Micrometeorite collections: a review and their current status

Abstract

Micrometeorites are estimated to represent the main part of the present flux of extraterrestrial matter found on the Earth's surface and provide valuable samples to probe the interplanetary medium. Here, we describe large and representative collections of micrometeorites currently available to the scientific community. These include Antarctic collections from surface ice and snow, as well as glacial sediments from the eroded top of nunataks-summits outcropping from the icesheet-and moraines. Collections extracted from deep-sea sediments (DSS) produced a large number of micrometeorites, in particular, iron-rich cosmic spherules that are rarer in other collections. Collections from the old and stable surface of the Atacama Desert show that finding large numbers of micrometeorites is not restricted to polar regions or DSS. The advent of rooftop collections marks an important step into involving citizen science in the study of micrometeorites, as well as providing potential sampling locations over all latitudes to explore the modern flux. We explore their strengths of the collections to address specific scientific questions and their potential weaknesses. The future of micrometeorite research will involve the finding of large fossil micrometeorite collections and benefit from recent advances in sampling cosmic dust directly from the air. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Keywords: cosmic dust; micrometeorites; planetary science.

Figure 1.

Scanning electron backscatter images of sectioned micrometeorites from the Transantarctic Mountains (a,b) and Larkman Nunatak (c–i) collections. (a) A fine-grained unmelted micrometeorite. (b) A coarse-grained unmelted micrometeorite. (c) A scoriaceous micrometeorite. (d) A I-type cosmic spherule. (e) A G-type cosmic spherule. (f) A V-type cosmic spherule. (g) A CC cosmic spherule. (h) A barred olivine (BO) cosmic spherule. (i) A porphyritic olivine (Po) cosmic spherule. Arrows indicate relict olivine. Scale bars 100 µm.

Figure 2.

Sampling locations of Antarctic collections (a). (b) Snow sampling in a trench near Dome C. Photo credit: J. Duprat, MNHN. (c) Backscatter electron image of an UCAMM from Dome C [32]. (d) Approximate size and shape of the South Pole water well (SPWW) in December 1995. (e) Secondary electron image of CP micrometeorite D07IB39 [33]. (f) Detail of the sampling area at Larkman Nunatak. Photo credit: Matthew Genge, ICL. (g) Glacially eroded surface of Walnumfjellet in the Sør Rondane Mountains (inset shows the 30 cm × 30 cm × 6 cm sampling area). (h) Sampling location on a moraine near Wideroefjellet in the Sør Rondane Mountains. Photo credit for (g,h): Matthias van Ginneken, UKC. (i) Sampling of glacial sediment on a flat eroded summit of the Transantarctic Mountains. Photo credit: Luigi Folco, UniPi. The map was made using the Quantarctica package for QGIS [34].

Figure 3.

Geographical area of DSS was sampled in the Indian Ocean (a). (b) Electron backscattered image of a sectioned unmelted micrometeorite from the DSS collection. Scalebar is 100 µm. (c) Result of a Grab Sampler operation showing a large quantity of DSS from the Indian Ocean. (d) Spherules were extracted from the DSS on the research vessel shortly after sampling in the Indian Ocean. Photo credit: NIO members.

Figure 4.

Sampling locations in the Atacama Desert in Chile (a). (b) Desert soil is being gathered before magnetic extraction and sampling. Photo credit: Jérôme Gattacceca, CEREGE. (c,d) Backscattered electron images of cosmic spherules from the Atacama Desert. The scalebars are 100 µm.

Figure 5.

Photos of urban micrometeorites. (a) The rooftop of the farm from which the Budel collection was established (Photo credit: Guido Jonker, VUA). (b) Photomicrograph of an urban micrometeorite collected by Scott Peterson showing a metal bead that appears to be in the process of being ejected from S-type cosmic spherule. Photo credit: Scott Peterson. (c) Photomicrographic montage of cosmic spherules from the Project Stardust collection, showing a wide range of colours and the presence of elongated specimen. Photo credit: Jon Larsen.

Figure 6.

Proportions of unmelted, scoriaceous and cosmic spherules in the collections.

Figure 7.

Cumulative size distributions from the SPWW [41], the Transantarctic Mountains collection (TAM; [95]), Larkman Nunatak moraine [42], Deep Sea Spherules from the Indian Ocean Collection (Indian O.; [44]), the Atacama Desert and the Sør Rondane Mountains (SR; [43]). The absolute cumulative number relates to the total number of particles collected. Inflection points are likely relate to the removal of particles by weathering or accumulation processes.

Figure 8.

Photos of air sampling: (a) one of the high-volume air samplers located on the airport building at Kwajalein. (b) Filter change being performed. (c,d) Backscattered electron image images of exterior (c) and interior (d) of a cosmic spherule candidate identified on surveyed areas of Kwajalein filters. Scalebar is 5 µm. (e) Photo of building housing the air sampler at SPWW [119]. (f) Schematic of the collector, arrow shows the location of the filter unit in the intake pipe. (g) Schematic of the filter unit. (h) Image of the filter unit in the pipe and toggles used to clamp it shut. (a–d) Modified from [118].