The Diversity of Interplanetary Dust

The Diversity of Interplanetary Dust Walter van Dijk September 2020 Abstract The space between planets in the solar system is all but empty. All solid bodies in the solar system produce dust particles, which populate the interplanetary space. These particles can provide opportunities for research in many fields including the mechanics of the solar system and Earth's history. They can also pose collision risks for spacecraft and influence the Earth's climate by blocking solar radiation. Due to their small size the orbits of dust particles are influenced by solar radiation, which makes it possible for the material to travel throughout all of the solar system. Dust particles can be small enough to pass through the Earth's atmosphere without being vaporised as a result of friction, which makes it possible to collect samples on the Earth itself. The main goal of this review is to provide an introduction to interplanetary dust research and give some insight in the wide variety of disciplines that are involved. To achieve this, I summarise and describe the research on distribution, abundance, collection methods and modelling of interplanetary dust, and discuss potential future developments in the field. The review is focused around investigating the physical characteristics of dust particles and the methods to study them, along with the associated motivations. Studying dust can include a wide variety research areas. Remote sensing of dust can provide insights in their distribution and composition and samples can provide valuable insights properties of their origin object, but also modelling and in-situ experiments are used for studying dust in space. Extraterrestrial dust can provide unique insights in the development of their host object and subsequently provide clues for how our solar system works and other topics considering origin and development of the universe. Interplanetary dust occurs all over the Earth and there is a constant influx of material. However, although it is abundant, it can be difficult to find extraterrestrial dust on Earth because terrestrial materials can be similar. Therefore, terrestrial research usually takes place on locations with limited anthropogenic influence, weathering and erosion rates, such as Antarctica, the deep sea and deserts. Besides analysis on Earth, dust particles are also studied in the upper atmosphere and in space. Dust research has expanded to involve various fields, from paleogeology through astrobiology, which highlights the interdisciplinary nature of dust research. Similarly, there are many different methods for collecting cosmic dust on and around Earth, the results of which complement each other because the obtained samples differ in size distribution and composition. Interplanetary dust research appears to be highly interdisciplinary, and some research questions might only be answered by combining disciplines. One example is the urgent need for the development of methods to reduce the concentration of orbital debris around Earth. This problem is technically complex, but also involves economic and geopolitical aspects that requires collaboration among all these fields. 1 1 Introduction Dust in the interplanetary medium is produced from a wide variety of host objects. All Extraterrestrial materials have been of interest to solid bodies in our solar system can inject dust humanity for a long time. They occur throughout into space (Carrillo-Sánchez et al., 2016), and history as sacred objects and were often deemed some of the dust in our solar system even has to have religious significance. It wasn't until interstellar origins (Talbot Jr & Newman, 1977), the early 19th century however, that scientists however the most common sources of interplane- started to accept the hypothesis that rocks falling tary dust are asteroids and comets. from the sky had extraterrestrial origins (Mar- The aim of this literature review is to sum- vin, 2006). The report on meteorites falling near marise the current knowledge about dust in the L'Aigle in 1803 is considered a turning point in interplanetary medium and provide an overview the recognition of the extraterrestrial origin of of the various ways it is studied. This includes meteorites (Gounelle, 2006). Since then, a great the abundance and distribution of interplanetary effort has been made studying the composition, dust, physical collection, in-situ measurements, origin and implications of extraterrestrial matter. modelling and a discussion of the most impor- It is not surprising that many scientists are tant associated phenomena such as the Zodiac interested in (micro)meteorites. Extraterrestrial Light and the interstellar component. The de- matter can provide insight in many questions re- velopment of methods to collect, analyse and ob- garding the origins and development of the uni- serve interplanetary dust particles (IDPs), as well verse, because it resembles the composition of as some promising new technologies that can aid materials that formed planets billions of years this field of study are discussed as well. ago. This allows for unique insights in big topics The research questions to be investigated in such as the formation of stars or the origin of life. this review are: The vast majority of extraterrestrial matter that arrives at the Earth is in the form of dust. 1. What does the life cycle of IDPs look like? An estimated 40,000 metric tonnes of dust parti- 2. How do IDPs populate our solar system? cles arrive on Earth per day (Love & Brownlee, 1993). This implies that, although meteorites are 3. In which ways are IDPs studied? quite rare, everyone who sets a foot outside will probably come in contact with a fragment of ex- 4. What are the reasons to study IDPs? traterrestrial material in the form of cosmic dust. The abundance of dust particles is almost I aim to provide a comprehensive overview never directly visible to the untrained eye, but of the field of dust research, understandable even the particles can have major implications for without prior knowledge of cosmic dust. This pa- our understanding of cosmological and terres- per is based on three key review articles (Koschny trial phenomena. They are involved in the de- et al., 2019; Grünet al., 2019; Nesvorn`yet al., velopment of solar systems and how light travels 2010) and references therein. Some words and through space. As a result, the particles can in- terms essential to the field might be unfamiliar to fluence climate and interfere with cosmological readers without background knowledge, therefore observations. Besides these natural phenomena a glossary is provided, and the included words dust particles can also pose a danger to space- and terms are printed bold in the text. craft due to their high speed. Even some extinc- tion events might be related to changes in the amount of cosmic dust particles Earth encoun- 2 What are IDPs? ters (Kataoka et al., 2013). Consequently, it is of interest to develop methods to obtain and iden- Extraterrestrial matter occurs in a variety of tify these dust particles and improve our insight shapes, sizes and compositions. The size can in their behaviour. range from electrons (Grimani et al., 2009) to 2 gas-giants like Jupiter, with everything in be- particles are achondrites. By far most particles tween. The IAU has classified extraterrestrial ob- fall in the chondrite category. Chondrites can jects according to their size. The smallest objects be further classified in three groups: carbona- are classified as dust, having a size smaller than ceous, ordinary or enstatite. These groups divide 30 µm. Objects measuring between 30 µm and the chondrites in classes based on their degree of 1m are classified as meteoroids. Although this oxidation, carbonaceous being the least and en- scale is somewhat arbitrary, as there is a continu- statite being the most oxidised. ous population of bodies with sizes from <30 µm To describe dust in the interplanetary to >1m. Confusingly, the zodiacal dust cloud medium, currently the term 'interplanetary dust (Zodiacal Light) and cometary dust trails con- particles' or 'IDPs' is used most often, but in tain particles >30 µm which would not be clas- the past the term 'Zodiac Light', 'Zodiacal dust sified as dust, but as meteoroids, though they cloud' or similar wording was used. The Zodiacal are discussed in the context of dust populations. Light is a glowing along the zodiac in the night This results in some discrepancies in the litera- sky, on some occasions visible with the naked eye, ture regarding the exact definition of dust. In this produced by the reflection of sunlight off dust review paper dust particles (sizes smaller than particles. In this review 'IDPs' will be used to 30 µm) are discussed, but there is an inevitable describe the dust particles, as is common in other overlap with meteoroids. Further information re- recent literature, but research about the Zodiacal garding the current classification of particles can Light is also included when it is relevant. be found on the IAU web site1. Some aspects of the life cycle of IDPs make Dust that occurs in space can be classified them especially interesting. Generally, the dust according to its location: there is intergalactic particles in our solar system have a lifetime of 105 dust, interstellar dust, interplanetary dust years. Because dust has existed in the interplane- and circumplanetary dust. On the largest spa- tary medium for billions of years (D. Brownlee & tial scale there is intergalactic dust, which occu- Rajan, 1973), this implies that dust is constantly pies the space between galaxies (Wszolek et al., being created and destroyed at an approximately 1988). Within galaxies interstellar dust can be equal rate (Leinert et al., 1983). Lunar micro- found in the space between solar systems (Draine, crater studies, i.e. studies of impact craters on lu- 2003). Within solar systems there is interplan- nar rocks, indicate that this process has had pro- etary dust, a part of which is circumplanetary found effects on shaping planetary surfaces since dust.

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