Over the course of its 12-year orbit around Saturn, the Cassini spacecraft has studied the ringed planet and its moons. One of the tasks the spacecraft performs is sampling the myriads of ice-rich dust grains that shoot out in jet sprays from Saturn’s moon Enceladus. The task is performed with the spacecraft’s Cosmic Dust Analyzer. This instrument is capable of detecting nanodust particles one-millionth of a millimeter in size. According to NASA, the task is equivalent to detecting a single raindrop that fell into the Gulf of Mexico.
But during its mission, Cassini has detected some grains from beyond the solar system’s reaches—36 grains to be exact, originating from interstellar space. Research behind the discovery was recently published in Science.
According to NASA and the European Space Agency (ESA), the microscopic dust particles were speeding through Saturn’s system at about 45,000 miles per hour. At such a speed, the dust particles would have avoided being stuck by gravitational bodies in the solar system.
“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 Cassini’s project scientist Nicolas Altobelli in a statement. “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.”
Such interstellar dust grains have been detected by previous spacecrafts, such as the ESA/NASA Ulysses mission and NASA’s Galileo. But unlike Ulysses and Galileo, Cassini was able to discern the composition of the microscopic particles.
The researchers said the chemical make-up of the particles consisted of rock-forming elements, such as magnesium, silicon, iron, and calcium, while sulfur and carbon were less abundant. Unlike the stardust grains found in meteorites—which are diverse in their composition—the grains detected by Cassini were quite uniform. This suggests, according to the researchers, that some repetitive processing occurred in the interstellar medium.
Of that process, NASA said, “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.”
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