Space Rocks Like This One Probably Helped Deliver Earth's Oceans
Comet Hartley 2 NASA/JPL Earth's oceans likely started out as space snowballs born far beyond the orbit of Pluto, a new study says. Water-rich comets collided with the young planet after hurtling through the nascent solar system, and probably delivered a significant amount of the water on this planet. After its formation, Earth was too hot to hold on to its original water, yet 71 percent of the planet is oceans, meaning something else must have deposited it here. Comets contain much more water than asteroids, but all previously studied comets had the wrong water isotope ratios, so scientists figured only about 10 percent of Earth's water was cometary in origin. Researchers thought meteorites, which may have also delivered our gold and other precious metals, must have brought Earth its water. But the comet Hartley 2, a peanut-shaped Jupiter-family comet, contains water with almost exactly the same chemical signature as water...