In our never ending search for answers to the origins of the earth we sent the Rosetta spacecraft to the comet 67P/Churyumov-Gerasimenko and the data that has been sent back from it has been invaluable to understanding the formation of planets. The Rosetta has sent back data that has shown water content present on the surface of the comet which has brought up the century old question that “Are comets responsible for the presence of water on the earth ?”
The advanced instrument called ROSINA on the Rosetta has been responsible for looking at chemical compounds present on the comet, the water that was discovered on the comet has different molecular make up than the water found on earths oceans. The deuterium-to-hydrogen ratio in the water molecules on the comet throws a hitch into the theory that comets from Comet 67P/C-G’s region of space brought water to the Earth not long after the solar system formed.
Kathrin Altwegg the principal investigator for ROSINA says that if even a small number of comets like 67P/C-G impacted Earth in the early days of the solar system, it still would have greatly changed the molecular composition of the planet’s water today. Therefore, it seems unlikely that these kinds of comets brought water to Earth. Altwegg thinks it’s more probable that asteroids brought water to Earth.
Even though the asteroids of today are dry, rocky bodies now, it’s possible that these space rocks were water-rich during the early days of the solar system. Altwegg says that asteroids may have bombarded the Earth about 800 million years after the formation of the solar system, bringing water to the early planet once it cooled after formation.