Scientists say measurements taken by the US space agency's Mars Odyssey craft prove that a human mission could survive on the Martian surface.
Mars Odyssey has been orbiting the Red Planet for two years
Instrument data show radiation around the Red Planet might cause some health problems but is unlikely to be fatal.
Mars Odyssey has sent back a wealth of information about Earth's neighbour since it went into orbit two years ago.
The new research was presented at the annual meeting of the American Geophysical Union in San Francisco.
On Earth, we are protected from the worst cosmic radiation. The Earth's magnetic field acts like a shield, diverting radiation away.
But for astronauts on the Martian surface - or travelling between Earth and Mars - there is no such protection.
Nasa scientists have been measuring radiation around Mars with an instrument on board the Mars Odyssey orbiting probe.
According to Cary Zeitlin, from the National Space Biomedical Research Institute, it has found that astronauts on the Red Planet would be exposed to roughly double the radiation dose they currently experience on the International Space Station.
"The dose [an] astronaut would receive on a Mars mission is large enough to be beyond what they've experienced in Earth orbit," he told BBC News Online.
"Therefore it opens some questions about the biological effects of this radiation that we haven't really fully addressed yet."
He continued: "People are going to the space station for about six months.
"A Mars mission would last around three years. And it's the duration of the exposure that becomes the issue; it's also the fact that the radiation is quite exotic.
"It's galactic cosmic radiation. It comes from all over the galaxy. We call it heavy ion radiation."
This radiation could perhaps lead to more cancers, more cataracts and nervous system damage.
But overall, Dr Zeitlin says, it is manageable - humans could go on Mars missions relatively safely.
They would need to use the planet itself to shield them, building their shelters in hollows, and perhaps taking materials which would reduce radiation further.
What is somewhat ironic about this is that the Odyssey instrument, named Marie, has itself been damaged, apparently beyond repair, by excessive radiation from the Sun.
It stopped functioning following a massive solar flare in October.
But Nasa says it sent back enough data before its demise to reassure us about the feasibility of human missions to Mars.
Other Odyssey results released here in San Francisco suggest Mars may be going through a period of climate change.
The amount of frozen water near the surface in some relatively warm low-latitude regions on both sides of Mars' equator appears too great to be in equilibrium with the atmosphere under current climatic conditions.
Dr William Feldman, of Los Alamos National Laboratory in New Mexico, said: "One explanation could be that Mars is just coming out of an ice age.
"In some low-latitude areas, the ice has already dissipated. In others, that process is slower and hasn't reached an equilibrium yet.
"Those areas are like the patches of snow you sometimes see persisting in protected spots long after the last snowfall of the winter."
Odyssey assesses water content indirectly, through measurements of neutron emissions.
Frozen water makes up as much as 10% of the top metre of surface material in some regions close to the equator. Dust deposits might be covering and insulating the lingering ice, Dr Feldman said.
Read a selection of your comments below.
Radiation problems on Mars - that must be why Martians are green.
Rupert Merrick, Brazil
We better hurry up and go somewhere because we are ruining our own planet.....
Darrell P. Gates, USA
I think before going to other planets humans need to evolve into a different species and this can't be your usual natural selection mutation or something, we need to create new humans with better developed brains, much greater lifespan and the ability to withstand space radiation without any damage to their organisms. These would be the general specs, I think if we really want to go to other planets.
Sign me up!
Jon Franklin, USA
The thought is cool, but the practicality seems unnecessary at this point. Unless there was a serious need for populating another planet, it appears as a misuse of finances.
The ideological / fantasy-esque scope of the possibility seems cool, though.
John Doe, USA
Did the astronauts who visited the moon overcome the risks of radiation? How has their health been since then?
What would the health and life insurance premiums amount to for a trip to Mars?
There are many issues to be explored before we even think about visiting yet another ball of rock in the sky.
Gillian Almeida, England
Can we get off this rock already? Why NOT go to Mars?! With present political and environmental conditions as they are, space exploration is possibly the only thing that will help save the human race. When your family gets bigger, do you not look for a bigger house?
James Deane, Canada
We go because we can, because it is our next frontier and because the seed of the human species needs to be preserved beyond this fragile world. Do we want to back off from the next great challenge to mankind?
Dick Baird, USA
Every major social achievement of the human race was the direct result of men (and women) "boldly going where no-one has gone before". The question should be: Why are we not already colonizing Mars?
Stelios S. Grigoriou, Hellas- Greece
Visiting Mars would be bigger than the Pyramids, bigger than a cure for cancer, it is truly the most fantastic human endeavour yet imagined. As for radiation, a lead shield of at least 6 inches would sufficiently protect the astronauts. It's not the travelling but the staying that is the issue.
Aaron Vandenberg, Canada
Will it be OK to smoke on Mars?
Andrew Forrow, Key West, Florida, USA
The next great adventure of mankind is not for people who ask, "What exactly is the point?" They will never get it.
Bob Coleman, USA
Hey please stop this extravagant expenditure of funds. There still a lot to be done here on Earth like Aids, poverty etc. All these need money.
John Shaush, Tanzania
An important front I have not seen being addressed is the human psychology in space. I can NOT survive either being alone or staying with the same people (whom I love/like/neutrual/don't like/hate) for three or more years. Even if one day we can travel at the speed of light, this will STILL be a problem for even farther missions.
Xibei Tian, US
I think the prospect of going to Mars is a very interesting one, but we should sort out our problems on this planet before we start messing up others. If they need volunteers, I'd love to go. It's not like we aren't exposed to lots of harmful things already, with UV rays from the sun, additives to the food, pollution, etc.
I have an idea, how about exploring areas of our oceans that still remain unknown and untouched? I feel this a a huge waste of money and time!
Jason O, Canada
Well, Mars is very dangerous for the radiation the sun outside our atmosphere spreads. But is it possible, that if someone go to the moon more than once a life, they get the same doze of radiation, as they would go to the Mars?
I don't suppose sun block factor 38,000,000 would help?
And has anyone considered how friendly the locals are going to be towards a visit?
Jon Harrold, UK
The quest for Mars, is ultimately the quest to better understand our universe and ourselves.
It is now clearer to us that life is most probably NOT unique to this planet.
So we can no longer afford to limit our understanding of life to this small planet.
A more pressing reason for the colonization of Mars or other uninhabited planets is that the human population is increasing exponentially, and along with it, the consumption of resources. Unless we reduce the population pressure on this planet, we risk not having much left on earth to sustain our growth, and then the question of colonization of other planets must then be answered.
So why wait until we have destroyed our planet???
Spacecraft need to be more heavily protected, and new spacesuits should be developed for EVA on Mars. Without nuclear energy, Mars is a no-go. That means a heavy design for the Mars ship. The lander alone will be a great feat of engineering skill.
Ville Ylipekkala, Finland
Sort the Earth out first; then tackle Mars.
Jonathan, Northern Ireland
Why would humans achieve anything new on Mars that they haven't already tried on Earth? What really IS the point of an Earth mission to Mars? Are humans honestly to be trusted with another planet with our track record?
Kim Jones, Australia
So, we can go to Mars now. Where do I sign up?
Iain McC, UK
How did the astronauts overcome the risks of radiation when they visited the moon?
Dave Sterlini, England
To Dave Sterlini: Firstly they were travelling at 24,000 mph and spent only 1-2 hours within the Van Allen radiation belts, resulting in 1-2 rem's of radiation dosage. 10 times less then would cause radiation sickness. Radiation exposure was monitored by on-person dosimeters and in cabin radiation detectors and readings were relayed to mission control. Secondly, the sun was closely monitored by the the Solar Particle Alert Network (SPAN), all missions were launched when there were fewer sun spots and a reduced chance of solar flares.
David Jordan, Ireland
Possible cancers, cataracts and nervous system damage? Test spacecraft irreparably damaged by radiation from the sun? And Dr. Zeitlin still thinks a Mars mission would be relatively safe - I will believe that when I see him volunteer for it!!
Joel Lewis, UK