The spherical shell known as the Oort Cloud is virtually invisible. Its particles are spread so thinly and so far from the light of any star, including the Sun, that astronomers simply cannot see the cloud, even though it envelops us like a blanket. It may be hard for the human mind to comprehend: a cosmic cloud so colossal that it encircles the Sun and eight planets, stretching trillions of miles into deep space.