Lab-grown space dust more like ‘badly baked cherry cake’ than an onion

4 Oct 2019177 Views

The Eagle Nebula. Image: NASA/PA

Researchers have grown space dust in the lab and found that its consistency is not like what was once thought.

The dust that forms the stars and planets of our galaxy has been recreated in a laboratory. Prof Martin McCoustra and a team of scientists from Heriot-Watt University in Edinburgh have spent the last 12 years investigating how ice forms and behaves around tiny specks in the interstellar environment.

From that, new stars and planets are formed, as well as structures such as the Eagle Nebula, providing a source of complex organic molecules from which life can originate. The astrochemists recreated deep space in their lab and found the dust to be much more structurally complex than first thought.

McCoustra compared it to a “badly baked cherry cake” instead of the widely-held belief that the dust is structured like an onion.

Important little snowballs

“These tiny little snowballs have key roles to play in the evolution of the current universe, from controlling the process of star formation to providing an inventory of organic molecules from which biology might evolve. If we understand their formation and evolution then we can more fully appreciate those roles,” McCoustra said.

“The onion model visualises the icy coat of the grains as a series of layers, where the core dust grain is first fully covered by a thick layer of water-rich ice.

“On top of that layer, other species are adsorbed depending on temperature. This means only a relatively pure layer of water interacts directly with the dust grain surface while other species, such as carbon monoxide, will interact with the water surface.

“We discovered that water is more mobile on the dust grain surface and tends to form little islands of ice as opposed to a uniform film. This leaves parts of the grain surface free on which other species can adsorb.

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“So instead of an onion, picture a badly baked cherry cake, where the cherries of water have sunk to the bottom of the icy cake as it is baked.”

How does the dust grow?

A space dust proxy – copper plate coated in tiny silica particles, cooled to a few degrees above absolute zero and in an ultra-high vacuum – was used for the experiments on various species found in the environment. The team now hopes other scientists will test out the ideas to help develop understanding.

McCoustra added: “We are refining our model of how space dust grows and have, through a combination of observation and computer simulation, developed a yet-to-be-proven hypothesis.

“This work has stimulated an international collaboration to study the development of ices in space that has been awarded observing time on the James Webb Space Telescope during the first months of its operation.

“Aspects of this complex process still need more detailed exploration, particularly the role of cosmic rays and ultraviolet light in driving non-thermal processes on and in the icy grain mantles.”

The paper – ‘Surface science investigations of icy mantle growth on interstellar dust grains in cooling environments’ – can be read in full online.

– PA Media