Snow Line in Infant Planetary System Reveals Secrets about the Formation of Planets and Comets

For the first time a snow line has been imaged in a far off infantry planetary system that offers clues about the formation of planets and comets. The snow line was observed around the sun-like star, TW hydrae, which is a young star located at a distance of 175 light years from Earth.

The Atacama Large Millimeter/submillimeter Array (ALMA) was used by astronomers to take images of the snow line in the far off infant planetary system.

Snow lines are formed at high altitudes on mountain peaks when the temperature drops converting the moisture in the air into snow. Snow lines in the planetary system also form in a similar way, although at a much larger scale compared to mountains on Earth.

In an emerging planetary system, the temperature at the center of the star is warmer. The temperature falls as the galactic dust moves away from the star, water freezes and the snow line forms. Greater the distance from the star, more the numbers of molecules react as the temperature drops, turning to snow, reports Nature World News.

Carbon monoxide, methane and carbon dioxide all turn into a form of snow and these different types of snow turn the galactic dust sticky and play a crucial role in preventing the dust from breaking up in collisions thereby permitting them to become the crucial building blocks of planets and comets.

The astronomers also believe that this snow doubles the amount of solid matter available and enhances the planetary formation process. Apart from this, they state that each of this elemental snow line like water, methane, carbon monoxide and carbon dioxide may be tied to formation of particular types of planets. For a sun like solar system, water snow line would correspond to a distance between the orbits of Mars and Jupiter, and an elemental snow line like carbon monoxide would correspond to the orbit of Neptune.

But the elemental snow line of carbon monoxide identified by ALMA is the first glimpse seen around TW Hydrae, which astronomers believe shares similar characteristics to the Solar System when it was few million years old.

"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 Chunhua "Charlie" Qi (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA), one of the two lead authors of the paper. "We can now see previously hidden details about the frozen outer reaches of another solar system similar to our own."

The researchers were more interested in the carbon monoxide snow line because carbon monoxide is required for the formation of methanol,a building block of more complex organic molecules that are necessary for life. These researchers believe that if these comets carried these molecules to newly forming planets like Earth then maybe they carried with them elements necessary to sustain life.

Till date, snow lines have never been imaged directly as they always form in a narrow central plane of a protoplanetary disc, which makes it difficult to spot them. The star's radiation also prevents the formation of snow lines above and below the narrow region. But this time the astronomers were successful in locating the snow formation. Since snow cannot be observed directly they looked for the presence of a molecule called 'diazenylium'.

Diazenylium shines brightly in the millimeter portion of the spectrum said the researchers, and is easily destroyed in the presence of carbon monoxide and hence, it is visible where carbon monoxide turns into snow and can no longer destroy it.

For the astronomers the key to finding carbon monoxide snow lines is by tracing the existence of diazenylium. With the help of ALMA astronomers have traced the presence and distribution of diazenylium and discovered a clear defined boundary that is nearly 30 astronomical units away from the star.

Michiel Hogerheijde from Leiden Observatory, Netherlands, stated that the observations were made using only 26 of ALMA's full complement of 66 antennas. 

The findings were published in Science Express.