An artist's concept of the snow line in TW Hydrae showing water ice covered dust grains in the inner disc (4.5–30 astronomical units, blue) and carbon monoxide ice covered grains in the outer disc (>30 astronomical units, green). The transition from blue to green marks the carbon monoxide snow line. The snow helps grains of dust to adhere to each other by providing a sticky coating, which is essential to the formation of planets and comets. Due to the different freezing points of different chemical compounds, different snow lines can be found at various distances from the star. (Photo : B. Saxton & A. Angelich/NRAO/AUI/NSF/ALMA (ESO/NAOJ/NRAO))
Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) of radio telescopes have spotted the first carbon monoxide snow line in a distant, infant solar system for the first time ever. The findings reveal more about solar systems in general, and how frozen molecules could speed up the formation of planets.
The study detailing the snow line can be found online in the journal Science.
"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 from the Harvard-Smithsonian Center for Astrophysics and one of the two lead authors of the study. "We can now see previously hidden details about the frozen outer reaches of another solar system similar to our own."
Snow lines for a star work in a similar fashion to snow lines on Earth, which can clearly be seen on mountain tops where the temperature gets low enough to freeze water. In a solar system, there are multiple snow lines as temperatures drop the further one gets from the parent star. Water is usually the first to freeze, with other molecules such as methane and carbon dioxide freezing further out. These icy particles give rocks and dust a sticky coating that allows them coalesce much easier into larger bodies such as planets. Thus, snow lines could give researchers unique insights into planet formation.
Snow lines are hard to spot, and to discover the far-off snow line surrounding the sun-like star TW Hydrae 175 light-years away, the scientists looked for diazenylium (N2H+), a molecule that cannot exist if carbon monoxide is present as a gas. The only way it can exist is if carbon monoxide has been turned to ice, and this is what the astronomers focused ALMA's efforts on.
"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," stated Michiel Hogerheijde from Leiden Observatory, the Netherlands.