Interstellar dust at Saturn
Copyright: ESA; dust grain inset: NASA/JPL; Saturn image: NASA/JPL/Space Science Institute
Local interstellar cloud
The local interstellar cloud is an almost empty bubble of gas and dust
that our Solar System is travelling through with a distinct direction
and speed.
Copyright: ESA
The international Cassini spacecraft has detected the faint but distinct signature of dust coming from outside our Solar System.
Cassini has been flying around the Saturnian system for 12 years,
studying the giant planet and its rings and satellites. It has also
found millions of ice-rich dust grains with its Cosmic Dust Analyser,
the vast majority of which are from icy satellite Enceladus and which
make up one of Saturn’s outer rings.
Amongst the grains detected, 36 stick out from the crowd – and scientists conclude they came from beyond our Solar System.
Alien dust in the Solar System is not entirely unexpected. In the 1990s, the ESA/NASA Ulysses mission made the first in-situ discovery of interstellar dust, later confirmed by NASA’s Galileo spacecraft.
The dust was traced back to the local interstellar cloud: an almost
empty bubble of gas and dust we are travelling through with a distinct
direction and speed.
“From that discovery, we always hoped we would be able detect these
interstellar interlopers at Saturn with Cassini: we knew that if we
looked in the right direction, we should find them,” says Nicolas
Altobelli, ESA’s Cassini project scientist and lead author of the study
reporting the results in Science.
“And indeed, on average, we have captured a few per year, travelling at
high speed and on a specific path quite different to that of the usual
icy grains we collect around Saturn.”
The tiny dust grains were speeding through at over 72 000 km/h, fast
enough to avoid being trapped inside the Solar System by Saturn’s – or
even the Sun’s – gravity.
Importantly, unlike Ulysses and Galileo, Cassini analysed the
composition of the dust for the first time, showing them to be made of a
very specific mixture of minerals, not ice.
They 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
sulphur and carbon were found to be less abundant compared to the
average.
“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,” says Frank
Postberg, co-author on the paper and co-investigator of Cassini’s dust
analyser, of the University of Heidelberg.
“Surprisingly, the grains we’ve detected aren’t old, pristine and
compositionally diverse like the stardust grains we find in ancient
meteorites,” says Mario Trieloff, a co-author also at the University of
Heidelberg.
“They have apparently been made rather uniform through some
repetitive processing in the interstellar medium.”
The team speculate that dust in a star-forming region could be destroyed
and recondense multiple times as the shockwaves from dying stars passed
through, before the resulting similar grains ended up streaming towards
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,” adds Nicolas.
Notes for editors
“Flux and composition of interstellar dust at Saturn from Cassini’s
Cosmic Dust Analyzer,” by N. Altobelli et al, is published in Science.
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 Analyser is supported by the German Aerospace Center
(DLR); the instrument is managed by the University of Stuttgart,
Germany.
For more information, please contact:
Nicolas Altobelli
ESA Cassini–Huygens Project Scientist
Tel: +34 91 813 1201
Email: nicolas.altobelli@esa.int
Frank Postberg
Institut für Geowissenschaften, University of Heidelberg, Germany
Email: Frank.Postberg@geow.uni-heidelberg.de
Mario Trieloff
Institut für Geowissenschaften, University of Heidelberg, Germany
Email: Mario.Trieloff@geow.uni-heidelberg.de
Markus Bauer
ESA Science Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Source: ESA/ Cassini-Huygens
