Finding water on comet 67P/Churyumov-Gerasimenko comes as no surprise. Comets have been known to carry large patches of ice on them. What does come as a surprise, however, is the general makeup of this water. It is a finding that turns previously held beliefs on their head.
The makeup of the water found on comet 67p is unlike anything found on Earth, containing about three times more deuterium, a heavy form of hydrogen. Why is this significant? For a long time scientists have held the belief that most of Earth’s water came from comets slamming into our planet’s surface in its early stages of development.
According to Kathrin Altwegg at the University of Bern, water may have arrived on Earth via asteroids rather than ferried here by comets. “Today asteroids have very limited water, that’s clear. But that was probably not always the case,” Altwegg said. “In the earliest period of the solar system, 3.8 billion years ago, asteroids are thought to have crashed into Earth regularly in what is called the late heavy bombardment. At that time, asteroids could well have had much more water than they have today.”
This discovery was made when the Rosetta spacecraft measured the water coming off the comet as it flew around the body. The water’s strange composition suggests that our theory on comets bringing water to Earth is too simplistic. Altwegg told New Science magazine that, “in the end, Earth’s oceans are probably a mix of many things.”
The plan is for the Philae lander to resume its measurement of the comets surface to confirm the findings accuracy; however, the Philae lander is in a dark spot on the comet, causing its batteries to run out of power. Matt Taylor, Rosetta project scientist, says that “once we get the identification of where the lander is, it will give us a better fix on what we believe the illumination conditions are and a better idea of when we would expect the lander to have sufficient illumination to be able to start charging its batteries and come back online.”
If-and-when the Philae lander can come back online a British instrument called Ptolemy can assist in verifying the findings. Yet another option is for Rosetta to fly through the jets of debris that will grow as the comet closes in on the sun.
As an added note, here is a size comparison to just how big comet 67p actually is: