What Philae Did During Its 60 Hours on a Comet

The simple reason why the lander was sent all the way to a comet was to do chemistry that can explain the origin of life

Editor's note: The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.

The drama of Philaesslow fall,bounceandunfortunate slide into hibernationwas one of the most thrilling science stories of a generation. But what in its short 60 hours of life on Comet 67P did it achieve?

The short answer is analytical chemistry.

Philaes payload included three instruments that are quite common in chemistry labs, but when deployed on a comet could answer questions about the origins of the solar system and life itself.

Right- or left-handed life Four billion years ago the solar system was an unsettled place. Earth was undergoing heavy bombardment by asteroids and comets. This continuous shower may have delivered a significant amount of water to our planet. But the comets werent just dirty snowballs. A third of their contents was probably complex organic (that is, carbon-based) molecules. These compounds may well have triggered the chemistry that led to life on our planet.

One of Philaes goals is to provide evidence that the organic chemicals on a comet are sufficiently similar to the building blocks of life to support the comet impact theory forabiogenesis. A key factor is whether Comet 67P (and by extension other comets) contain predominantly right- or left-handed molecules.

Many molecules come in one of two forms, known as stereoisomers, which chemists designate as left- or right-handed. These two forms are identical apart from the fact that they are mirror images of each other.

Your hands are a perfect analogy. Structurally, they are the same except for the fact that you cant superimpose one on the other. And so it is with stereoisomers.

Strangely, life on Earth is based entirely on left-handed molecules. It is perfectly possible to make the right-handed versions, but life just doesnt. Where this preference for left-handedness comes from is amystery. One theory is that the bias came from within the chemistry of comets. In the comets, right-handed molecules may have been preferentially destroyed by a combination of sunlight (to provide energy to trigger chemical reactions) and liquid water (with which the organic compounds could react).

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What Philae Did During Its 60 Hours on a Comet