Although the numbers vary widely, Oort’s estimate that the Oort cloud contains billions of objects remains valid, and even numbers in the trillions have been suggested. Even so, the amount of material contained in the Oort cloud is thought to be fairly small (of the order of tens of Earth masses) since the majority of the objects are expected to be small (measured cometary nuclei have diameters of ~20 km or less) and the distances between them on the order of tens of millions of kilometres.