NASA's Cassini orbiter has become the first spacecraft to determine the composition of dust particles originating outside of our solar system. The discovery grants a rare insight regarding the processes that may be occurring in the interstellar medium.
Cassini's longevity has allowed the spacecraft to undertake a wide variety of roles since arriving in the Saturnian system in 2004. The probe has characterized the ringed gas giant and her moons, as well as using its Cosmic Dust Analyzer (CDA) instrument to examine particles ejected from vast geysers in the southern hemisphere of Enceladus.
Now, among the multitude of particles harvested from Enceladus, the Cassini science team have detected 36 particles that originated from beyond our solar system. Had the particles not been intercepted by the CDA, the velocity of the micrometeorites, which were thought to be moving in excess of 45,000 mph (72,000 km/h), would likely have passed straight through our solar system.
Upon analysis, it became apparent that the particles bore a striking resemblance to one another. Furthermore, the CDA determined that the samples contained an abundance of known rock forming elements such as magnesium and iron, yet exhibited a deficiency of minerals such as sulphur and carbon compared to the cosmic norm.
Many of the particles detected by Cassini's CDA instrument are thrown out by geysers on the Saturnian moon Enceladus
The uniformity of the particles surprised the Cassini team. Micrometeorites of the type recently detected by the spacecraft are thought to be created and distributed through the death throws of innumerable stars. The sheer variety of progenitor stars were expected to create dust particles with widely contrasting compositions. Yet, this trend is not apparent in the particles captured by Cassini.
The uniformity could be explained were it to be proved that there is some process at work in interstellar space that is processing the particles after they are created. The Cassini team has put forward the theory that, as the newly-created particles travel, subsequent supernovae send shockwaves through the interstellar medium, destroying and reconstructing the dust grains multiple times. This would have the effect of mixing the materials into the particles we see today.
Our knowledge of the processes that take place in the interstellar medium is still relatively juvenile. To date, humanity has succeeded in sending only one spacecraft beyond the heliosphere – the name given to the border of our Sun's influence, and the beginning of the realm beyond.
Voyager one, which has been charting interstellar space since its entry (depending on who you asked) in August 2012, will soon be joined by its twin, Voyager 2. Together, they serve as our most distant emissaries, working to shed light on mankind's new frontier, and in so doing gather data to support theories such as those posed by the Cassini science team.