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During Earth’s early years, comets and asteroids pummeled the planet and brought water and organic molecules with them. Billions of years ago, Earth was much warmer and much drier. A molten world tends to make having water a problem.
One popular theory is that as Earth cooled down, comets (which are pretty much water ice and rock) seeded Earth with water and other necessary ingredients for life to grab hold. A discovery by the Rosetta probe orbiting Comet 67P throws more weight behind this theory.
Spectrum showing glycine detection in 2015. Credit: ESA
This isn’t the first time glycine has been detected. In 2006, NASA’s Stardust mission brought samples back from Comet Wild-2. Within these samples were hints of glycine. Why is Rosetta’s discovery making news? Because when those samples were brought back to Earth, scientists couldn’t rule out terrestrial contamination.
Rosetta’s measurements come directly from the coma of the comet. “This is the first unambiguous detection of glycine at a comet,” says Kathrin Altwegg, lead author and the principal investigator of the ROSINA instrument aboard Rosetta.
This wasn’t a one-off detection either. Rosetta detected glycine multiple times at varying distances. The first detection came in October 2014 when the spacecraft was 10 kilometers from the comet. Glycine was spotted again during a March 2015 flyby at distances ranging from 15 kilometers to 30 kilometers.
As Comet 67P reached its closest point to the sun, Rosetta backed off to more than 200 kilometers from the comet’s nucleus. Even at this distance, the spacecraft detected glycine among all the dust making up the comet’s coma.
“We see a strong link between glycine and dust, suggesting that it is probably released perhaps with other volatiles from the icy mantles of the dust grains once they have warmed up in the coma,” says Altwegg.
Altwegg goes on to describe just how strong this link between glycine and dust is.
“Glycine is the only amino acid that is known to be able to form without liquid water, and the fact we see it with the precursor molecules and dust suggests it is formed within interstellar icy dust grains or by the ultraviolet irradiation of ice, before becoming bound up and conserved in the comet for billions of years,” says Altwegg.
The discovery doesn’t stop at glycine. Phosphorus, a key ingredient of DNA, was also detected.
A 4.5 billion year old snapshot
Rosetta’s discovery doesn’t mean the comet theory is a lock. There’s a healthy gap between comets hitting Earth and life flourishing that we still can’t explain.
What comets like 67P do is give us a snapshot of what things looked like 4.5 billion years ago. “They grant us direct access to some of the ingredients that likely ended up in the prebiotic soup that eventually resulted in the origin of life on Earth,” says co-author Hervé Cottin.
Matt Taylor, ESA’s Rosetta project scientist, is thrilled with the spacecraft hitting one of its key goals. “The multitude of organic molecules already identified by Rosetta, now joined by the exciting confirmation of fundamental ingredients like glycine and phosphorous, confirms our idea that comets have the potential to deliver key molecules for prebiotic chemistry.”
What is Rosetta doing today?
The spacecraft continues to fly around the comet snapping pictures and gathering data. Some of the latest images were captured at distances of just 7 kilometers. Check out the OSIRIS Image of the Day website for more stunning images.
Rosetta’s mission will come to an end soon. Right now, the Rosetta team expects the mission to wrap up in September 2016. Funding will run out by then, and the spacecraft won’t receive enough sunlight to remain powered. It could shut down and hibernate, but the extreme cold would likely damage it too much to power back up.