“This is the first unambiguous detection of glycine at a comet,” Kathrin Altwegg, lead author of a paper on the molecules published Friday in Science Advances, said in a statement. Glycine is the simplest of the amino acids — the molecules that come together to form proteins — and it's the only one known to form in the absence of liquid water.
This sweet-tasting combination of carbon, oxygen, hydrogen and nitrogen was sniffed out of the dusty cloud around the comet using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), which Altwegg oversees. The team had worried that any glycine present on the comet would be locked away in its icy core, because the amino acid doesn't turn into gas until things get quite hot. But ROSINA successfully detected molecules released into the comet's coma, or gas cloud, as the core was baked during its closest approach of the sun last August.
“At the same time, we also detected certain other organic molecules that can be precursors to glycine, hinting at the possible ways in which it may have formed," Altwegg added. She believes that the glycine was formed and locked away in ice back in the days before our sun even existed, when a nebula created by the collapse of a giant molecular cloud was busy churning out the building blocks of our would-be star. Because of its small size and far-flung orbit, 67P is brilliant at staying cool and keeping molecules like these intact and pristine for billions of years. That's why scientists are studying it — to get a glimpse of the ingredients that were present when our solar system's primordial soup first started simmering.
It's not the first time glycine has been found on a comet — that was in 2006, when scientists working on NASA's Stardust mission extracted the molecule from samples of Comet Wild-2 – but it's the first time it's been detected using instruments out in space. Because the detection was made without samples being returned to Earth and handled by humans, the likelihood of contamination with Earth's own glycine is much lower. Now that the molecule has been spotted in two different comets, scientists can start to hope that its presence in these icy bodies is commonplace.
The Rosetta scientists also announced the detection of phosphorus, a mineral vital for the construction of cells and DNA. When combined with previous discoveries of oxygen, alcohol and sugar compounds on the comet, these finds make 67P look like the planetary equivalent of a box of cake mix: Just add water, heat and the right environment, and life can start to emerge.
“The beauty of it is that now we see all the ingredients which are needed for life in one place,” Altwegg told New Scientist.
That supports the idea that comets delivered an evolutionary starter kit like the one on 67P to a prebiotic Earth.
"The multitude of organic molecules already identified by ROSINA, now joined by the exciting confirmation of fundamental ingredients like glycine and phosphorus, confirms our idea that comets have the potential to deliver key molecules for prebiotic chemistry," Matt Taylor, Rosetta project scientist, told Agence France-Presse.
If this is really how Earth got started down the path to intelligent life, that's great news in the hunt for aliens. For now, we have only a sample size of two, but with any luck, future cometary research will confirm that glycine (and other pre-life molecules) are abundant on many comets. We already know that comet and asteroid impacts are common in the grand scheme of things, especially in the hectic, crowded early days of a new solar system. So it follows that the kind of impact that theoretically sparked life on Earth could be common in other star systems.
"Amino acids are everywhere, and life could possibly also start in many places in the universe," Altwegg told Reuters.
The Rosetta orbiter is set to end its two-year mission in September, when it will crash-land on comet 67P's dusty surface.