Water in Space Does Indeed Exist

Where did Earth's water come from? That's a question astronomers and planetary scientists want to answer in great detail. Until very recently, people thought that perhaps comets supplied much of our planet's water. It's very likely that this did happen, although there's also a great deal of evidence that asteroids and other rocky bodies also brought water to our growing planet early in its history.

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Sources of Water on Planets

Earth from space showing the United States, Mexico, Central America and Cuba
Ian Cuming / Getty Images

Water escaped to the surface of the young Earth and joined whatever icy material had been deposited by comets crashing onto the landscape. How much water was brought by asteroids and comets, and how much was part of the original "pileup" of material that created Earth is still under debate.

However, astronomers now know that not all the water came from comets -- astronomers studying Comet 67P/Churyumov-Gerasinko with the Rosetta spacecraft discovered that there are tiny but important chemical differences in the water of that comet (and its siblings) and the water found on Earth. Those differences mean that comets may not have been the solar source of water on our planet. There's still a lot of work to be done to figure out exactly where all of Earth's water originated, and that's why astronomers want to understand how and where it existed when the Sun was still an infant star.

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Seeing Water Around Young Stars

The Ice Fountains of Enceladus
The ice fountains of Saturn's moon, Enceladus. Ron Miller/Stocktrek Images / Getty Images

It may surprise you to learn that there is water in space. We tend to think of it as something that exists on Earth, or may once have existed on Mars. Yet, we also know that there's water on the icy moons of Jupiter and Saturn's moon Enceladus, and of course the comets and asteroids.

Since water is found in our solar system, astronomers want to chart where it exists around other stars. Water is found mostly in the form of ice particles. However, sometimes it can be a thin cloud of water vapor, particularly close to the star. You can find water in the disks of material around newborn stars. To search for water around a hot young star, astronomers used the Atacama Large Millimeter Array radio telescopes to focus on a young star called V883 Orionis (in the Orion Nebula). It has a protoplanetary disk of material surrounding it. That region is where planetary bodies are busily forming. ALMA is particularly useful for peering into planetary nurseries

As young stars do, this one is prone to outbursts that heat up the surrounding area. Heat from a young Sun-like star normally keeps things pretty warm in its immediate vicinity -- say within about 3 astronomical units from the star. That's three times the distance between the Sun and Earth. However, during an outburst, that heated area can expand the snow line (the region where water freezes into ice) out quite far. In the case of V883, the snow line got pushed out to about 40 AU (a line equivalent to roughly the orbit of Pluto around the Sun).

As the star calms down, the snow line will likely move back in closer, creating water ice particles in a region where rocky planets are likely to grow. Water ice is important to the growth of planets. It helps rocky particles stick together, creating ever-larger rocks from smaller dust grains. Cometary bodies will eventually form, and those are important in the formation of giant planets -- as well as the creation of oceans on worlds inside the snow line. Since there's more water ice in the more distant areas of the protoplanetary disk, they play a bigger role in creating the gas and ice giants.

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Water and the Early Solar System

Water on Mars, artwork
Depiction of water on Mars 4 billion years ago. DETLEV VAN RAVENSWAAY / Getty Images

Successive Sun flare-ups happened in our own solar system some 4.5 billion years ago. As the young Sun was born, grew, and matured, it, too was temperamental from time to time. The heat from its outbursts drove ices outwards, leaving behind the material that made the planets Mercury, Venus, Earth, and Mars. They survived several heating events, as did the water locked into their rocky components. Each successive outburst drove more ice and gas out, eventually building up enough to form Jupiter, Saturn, Uranus, and Neptune. They likely formed much closer to the Sun than their present positions and migrated outwards afterward, along with a significant number of comets and the parent bodies that created Pluto and other distant dwarf planets. 

Studies like the one at V883 Orionis tell scientists not only more about the process of planet formation but also hold up a mirror to the infancy of our own solar system. The ALMA observatory enables those studies by looking for radio emissions from the region that allowed astronomers to map the distribution of material around the hot young star.