Since 2004, NASA's spacecraft has been orbiting Saturn. Using its onboard cosmic dust analyzer, Cassini has sampled millions of space dust as it studies the ringed planet, its moons and its rings.
Most of the dust Cassini has sampled came from Saturn's moon Enceladus, which houses many active jets on its surface. However, in its course of dust analysis, 36 grains stood out.
These "alien" dust particles come from outside our solar system, and they are called interstellar dust because they emerge from the space between stars.
Interstellar dust discovery is not surprising. In the 1990s, a joint NASA and ESA mission already discovered one.
"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," said study lead author and ESA Cassini project scientist Nicolas Altobelli.
Detection was just phase one. Cassini's instrument also analyzed the interstellar dust's composition for the first time.
The analysis found that the grains are not made of ice. Rather, they are made of a mineral mix. All 36 grains shared the same chemical makeup, and they all included traces of silicon, calcium, iron and magnesium.
Carbon and sulfur, both reactive elements, are quite abundant in the cosmos, but analysis of the interstellar dust revealed their traces were less than the average rates.
Stardusts are created when stars die. Stardust grains are normally found in specific meteorite types.
These meteorites managed to preserve these grains since the solar system was formed. In general, these stardust are very old but they are in pristine condition. Their compositions also vary from one another.
Here's where it gets interesting. The interstellar dust Cassini recently analyzed were quite different. The authors said they seemed to have been made uniformly through a repetitive process.
They theorized that the stardust in star-forming regions in the universe may have been shattered and recondensed repetitively by the shockwaves coming from dying stars. This process could have resulted in the formation of more uniform interstellar dust.
These tiny interstellar dust grains traveling through Saturn's system at an astonishing speed – 72,000 kilometers per hour (44,700 mile per hour). The speed prevents these alien dust particles from being trapped in our own solar system because of the sun's and other planets' gravity.
Study co-author Marcia Burton from the Jet Propulsion Laboratory in California added that the team is thrilled to know they could detect interstellar dust using an instrument that was mainly designed to analyze dust inside Saturn's system. Burton is a particles and fields scientist in the Cassini team.
The research was published in the Science journal.
