Water, Water, Everywhere: The Origins of Earth’s Oceans
The fantastic productivity of the stars means we live in a universe filled with hydrogen and oxygen—and thus filled with the potential for water. In fact, says Kudritzki, there is water throughout the universe. Right here at home, Jupiter’s moon Europa is covered in a thick crust of water ice, and even our own moon was just discovered to have water. The real rarity is finding H2O in liquid form. Too close to a star and it vaporizes, too far away and it freezes.
When Earth formed, astronomers believe, the new planet would have been far too hot to hold water, so the oceans must have formed later. But where from? Astronomers began rooting around the solar system for answers. For a long time they hypothesized that the oceans came from comets that had crashed into Earth. Comets are, in essence, snowballs. Their surfaces are covered with ice, and their spectacular tails, sparked to life when a comet comes close to the heat of a star, are trails of evaporating water.
And yet … astronomy, like all sciences, is a field in which discoveries keep undermining theories. When scientists analyzed the water in comets, they discovered it wasn’t the same as the water in our oceans. Heavy water forms when deuterium (which has one proton and two neutrons) is present along with hydrogen (which has one proton and one neutron). And the water in comets is significantly heavier than the water in our oceans. So astronomers kept looking.
Three years ago, using the UH 2.2-m telescope on Mauna Kea, astronomers came across what could be the answer in the Asteroid Belt, that badlands between Mars and Jupiter where a gang of at least two hundred million asteroids orbits. Asteroids, first detected at the beginning of the nineteenth century, are a relatively new discovery in the world of astronomy; they are, in essence, big pockmarked chunks of rock, orphans from the solar system’s early days when most of the material in the sun’s proto-planetary disc was compressing to form Venus, Mercury, Saturn, Neptune and the other planets. Unlike comets, asteroids weren’t thought to contain water—until the astronomers using the UH telescope detected a new subclass of asteroids with large chunks of ice on their surfaces. Could a rogue asteroid or two be responsible for our oceans? UH is now lobbying NASA to send a spacecraft to the Asteroid Belt to take a sample of the ice and see whether it matches.