Much of Earth’s Water Is Older than the Sun
October 3, 2014
Up to half of the water in Earth’s oceans may be older than the sun and the rest of the solar system, including Earth itself, according to a new study. The findings indicate that Earth and other bodies in the solar system “inherited” their water—in the form of water ice—from interstellar space. The findings also suggest that if interstellar water ice survived the formation of the solar system, other planetary systems in our Milky Way Galaxy may also have had access to the single most important ingredient necessary for life as we know it.
The solar system is actually awash in water. Oceans make up about 70 percent of Earth’s surface. But water ice also exists in comets and on Jupiter’s moons Europa and Ganymede and on Saturn’s moon Titan. Mars has vast amounts of water ice at its polar regions, and the planet Mercury and Earth’s moon also have water ice within craters that are never fully exposed to the sun. Where did all this water and water ice came from? Scientists already knew that the clouds of gas and dust from which stars form contain water in the form of ice. But they weren’t sure whether water ice could survive that violent processes that occurred when the sun was born. Perhaps the radiation given off by the new sun vaporized most or all of the water ice or broke the water molecules into atoms of hydrogen and oxygen. In that case, the water in the solar system must have reformed in some way.
Stars are born from clouds of gas and dust that contain water in the form of ice. (NASA)
To determine how much of the solar system’s water or water ice is “original,” the scientists created a computer model that mimicked conditions in the early solar system. In particular, they wanted to know whether the processes that led to the formation of the solar system could account for the amount of deuterium in Earth’s oceans and in comets and meteorites. Deuterium, an isotope (form) of hydrogen, is a key part of a kind of water called heavy water. The nucleus of an ordinary hydrogen atom consists of a single negatively charged particle called a proton. The nucleus of a deuterium atom consists of a proton and a single electrically neutron particle called a neutron. Deuterium forms only under certain circustances, in extremely cold environments, such as interstellar space, for example.
When the scientists ran the model, they discovered that radiation given off by the newly formed sun could not account for the deuterium in the solar system. In fact, they calculated that up to 50 percent of the water in Earth’s oceans comes from water ice that formed in interstellar space before the solar system even existed. As much as 70 percent of water in comets may have survived the transition from insterstellar space to the solar system.
