Drop in the ocean? Scientists link comet ice to Earth’s water

Published on Thursday 6 October 2011 00:25

WATER with properties similar to that found in our oceans has been discovered in a comet for the first time.

The discovery is the first evidence to support a theory that water first arrived on Earth when comets smashed onto our planet’s surface.

When scientists analysed the water in a comet called Hartley 2 they were excited to find it had the same chemical composition as our oceans.

The new evidence could help solve the mystery of where our water came from, a question that has puzzled astronomers for decades.

It is no surprise water was present in the comet studied by the international team of scientists – comets are largely made of ice and their distinctive tails are formed by evaporating water.

However, when infrared equipment on the European Space Agency’s Herschel Space Observatory was used to measure the composition of the water they discovered it had so-called “heavy hydrogen” atoms, just like our oceans.

Professor Ted Bergin, an astronomer for the University of Michigan involved in the research, said he was “surprised” by the results.

He added: “Life would not exist on Earth without liquid water, and so the questions of how and when the oceans got here is a fundamental one. It’s a big puzzle and these new findings are an important piece.”

The water in Hartley 2 had a similar proportion of deuterium, or heavy hydrogen, as the water in our oceans. A deuterium atom is a hydrogen atom with an extra neutron in its nucleus.

Six other comets measured by the infrared instrument on the space observatory had water of a very different composition.

The astronomers think Hartley 2 was born in a different part of the solar system, probably in an area known as the Kuiper belt, which starts near Pluto, whereas the other six were born much further away.

Many scientists believe Earth’s oceans formed about eight million years after the planet itself. However, the source of Earth’s oceans has been a subject for considerable debate.

“The results show that the amount of material out there that could have contributed to Earth’s oceans is perhaps larger than we thought,” Prof Bergin said. However, he told The Scotsman: “It’s not definitive. It doesn’t prove Earth got its water from comets but it shows that it’s possible there could have been some contribution from comets.”

The most popular theory among astronomers is that asteroids and comets smashed into Earth and deposited their water.

However, another theory is that water formed with the Earth. The material out of which the Earth formed trapped small amounts of water molecules, which later became oceans.

Professor John Brown, Astronomer Royal for Scotland, said he thought the new research was interesting, but not conclusive.

“There’s still an open question and a puzzle,” he said. It’s a very interesting step forward.

“It’s not at all surprising to see something that appears to be water in a comet. Everyone knew that already. They are basically gigantic dirty snowballs full of dirt and ice. But the composition of the water is the interesting thing. That’s the breakthrough.”

The research is published online today in Nature.

Herschel is the largest infrared space telescope ever launched. It is named after the British astronomer Sir Frederick William Herschel (1738-1822), who in 1800 discovered infrared radiation while studying the Sun. He won fame for discovering the planet Uranus.