A spacecraft of Saturn samples interstellar dust
Cassini has been in orbit around Saturn since 2004, studying the giant planet, its rings, and its moons. The spacecraft has also sampled millions of ice-rich dust grains with its cosmic dust analyzer instrument. The vast majority of the sampled grains originate from active jets that spray from the surface of Saturn’s geologically active moon Enceladus.
But among the myriad microscopic grains collected by Cassini, a special few — just 36 grains — stand out from the crowd. Scientists conclude these specks of material came from interstellar space — the space between the stars.
Alien dust in the solar system is not unanticipated. In the 1990s, the ESA/NASA Ulysses mission made the first in-situ observations of this material, which were later confirmed by NASA’s Galileo spacecraft. The dust was traced back to the local interstellar cloud — a nearly empty bubble of gas and dust that our solar system is traveling through with a distinct direction and speed.
“From that discovery, we always hoped we would be able to detect these interstellar interlopers at Saturn with Cassini. We knew that if we looked in the right direction, we should find them,” said Nicolas Altobelli from the European Space Agency (ESA). “Indeed, on average, we have captured a few of these dust grains per year, traveling at high speed and on a specific path quite different from that of the usual icy grains we collect around Saturn.”
The tiny dust grains were speeding through the Saturn system at over 45,000 mph (72,000 kilometers), 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,” said Marcia Burton from NASA’s Jet Propulsion Laboratory in Pasadena, California.
Importantly, unlike Ulysses and Galileo, Cassini was able to analyze the composition of the dust for the first time, showing it to be made of a specific mixture of minerals, not ice. The grains all had a surprisingly similar chemical make-up, containing major rock-forming elements like magnesium, silicon, iron, and calcium in average cosmic proportions. Conversely, more reactive elements like sulfur and carbon were found to be less abundant compared to their average cosmic abundance.
“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.
source: http://www.astronomy.com/news/2016/04/saturn-spacecraft-samples-interstellar-dust
