Recently Discovered Interstellar Dust Challenges Views on Its Origins

April 20, 2016 | Joanne Kennell

Artist's impression of Saturn from a distance

"Our data tells a completely different story."

A dust detector, known as the cosmic dust analyzer (CDA), on the Cassini space probe, which has been in orbit around Saturn since 2004, has identified faint but distinct particles of interstellar dust coming from beyond our solar system.

Among the numerous microscopic grains collected by Cassini, only a special few — just 36 grains — stood out from the rest. Cassini examined their chemical composition, and scientists have concluded that these materials came from interstellar space — the space between the stars, consisting of gas and helium, as well as heavy metals, which can arise from the condensation of stars and planets.

It is these extremely rare particles that were the main building blocks for Earth and other terrestrial planets.

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"Interstellar dust is one of the last bastions of the unknown in space, its individual particles being only about 200 nanometres in size and very hard to find," explained Mario Trieloff, an Earth Scientist from Heidelberg University, in a press release.

The tiny dust grains were speeding through the Saturn system at over 45,000 miles per hour (72,000 kilometers per hour), fast enough to avoid being trapped inside the solar system by the gravity of the sun and its planets.

"We're thrilled Cassini could make this detection, given that our instrument was designed primarily to measure dust from within the Saturn system, as well as all the other demands on the spacecraft," Marcia Burton, a Cassini fields and particles scientist at NASA's Jet Propulsion Laboratory, and a co-author of the paper, said in a media release.

Stardust grains, which are found in some types of meteorites, contain grains that have been preserved since the birth of our solar system. They are generally old, pristine, and diverse in their composition.

On the other hand, cosmic dust "is produced when stars die, but with the vast range of types of stars in the universe, we naturally expected to encounter a huge range of dust types over the long period of our study," said Frank Postberg of the University of Heidelberg, co-author of the paper and co-investigator of Cassini's dust analyzer, in the press release.

However, the researchers discovered that the different interstellar dust particles were actually very alike in composition, containing a similar mixture of the most important rock-forming elements — magnesium, iron, silicon, and calcium.

Most scientists expected the dust populations to have different compositions that resulted from the different processes in the atmospheres of dying stars, but the "data tells a completely different story," stated Postberg.

Experts now suspect that interstellar dust is continually destroyed, recondensing multiple times as shockwaves from dying stars pass through them, and eventually homogenizing into a "standard" outer space composition — and only a few "lucky survivors" succeed in reaching newly forming planetary systems as intact stellar dust.

Read next: Scientist May Have Had First Ever Glimpse of a Parallel Universe

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