A US-German team of scientists from the Max Planck Institute for Astrophysics and NASA have used NASA's Rossi X-ray Timing Explorer to estimate the depth of the crust on a neutron star, the densest object known in the universe. The crust, they say, is approximately 1.6 kilometres deep and so tightly packed that a teaspoon of this material would weigh about 10 million tonnes on Earth.