Science & Exploration
09/03/2026
465 views
12 likes
When packing your spacecraft for a return trip to Mars, it would be better to launch during a period of maximum solar activity.
Travelling through deep space when the chance of solar storms and flares is at its highest sounds counterintuitive, but new research demonstrates that embarking on such a journey when the Sun is most active is safer.
Enhanced solar activity sweeps away energetic space radiation coming from beyond our Solar System. A crewed Mars mission during a next peak in the solar cycle could perhaps reduce the exposure to harmful radiation by half compared to a trip during a solar minimum.
Terrae Novae destinations: Mars
Radiation measurements from ESA’s ExoMars Trace Gas Orbiter (TGO) confirm the paradoxical finding that travelling during solar maximum is the best time to go. An international research team concluded that a crew could complete the round trip without breaching radiation guidelines. They also provided the estimated doses a crew would sustain during different mission scenarios.
Radiation doses for astronauts
One of the greatest challenges of sending humans to Mars is their exposure to space radiation. Ionising radiation poses serious health hazards, including an increased risk of cancer, cardiovascular effects and cataracts.
Beyond Earth’s protective magnetic field, an astronaut on a Mars mission could be exposed to radiation doses tens of times higher than on our planet. ESA’s radiation limit for an astronaut’s career is 1000 millisieverts, the unit for the effective dose that could cause damage to human tissue. Higher doses delivered over short periods pose acute risks, while lower dose rates mainly contribute to long-term health risks.
Previous studies already indicated that flying a mission to Mars at solar minimum would bring dose levels from galactic cosmic rays dangerously close to the ESA career limits.
The new analysis widens the scope using data from the Liulin-MO dosimeter onboard TGO and the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on board the Lunar Reconnaissance Orbiter over a 15-year period.
Nowhere to hide
On the way to the Moon and Mars, astronauts face two major sources of space radiation: galactic cosmic rays and solar energetic particles. The first originate from energetic events beyond our Solar System, such as supernovae; the second from powerful solar eruptions.
Astronauts can seek protection inside their spacecraft during solar energetic particles events. These storms are unpredictable, but given enough warning and shielding, crews can retreat to ‘storm shelters’ – areas with extra shielding. On the International Space Station, astronauts take refuge in the sleeping quarters or kitchen.
Space risks – Fighting radiation
There is, however, nowhere to hide from the constant bombardment of galactic cosmic rays. These particles travel close to the speed of light and penetrate both spacecraft shielding and the human body. When stopped, cosmic rays often trigger showers of secondary particles that can be even more damaging to humans.
Once on the martian surface, astronauts would be exposed to doses up to 60% lower than during the interplanetary travel. Caves and lava tubes could make good habitats to reduce radiation exposure.
Best cruise to Mars
The study calculated the radiation dose for simulated Mars missions under different levels of solar activity and across three trajectories: the most energy-efficient but longest route, the most energy-consuming but shortest route and a compromise of the two.
Radiation doses on the way to Mars
Across all three, the cumulative radiation dose from cosmic rays decreases significantly near solar maximum. A boisterous Sun seems to be the only solace against galactic cosmic rays.
The team analysed transfer orbits to Mars over the past 60 years and used a layered water-ball to simulate how much radiation the organs inside a human body would absorb. Faster transfer orbits could reduce radiation exposure by 55% by travelling in solar maximum rather than during solar minimum, while missions with trajectories saving fuel could see reductions of up to 45%.
Earth to Mars trajectories for radiation study
“To remain within the career radiation limits, mission planners should carefully target specific transfer trajectories and launch windows,” says Robert Wimmer‐Schweingruber, co-author from the University of Kiel, Germany.
Protecting astronauts as they venture deeper into space is a critical priority for ESA. “This study helps us convert solar cycle variations into clear targets for mission trajectories and risk reduction. We can quantify how much we can gain from targeting a certain launch window and faster trajectories, and when we still need better shielding and operational concepts to make Mars missions genuinely safer,” says Anna Fogtman, ESA’s radiation protection lead.
Paper published in Space Weather on 9 March 2026, “The constraint of crewed Mars missions based on current radiation dose measurements,” by Chao Zhang and researchers from the University of Science and Technology of China, the University of Kiel in Germany and the University of Michigan, USA.
Like