Friday, July 19, 2013
Snow on a very early our solar system
For the first time obtained an image of a line in a remote snow extremely young planetary system. The snow line, located in the disk surrounding the solar-type star TW Hydrae, promises to reveal more about the formation of planets and comets, the factors that influence their composition and history of our Solar System. The results are published today in the journal Science Express.
Using the Atacama Large Millimeter / submillimeter Array ( ALMA ), astronomers have obtained the first image of a snow line in a planetary system baby. On Earth, snow lines are formed at high altitudes where temperatures, dropping, transform humidity in snow. This line can be clearly seen on a mountain, where we see the snow-capped well defined and the area in which we begin to distinguish the rocky surface, free of snow.
Snow lines around young stars are formed in a similar way, in the most remote and cold regions of the disks from which planetary systems form. Beginning in the star and moving outward, the water (H 2 O) is the first to freeze, forming the first line of snow. Beyond the star, as the temperature falls, more exotic other molecules may freeze and become snow, as is the case of carbon dioxide (CO 2), the methane (CH 4) and carbon monoxide carbon (CO). These different types of snow onto dust grains outer cover serves as glue and plays an essential role in helping these grains to overcome their habitual tendency to break after a collision, allowing, however, become building blocks for the formation of planets and comets. The snow also increases the amount of solids available and surprisingly can accelerate from planet formation process.
Each of these different snow lines - for water, carbon dioxide, methane and carbon monoxide - may be related to the formation of different types of planets  . Around a star similar to our sun in a solar system similar snow the water line would correspond to the distance between the orbits of Mars and Jupiter, and the snow line carbon monoxide would correspond to the orbit Neptune.
The snow line detected by ALMA is the first detection of a line of carbon monoxide snow around TW Hydrae, a young star is located 175 light years from Earth. Astronomers believe that this emerging planetary system shares many features with our own solar system when he was only a few million years.
"ALMA has provided the first real image of a line of snow around a young star, which is the extremely exciting, as this speaks of a very early period in the history of our solar system," says Chunhua "Charlie" Qi (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA) one of the two lead authors. "Now we can see details previously hidden on the distant icy regions of another planetary system similar to ours."
But the presence of carbon monoxide could have consequences beyond the simple formation of planets. Carbon monoxide is required for methanol formation, a key part of organic molecules, complex and essential to life. If comets transportation ties molecules forming planets similar to Earth, then those planets would be equipped with the necessary ingredients for life.
Until now, they had never directly imaged snow lines because they always form in the central plane of the protoplanetary disk, a relatively narrow, so that their location could not be clarified or size. Above and below this narrow region in which lines are snow stellar radiation prevents the formation of ice. The concentration of dust and gas in the central plane is necessary to protect the area of radiation, so that the carbon monoxide and other gases can be cooled and frozen.
With the help of a nifty trick, the team of astronomers managed to penetrate the disc and look very closely where snow formed. Instead of looking snow - since it can not be directly observed - sought a molecule known as diazinio (diazenylium) (N 2 H +), glowing in the millimeter spectrum and is therefore a perfect target for a telescope as ALMA. This fragile molecule is easily destroyed in the presence of carbon monoxide gas, so that only appear in detectable quantities in regions in which the carbon monoxide had been transformed into snow and could destroy it. Essentially, the key to finding snow carbon monoxide is finding diazinio.
The extraordinary sensitivity of ALMA and high resolution has allowed astronomers to track the presence and distribution of diazinio and find a clear and definite limit, which is approximately about 30 astronomical units from the star (30 times the distance between Earth and the Sol). In fact, this provides a negative image of the carbon monoxide snow in the disk around TW Hydrae, which can be used to accurately see the snow line of carbon monoxide in the place where theories predict that it should be - the inner edge diazinio ring.
"For these observations we used only 26 of the 66 antennas that make up the total of ALMA. ALMA observations in other there are already signs snow lines around other stars, and we are convinced that future observations with the whole antenna will reveal much more and provide much more revealing information about the formation and evolution of planets. Wait and see, "says Michiel Hogerheijde, Leiden Observatory in the Netherlands.
 For example, the planets rocky and dry form on the inside of the water snow line (closer to the star), where there can be only dust. At the other extreme are the gas giant planets, which are formed beyond the snow line carbon monoxide.
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