Astronomers map space’s icy wastes

In space, ice forms by building up a “frost-like” layer on dust grains at a temperature of –441° Fahrenheit (–263° Celsius). The layer that results is a bit like the frost that forms on a car windscreen on a (somewhat less) cold morning on Earth. In this image, the dust layer is represented by the blue colored molecules at the bottom of the image. Water molecules have two hydrogen atoms (shown here in white) and one oxygen atom (shown here in red). Here the ice forms without structure (so-called amorphous ice), quite unlike the more familiar cubes of ice that you might find in a drink. This results in pores forming in the ice — the big “hole” in the middle of this simulation. The hole here is nano-sized — about a million times smaller in diameter than the diameter of a human hair. Gases get trapped in these pores, which can have a profound effect on temperatures and densities in regions of star formation.

Helen Fraser (Open University)

Using the AKARI orbiting observatory, astronomers from the Open University (OU) in the United Kingdom have made the first large-scale maps of icy material where stars are forming. In a challenge to conventional ideas about the formation of water in space, have found ice in regions with little dust or gas.

Launched by the Japanese space agency JAXA in 2006, AKARI — meaning “light” in Japanese — surveyed 90 percent of the sky at infrared wavelengths until it ceased operations in 2011. The OU team used data from the observatory to make maps of the icy material in 28 star-forming regions, covering sections of the sky 10 arcminutes by 10 arcminutes (1 arcminute is 1/60th of a degree).

In the regions covered in the survey, temperatures are very cold (–441° Fahrenheit [–263° Celsius]), 10° above absolute zero) and pressures are low, with only a few hundreds to a few thousands of molecules in each cubic centimeter of space. Under these conditions, atoms and molecules of gas collide with the dust that is found there and form layers of “frost” on the dust surfaces. These nanoscale icy dust grains are the chemical factories of star formation where successively more complex chemistry occurs. This, in turn, seeds the prebiotic organic molecules that astronomers search for in the “habitable zones” (where temperatures are right for water to be a liquid) around newly forming stars that may be inextricably linked to the origins of life.

The new AKARI maps are the first of their kind and, in contrast to the prevailing model, suggest that ice is found in regions without much dust or gas. If ice can even form in these zones, it can quickly suck up or “sorb” nearby gases, in the process changing local conditions — for example, the amount of material available to form new stars and planets.

Helen Fraser from OU sees this as a surprising discovery and one that could change our model for the formation of stars and planets.

“Until this research, we never previously had a view of the cold solid-state universe, the icy freezers from which stars and planets ultimately form,” said Fraser. “Given that the results in our own local galaxy are so surprising, the question remains what other galaxies look like when we map their ice features.”

Telescopes due to start operations in the 2020s, the James Webb Space Telescope and the European Extremely Large Telescope, will help researchers answer that question.

“The coming decade could be astounding,” said Fraser. “We could be able to apply the same technique to nearby galaxies and see if the nano-fabrication factories that make organic matter work in the same way across the different epochs of the history of the cosmos.”

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