How exactly life got started here on Earth is a great mystery that has spawned countless scientific theories. The possibility that at least some of the vital building blocks for life were delivered by comets is one such line of thinking, and is also one of the reasons the Rosetta spacecraft has been circling comet 67P/Churyumov-Gerasimenko since 2014. The probe has now discovered evidence that key amino acids and molecules do indeed exist in the comet's atmosphere, throwing further weight behind the idea that these icy trailblazers can double as life-giving space couriers.
Back in 2009, NASA announced for the first time that amino acids could be found on comets. Often described as the building blocks of life, amino acids are compounds that contain things like carbon, oxygen and form the basis of proteins. After having the Stardust probe track the comet Wild 2 in 2004, NASA scientists gathered samples of its tail and after years of analysis announced the discovery of glycine, the simplest of amino acids.
But some doubt was cast on these claims when it emerged that the samples may have become contaminated on their return to Earth. There can be no such reservations with the European Space Agency's latest announcement, however, as Rosetta carries out the analysis onboard with its Rosina Orbiter Spectrometer and beams the results back to Earth.
"This is the first unambiguous detection of glycine at a comet," says Kathrin Altwegg, principal investigator of the ROSINA instrument and lead author of the paper. "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."
Glycine is difficult to detect because it only switches from a solid to gas state at temperatures nearing 150° C (302° F). Because of the low temperatures at the core of the comet, the scientists instead study its fuzzy atmosphere that forms as it heats up while heading toward the Sun. The team made its detections in October 2014 and in March 2015, before the comet reached its closest point to the Sun in August 2015.
Here the scientists also discovered phosphorous, which is a key part of cell membranes, the structural framework of DNA and plays a role in moving chemical energy within cells.
"There is still a lot of uncertainty regarding the chemistry on early Earth and there is of course a huge evolutionary gap to fill between the delivery of these ingredients via cometary impacts and life taking hold," says co-author Hervé Cottin. "But the important point is that comets have not really changed in 4.5 billion years: 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."
The research was published in the journal Science Advances.
Source: European Space Agency