A human expedition to Mars has long been on the radar of space explorers’ aspirations. Two years ago, it was even said that humans could reproduce on Mars, as sperm can live there for up to 200 years, according to scientists.

However, these hopes may be short-lived, as experts now recommend that people spend no more than four years on any mission on the planet.

According to one of the latest studies on the viability of human life on the Red Planet, scientists have said that radiation levels become dangerous if people stay there longer.

The findings, published in the Advancing Earth and Science Journal, said: “Our calculations clearly show that the best time to launch a manned spaceflight to Mars is during the solar maximum, as shielding from solar particles is possible.”

“Our simulations show that increased shielding creates an increase in secondary radiation produced by the most energetic GCR, resulting in a higher dose, putting a limit on mission duration.

“We estimate that a potential mission to Mars should not take more than four years. This study shows that cosmic radiation poses serious limitations and poses technological challenges to a still viable human mission to Mars.”

Another study by a team from the University of California, Los Angeles showed that a spacecraft traveling to and from Mars must provide adequate protection during travel there and back.

However, if the material the spacecraft is made of is too thick, it can actually increase the amount of secondary radiation.

Other findings included intelligence that the best time to leave Earth is when solar activity is at its peak. This is because the “solar maximum” is at the least dangerous level.