The Rosetta Probe is busy in the asteroid belt, snapping unprecedented high-res pictures. These images will enable scientists to figure out the density of various asteroids. That information could save the planet if an asteroid ever heads towards us.
The probe just completed the fly-by phase past Lutetia, an asteroid first discovered 150 years ago that measures 85 miles wide. Flying within 2,000 miles of the asteroid, Rosetta has taken enough photos that its operators at the European Space Agency should be able to calculate the mass of the asteroid. The images are crucial to this because they will give the scientists the clearest idea yet of its particular composition, which is known to include primitive carbon compounds. Once we have a good handle on its composition, we can figure out its mass and, coupled with its already known volume, its density.
That's a crucial figure to know. If Lutetia - or any of the other asteroids Rosetta will soon be flying by - ever broke free from the asteroid belt and found themselves on a collision course with Earth, we wouldn't have much time to figure out our response. Depending on the asteroid's density, we would either need to blow the asteroid up or simply deflect the rock back into space. However, we likely wouldn't have time for a do-over if we chose wrong, so the more we know about asteroid density, the better off our future selves will be.