Cosmic Dust Analyzer

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Cassini Cosmic Dust Detector, CDA Cassini Cosmic Dust Detector, CDA.jpg
Cassini Cosmic Dust Detector, CDA

The Cosmic Dust Analyzer (CDA) on the Cassini mission is a large-area (0.1 m2 total sensitive area) multi-sensor dust instrument that includes a chemical dust analyzer (time-of-flight mass spectrometer), a highly reliable impact ionization detector, and two high rate polarized polyvinylidene fluoride (PVDF) detectors. During 6 years en route to Saturn the CDA analysed the interplanetary dust cloud, the stream of interstellar dust, and Jupiter dust streams. During 13 years in orbit around Saturn the CDA studied the E ring, dust in the plumes of Enceladus, and dust in Saturn's environment.

Contents

Overview

Dust impacts on the Compositional Analyzer Target (CAT) of CDA and generated signals. CDA CAT3.gif
Dust impacts on the Compositional Analyzer Target (CAT) of CDA and generated signals.

The Cosmic Dust Analyzer, CDA [1] was the seventh dust instrument from the Max Planck Institute for Nuclear Physics (MPIK), Heidelberg (Germany) following the dust detectors on the HEOS 2 satellite and dust detectors on the Galileo and Ulysses space probes and the more complex dust analyzers on the Helios spacecraft, the Giotto and VeGa spacecraft to Halley's Comet. The new dust analyzer system was developed by a team of scientists led by Eberhard Grün and engineers led by Dietmar Linkert to analyze dust in the Saturn system on board the Cassini spacecraft. This instrument employs a larger sensitive area (0.1 m2) impact detector, a smaller time-of-flight mass spectrometer chemical analyzer and two high rate polarized polyvinylidene fluoride (PVDF) detectors, in order to cope with the high fluxes during crossings of the E ring. The Max Planck Institute for Nuclear Physics in Heidelberg was responsible for the overall instrument development and test. Major contributions were provided by the DLR in Berlin-Adlershof (mechanics, cleanliness, thermal design, tests), Tony McDonnell from University of Canterbury (chemical analyzer, UK), Rutherford Appleton Laboratory (spectrometer electronics, UK) and G. Pahl (mechanical design, Munich, Ger). The PVDF detectors were provided by Tony Tuzzolino from the University of Chicago. The proposing Principal Investigator for CDA was Eberhard Grün. In 1990 the PI-ship was handed over to Ralf Srama from the Max Planck Institute for Nuclear Physics, who is now at the University of Stuttgart, Germany. Ralf Srama got his degree “Dr.-Ing.” from the Technical University of Munich for his Thesis (10 Nov. 2000, in German), "From the Cosmic-Dust-Analyzer to a model describing scientific spacecraft". [2]

Cassini spacecraft with instruments Cassini SC43713.gif
Cassini spacecraft with instruments

The main sensor of CDA is an impact ionization detector (IID) like the Galileo and Ulysses Dust Detectors. In the center of the hemispherical target is the smaller (0.016 m2) Chemical Analyzer Target, CAT, at +1000 V electric potential. Three millimeter in front of the target is a grid at 0 V potential. Dust impacts onto CAT generate a plasma that is separated by the high electric field. Ions obtain an energy of ~1000eV and are focused towards the center collector. Ions are partly collected by the semi-transparent grid at 230 millimeter distance and the center electron multiplier. The waveforms of the charge signals are measured, stored and transmitted to ground. The multiplier signal represents a time-of-flight mass spectrum of the released ions. Two of the four grids at the entrance of the analyzer pick-up the electric charge of the dust particle. With these capabilities CDA can be considered a prototype dust telescope.

CDA measured the micrometeoroid environment for 18 years, from 1999 until the last active seconds of Cassini in 2017 without major degradation. The instrument fly-away-cover was released already in 1997 on day 317. Science planning and operations were managed by Max-Planck-Institute for Nuclear Physics and later by the University of Stuttgart.

The Cassini spacecraft was a three-axes stabilized spacecraft with the antenna occasionally pointing to Earth in order to download data and receive operational commands. In the mean time Cassini’s attitude was controlled by requested observations from one or more of the 12 instruments onboard. In order to obtain some more control of its pointing attitude, CDA employed a turntable between the spacecraft and the dust analyzer.

Major discoveries and observations

During interplanetary cruise

From launch in 1997 until arrival at Saturn in 2004, Cassini–Huygens cruised interplanetary space from 0.7 to 10 AU. During this time there were long periods useful for observations of interplanetary and interstellar dust [3] in the inner planetary system. Highlights were the detection of electrical charges [4] of dust in interplanetary space and the determination of the composition [5] of interplanetary dust particles. No measurements were possible during the crossing of the asteroid belt. During Jupiter flyby in 2000 there was a chance to analyze nanometer-sized dust stream particles [6] and demonstrate their compositional relation to Jupiter's moon Io where they originate from. On approach to Saturn in 2004, similar streams of submicron grains with speeds in the order of 100 km/s were detected. [7] These particles originate mostly from the outer parts of the dense rings. They were ejected by Saturn’s magnetic field until they become entrained in the solar wind magnetic field. The Saturn stream particles consist of silicate impurities of the primary icy ring particles.

In Saturn orbit

During Cassini’s 292 orbits around Saturn (2004 to 2017) CDA measured several million dust impacts that characterize dust mostly in Saturn’s E ring. [8] [9] In this process CDA found that the E ring extends about twice as far from Saturn as optically observed. Measurements of variable dust charges [10] depending on the magnetospheric plasma conditions (allowed the definition of a dynamical dust model [11] of Saturn's E ring describing the observed properties. In 2005 during Cassini’s close flyby of Enceladus within 175 km from the surface CDA together with two other Cassini instruments discovered active ice geysers [12] located at the south pole of Saturn's moon Enceladus. Later, detailed compositional analyses [13] of the water ice grains in the vicinity of Enceladus led to the discovery of large reservoirs of liquid water oceans [14] below the icy crust of Enceladus. During the Cassini spacecraft’s Grand Finale mission in 2017, it performed 22 traversals of the region between Saturn and its innermost D ring. During this path CDA detected of dust from Saturn's dense rings. [15] Most analyzed grains were a few tens of nanometers in size and had silicate and water-ice composition. For most of Cassini’s orbital tour CDA observed a faint signature of interstellar dust in the largely dominant foreground of E ring water-ice particles. Mass spectra of the interstellar grains suggest the presence of magnesium-rich grains of silicate and oxide composition, some with iron inclusions. [16] Major discoveries until 2011 were summarized in a dedicated paper. [17]

See also

Related Research Articles

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<span class="mw-page-title-main">Saturn</span> Sixth planet from the Sun

Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about nine and a half times that of Earth. It has an eighth the average density of Earth, but is over 95 times more massive. Even though Saturn is almost as big as Jupiter, Saturn has less than a third the mass of Jupiter. Saturn orbits the Sun at a distance of 9.59 AU (1,434 million km), with an orbital period of 29.45 years.

<i>Cassini–Huygens</i> NASA/ESA mission sent to study Saturn and its moons (1997–2017)

Cassini–Huygens, commonly called Cassini, was a space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class robotic spacecraft comprised both NASA's Cassini space probe and ESA's Huygens lander, which landed on Saturn's largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit, where it stayed from 2004 to 2017. The two craft took their names from the astronomers Giovanni Cassini and Christiaan Huygens.

<span class="mw-page-title-main">Tethys (moon)</span> Moon of Saturn

Tethys, or Saturn III, is the fifth-largest moon of Saturn, measuring about 1,060 km (660 mi) across. It was discovered by Giovanni Domenico Cassini in 1684, and is named after the titan Tethys of Greek mythology.

<span class="mw-page-title-main">Janus (moon)</span> Moon of Saturn

Janus is an inner satellite of Saturn. It is also known as Saturn X. It is named after the mythological Janus. This natural satellite was first identified by Audouin Dollfus on December 15, 1966, although it had been unknowingly photographed earlier by Jean Texereau. Further observations led to the realization that Janus shares a unique orbital relationship with another moon, Epimetheus. The discovery of these two moons' peculiar co-orbital configuration was later confirmed by Voyager 1 in 1980.

<span class="mw-page-title-main">Enceladus</span> Natural satellite orbiting Saturn

Enceladus is the sixth-largest moon of Saturn and the 19th-largest in the Solar System. It is about 500 kilometers in diameter, about a tenth of that of Saturn's largest moon, Titan. It is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon reaches only −198 °C, far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide variety of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrain.

<span class="mw-page-title-main">Rings of Saturn</span> Planar assemblage of icy particles orbiting Saturn

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<span class="mw-page-title-main">Rings of Jupiter</span> Rings of the planet Jupiter

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The interplanetary dust cloud, or zodiacal cloud, consists of cosmic dust that pervades the space between planets within planetary systems, such as the Solar System. This system of particles has been studied for many years in order to understand its nature, origin, and relationship to larger bodies. There are several methods to obtain space dust measurement.

<span class="mw-page-title-main">Impact ionization</span>

Impact ionization is the process in a material by which one energetic charge carrier can lose energy by the creation of other charge carriers. For example, in semiconductors, an electron with enough kinetic energy can knock a bound electron out of its bound state and promote it to a state in the conduction band, creating an electron-hole pair. For carriers to have sufficient kinetic energy a sufficiently large electric field must be applied, in essence requiring a sufficiently large voltage but not necessarily a large current.

<span class="mw-page-title-main">Tiger stripes (Enceladus)</span>

The tiger stripes of Enceladus consist of four sub-parallel, linear depressions in the south polar region of the Saturnian moon. First observed on May 20, 2005, by the Cassini spacecraft's Imaging Science Sub-system (ISS) camera, the features are most notable in lower resolution images by their brightness contrast from the surrounding terrain. Higher resolution observations were obtained by Cassini's various instruments during a close flyby of Enceladus on July 14, 2005. These observations revealed the tiger stripes to be low ridges with a central fracture. Observations from the Composite Infrared Spectrometer (CIRS) instrument showed the tiger stripes to have elevated surface temperatures, indicative of present-day cryovolcanism on Enceladus centered on the tiger stripes.

Eberhard Grün is a German planetary scientist who specialized in cosmic dust research. He is an active emeritus at the Max Planck Institute for Nuclear Physics (MPIK), Heidelberg (Germany), research associate at the Laboratory for Atmospheric and Space Physics (LASP) in Boulder (Colorado), and was a professor at the University of Heidelberg until his retirement in 2007. Eberhard Grün has had a leading role in international cosmic dust science for over 40 years.

<span class="mw-page-title-main">Explorer of Enceladus and Titan</span> NASA/ESA Saturnian moon probe concept

Explorer of Enceladus and Titan (E2T) is a space mission concept that would investigate the evolution and habitability of the Saturnian satellites Enceladus and Titan and is proposed by the European Space Agency in collaboration with NASA.

<span class="mw-page-title-main">DESTINY+</span> Planned asteroid flyby mission by JAXA, using solar electric propulsion

DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science) is a planned mission to flyby the Geminids meteor shower parent body 3200 Phaethon, and sample dust originating from the "rock comet". The spacecraft is being developed by the Japanese space agency JAXA, and will demonstrate advanced technologies for future deep space exploration. As of 2023, DESTINY+ is planned to be launched in 2025.

The Enceladus Icy Jet Analyzer (ENIJA) is a time-of-flight mass spectrometer developed to search for prebiotic molecules like amino acids and biosignatures in the plumes of Saturn's moon Enceladus.

<span class="mw-page-title-main">Surface Dust Analyser</span>

The SUrface Dust Analyser (SUDA) is a time-of-flight mass spectrometer of reflectron-type that employs impact ionization and is optimised for a high mass resolution. The instrument was selected in May 2015 to fly on board the Europa Clipper mission, that is planned for 2025 to Jupiter's moon Europa.

<span class="mw-page-title-main">Galileo and Ulysses Dust Detectors</span> Dust instruments on the Galileo and Ulysses missions

The Galileo and Ulysses Dust Detectors are almost identical dust instruments on the Galileo and Ulysses missions. The instruments are large-area highly reliable impact ionization detectors of sub-micron and micron sized dust particles. With these instruments the interplanetary dust cloud was characterized between Venus’ and Jupiter's orbits and over the solar poles. A stream of interstellar dust passing through the planetary system was discovered. Close to and inside the Jupiter system streams nanometer sized dust particles that were emitted from volcanoes on Jupiter's moon Io and ejecta clouds around the Galilean moons were discovered and characterized.

<span class="mw-page-title-main">Space dust measurement</span> Space dust measurements

Space dust measurement refers to the study of small particles of extraterrestrial material, known as micrometeoroids or interplanetary dust particles (IDPs), that are present in the Solar System. These particles are typically of micrometer to sub-millimeter size and are composed of a variety of materials including silicates, metals, and carbon compounds. The study of space dust is important as it provides insight into the composition and evolution of the Solar System, as well as the potential hazards posed by these particles to spacecraft and other space-borne assets. The measurement of space dust requires the use of advanced scientific techniques such as secondary ion mass spectrometry (SIMS), optical and atomic force microscopy (AFM), and laser-induced breakdown spectroscopy (LIBS) to accurately characterize the physical and chemical properties of these particles.

<span class="mw-page-title-main">Helios Dust Instrumentation</span>

The Helios 1 and 2 spacecraft each carried two dust instruments to characterize the Zodiacal dust cloud inside the Earth’s orbit down to spacecraft positions 0.3 AU from the sun. The Zodiacal light instrument measured the brightness of light scattered by interplanetary dust along the line of sight. The in situ Micrometeoroid analyzer recorded impacts of meteoroids onto the sensitive detector surface and characterized their composition. The instruments delivered radial profiles of their measured data. Comet or meteoroid streams, and even interstellar dust were identified in the data.

<span class="mw-page-title-main">Dust astronomy</span> Branch of astronomy

Dust astronomy is a subfield of astronomy that uses the information contained in individual cosmic dust particles ranging from their dynamical state to its isotopic, elemental, molecular, and mineralogical composition in order to obtain information on the astronomical objects occurring in outer space. Dust astronomy overlaps with the fields of Planetary science, Cosmochemistry, and Astrobiology.

References

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