Cassini caught 36 motes from outside the solar system
A very specific blend of minerals.
The Cassini spacecraft has been orbiting Saturn since 2004, studying a giant planet, its rings and satellites. For more than ten years, millions of dust particles, mainly from the volcanoes of the geologically active satellite Enceladus, have passed through the scientific instrument Cosmic Dust Analyzer.
But among the millions of particles there were several special ones - 36 pieces, which stand out among the general crowd. These motes came to us from interstellar space. Although we can say that we flew to them.
The emergence of interstellar dust in the solar system was not a surprise. In the 90s, the ESA / NASA Ulysses first observed this substance, which was later confirmed by the Galileo apparatus. Dust comes from the local interstellar cloud, through which the Solar System is now flying through with constant direction and speed.
Since the speed and direction of flight of interstellar dust are known, an idea emerged to trap it in the Cassini spacecraft. “We knew that if we turned in the right direction, we had to find them,” said Nicolas Altobelli, a Cassini project researcher at the European Space Agency and lead author of a scientific paper published today in the journal Science .
They decided to put such a task in front of Cassini for the reason that the station should be practically at one point for many years. This provides a unique opportunity for a long-term experiment.
Unlike Ulysses and Galileo, the Cassini spectrograph made a chemical analysis of interstellar dust and showed that there is not ice, but a very specific mixture of minerals. Dust consists of basic rock-forming elements, such as magnesium, silicon, iron and calcium, in normal proportions for space. But more reactive sulfur and carbon are found in quantities less than the average for space.
The chemical composition of interstellar dust is shown in the diagrams. It should be noted that interstellar dust crashes into the vehicle (or the vehicle crashes into dust, which is not important) at a speed of more than 20 km / s, therefore it completely evaporates from the impact. This explains that the spectrograph records the ions of the elements, and not the molecules. Rhodium and a significant portion of carbon are trap material, which also partially evaporates from a collision. By the way, it is high speed that allows you to avoid the gravitational trap of the solar system, which dust flies through.
“We are delighted that Cassini was able to make such a discovery, given that our tools are designed to evaluate dust specifically in the Saturn system, like all other apparatus systems,” said Marcia Burton, a particle analyst from the Jet Laboratory. NASA movement in Pasadena, co-author of the scientific work.
All 36 particles were surprisingly almost identical in chemical composition. "Space dust remains after the death of stars, but given the large variety of stars in the Universe, we naturally expected a huge variety of dust types for a long time of our research," commented the results of Frank Postberg from the University of Heidelberg, co-author of a scientific article.
For example, interstellar dust from meteorites was very diverse in composition. “Cassini” also collected only a filtered selection. Scientists are pushing versions of how such filtering could be done in interstellar space. It is possible that a cloud of dust has been subjected to repeated impact by passing shock waves from stellar explosions.
The scientific work was published on April 15, 2016 in the journal Science (doi: 10.1126 / science.aac6397).