DARMSTADT, Germany, Dec. 12 (UPI) — The European Space Agency’s Rosetta probe was able to capture and analyze water vapor trailing from comet 67P/Churyumov-Gerasimenko using its ROSINA instrument suite. The evidence, newly parsed by scientists back at mission headquarters, suggests Earth’s oceans came from older asteroids.
Most scientists believe infant Earth was too hot to host water. Any lingering H2O, they say, would have been vaporized immediately. Instead, planet formation experts suggest icy asteroids (and maybe comets, too) supplied a slightly cooler adolescent Earth with its water.
To confirm their suspicions, scientists have long been trying to match the chemical signature of Earth’s water to the molecules of the outer solar system. The chemical signature is found inside the hydrogen atoms of the ocean’s H2O molecules. Most hydrogen atoms have a single proton in their nucleus, but occasionally there’s a deuterium — a distinct hydrogen isotope with one proton and one neutron in the nucleus. In Earth’s oceans, the ratio of deuterium to hydrogen (the D/H ratio) is roughly three in 20,000.
The ratio detected in the vapors trailing off 67P/Churyumov-Gerasimenko is three times the D/H ratio of Earth’s water. But scientists say the discovery doesn’t diminish the overall theory about how Earth got its water. Previous research has already isolated cosmic dust with matching D/H signatures.
Instead, the new data confirms suspicions that Earth’s water came from asteroids, not comets — ones from the Asteroid Belt that runs between Mars and Jupiter. Comets and asteroids are similar. Both are larger chunks of space material, unaffiliated with any planet or moon, that rotate about the sun — but with orbits that can frequently be manipulated and rerouted. But where asteroids are mostly rock, comets are primarily ice and dust.
Comets like 67P/Churyumov-Gerasimenko are part of the Jupiter-family comets, which formed farther out and are occasionally thrown off course and pulled into a closer orbit by the gravity of Jupiter. They have more water, but their path from the Oort cloud of the outer solar system to a collision with Earth is more convoluted.
“Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans,” Kathrin Altwegg, principal investigator for the probes ROSINA instruments, said in a press release.
Altwegg is the lead author of the new study using Rosetta’s water vapor analysis data. The paper was published this week in the journal Science.
“We knew that Rosetta’s in situ analysis of this comet was always going to throw up surprises for the bigger picture of Solar System science, and this outstanding observation certainly adds fuel to the debate about the origin of Earth’s water,” Matt Taylor, ESA’s Rosetta project scientist, explained.
“As Rosetta continues to follow the comet on its orbit around the Sun throughout next year, we’ll be keeping a close watch on how it evolves and behaves, which will give us unique insight into the mysterious world of comets and their contribution to our understanding of the evolution of the Solar System.”
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