We used to believe that comets are the reason for water on Earth, but the Rosetta Mission has proved that theory incorrect. Asteroids might actually be the reason we are "the blue planet," according to Space.com.
Before Rosetta started orbiting Comet 67P/C-G in August, it used ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis), which analyzed gases surrounding the comet. The heavy water molecules of the "dirty snowballs," make it unlikely that the water from comets formed our planet.
A typical water molecule is comprised of two hydrogen atoms and one oxygen atom. Heavy water is made of one hydrogen atom, one oxygen atom and on deuterium atom. Deuterium is similar to hydrogen, except it has an extra neutron in its nucleus (whereas hydrogen has only one proton in its center).
In 1986, the European Space Agency's (ESA) probe, Giotto, passed by Halley's Comet and discovered that the comet had double the amount of heavy water as Earth has normal water. Halley's Comet hailed from the Oort Cloud, so Giotto ruled out comets from the Oort Cloud as sources of Earth's water.
But the Oort Cloud isn't the only comet-producer in the galaxy. The Kuiper Belt, which is closer to Earth than the Oort Cloud, was studied by ESA's Herschel Space Observatory. Scientists found that Comet 103P/Hartley 2 had a deuterium-to-hydrogen ratio "that matched terrestrial water's perfectly," according to Space.com.
Comet 67P is from the Kuiper Belt, so obviously, not all comets are the same. "This probably rules out Kuiper Belt comets from bringing water to Earth," said Kathrin Altwegg, principal investigator for the ROSINA mass spectrometer on Rosetta from the University of Bern in Switzerland.
So, the task of terrestrial water toting probably fell on asteroids... or, rather, from them.
"Today's asteroids have very little water - that's clear," Altwegg said. "But that was probably not always the case. During the Late Heavy Bombardment 3.8 billion years ago, at that time, asteroids could have had much more water than they could now."
Today's asteroids "have stayed in the vicinity of the sun for 4.6 billion years," Altwegg said.
"They've lost water due to the sun, due to heat. But to start with, they might have had much more water than they have now."
The new comet findings are published in the journal Science.
