The Big Event, Blog Post 3.5

Although the debate about where Earth's water may have come from dates back to the initial studies of Geologic Time, there is a much more recent event that helped to reignite the controversy. In late 2010, the comet 103/Hartley 2 passed close enough to Earth to be seen by astronomers. The comet looked oblong and thin around the middle; a bit like a dumbbell. Using spectrum analysis of the comet from NASA's EPOXI probe, scientists discovered that the deuterium (hydrogen atom plus one neutron) to regular hydrogen ratio (D-H ratio) in water vapor on comet Hartley 2 was very similar to the D-H ratio of water here on Earth. This discovery reignited the debate over Earth's water.

Fast forward now to 2014. The Rosetta Spacecraft, launched by a powerful and ear-splitting rocket back in 2004, begins to approach the comet 67P/Churyumov-Gerasimenko (67P/C-G). As the spacecraft approaches, it detaches a lander to the surface of the comet. The lander makes contact with rough, hard, and rocky ground. Not long after, the lander begins to collect samples of rock and ice from the comet.

The data from the lander eventually revealed that comet 67P/C-G had a D-H ratio much higher than water here on Earth. To many scientists, this discovery signified that comets probably did not bring water to the early Earth. However, the debate still raged on. After all, comet Hartley 2 had water ice very similar to the water on Earth.

The analysis of these two comets has created 3 distinct stakeholders in the controversy: Those who believe that volcanic action or other Earth process are responsible for much of the water on Earth, those who believe, regardless of the data from Rosetta, that comets did bring much of Earth's water to the planet, and those who believe that instead of comets other celestial bodies, such as asteroids, seeded Earth with most of it's early water.

DLR German Aerospace Center. Landung von Philae auf dem Kometen. January 14th, 2014 via Flickr. Attribution license.