Deciphering the Rosetta Stone: 67P

In 1799, French soldiers uncovered a stone slab near Rosetta, Egypt, during Napoleon's Campaign in Egypt and Syria. This stone, called the Rosetta Stone, was covered with three versions of text—two using ancient Egyptian scripts and the other ancient Greek. The Rosetta Stone, and later the Philae Obelisk, was used to decipher Egyptian hieroglyphs thus unlocking Ancient Egyptian literature and culture. About 200 years later, a new campaign bearing the names Rosetta and Philae was launched, but this time it would unlock the history of the solar system.

This past term, I took Cosmochemistry (Ge/Ch 128), which looked at the evolution of chemistry since the earliest stages of star formation and how it culminated into what supports life as we know it. The course was taught in the context of the Drake Equation, a probabilistic argument for the number of advanced civilizations in the Milky Way galaxy. For my final project, I wrote about and gave a presentation on the Rosetta mission to comet 67P/Churyumov-Gerasimenko.

In my final paper, I discussed the Rosetta spacecraft that embarked on a ten-year journey to comet 67P. Not only was the Rosetta mission the first in which a spacecraft orbited a comet, but it was also the first time a comet would be directly observed as it was warmed by the Sun.

The Rosetta mission gave us numerous physical and chemical findings, including observations of water, molecular oxygen, and organics. The water composition (specifically, the D/H ratio or "heavy water" to "light water" ratio) in 67P showed that it is unlikely comets were the primary source of Earth's ocean waters. It also showed that 67P, while currently having a short orbit that extends just past Jupiter's orbit, probably formed further out, perhaps in the Kuiper Belt (where Pluto is). Molecular oxygen, or O₂, was detected in a comet for the first time with the Rosetta mission. The presence of O₂ was unexpected but is thought to be either primordial O₂ trapped in 67P's water ice 4.5 billion years ago or perhaps a more contemporary phenomenon resulting from the breakdown of water into hydrogen gas and oxygen gas. Finally, numerous organic compounds were detected in the coma of 67P, including glycine, the simplest amino acid. This supports the idea that life's building blocks could have been transported to the early Earth by comets. While the Rosetta mission gave us some insights into 67P and comets generally, it also raised many questions and showed that we have much to learn about cometary chemistry.

You can learn more about these ideas by reading my final paper or watching my practice run of my talk (embedded below).