Where Did Oceans Come From? A Comet Has the Answer

Touchdown! In November, a washing-machine-sized probe landed on the surface of a 2.5-mile-long comet, comet 67P/Churyumov–Gerasimenko. It's the first probe to land successfully on a comet, after NASA's Deep Impact smashed a spacecraft (intentionally) into one to discover what materials a comet is made of. New findings from the comet 67P's surface have been published, revealing an interesting bit about the origins of Earth's oceans. Scientists also found that the comet weighs so little, it could float on water.

Scientists first thought that water was brought to Earth by comets like comet 67P. While most theorists agree that terrestrial water was delivered at a later stage in the planet's evolution, the messenger is still unknown. It could be one of three possibilities: asteroid-like from near Jupiter, comets formed near Neptune, or Kuiper belt comets. Researchers can test which comets delivered water to Earth by measuring its levels of deuterium, a heavier form of hydrogen. The water vapor on comet 67P had water vapor that was too different from Earth's. "The bigger picture of solar-system science, and this outstanding observation, certainly fuel the debate as to where Earth got its water," said Matt Taylor, the project's scientist.

The probe currently aboard comet 67P is controlled by the European Space Agency, and its name is the Philae lander. Philae left Earth nearly 10 years ago aboard the Rosetta orbiter, which circled the Earth three times, using the planet's gravity to propel Rosetta into space and catch comet 67P. Many years later, the comet landing took a grueling seven hours to complete. After separating from its parent spacecraft, Rosetta, the Philae lander slowly descended before touching the comet's surface and immediately firing harpoons to anchor itself to the extraterrestrial landscape.

Both orbiter spacecraft and lander are part of the Rosetta mission, which aims to research how the solar system was formed by investigating the comet, one of the oldest and primordial of heavenly bodies. Philae will stay put on the comet for two months, to the point at which the comet is closest to the sun. Few things could be more fascinating than watching humanity land a robot that's very, very far away! Relive the live stream here.