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.
Eberhard Grün et al. stated in the 2002 Kuiper prize lecture "Dust particles, like photons, carry information from remote sites in space and time. From knowledge of the dust particles' birthplace and their bulk properties, we can learn about the remote environment out of which the particles were formed. This approach is called Dust Astronomy which is carried out by means of a dust telescope on a dust observatory in space".
History
Early observations Three phenomena that relate (we know today) to cosmic dust were noticed by humans for millennia: Zodiacal light, comets, and meteors (cf. Historical comet observations in China). Early astronomers were interested in understanding these phenomena.
Zodiacal light or false dawn can be seen in the western sky after the evening twilight has disappeared, or in the eastern sky just before the morning twilight appears. This phenomenon was investigated by the astronomer Giovanni Domenico Cassini in 1683. He explained Zodiacal light by interplanetary matter (dust) around the Sun according to Hugo Fechtig, Christoph Leinert, and Otto E. Berg in the book Interplanetary Dust. In the past, unexpected appearances of comets were seen as bad omens that signaled disaster and upheaval, as described in the Observational history of comets. However, in 1705, Edmond Halley used Isaac Newton's laws of motion to analyze several earlier cometary sightings. He observed that the comets of 1531, 1607, and 1682 had very similar orbital elements, and he theorized that they were all the same comet. Halley predicted that this comet would return in 1758-59, but he died before it did. The comet, now known as Halley's Comet and officially designated 1P/Halley, ultimately did return on schedule. A meteor, or shooting star is a streak of light caused by a meteoroid entering the Earth's atmosphere at a speed of several tens of kilometers per second, at an altitude of about 100 km. At this speed the meteoroid heats up and leaves a trail of excited atoms and ions which emit light as they de-excite. In some cultures, meteors were thought to be an atmospheric phenomenon, like lightning. While only a few meteors can typically be seen in one hour on a moonless night, during certain times of the year, meteor showers with over 100 meteors per hour can be observed. Italian astronomer Giovanni Schiaparelli concluded in 1866 that the Perseid meteors were fragments of Comet Swift–Tuttle, based on their orbital similarities. The physical relation between the three disparate phenomena was demonstrated by the American astronomer Fred Lawrence Whipple who in the 1950th, proposed the "icy conglomerate" model of comet composition. This model could explain how comets release meteoroids and dust, which in turn feed and maintain the Zodiacal dust cloud.
Compositional analyses of extraterrestrial material
For a long time, the only extraterrestrial material accessible for study were meteorites that had been collected on the Earth's surface. Meteorites were considered solid fragments from other astronomical objects such as planets, asteroids, comets, or moons. Most meteorites are chondrite meteorites that are named for the small, round particles they contain. Carbonaceous chondrites are especially primitive; they have retained many of their chemical properties since they accreted 4.6 billion years ago. Other meteorites have been modified by either melting or planetary differentiation of the parent body. Analyzing the composition of meteorites provides a glimpse into the formation and evolution of the Solar System. Therefore, meteorite analyses have been the cornerstone of cosmochemistry.
The first extraterrestrial samples – other than meteorites – were 380 kg of lunar samples brought back in the seventies by the Apollo missions and at about the same time 300 g were returned by the uncrewed Luna spacecraft. Recently, in 2020 Chang'e 5 collected 1.7 kg of lunar material. From the isotopic, elemental, molecular, and mineralogical compositions important conclusions about e.g. the origin of the Moon like the giant-impact hypothesis were drawn.
Thousands of grains were collected during fly by of comet 81P/Wild by Stardust that returned the samples to Earth in 2006. Their analysis provided insight into the early Solar System. Also some probable interstellar grains were collected during interplanetary cruise of Stardust and were returned by the same mission.
Asteroids and meteorites have been linked via their Asteroid spectral types and similarities in the visible and near-infrared, which implies that asteroids and meteorites derived from the same parent bodies.
The first asteroid samples were collected by the JAXA Hayabusa missions. Hayabusa encountered asteroid 25143 Itokawa in November 2005, picked up 10 to 100 micron sized particles from the surface, and returned them to Earth in June 2010. Hayabusa 2 mission collected about 5 g surface and sub-surface material from asteroid 162173 Ryugu a primitive C-type asteroid and returned it in 2020.
Sample return missions are very expensive and can address only a small number of astronomical objects. Therefore, less expensive methods to collect and analyse extraterrestrial materials have been looked for. Cosmic dust surviving atmospheric entry can be collected by high (~20 km) flying aircraft. Donald E. Brownlee identified reliably the extraterrestrial nature of such collected dust particles by their chondritic composition. Proceedings Volume 1. (A78-41551 18-91) New York, Pergamon Press, Inc. A large portion of the collected particles may have a cometary origin while others come from asteroids. These stratospheric dust samples can be requested for further research from a catalogue that provides SEM photos together with their EDS spectra.
Methods Since the beginning of Space Age the study of space dust rapidly expanded. Freed from peeking through narrow infrared windows in the atmosphere infrared astronomy mapped out cold and dark dust clouds everywhere in the universe. Also, in situ detection and analysis of cosmic dust came in the focus of space agencies (cf. Space dust measurement).
In situ dust analyzers Numerous spacecraft have detected micron-sized cosmic dust particles across the Solar System. Some of these spacecraft had dust composition analyzers that used impact ionization to determine the composition of ions generated from the cosmic dust particle. Already the first dust composition analyzer, the Helios Micrometeoroid Analyzer, searched for variations of the compositional and physical properties of micrometeoroids. The spectra did not demonstrate any clustering of single minerals. The continuous transition from low to high ion masses indicates that individual grains are a mixture of various minerals and carbonaceous compounds. The more advanced dust mass analyzers on the 1986 comet Halley missions Vega 1, Vega 2, and Giotto recorded an abundance of small particles. In addition to silicates, many of these particles were rich in light elements such as H, C, N, and O. This indicates that Halley dust is even more primitive than carbonaceous chondrites. The identification of organic constituents suggests that the majority of the particles consist of a predominantly chondritic core with a refractory organic mantle.
The Cassini Cosmic Dust Analyzer (CDA) analyzed dust throughout its interplanetary cruise to Saturn and within the Saturn system. During Cassinis flyby of Jupiter CDA detected several 100 dust impacts within 100 million km from Jupiter. The spectra of these particles revealed sodium chloride (NaCl) as the major particle constituent, along with sulphurous and potassium-bearing components that demonstrated their relation to Jupiter's volcanic moon, Io. Saturn's E ring particles consist predominantly of water ice but in the vicinity of Saturn's moon Enceladus CDA found mostly salt-rich ice particles that were ejected by active ice geysers on the surface of this moon. This finding led to the belief that an underground salt-water ocean is the source for all matter observed in the plumes. At large distance from Saturn CDA identified and analyzed interstellar grains passing through the Saturn system. These analyses suggested magnesium-rich grains of silicate and oxide composition, some with iron inclusions.
The detection of electric dust charges by CDA provided means for contact-free detection and analysis of dust grains in space. This discovery led to the development of a trajectory sensor that allows us to determine the trajectory of a charged dust particle prior to impact onto an impact target. Such a dust trajectory sensor can be combined with an aerogel dust collector in order to form an active dust collector or with a large-area dust composition analyzer. in order to form a dust telescope With its capabilities CDA can be considered a prototype dust telescope.
Dust telescopes
In situ methods of dust astronomy like dust composition analyzers aim for the exploitation of the cosmochemical information contained in individual cosmic dust particles. Not so costly as sample return missions are rendezvous missions to a comet or asteroid like the Rosetta space probe to comet 67P/Churyumov–Gerasimenko. Rosetta characterized collected comet dust by sophisticated dust analyzers like the dust detector GIADA, a high-resolution secondary ion mass spectrometer COSIMA, an atomic force microscope MIDAS, and the mass spectrometers of ROSINA.
Several large-area dust composition analyzers and dust telescopes are in preparation in order to study astronomical objects or interplanetary dust from comets and asteroids and interstellar dust.
The Surface Dust Analyser (SUDA) on board the Europa Clipper mission will map the composition of Europa's surface and search for cryovolcanic plumes. The instrument is capable of identifying biosignatures and other complex molecules in ice ejecta.SUDA: A Dust Mass Spectrometer for Compositional Surface Mapping for a Mission to Europa (PDF). S. Kempf, N. Altobelli, C. Briois, E. Grün, M. Horanyi, F. Postberg, J. Schmidt, R. Srama, Z. Sternovsky, G. Tobie, and M. Zolotov. EPSC Abstracts Vol. 9, EPSC2014-229, 2014. European Planetary Science Congress 2014.
The DESTINY+ Dust Analyzer (DDA) will fly on the Japanese-German space mission DESTINY+ to asteroid 3200 Phaethon. Phaethon is the parent object of the December Geminids meteor stream. DDA's will study Phaeton's dust environment during the encounter and will analyze interstellar and interplanetary dust on cruise to Phaethon
The Interstellar Dust Experiment (IDEX) will fly on the Interstellar Mapping and Acceleration Probe (IMAP) at the Sun–Earth L1 Lagrange point. IDEX will provide the mass distribution and elemental composition of interstellar and interplanetary dust particles.
Sources of cosmic dust The ultimate source of cosmic dust are stars in which the elements – out of which stardust is composed of – are produced by fusion of hydrogen and helium or by explosive nucleosynthesis in supernovae. This stardust from various stellar sources is mixed in the interstellar medium and thermally processed in star forming regions. Solar System objects like comets and asteroids contain this material in more or less further processed form. Geologically active satellites like Io or Enceladus emit dust that condensed out of vapor from the molten interior of these planetary bodies.
Stars
After the Big Bang existed only the chemical elements Hydrogen, Helium, and Lithium.