serve to amplify the incoming radiation, which it would do by bouncing the radiation around inside the spacecraft.

Aluminium shielding at the designated optimal thickness would expose astronauts to 0.5 Sieverts during missions lasting 1.9 years, while the maximum allowable career dose for astronauts of 1 Sieverts would be accumulated after a flight lasting 3.8 years, according to the study, co-authored by Yuri Shprits, a geophysicist at UCLA.

As the researchers admit, however, their analysis was limited to aluminium shielding. “Composite materials including hydrogen-rich composites have often been discussed for use in deep space habitats,” they write. “Materials such as a carbon composite with significant hydrogen content may potentially improve shielding and allow for longer flight times, as materials containing light elements result in lower fluxes of secondary [i.e. bounced] particles.”

So this is really good news, but it shows how much work still needs to be done to protect astronauts during long-duration missions. The new paper doesn’t even get into the deleterious effects of microgravity, which is also very bad for human health. We’re highly motivated when it comes to exploring and living on Mars, but making it safe will prove to be a formidable challenge.