After an arduous ten year journey throughout some tough terrain of space, the European Space Agency's (ESA) Rosetta mission set records this past summer for being the first spacecraft to orbit a comet in mid-flight. And while many expected the mission to reveal a bit more insight into the behavior and composition of comets from the outer edges of our solar system, no one expected to learn exactly how Earth came to be so unique and the perfect host to life, only three planets away from our sun.
In a study published this Wednesday, Dec 10, in the journal Science, researchers from the ESA reveal that the Rosetta mission's ROSINA instrument has captured water residue released by the comet 67P/Churyumov-Gerasimenko, and it turns out that it contains a very different chemical fingerprint than that of water on Earth.
"The provenance of water and organic compounds on the Earth and other terrestrial planets has been discussed for a long time without reaching a consensus" lead researcher of the study, Kathrin Altwegg from the University of Bern says.
As part of the mystery, researchers involved with Rosetta had hoped that the mission may reveal how the Earth has become inundated with H2O, however, the new data and chemical signatures identified by ROSINA indicate that the Earth likely inherited its water from an asteroid, rather than from primitive comets.
"When Earth was born 4.6 billion years ago, it was too hot to sustain liquid water on its surface" Altwegg says. "Some of Earth's original water from those early years might have been preserved in its crust and at the poles, but at least some of the water that fills our oceans today probably came from extraterrestrial sources."
Though many know water on Earth to be H2O, it so happens that roughly 3 out of every 10,000 water molecules are "heavier" than the rest. This "heavy water" occurs when one hydrogen bonds with one deuterium and an oxygen, and it is best known as HDO. The Deuterium isotope of Hydrogen not only makes the overall molecule a bit heavier, but also allows researchers to trace similar sources of water based on the HDO presence. And while researchers once hoped that the comets of the Kuiper Belt would hold the answer to the origins of our Earth's water, Comet 67P/Churyumov-Gerasimenko revealed a high HDO that concluded comets were an unlikely source for our particular brand of H2O.
"It is probably one of the highest ever measured" Altwegg says. In fact, due to the abnormally high presence of HDO, Altwegg was also able to indicate the invalidity of past results on other comets, whose HDO values were much more similar to those of Earth. "Because Comet 67P/Churyumov-Gerasimenko is so high, you would only need a fraction of comets like it to spoil other results."
So, where do they think that our water came from originally? Well, this much is clear: it likely came from an extraterrestrial source, and the likely culprits may include meteorites and asteroids that once fell to Earth, giving us water and a distinct cosmic footprint in the process.
