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Water in space

October 24, 2011

ESA's Hershel Space Observatory has helped scientists identify a massive water source around a nearby star - a find that could shed light on how our oceans were formed.

An illustration of the cold water vapor detected around the star TW Hydrae
An illustration of the cold water vapor detected around the star TW HydraeImage: Tim Pyle CalTech

Researchers generally agree that the world's oceans contain more than 1.3 billion cubic kilometers of water. Multiply that by several thousand and you'll get the amount of water that astronomers detected in space, just 175 light years away.

This huge reservoir belongs to the young star TW Hydrae - and astronomers believe it's not the only star in the universe with such ample supplies of water.

The team, led by researchers from Leiden University in the Netherlands, hopes to be able to observe three more watery disks like this over the next two years.

In a paper published last Friday in the journal Science, astronomers described what they saw via the Hershel telescope in space. With the help of super-sensitive infrared technology, they were able to detect a cloud of cold water vapor around TW Hydrae.

Yet even more interesting was what they couldn't see: the disk of vapor indicates there's also a huge reservoir of water present, "sufficient to form several thousand Earth oceans' worth of icy bodies," the paper says.

Carsten Dominik, an astronomy professor at the University of Amsterdam who co-authored the report, offered a terrestrial comparison: "If you see an iceberg, you only see a small fraction," he told Deutsche Welle.

The same concept applies in space. The water stores in this rotating, protoplanetary disk are actually located deep beneath its surface.

Researchers say this water produces icy comets capable of smashing into new worlds and bringing with them enough water to form oceans - making the star itself a solar system in the making.

A satellite view of Earth
Astronomers say the water reservoir is equivalent to several thousand oceansImage: picture alliance / dpa

When particles collide

A number of basic questions came to bear in the team's research. Ewine van Dishoeck, a professor at Leiden University and the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, listed two of them: where did the water in the ocean and our bodies come from? And how were they transmitted to a planet like our Earth?

"We know that planets are being formed in these swirling disks of gas and dust around stars, and one of the questions has always been, what is the reservoir of water that is available in these disks?" she told Deutsche Welle.

The dust particles present in the cloud are much like grains of sand on a beach - just some 10,000 times smaller. Yet eventually, these bits collide and grow bigger and bigger, from a single square kilometer to an entire planet.

But the disk doesn't just contain dust - it also contains water molecules. And the farther the distance from the star itself, the colder the water is in the disk.

Van Dishoeck said scientists had already noticed the presence of hot water closer to the center, "but that's not necessarily the water that makes it to a new planetary system," she said. The HIFI, or Heterodyne Instrument for Far-Infrared, on the European Space Agency observatory allowed them to see the colder water on the edge of the disk.

Van Dishoeck described the icy water as what is "most likely the feeding zone for the atmospheres of new planets," from Earth-like bodies to so-called "waterworlds," or giant planets like Jupiter.

An undated artist's impression of asteroid Steins
Asteroids containing water could have collided to bring oceans to EarthImage: picture-alliance/dpa

Thanks, technology

The team gave ample credit to the capacity of the HIDI device itself. The instrument was able to detect the water vapor from the reservoir via ultraviolet photons, which liberate the vapor upon contact with the ice.

"When that happens, then they can actually emit radiation that we can detect," said Dominik. "We can see that there is a certain amount of these molecules flying around emitting radiation," he added.

The ice particles act much like the bits of dust in the cloud: They swirl around, "and every now and then, they collide and just stick together," he said. As more collisions occur, more icy comets are formed.

According to one theory of how the Earth's oceans formed, these comets serve as the vehicles to transmit water - mostly in the form of ice - to new worlds. Some astronomers, meanwhile, favor another possibility: that asteroids served as the Earth's waterboys.

"It's very likely that the water arrived on the Earth in frozen form but the question is, where exactly from," Dominik said, adding that most researchers realized that both possibilities - asteroid and icy comet - are valid.

Author: Amanda Price
Editor: Cyrus Farivar