You have been given a job working on a team that is examining telescope pictures for asteroids which might collide with the Earth. In your orientation, your team was told how important these observations might be. Current theories indicate that dinosaurs and many other organisms became extinct when the Earth was struck by a large asteroid. 65 million years ago dust from an asteroid impact was lofted into the upper atmosphere all around the globe, where it lingered for at lest several months and blocked the sunlight reaching the Earth’s surface. On the dark and cold Earth that temporarily resulted, many forms of life became extinct. It has been suggested that such an asteroid collisions likely to happen again, perhaps causing the extinction of the current dominant life form on Earth, namely us. As you scan space for this danger, how large an asteroid should you be watching for if the dangerous asteroid size is roughly the same as the one that wiped out the dinosaurs? Available evidence suggests that about 20% of that asteroid’s mass ended up as dust spread uniformly over Earth after eventually settling out of the upper atmosphere. About 0.020g/cm2 of dust, which is chemically different than the Earth’s rock covered the Earth’s surface. Typical asteroids have a density of about 2.0 g/cm3.