This is an artist's concept of NASA's Mars Science Laboratory
spacecraft during its cruise phase between launch and final
approach to Mars.
Image credit: NASA/JPL-Caltech
A short while ago, the Curiosity rover was sent on its long journey to Mars, where it will study the red planet to determine whether the planet has ever been capable of hosting life, and whether it could do so in future. But even though at is still over 200 days from its destination, at least one instrument in its on-board laboratory is already hard at work, collecting data and reporting back to Earth: the Radiation Assessment Detector (RAD), which monitors high-energy atomic and subatomic particles.
The radiation detected by RAD is known to permeate most of the universe, and is emitted by the Sun, more distant stars and supernovae, and other more exotic objects. On Earth, we are fortunate enough to have both a thick atmosphere and a strong magnetic field, which shield us from this radiation, but Mars has neither of these things. If we are ever to visit Mars, we will need protection, and RAD will let us know how good that protection needs to be.
Radiation sensors have been sent out before on many other spacecraft, but they have always been placed outside the craft, for maximum sensitivity. RAD is different because it is inside the Curiosity rover, behind all the machinery and bodywork of the Mars Science Laboratory - exactly where a human crew would be. While the data collected at this point of the mission are less useful for scientists studying space radiation levels, it does have the practical benefit of letting us know how much shielding is already provided by the basic hardware of a spaceship, and that's vital information when planning a manned mission.