Surprise found in comet dust

Odd mineral offers clues to solar system's origins

Researchers have found a new mineral within an interplanetary dust particle. The substance — a manganese silicide named Brownleeite — appears to have come from comet 26P/Grigg-Skjellerup, NASA announced June 12.

Originally seen in 1902, the comet reappears every five years.

In 2002, NASA space scientist Scott Messenger predicted that as they pass, comets shed dust grains that fall into Earth’s upper atmosphere. Using a high-altitude spacecraft, NASA performed periodic dust collections in the stratosphere and gathered 26P/Grigg-Skjellerup’s particles in April 2003.

Studying the sample, the science team began to tease out what mineral made up the individual grains. But a few months ago, researchers saw one substance they hadn’t seen before, says Simon Clemett, a NASA space scientist on the team.

“Manganese silicide has a strange composition. It’s hard to make synthetically,” he says. “And, it’s never actually been seen in nature and was certainly not thought to be found in comets.”

Seeing this mineral amidst the dust grains means scientists must now figure out how this unexpected substance could have formed and been trapped in a comet, Clemett adds.

Comets coalesced about the time the solar system began to form, so “what really makes this discovery intriguing is that it adds an extra dimension to trying to understand how things here got started,” he says. “We really know less and have more questions about the beginning, now that we see this stuff in nature.”

After its identification, the manganese silicide became mineral number 4,325, according to the International Mineralogical Association, which christened it Brownleeite after Donald E. Brownlee. An astronomer at the University of Washington in Seattle, Brownlee founded the field of interplanetary dust particle research.

“The real question,” says University of Maryland comet astronomer Michael A’Hearn, who was not involved in the research, “is why this mineral would appear in a cometary particle but not in any of the asteroidal particles,” that have been studied.

photo of Ashley Yeager

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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