A study released on Wednesday shows early results from Europe's Rosetta spacecraft challenge a theory that comets delivered water to early Earth.
Chemical analysis of water coming from Comet 67P/Churyumov-Gerasimenko shows it has three times more deuterium, or an atomic variation of regular hydrogen, as hydrogen in water molecules on Earth, said Rosetta scientist Kathrin Altwegg, with the University of Bern, according to Reuters.
Rosetta has been orbiting the comet since August.
Water is made of two hydrogen atoms bonded with one oxygen atom. On Earth, three in three in 10,000 water molecules have the heavy hydrogen isotope deuterium.
Altwegg added that the finding eliminates comets as the source of Earth's water, and likely its organics as well, according to the study.
Both carbon compounds and water were needed for life to evolve.
"Asteroids could well have had much more water than they have today," Altwegg said. "They have just lived in the vicinity of the sun for 4.6 billion years."
Click here to read the full study.
Comet 67P comes from the Kuiper Belt region of the solar system, found past Neptune's orbit 30 to 40 times farther from the sun than Earth, according to Reuters.
Scientists also said on Wednesday that the search for Rosetta's companion probe, Philae, continues.
Philae made a descent to the surface of the comet on Nov. 12, bounced twice and settled in what seems to be a crater. Its battery died after running through 2-1/2 days of preprogrammed science experiments.
Results of those studies have not been released yet.
Rosetta became the first spacecraft to put itself in orbit around a comet back in August. The probe will continue to accompany 67P for nearly another year.