Nasa data shows radiation doses would be so high on a manned Mars mission that we must now debate the ethics of deep space exploration – or wait decades to develop safer technology

It is time for idealism about missions to Mars to end. Going there with current technology would carry a significant risk of harmful radiation exposure.

This was made clear at last Thursday's teleconference of results from the Radiation Assessment Detector (RAD) onboard Nasa's Curiosity rover.

During the rover's cruise to Mars between December 2011 and July 2012, RAD showed that an astronaut would clock up the same radiation dose in a day that the average American receives in a year. If you exclude medical dosages, it would be 10 times more than the average American.

Taking these numbers at face value, the radiation from a 500-day round-trip to Mars would exceed Nasa's current safety guidelines.

The data also highlights that the radiation comes in two forms.

Firstly, there are the solar storms. Five times during the cruise, RAD detected precipitous rises in the amount of radiation due to solar flares. However, these turned out to be the least of an astronaut's problems. Although such storms can be dangerous, the particles released accounted for just 5% of the total radiation measured by RAD.

By far the greatest dose came from a second source: the natural bombardment of galactic cosmic rays. These are produced mainly in the dying remnants of exploded stars that litter our galaxy.

Galactic cosmic rays (GCRs) usually carry more energy than particles ejected by the Sun, so thicker shielding is required to stop them. And they are constant: day in, day out they will strike the spacecraft and the astronauts inside.

Whereas solar particles could effectively be blocked by the spacecraft's water tanks or special suits that the astronauts could put on, metres of dense shielding would be needed to provide any barrier against the GCRs. Such extreme shielding is not possible on today's spacecraft because it would make them too heavy to launch. So how do we progress?

Either we develop new propulsion technology to get to Mars faster, or we develop lighter shielding. Both approaches are being worked on at Nasa but they will take time.

Better propulsion could come in the form of Nuclear Thermal Propulsion. Better shielding is also being designed.

Nasa says that by planning trips to Mars in the mid-2030s, these technologies have time to develop. So, what should we make of entrepreneurial plans to send humans to Mars sooner?

The Dutch organisation Mars One says its wants to put humans on the surface in 2023. The Inspiration Mars Foundation plans to fly astronauts to Mars and back on a 500-day mission in 2018.

During Thursday's press conference, the experts said that the radiation data would be made fully available to everyone. Beyond that, they would not be drawn into saying whether such missions were safe.

However, it is now impossible to ignore the fact that a trip to Mars carries a radiation exposure risk higher than current guidelines recommend. So, do we abandon the current guidelines and let astronauts take their chances? After all, the links between tobacco and cancer are well known yet people still choose to smoke.

One thing is certain: there can be no more romantic idealism. No amount of wishful thinking, or crowdsourcing, or press releasing can circumvent this problem. Space radiation is dangerous, potentially deadly. Manned missions to Mars with current technology will carry significant exposure risks.

At what price ethically do we want the Red Planet?

• Stuart Clark is the author of The Day Without Yesterday (Polygon).