Artist concept of snow line in TW Hydrae showing water covered ice grains colored blue in the inner disk and green colored CO ice covered grains in the outer disk. (Bill Saxton and Alexandra Angelich, NRAO/AUI/NSF)
New fallen snow on a crisp winter morning can be a beautiful and inspiring sight. But astronomers using the new Atacama Large Millimeter/submillimeter Array (ALMA) in Chile got really got a real thrill recently when they saw and imaged a snow fall in a very young solar system some 175 light years from Earth.
The astronomers say that this never-before-seen icy feature may play an important role in providing scientists with insight into the chemical make-up and the way that both comets and developing planets take shape.
Up until now, these alien snow lines have never been directly imaged and could only be spotted by their spectral signatures – a specific pattern of electromagnetic radiation that is used to identify a chemical or compound.
In a study published yesterday in Science Express, the authors speculate that the solar system where they found the deep space snow line surrounds a young star called TW Hydrae and that this solar system has many of the same characteristics that our own did when it was only a few million years old.
According to the research team’s co-leader, Chunhua “Charlie” Qi, from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass, “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 our own Solar System. We can now see previously hidden details about the frozen outer reaches of another solar system, one that has much in common with our own when it was less than 10 million years old.”
Here on Earth snow lines that can often be seen near the summit of mountains are usually formed when freezing or sub-freezing temperatures, that are common at high elevations, turn atmospheric water vapor into snow.
The astronomers said that the snow lines found in the outer reaches of young solar systems are formed pretty much the same way as they do on Earth. But instead of simply water vapor freezing and turning into ice and snow like here on Earth, the scientists said that the frozen material found in the distant solar system are formed when gases such as methane, carbon dioxide and carbon monoxide form layers and freeze around grains of interplanetary dust.
ALMA image of the region where snow made of carbon monoxide (CO) has formed around the star TW Hydrae (center). (Karin Oberg, Harvard University/University of Virginia)
They add that even more unusual molecules can also freeze and turn into snow and ice, depending how far the materials are from its star. Also, molecules like carbon monoxide are able to freeze a lot easier when they’re insulated by a surrounding fog of concentrated dust and gas.
It’s that insulation that surrounds the frozen matter that has kept scientists from getting a good look, until now, at the icy element hidden inside.
“It would be like trying to find a small, sunny patch hidden within a dense fogbank,” said the research team’s other co-leader Karin Oberg, from Harvard University and the University of Virginia in Charlottesville.
The astronomers behind this discovery said that they were able to poke through that insulating fog of gas by looking for molecules known diazenylium or N2H+, which can be spotted at great distances by a sensitive and advanced radio telescope like ALMA. Since the substance doesn’t survive when it’s in the presence of carbon monoxide – CO, the researchers came to realize that finding the fragile molecule would indicate that the carbon monoxide gas surrounding it was frozen.
“Using this technique, we were able to create, in effect, a photonegative of the CO snow in the disk surrounding TW Hydrae,” said Oberg. “With this we could see the CO snow line precisely where theory predicts it should be — the inner rim of the diazenylium ring.”
Snow lines, like the one found in the TW Hydrae solar system, are believed by astronomers to play an important part in the formation of a solar system.
They say that the frozen material surrounding the grains of planet-and-comet-forming dust provides it with a sticky coating which prevents the particles from self-destructing by smashing into each other. Scientists also theorize that the ice-covered dust grains help increase the amount of solids available and may dramatically speed up the planet formation process.
Antennas that make up the ALMA array of radio telescopes located on Chile’s Chajnantor Plateau (ALMA (ESO/NAOJ/NRAO), O. Dessibourg)
Since many different kinds of snow lines have been found, each variety may be linked to the formation of specific kinds of planets, according to the research team.
For example, in our own solar system a snow line formed from water could be located where Jupiter currently orbits the Sun and a snow line made from carbon monoxide would correspond to the Neptune’s solar orbit. They also speculate that an area of space where the snow line transitions to one made from CO could also denote the beginning of a region within a solar system where smaller icy bodies such as dwarf planets like Pluto as well as comets would develop.
The scientists said that they found CO snow lines especially interesting, since ice made with carbon monoxide is an important ingredient in making methanol or methol-alcohol, which they say is an element of more complex organic molecules essential for the formation of life. They think that comets and asteroids could then transport these molecules to developing Earth-like planets and seed them with the components that would help foster life.
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