Just some more space facts: • One teaspoon of a neutron star weighs about a billion tons. These collapsed cores of massive stars are so dense that a tiny piece matches the weight of a massive mountain on Earth. • Saturn could float in water. Because the gas giant is mostly made of hydrogen and helium, its overall density is less than that of water. • There are more stars in the universe than grains of sand on Earth. Scientists estimate there are at least a billion trillion stars in the observable universe. • A day on Venus is longer than its year. Venus takes 243 Earth days to spin once on its axis, but only 225 Earth days to complete an orbit around the Sun. • Space is completely silent. Sound waves need molecules (like air) to vibrate and travel through, but space is a vacuum with far too few molecules to carry sound. • The footprints on the Moon will stay there for millions of years. Because the Moon has no atmosphere, wind, or water erosion, the marks left by Apollo astronauts are permanent. • Olympus Mons on Mars is three times taller than Mount Everest. This gigantic Martian volcano stands 16 miles high and has a base roughly the size of Arizona
