Using the Atacama Large Millimeter / submillimeter Array (ALMA), astronomers have obtained thefirst image of a snow line in a “baby” planetary system, specifically in the disk that surrounds thesolar type star TW Hydrae. The finding promises to reveal new data on the formation of planets and comets, the factors that influence their composition and the history of our solar system.
On Earth, lines of snow form at high altitudes where temperatures drop, turning air humidity into snow. This line can be clearly identified in a mountain, in which we can see the snowy summit and the area in which we begin to distinguish the rocky surface, free of snow.
Thelines of snow around young starsare formed in a similar way, infarthest and coldest regions of the discs from which planetary systems are formed. Starting at the star and moving outward, the water is the first to freeze, forming the first line of snow. Beyond the star, as the temperature drops, other more exotic molecules can freeze and turn into snow, such as carbon dioxide, methane and carbon monoxide. Thesedifferent types of snow give the dust grains an external coating that acts like glueand it plays an essential role in helping these grains overcome their usual tendency to break apart after a collision, allowing them, on the contrary, to become fundamental pieces for the formation of planets and comets. Snow also increases the amount of solid matter available and can dramatically accelerate the planetary formation process.
Each of these different lines of snow – for water, carbon dioxide, methane, and carbon monoxide – can be related to the formation of different types of planets. Around a star similar to our Sun, in a similar solar system,the snow line of the water would correspond to the distance between the orbits of Mars and Jupiter, and the carbon monoxide snow line would correspond to the orbit of Neptune.
The ALMA snowline is the first carbon monoxide snowline found around TW Hydrae, a young star 175 light-years from Earth. Astronomers believe that this fledgling planetary system shared many characteristics with our own solar system when it was only a few million years old.
The presence of carbon monoxide could have consequences beyond simple planet formation. TheCarbon monoxide is necessary for the formation of methanol, a fundamental part of organic molecules, more complex and essential for life. If comets transported these molecules to forming planets similar to Earth, then those planets would be equipped with the ingredients necessary for life.
