Rosetta Finds Strange Water, Fueling Ocean Origin Debates

An analysis of water vapors from comet 67P/Churyumov-Gerasimenko, the quarry of the Rosetta Spacecraft and its history-making Philae lander, has revealed that its water is not at all like Earth's. This revelation casts some serious doubt on one theory of how our oceans formed, and raises many new questions.

It has long been argued by leading astronomical experts that when our planet first formed 4.6 billion years ago, it was far too hot to keep whatever water was formed - literally boiling off the surface and releasing the vapors back into space.

So where could our oceans have come from? One theory is that later in its juvenile years, a cooling Earth was bombarded with a wave of asteroids and comets - an ancient delivery system for the ice and water that would eventually turn our planet blue.

Being giant balls of ice and dust, comets in particular were popular candidates to be the main water deliverymen, especially after analysis of water properties from the comet 103P/Hartley 2 was found to match the composition of Earth's waters back in 2011.

According to the European Space Agency (ESA), comet 67P is what scientists call a "Jupiter-family comet," indicating that it came from the same part of the solar system as 103P. This region - in the Kuiper Belt beyond Neptune - occasionally becomes disrupted, throwing comets that date back to the birth of the solar system into wide orbits that slingshot around the heavy gravity of Jupiter and head between Earth and Mars.

It was suspected then, that all Kuiper Belt comets would contain Earth-like water. However, Rosetta has proven that this is not the case.

Back in August, when Rosetta first finally caught up to its quarry, the space probe immediately began gathering samples of the water vapor the comet leaks as it drifted closer and closer to the Sun in a slowly spiraling orbit.

Now, four months later, the results have come in, with the analysis of this water published in the peer-reviewed journal Science.

According to the study, the deuterium/hydrogen ratio measured by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) is more than three times greater than that of Earth's oceans. This likewise makes it very unlike the water found on 103P. (Scroll to read on...)

"This surprising finding could indicate a diverse origin for the Jupiter-family comets - perhaps they formed over a wider range of distances in the young Solar System than we previously thought," Kathrin Altwegg, principal investigator for ROSINA and lead author of the study, said in a statement.

"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," she added.

This revelation also supports claims made back in October that our oceans did not form from the impacts of large comets and asteroids, but instead from a heavy "rain" of water-laden meteorites just large enough to pierce Earth's fledgling atmosphere 14 million years after the birth of our solar system.

A study published in Science at the time revealed that the deuterium and hydrogen ratio of the 14-million-year-old asteroid 4-Vesta matches Earth's ocean signature to a T. However, more samples of the same nature will need to be found to confirm this theory.

Still, many experts will admit that this does make the most sense. If Earth was too hot for water in its youngest years, the impacts of asteroids and comets like 67P may have helped cool it (similar to beating a fire), but the resulting blasts would have likely thrown water particles right back into space.

"Surface water as it exists on our planet today, must have come much, much later - hundreds of millions of years later," geologist Horst Marschall said in a statement.

One of the ESA's leading Rosetta project scientists, Matt Taylor, added Wednesday that this is one of the best parts about the Rosetta probe, as it keeps exposing new mysteries to explore.

"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," he said.

"As Rosetta continues to follow the comet on its orbit around the Sun throughout next year," Taylor continued, "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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