An international team of scientists led by University of Hawai‘i at Mānoa Chemistry Professor Ralf I. Kaiser, Alexander M. Mebel of Florida International University, and Tom J. Millar of Queen’s University Belfast (Northern Ireland) discovered a novel chemical route to form silicon dioxide (SiO2) - the key molecular building block of terrestrial sand and silicates - in interstellar space at temperatures as low as 10 Kelvin (-442 ℉). The team announced their findings in the February 2018 issue of Nature Communications in the paper “Directed Gas Phase Formation of Silicon Dioxide and Implications to the Formation of Interstellar Silicates” coauthored by Tao Yang, Aaron M. Thomas, and Beni B. Dangi. Funding for the study was provided by the US National Science Foundation (NSF) and by a grant from the Science and Technology Facilities Council (UK).
“The origin of interstellar silicate grains – nanoparticles consisting primarily of olivine-type refractory minerals – has remained a controversial topic for more than half a century since, in deep space, interstellar silicates are destroyed faster than they are formed during the late stages of stellar evolution”, Professor Millar stated. “These nanoparticles have also been associated with the prebiotic evolution of the interstellar medium through the synthesis of molecular building blocks of life such as amino acids and sugars on their ice-coated surfaces by ionizing radiation,” Dr. Tao Yang – lead author of this study – added. “Therefore, the elucidation of the origin of interstellar silicates is of vital importance to help the astrochemistry and astrobiology communities eventually understand the fundamental processes that create stars and planets like our own.”
In their laboratory in Hawaiʻi, Kaiser and coworkers exploited crossed molecular beam techniques and intersected a supersonic beam of highly reactive silylidyne radicals (SiH) with molecular oxygen (O2) to replicate chemical reactions in cold molecular clouds leading to silicon dioxide (SiO2) - the fundamental building block of silicates and sand grains - under ultra high vacuum conditions. Merged with electronic structure calculations, Professor Mebel revealed that these reactions are very fast even at ultra-low temperatures, highlighting that a cold synthesis of silicon oxides might easily offset the fast destruction of silicates in space. “Our work challenges conventional wisdom and provides a hitherto overlooked low temperature path to silicon oxides, eventually enabling the formation and growth of silicates in the interstellar medium needed to offset their fast destruction,” the authors deduced. “Ultimately, since this interstellar material provides the feedstock for the matter from which Solar Systems are formed, interstellar silicon dioxide ended up in Earth’s beaches billions of years ago and is also expected to be omnipresent on those sandy beaches to be encountered on extrasolar worlds by future space farers,” Aaron M. Thomas concluded.