Data from the Mars Science Laboratory (MSL) on board the Curiosity Rover reveal that the levels of radiation on the Martian surface would be safe for astronauts - roughly the same levels as on-board the International Space Station. Unlike our home planet, Mars does not have a magnetosphere (our north and south poles) which naturally protect us from the Sun's harmful radiation so it was expected that the levels of radiation may proved lethal to humans. However, Curiosity instruments show that Mars's thin atmosphere provides some protection against the Sun's harmful rays.
Curiosity monitors the weather carefully on Mars and have detected daily changes in the atmospheric pressure. The daily cycle of higher pressure in the morning and lower pressure in the evening results from daytime heating of the atmosphere by the Sun, resulting in what scientists call "thermal tides". The Sun heats the atmosphere on the side of Mars it is facing. This causes the air to expand upwards, triggering a decrease in air pressure. On the dark side, the atmosphere deflates and becomes denser as the temperature drops quickly. The net effect is that the denser atmosphere provides a better level of shielding so charged-particle radiation is less when the atmosphere is thicker. This shielding effect could protect astronauts who visit the red planet, although Curiosity has yet to see the effects of solar flares on Mars's atmosphere.
This latest news comes amidst huge speculation that the Curiosity team have made a major discovery. One of the scientists which built and now operate the rover has said the mobile laboratory has made an "earth-shattering" discovery. Officials from NASA are keeping schtum on the matter. The speculation is that organic compounds, like amino acids or carbohydrates, may have been discovered by Curiosity's SAM (Sample Analysis at Mars). These would indicate that life exists or had existed on the red planet. Only time will tell if this latest rumour is true or over-hyped.