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Michikami, T., Hagermann, A., Tsuchiyama, A., Otsuka, Y., Nakamura, M., Okumura, S., . . . Hasegawa, S. (2024). The influence of chondrules on sub-mm fragment shape distributions in Allende impact experiments. Icarus, 415, Article ID 116068.
Open this publication in new window or tab >>The influence of chondrules on sub-mm fragment shape distributions in Allende impact experiments
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2024 (English)In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 415, article id 116068Article in journal (Refereed) Published
Abstract [en]

The surfaces of sub-kilometer-sized asteroids directly explored by spacecraft, such as Itokawa, Ryugu and Bennu, are covered with blocks and/or regolith particles, whose shapes are considered clues to understanding their formation and evolution on the asteroid's surface. Ryugu particles returned by the Hayabusa2 mission are likely fragments resulting from impacts because their shapes resemble impact fragments from laboratory experiments. However, there is a lack of laboratory impact experiments examining the shapes of fragments in carbonaceous chondrites, thought to originate from carbonaceous asteroids such as Ryugu and Bennu. The measured sizes of Ryugu particles are in the mm and sub-mm range, similar to the sizes of chondrules. Also, carbonaceous chondrites are generally structurally weaker than the basalts and granites often used in previous laboratory impact experiments. Differences in the strength of the chondrules and matrix might affect the overall strength of the meteorite. In this study, as a first step towards a better understanding of impact fragment shapes in carbonaceous chondrites, we conducted impact experiments on the carbonaceous meteorite Allende (CV3). A spherical alumina projectile with 1.0 mm and a glass projectile with 0.80 mm in diameter were fired into 1–2 cm-sized Allende targets at nominal impact velocities of 2.0 and 4.0 km/s, respectively. To investigate the correlation between the chondrules (typically sub-mm in size) and the shapes of fine fragments, we measured the shape distributions of sub-mm impact fragments using X-ray microtomography. We observed several impact fracture surfaces along the chondrule boundaries. In addition, these fragments tended to be rounder than fragments from previous impact experiments. However, because the total number of these fragments is relatively small, the fragments were found to have the same overall shape distribution as previous laboratory impact fragments, Itokawa particles and Ryugu particles. This may imply that impact fragment shapes are independent of the bulk material strength. These findings will be useful for understanding the formation process of regolith layers on asteroid surfaces, Itokawa particles, Ryugu particles, and Bennu particles.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Asteroid, Asteroids surfaces, Impact phenomena, Meteorites, Regolith
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Atmospheric Science
Identifiers
urn:nbn:se:ltu:diva-105184 (URN)10.1016/j.icarus.2024.116068 (DOI)001230185700001 ()2-s2.0-85189983809 (Scopus ID)
Note

Validerad;2024;Nivå 2;2024-04-23 (signyg);

Funder: JSPS KAKENHI (JP20K04048;JP22H00162;BR230501); SNSA (2021-00078);

Full text license: CC BY

Available from: 2024-04-23 Created: 2024-04-23 Last updated: 2024-11-20Bibliographically approved
Zhaka, V., Bridges, R., Riska, K., Hagermann, A. & Cwirzen, A. (2023). Initial snow-ice formation on a laboratory scale. Annals of Glaciology, 64(91), 77-94
Open this publication in new window or tab >>Initial snow-ice formation on a laboratory scale
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2023 (English)In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 64, no 91, p. 77-94Article in journal (Refereed) Published
Abstract [en]

Snow ice (SI) forms from freezing wet snow, known as slush, and contributes to the thickness of level and brash ice. However, the mechanism of snow-slush-snow ice transformation has not been extensively investigated to date, despite the difference in the freezing rate of slush in comparison with water is important for estimating the ice thickness. In this study, we examined the growth of initial congelation ice (CI) and snow ice (SI) in a fresh water tank exposed to outdoor weather conditions in Luleå, northern Sweden. The tank of size 1.8 × 0.65 × 1.2 m in length, width and height was divided into two compartments to facilitate the simultaneous growth of CI and SI. A total of 12 experiments were conducted in the years 2021 and 2022. The transformation from slush to snow ice was achieved by submerging various amounts of snow in the compartments. It was observed that approximately 35% of the initial snow transformed into SI. Snow ice grew 4 mm°C-0.5 d-0.5 faster than congelation ice. The CI growth under SI was 1 mm°C-0.5 d-0.5 slower than the CI growth under CI. This study provides valuable insights for modelling snow-slush-snow ice transformation and designing future laboratory-scale experiments.

Place, publisher, year, edition, pages
Cambridge University Press, 2023
Keywords
Ice thickness measurements, ice/atmosphere interactions, sea-ice growth and decay, snow physics, snow/ice surface processes
National Category
Water Engineering
Research subject
Building Materials; Atmospheric Science
Identifiers
urn:nbn:se:ltu:diva-101211 (URN)10.1017/aog.2023.58 (DOI)001209570100002 ()2-s2.0-85168999353 (Scopus ID)
Note

Validerad;2024;Nivå 2;2024-06-26 (hanlid);

Funder: TotalEnergies;

Full text license: CC BY

Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2024-06-26Bibliographically approved
Michikami, T., Tsuchiyama, A., Hagermann, A., Takeda, A., Shishido, K., Otsuka, Y., . . . Hasegawa, S. (2023). Three-dimensional imaging of high-velocity-impact induced crack growth in carbonaceous meteorites. Icarus, 392, Article ID 115371.
Open this publication in new window or tab >>Three-dimensional imaging of high-velocity-impact induced crack growth in carbonaceous meteorites
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2023 (English)In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 392, article id 115371Article in journal (Refereed) Published
Abstract [en]

The material strength of meteorites provides useful information on the make-up and history of asteroids. However, the unique determination of the material strength of a meteorite is difficult because of the wide range of strengths many meteorites exhibit. Even within a single sample, complicated textures and mineral granular compositions make measurements difficult. Michikami et al. (2019) investigated the impact-induced crack growth in ordinary (L5) chondrites and indicated that crack growth is largely affected by the strength of individual mineral grains (and/or chondrules). In this study, we examine the strengths of mineral grains in carbonaceous meteorites qualitatively. To this end, we use X-ray microtomography to investigate how chondrules are affected by impact-induced crack growth in carbonaceous meteorites. Spherical alumina projectiles with a diameter of 1.0 mm were fired into the surfaces of seven Allende (CV) meteorite target samples with sizes of -1 to 2 cm at a nominal impact velocity of 2.0 km/s. In addition, spherical glass projectiles with a diameter 0.8 mm were fired into the target surfaces of two Murchison (CM) and two Aguas Zarcas (CM) meteorite target samples with sizes of -2 cm at a nominal impact velocity of 4.0 km/s. The results show that most cracks in CV chondrites tend to grow along the boundary surfaces of the chondrules, while most chondrule-related cracks in CM samples grow regardless of the boundary surfaces of the chondrules. This suggests that crack growth is largely affected by the chondrules' strength as indicated by Michikami et al. (2019). The weaker the strength of chondrules, the more likely crack growth tends to occur regardless of chondrule boundaries. We found that the mesostasis of chondrules in CM meteorite Murchison (and likely Aguas Zarcas) has experienced aqueous alteration and the chondrules have become structurally weak as a whole. This indicates that impact-induced crack propagation in CM chondrites differs from thermal-fatigue induced crack propagation inferred from previous studies. As the sample material to be returned from asteroid Bennu is considered to be related to CM chondrites, we propose that observation of the cracks in chondrules in Bennu samples might tell us whether those cracks are impact- or thermal-fatigue-induced.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Crack growth, Chondrules, C chondrites, X-ray microtomography, Laboratory impact experiments
National Category
Meteorology and Atmospheric Sciences Geosciences, Multidisciplinary
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-95238 (URN)10.1016/j.icarus.2022.115371 (DOI)000895788600001 ()2-s2.0-85146217596 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-01-16 (sofila);

Funder: JSPS KAKENHI (grant nos.  JP20K04048 and JP20H00205); Chinese Academy of Sciences International Fellowship for Visiting Scientists (grant no. 2019VCA0004); SNSA (Dnr. 2021-00078); Hypervelocity Impact Facility, ISAS, JAXA

Available from: 2023-01-16 Created: 2023-01-16 Last updated: 2025-02-01Bibliographically approved
Terliesner, S., Kaufmann, E., Grott, M. & Hagermann, A. (2022). A Simple Way of Simulating Insolation on a Rotating Body with a Commercial Solar Simulator. International journal of thermophysics, 43(7), Article ID 111.
Open this publication in new window or tab >>A Simple Way of Simulating Insolation on a Rotating Body with a Commercial Solar Simulator
2022 (English)In: International journal of thermophysics, ISSN 0195-928X, E-ISSN 1572-9567, Vol. 43, no 7, article id 111Article in journal (Refereed) Published
Abstract [en]

The surfaces of all solid bodies in the solar system, planets, moons, comets and asteroids, experience short-term temporal variations of solar irradiation which depend on their respective spin rates. These so-called insolation cycles affect temperature variations, climate, photosynthesis in plants, etc. Hence, experimental reproduction of these cycles is important for space analogue simulations. In this short note we describe a simple, low-cost method to simulate diurnal cycles in the laboratory using a type of commercial solar simulator commonly used for experimental investigation in planetary science.

Place, publisher, year, edition, pages
Springer Nature, 2022
Keywords
Insolation, Thermal simulations, Solar simulator, Thermal wave
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-91207 (URN)10.1007/s10765-022-03027-8 (DOI)000801144600001 ()2-s2.0-85130689627 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-06-15 (hanlid);

Part of special issue: Thermophysics of Advanced Spacecraft Materials and Extraterrestrial Samples

Available from: 2022-06-15 Created: 2022-06-15 Last updated: 2024-03-07Bibliographically approved
Lethuillier, A., Feller, C., Kaufmann, E., Becerra, P., Hänni, N., Diethelm, R., . . . Jäggi, N. (2022). Cometary dust analogues for physics experiments. Monthly notices of the Royal Astronomical Society, 515(3), 3420-3438
Open this publication in new window or tab >>Cometary dust analogues for physics experiments
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2022 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 515, no 3, p. 3420-3438Article in journal (Refereed) Published
Abstract [en]

The CoPhyLab (Cometary Physics Laboratory) project is designed to study the physics of comets through a series of earth-based experiments. For these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. This ‘CoPhyLab dust’ is planned to be mixed with water and CO2 ice and placed under cometary conditions in vacuum chambers to study the physical processes taking place on the nuclei of comets. In order to develop this dust analogue, we mixed two components representative for the non-volatile materials present in cometary nuclei. We chose silica dust as a representative for the mineral phase and charcoal for the organic phase, which also acts as a darkening agent. In this paper, we provide an overview of known cometary analogues before presenting measurements of eight physical properties of different mixtures of the two materials and a comparison of these measurements with known cometary values. The physical properties of interest are particle size, density, gas permeability, spectrophotometry, and mechanical, thermal, and electrical properties. We found that the analogue dust that matches the highest number of physical properties of cometary materials consists of a mixture of either 60 per cent/40 per cent or 70 per cent/30 per cent of silica dust/charcoal by mass. These best-fit dust analogue will be used in future CoPhyLab experiments.

Place, publisher, year, edition, pages
Oxford University Press, 2022
Keywords
methods: laboratory: solid state, techniques: miscellaneous, comets: general, comets: individual: 67P/Churyumov-Gerasimenko
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-92498 (URN)10.1093/mnras/stac1734 (DOI)000836707600005 ()2-s2.0-85136307177 (Scopus ID)
Projects
CoPhyLab-project
Note

Validerad;2022;Nivå 2;2022-08-19 (hanlid);

Funder: D-A-CH programme (DFG: GU 1620/3-1and BL 298/26-1 / SNF: 200021E 177964 / FWF: I 3730-N36); SwissNational National Science Foundation

Available from: 2022-08-16 Created: 2022-08-16 Last updated: 2022-09-05Bibliographically approved
Butcher, F. E. .., Arnold, N. S., Balme, M. R., Conway, S. J., Clark, C. D., Gallagher, C., . . . Woodley, S. Z. (2022). Eskers associated with buried glaciers in Mars' mid latitudes: recent advances and future directions. Annals of Glaciology, 63(87-89), 33-38
Open this publication in new window or tab >>Eskers associated with buried glaciers in Mars' mid latitudes: recent advances and future directions
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2022 (English)In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 63, no 87-89, p. 33-38Article in journal (Refereed) Published
Abstract [en]

Until recently, the influence of basal liquid water on the evolution of buried glaciers in Mars' mid latitudes was assumed to be negligible because the latter stages of Mars' Amazonian period (3 Ga to present) have long been thought to have been similarly cold and dry to today. Recent identifications of several landforms interpreted as eskers associated with these young (100s Ma) glaciers calls this assumption into doubt. They indicate basal melting (at least locally and transiently) of their parent glaciers. Although rare, they demonstrate a more complex mid-to-late Amazonian environment than was previously understood. Here, we discuss several open questions posed by the existence of glacier-linked eskers on Mars, including on their global-scale abundance and distribution, the drivers and dynamics of melting and drainage, and the fate of meltwater upon reaching the ice margin. Such questions provide rich opportunities for collaboration between the Mars and Earth cryosphere research communities.

Place, publisher, year, edition, pages
Cambridge University Press, 2022
Keywords
Debris-covered glaciers, extraterrestrial glaciology, geomorphology
National Category
Geology Physical Geography
Research subject
Atmospheric Science
Identifiers
urn:nbn:se:ltu:diva-96335 (URN)10.1017/aog.2023.7 (DOI)000952231700001 ()2-s2.0-85150453388 (Scopus ID)
Funder
EU, Horizon 2020, 787263
Note

Validerad;2023;Nivå 2;2023-11-07 (joosat);

Funder: French Space Agency CNES; STFC (ST/V50693X/1); NASA (80NSSC21K0908); UK Space Agency (ST/R001405/1, ST/T002913/1, ST/V005332/1, ST/W002744/1, ST/W002949/1)

Full text license: CC BY 4.0

Available from: 2023-04-06 Created: 2023-04-06 Last updated: 2023-11-09Bibliographically approved
Moore, A., Hagermann, A., Kaufmann, E., Granvik, M., Barabash, V., Murdoch, N., . . . Soria-Salinas, A. (2022). Penetrometry in Microgravity- From Brie to Bennu. In: EPSC Abstracts Vol. 16, 2022: . Paper presented at Europlanet Science Congress 2022, Granada, Spain, September 18–23, 2022. Copernicus GmbH, Article ID EPSc2022-178.
Open this publication in new window or tab >>Penetrometry in Microgravity- From Brie to Bennu
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2022 (English)In: EPSC Abstracts Vol. 16, 2022, Copernicus GmbH , 2022, article id EPSc2022-178Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

In this abstract we discuss a proposal for a microgravity flight campaign within which we will investigate penetrometry in a microgravity environment. Understanding the mechanical properties of solar system minor bodies is essential for understanding their origin and evolution. Past missions such as Hayabusa-2 and OSIRIS-REX have landed on asteroids and taken samples to discover what these bodies are made of. However, there has been conflicting evidence and reports into the physical properties of the granular surface material of these bodies. With future missions such as JAXA’s MMX mission travelling to Phobos to take a sample of the body the results from this campaign will be very important to that and future missions. Penetrometry, i.e. the determination of the reaction force an object experiences as it penetrates into a surface, can help to understand the essential properties regarding regolith such as grain size, grain shape, cohesion and bulk density. The usage of penetrometry however has mostly been limited ground-based studies such as soil sciences or even cheese maturation. Very little is known about the underlying physics of penetrometry. Results of penetrometry experiments are largely analysed based on empirical models, which presents us with a challenge if we want to apply the same parameters to understand granular materials on asteroid surfaces. Obviously, gravity cannot be eliminated in the laboratory. Hence, it is essential to verify penetrometry as a method and validate penetrometry instrument designs in microgravity.

For this purpose, we propose a parabolic flight campaign. Our experiment will test the use of penetrometry in asteroid-analogue environments by investigating samples with varying properties such as grain size and shape. The microgravity aspect of the experiment is one of the most important factors because it enables us to correlate laboratory experiments at 1g with identical setups in a gravity regime relevant to asteroids. The proposed experimental setup will include a variety of samples with varying grain sizes, grain shapes, porosities and grain size distributions. The penetrometer used will also have varying properties such as the diameter, shape, and velocity of penetration. A robotic arm will push a penetrometer into the samples to measure the reaction force which can then be used to determine the mechanical properties of the samples. By varying the samples and penetrometer properties it will be possible to better understand the relevant parameters affecting reaction force. The suitability of the setup will also be reviewed to understand its usage and applicability in microgravity environments such as the robotic arm that will be used. All of the experiments carried out during the parabolic campaign will also be done at 1g to compare the tests in varying gravity levels. With a better understanding of the science behind penetrometry and the effects of microgravity, future missions will be better prepared and be able to use penetrometry more effectively to understand small-body surfaces.

Place, publisher, year, edition, pages
Copernicus GmbH, 2022
Keywords
microgravity, penetrometry, planetary science, planetary surface, solar system bodies
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Atmospheric science; Onboard space systems
Identifiers
urn:nbn:se:ltu:diva-93105 (URN)10.5194/epsc2022-178 (DOI)
Conference
Europlanet Science Congress 2022, Granada, Spain, September 18–23, 2022
Available from: 2022-09-19 Created: 2022-09-19 Last updated: 2023-01-23Bibliographically approved
Michikami, T., Hagermann, A., Morota, T., Yokota, Y., Urakawa, S., Okamura, H., . . . Sugita, S. (2022). Three-axial shape distributions of pebbles, cobbles and boulders smaller than a few meters on asteroid Ryugu. Icarus, 381, Article ID 115007.
Open this publication in new window or tab >>Three-axial shape distributions of pebbles, cobbles and boulders smaller than a few meters on asteroid Ryugu
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2022 (English)In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 381, article id 115007Article in journal (Refereed) Published
Abstract [en]

Over a broad size range, the shapes of impact fragments from catastrophic disruptions are distributed around the mean axial ratio 2: √2: 1, irrespective of experimental conditions and target materials. Although most blocks on asteroids are likely to be impact fragments, there is not enough quantitative data for reliable statistics on their three-axial lengths and/or ratios because it is difficult to precisely estimate the heights of the blocks. In this study, we evaluate the heights of blocks on asteroid Ryugu by measuring their shadows. The three-axial ratios of ~4100 small blocks with diameters from 5.0 cm to 7.6 m in Ryugu's equatorial region are investigated using eight close-up images of narrower localities taken at altitudes below 500 m, i.e. at <5.4 cm/pixel resolution, obtained immediately before the second touch-down of the Hayabusa2 spacecraft. The purpose of this study is to investigate the block shape distribution, which is important for understanding the geological history of asteroid Ryugu. Specifically, the shape distribution is compared to laboratory impact fragments. Our observations indicate that the shape distributions of blocks smaller than 1 m on Ryugu are consistent with laboratory impact fragment shape distributions, implying that the dominant shape-determining process for blocks on Ryugu was impact fragmentation. Blocks several meters in size in the equatorial region seem to be slightly flatter than the rest, suggesting that some blocks are partly buried in a bed of regolith. In conclusion, the shape distributions of blocks from several-cm to several-m in the equatorial region of asteroid Ryugu suggest that these are mainly fragments originating from the catastrophic disruption of their parent body and/or from a later impact.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Asteroids, Surfaces, Impact process, Asteroid Ryugu, Regolith
National Category
Astronomy, Astrophysics and Cosmology Geology
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-90045 (URN)10.1016/j.icarus.2022.115007 (DOI)000793645100001 ()2-s2.0-85127897108 (Scopus ID)
Note

Validerad;2022;Nivå 2;2022-04-13 (joosat);

Funder: Japan Society for the Promotion of Science (JSPS) KAKENHI (20K04048, 20H00194, 15H02146); Chinese Academy of Sciences President's International Fellowship Initiative (2019VCA0004); Hypervelocity Impact Facility, ISAS, JAXA

Available from: 2022-04-01 Created: 2022-04-01 Last updated: 2023-03-28Bibliographically approved
Sakatani, N., Tanaka, S., Okada, T., Fukuhara, T., Riu, L., Sugita, S., . . . Tsuda, Y. (2021). Anomalously porous boulders on (162173) Ryugu as primordial materials from its parent body. Nature Astronomy, 5(8), 766-774
Open this publication in new window or tab >>Anomalously porous boulders on (162173) Ryugu as primordial materials from its parent body
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2021 (English)In: Nature Astronomy, E-ISSN 2397-3366, Vol. 5, no 8, p. 766-774Article in journal (Refereed) Published
Abstract [en]

Planetesimals—the initial stage of the planetary formation process—are considered to be initially very porous aggregates of dusts1,2, and subsequent thermal and compaction processes reduce their porosity3. The Hayabusa2 spacecraft found that boulders on the surface of asteroid (162173) Ryugu have an average porosity of 30–50% (refs. 4,5,6), higher than meteorites but lower than cometary nuclei7, which are considered to be remnants of the original planetesimals8. Here, using high-resolution thermal and optical imaging of Ryugu’s surface, we discovered, on the floor of fresh small craters (<20 m in diameter), boulders with reflectance (~0.015) lower than the Ryugu average6 and porosity >70%, which is as high as in cometary bodies. The artificial crater formed by Hayabusa2’s impact experiment9 is similar to these craters in size but does not have such high-porosity boulders. Thus, we argue that the observed high porosity is intrinsic and not created by subsequent impact comminution and/or cracking. We propose that these boulders are the least processed material on Ryugu and represent remnants of porous planetesimals that did not undergo a high degree of heating and compaction3. Our multi-instrumental analysis suggests that fragments of the highly porous boulders are mixed within the surface regolith globally, implying that they might be captured within collected samples by touch-down operations10,11.

Place, publisher, year, edition, pages
Springer Nature, 2021
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Atmospheric Science
Identifiers
urn:nbn:se:ltu:diva-85047 (URN)10.1038/s41550-021-01371-7 (DOI)000653643000001 ()2-s2.0-85106265874 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-08-17 (johcin)

Available from: 2021-06-07 Created: 2021-06-07 Last updated: 2024-01-22Bibliographically approved
Michikami, T. & Hagermann, A. (2021). Boulder sizes and shapes on asteroids: A comparative study of Eros, Itokawa and Ryugu. Icarus, 357, Article ID 114282.
Open this publication in new window or tab >>Boulder sizes and shapes on asteroids: A comparative study of Eros, Itokawa and Ryugu
2021 (English)In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 357, article id 114282Article in journal (Refereed) Published
Abstract [en]

In order to understand the geological evolution of asteroids Eros, Itokawa and Ryugu and their collisional history, previous studies investigated boulder size distributions on their surfaces. However, quantitative comparison of these size distributions is hampered by numerous differences between these studies regarding the definition of a boulder's size, measuring technique and the fitting method to determine the power-index of the boulder size distributions. We provide a consistent and coherent model of boulder size distributions by remeasuring the boulders on the entire surfaces of Eros and Itokawa using the Small Body Mapping Tool (SBMT) and combining our observations with the Ryugu data of Michikami et al. (2019). We derived power-indices of the boulder size distributions of −3.25 ± 0.14 for Eros, −3.05 ± 0.14 for Itokawa and −2.65 ± 0.05 for Ryugu. The asteroid with the highest number density of boulders ≥ 5 m turns out to be Ryugu, not Itokawa, as suggested by an earlier study. We show that the appearance of the boulders tends towards more elongated shapes as the size of an asteroid decreases, which can be explained by differences in asteroid gravity and boulder friction angles. Our quantitative observational results indicate that boulder migration preferentially affects smaller boulders, and tends to occur on larger asteroids.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Asteroids, Surfaces, Asteroid Eros, Asteroid Itokawa, Asteroid Ryugu, Regoliths
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-82254 (URN)10.1016/j.icarus.2020.114282 (DOI)000614115900052 ()2-s2.0-85106566338 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-01-11 (alebob);

Finansiär: JSPS KAKENHI (20K04048), Hypervelocity Impact Facility, ISAS, JAXA

Available from: 2021-01-11 Created: 2021-01-11 Last updated: 2023-10-11Bibliographically approved
Projects
Remote sensing of mining impacts in the Arctic [2023-00244_SNSB]; Uppsala University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1818-9396

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