TW Hydrae’s Snow Line Offers Insight Into Solar System Formation
July 18, 2013

TW Hydrae’s ‘Snow Line’ Offers Insight Into Solar System Formation

Brett Smith for - Your Universe Online

Astronomers at the Atacama Large Millimeter/submillimeter Array (ALMA) telescope have announced the discovery of a distant solar system's "snow line" about 175 light years away, according to a report in Science Express.

On Earth, a snow line can be seen at high altitudes, where a mountain's snowcap ends. The concept is similar in space, where a snow line forms at a certain distance from a star. Water, which has one of highest freezing points, forms the first band of snow. Further out, carbon dioxide, methane and carbon monoxide all form snow bands.

In a solar system like our own, the water snow line typically falls between the orbits of Mars and Jupiter, while a carbon monoxide snow line would be around Neptune's orbit.

The newly discovered snow line, which is around a young star called TW Hydrae, is significant because it offers a window in time back to the earlier days of our solar system. Many building blocks of life are contained within a snow line and if comets or asteroids were to transport them to a hospitable planet, it could theoretically set up favorable conditions for life.

"ALMA has given us the first real picture of a snow line around a young star, which is extremely exciting because of what it tells us about the very early period in the history of the Solar System," said report co-author Charlie Qi from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "We can now see previously hidden details about the frozen outer reaches of another planetary system similar to our own."

Snow lines are not easily found because above and below the thin region where they exist, the host star's radiation prevents ice from forming. Insular dust and gas in a solar system's central plane is necessary for carbon monoxide and other gases to cool and freeze.

To find the snow line around TW Hydrae, the astronomers searched for evidence of diazenylium, a molecule that is easily spotted by ALMA. Diazenylium is a signifier for frozen carbon monoxide because the gaseous form of the organic molecule destroys it.

ALMA's capabilities allowed the astronomers to trace the presence of diazenylium and therefore the snow line. Looking at the distribution of diazenylium essentially provides a negative image of the carbon monoxide snow surrounding TW Hydrae.

Researchers said the snow line sits exactly where conditions dictate it should - 30 times the distance between the Earth and the Sun.

"For these observations we used only 26 of ALMA's eventual full complement of 66 antennas. Indications of snow lines around other stars are already showing up in other ALMA observations, and we are convinced that future observations with the full array will reveal many more of these and provide further, exciting insights into the formation and evolution of planets. Just wait and see," concluded co-author Michiel Hogerheijde from Leiden Observatory, the Netherlands.

ALMA is operated through a partnership between European, North American and East Asian countries in conjunction with Chile, where the array is hosted.