Solar system reference diagram depicting the origin of water

In the early days of our solar system, when Earth and other planets were still taking shape, the dashed white line represents the snow line the transition from the hotter inner solar system, where water ice was not stable (brown), to the outer solar system, where water ice could exist (blue) encircling the inner edge of the snow line was a belt of asteroids that included a large one called Vesta. There are three hypotheses for how the inner solar system received water: 1) water molecules stuck to dust grains inside the snow line (inset), 2) meteoritic material was flung into the inner solar system by the effect of gravity from protoJupiter, and 3) comets brought water to the inner solar system after the planets were formed. Ph.D. student Adam Sarafians research showed that the second scenario most likely occurred within the first 14 million years of the solar systems history. (Illustration by Jack Cook, © Woods Hole Oceanographic Institution)