New measurements show that radiation levels on the moon are two to three times higher than on the International Space Station. The measurements were taken by an instrument on China’s Chang’e-4 lunar lander. The spacecraft touched down on the far side of the moon in January of 2019.

German and Chinese scientists involved in the experiment say the Chinese lander provided the first “active” measurements of radiation levels on the surface of the moon. The findings were recently reported in a study in the publication Science Advances.

The study comes as the United States and several other countries develop plans to send astronauts to explore the moon. The American space agency NASA has a goal of landing the first woman and next man on the moon by 2024 as part of its Artemis program. It also wants to set up a long-term base on the moon by 2028.

Earth’s atmosphere and magnetic shield protect humans from the extreme radiation present in the universe. But astronauts aboard the International Space Station receive higher levels of radiation that we receive on Earth.

The new study suggests that radiation exposure on the moon would be 2.6 higher than on the International Space Station. The researchers said astronauts on the moon would get about 200 times more radiation than we experience on Earth.

Robert Wimmer-Schweingruber is an astrophysicist at the University of Kiel in Germany, and predicted that astronauts would only be able to stay on the moon for about two months under current conditions. “Humans are not really made for these radiation levels and should protect themselves when on the moon,” Wimmer-Schweingruber said.

The radiation levels described in the study are similar to levels that models have already predicted. Kerry Lee is a space radiation expert at NASA’s Johnson Space Center in Houston. Lee said the measurements “agree nearly exactly” with those made by a detector on a NASA orbiter that has been circling the moon for more than 10 years.