Clearly, water ice is more abundant than we once thought. But did our solar system just get lucky? And where did it come from in the first place? The answers lie within water itself.
The components of water ice — hydrogen and oxygen atoms — have been around for much of the universe’s history, but of course it’s not water till they’re combined. Astrophysicists think that happened during the earliest days of our solar system, when the sun and planets were nothing more than a swirling cloud of hydrogen and dust particles. If high-energy particles from deep space, called cosmic rays, happened to hit one of those hydrogen atoms, it became ionized, stripped of its electron. Ionized hydrogen atoms could then easily combine with oxygen, forming our H2O ice.
The sun has a much lower deuterium concentration than our oceans, suggesting that much of Earth’s water comes directly from the initial pre-solar cloud. Just think: Part of every sip of water you drink could be older than the sun.
Planetary scientists tested this by examining the hydrogen atoms in today’s water. Deuterium, a type of hydrogen with a neutron, is heavier than regular hydrogen. Scientists can classify water samples, and compare their histories, by learning how many of those hydrogen atoms are deuterium. They’ve found that the ice on comets has deuterium concentrations very similar to the water in our oceans. The match means our water ice stores have the same cosmic origin as the solar system’s comets — among its oldest known objects.
So, we know our watery bounty is not unique, since the same conditions likely occurred during the formation of any other solar system. Water is likely similarly abundant around other planets, raising the odds of finding life as we know it, or at least habitable conditions, somewhere else.