A family of comets from the Kuiper Belt may have assisted asteroids with bringing water to early Earth, a key development in the planet's ability to host life.
Scientists believe Earth’s water was delivered sometime after the planet formed, as its close proximity to the sun would have boiled off water inside rocks that were part of the original building materials.
Previous studies of meteorites, which are bits of asteroids that land on Earth, show a water chemistry that is similar to Earth’s oceans. The analysis is based on the ratio of regular water -- two hydrogen atoms bound with an oxygen atom, or H2O -- and so-called “heavy water,” which has an extra neutron in its nucleus.
The ratio was different in a handful of measurements made of comets, so scientists theorized that asteroids were the primary source of Earth’s water.
Not so, concludes a new study that looked at a comet hailing from a different part of the solar system than previously studied comets.
The target, Comet Hartley 2, is believed to have formed in the Kuiper Belt region, located beyond Neptune's orbit. Hartley 2 is now a member of the Jupiter family of short-period comets that swing around the sun in less than 20 years. The comet's water chemistry matches that of Earth's.
"This is an important constraint on models of the formation of planets in the solar system, a field of science which is moving forward very rapidly at present," astronomer Miriam Rengel of the Max Planck Institute for Solar System Research in Germany, wrote in an email to Discovery News.
Previous studies, which looked at comets originating from the Oort cloud, a spherical cluster of icy bodies in the outer solar system, led scientists to conclude that only about 10 percent of Earth's water could have come from comets.
The finding significantly boosts the pool of resources available to carry water to Earth.
"The reservoir of material that has the same isotopic signature as the Earth’s water is much larger in our solar system than we had previously assumed," astronomer Ted Bergin, with the University of Michigan, told Discovery News.
The studies were made in October and November 2010 as Hartley 2 passed closely by Earth with the European Space Agency's Herschel space telescope. The research is reported in this week's Nature.