Though Curiosity the rover can explore and see Mars up close, curious men and women of Earth will have to wait a bit longer. NASA reports that a manned trip to Mars is likely impossible with current technology because of radiation.

Curiosity’s Radiation Assessment Detector (RAD) was able to measure the radiation of Mars from inside the spacecraft and found data that makes NASA reconsider the effectiveness of current radiation shielding. Specifically:

The findings, which are published in the May 31 edition of the journal Science, indicate radiation exposure for human explorers could exceed NASA’s career limit for astronauts if current propulsion systems are used.

Two forms of radiation pose potential health risks to astronauts in deep space. One is galactic cosmic rays (GCRs), particles caused by supernova explosions and other high-energy events outside the solar system. The other is solar energetic particles (SEPs) associated with solar flares and coronal mass ejections from the sun.

Right now, spacecrafts do a better job at shielding against SEPs than they do GCRs. GCRs are highly energetic and penetrate the shielding on current spacecrafts. In order to protect astronauts from being exposed to radiation, NASA might have to invent better shielding. Or invent better something.

Exposure to radiation, which is measured in units of Sievert (Sv), increases the risk of cancer. We know that. Exposure to 1 Sv over time is associated with a five percent increase in risk of developing cancer. NASA’s acceptable limit for its astronauts is a three percent increase in risk. Curiosity’s RAD instruments measured an average of 1.8milliSv per day on its trip to Mars. The accumulated dose of the trip, according to Cary Zeitlin, lead paper in the findings and a principal scientist at the Southwest Research Institute (SwRI) in San Antonio, would be equivalent to “getting a whole-body CT scan once every five or six days”. Yeah, that’s too much.

But knowing this doesn’t prevent a manned trip to Mars from ever happening. Knowing this helps protect the men and women who will take that manned trip to Mars. [NASA]