[meteorite-list] Cassini Spacecraft Samples Interstellar Dust

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=6421

Saturn Spacecraft Samples Interstellar Dust
Jet Propulsion Laboratory
April 14, 2016

NASA's Cassini spacecraft has detected the faint but distinct signature 
of dust coming from beyond our solar system. The research, led by a team 
of Cassini scientists primarily from Europe, is published this week in 
the journal Science.

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, 
Cassini project scientist at ESA (European Space Agency) and lead author 
of the study. "Indeed, on average, we have captured a few of these dust 
grains per year, travelling 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 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," said Marcia Burton, 
a Cassini fields and particles scientist at NASA's Jet Propulsion Laboratory 
in Pasadena, California, and a co-author of the paper.

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 
very 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, a co-author of the paper and co-investigator 
of Cassini's dust analyzer.

Stardust grains are found in some types of meteorites, which have preserved 
them since the birth of our solar system. They are generally old, pristine 
and diverse in their composition. But surprisingly, the grains detected 
by Cassini aren't like that. They have apparently been made rather uniform 
through some repetitive processing in the interstellar medium, the researchers 
said.

The authors speculate on how this processing of dust might take place: 
Dust in a star-forming region could be destroyed and recondense multiple 
times as shock waves from dying stars passed through, resulting in grains 
like the ones Cassini observed streaming into our solar system.

"The long duration of the Cassini mission has enabled us to use it like 
a micrometeorite observatory, providing us privileged access to the contribution 
of dust from outside our solar system that could not have been obtained 
in any other way," said Altobelli.

The Cassini-Huygens mission is a cooperative project of NASA, ESA and 
the Italian Space Agency. JPL, a division of the California Institute 
of Technology in Pasadena, manages the mission for NASA's Science Mission 
Directorate in Washington. The Cosmic Dust Analyzer is supported by the 
German Aerospace Center (DLR); the instrument is managed by the University 
of Stuttgart, Germany.

For more information about Cassini, visit:

http://www.nasa.gov/cassini

http://saturn.jpl.nasa.gov


News Media Contact

Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston.dyches at jpl.nasa.gov 

Markus Bauer
European Space Agency, Noordwijk, Netherlands
011-31-71-565-6799
markus.bauer at esa.int

Written by Emily Baldwin, ESA 

2016-105