July 20 (): Astronomers have snapped the first ever direct image of a carbon monoxide (CO) snow line – the point where carbon monoxide freezes around a far-off baby solar system, 175 light years away from the Earth. Such a snow line would give information that could help them understand how planets form.
The CO Snow line is located in the disc around the Sun-like star TW Hydrae and is discovered by a team of international scientists. They used the Atacama Large Millimetre/sub-millimetre Array to image the snow line in the infant solar system and the snow line spotted by ALMA is the first glimpse of the carbon monoxide snow line, around TW Hydrae.
This discovery promises to give out more information about the formation of comets and planets, the factors that decide their composition and the history of the Solar System.
Water (H2O) is the first molecule to condense and freeze when it reaches the necessary distance from the star, forming the first snow line. Moving further away from a star, other molecules start to freeze, such as carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO). As each species of molecule has a different freezing point, the snow line of each can be found at different distances from the star.
In the Solar System, the water snow line is roughly at 3 astronomical units (AU), or 3 times the average distance between Earth and the Sun. Carbon monoxide has a much lower freezing point than water, so its ice line in the Solar System is roughly 30 AU, about where Neptune orbits. Beyond that lies the Kuiper Belt, where Pluto, Eris, Quaoar, and other bodies of rock and ice lurk, along with many comets.
CO ice is also interesting as it serves as a starting point for more complex organic molecules, specifically the prebiotic molecules found in comets. Yet another advantage to looking for the CO snow line instead of water is that there’s another molecule that’s easier to spot. That molecule, diazenylium (N2H+), only occurs in large volumes where CO ice exists. At warmer temperatures, carbon monoxide reacts with diazenylium, destroying it; once CO freezes, that reaction is slowed down.
Researchers say finding these snow lines would give us guidelines or starting points of where these planets form and what their composition might look like.