Size-frequency statistics of boulders on global surface of asteroid 25143 Itokawa

Michikami, Tatsuhiro; Nakamura, Akiko; Hirata, Naru; Gaskell, R. W.; Nakamura, Ryosuke; Honda, T.; Honda, Chikatoshi; Hiraoka, K.; Saito, Junji; Demura, H.; Ishiguro, Masateru; Miyamoto, H.

doi:10.1186/bf03352757

Cited by 130 publications

(124 citation statements)

References 18 publications

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“…account. The presence of the same cumulative number in subsequent values is an indicator of a poor statistics that does not have to be considered by the fit: such effect typically occurs at the bigger boulder sizes, as presented in Pajola et al (2015) and Michikami et al (2008). This is valid for all plots presented in this work.…”

Section: Resultssupporting

confidence: 61%

Size-frequency distribution of boulders ≥10 m on comet 103P/Hartley 2

Pajola

Lucchetti

Bertini

et al. 2015

A&A

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Aims. We derive the size-frequency distribution of boulders on comet 103P/Hartley 2, which are computed from the images taken by the Deep Impact/HRI-V imaging system. We indicate the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the High Resolution Imager-Visible CCD camera on 4 November 2010. Boulders ≥10 m were identified and manually extracted from the datasets with the software ArcGIS. We derived the global size-frequency distribution of the illuminated side of the comet (∼50%) and identified the power-law indexes characterizing the two lobes of 103P. The three-pixel sampling detection, together with the shadowing of the surface, enables unequivocally detection of boulders scattered all over the illuminated surface. Results. We identify 332 boulders ≥10 m on the imaged surface of the comet, with a global number density of nearly 140/km 2 and a cumulative size-frequency distribution represented by a power law with index of −2.7 ± 0.2. The two lobes of 103P show similar indexes, i.e., −2.7 ± 0.2 for the bigger lobe (called L1) and −2.6 +0.2/ − 0.5 for the smaller lobe (called L2). The similar power-law indexes and similar maximum boulder sizes derived for the two lobes both point toward a similar fracturing/disintegration phenomena of the boulders as well as similar lifting processes that may occur in L1 and L2. The difference in the number of boulders per km 2 between L1 and L2 suggests that the more diffuse H 2 O sublimation on L1 produce twice the boulders per km 2 with respect to those produced on L2 (primary activity CO 2 driven). The 103P comet has a lower global power-law index (−2.7 vs. −3.6) with respect to 67P. The global differences between the two comets' activities, coupled with a completely different surface geomorphology, make 103P hardly comparable to 67P. A shape distribution analysis of boulders ≥30 m performed on 103P suggests that the cometary boulders show more elongated shapes when compared to collisional laboratory fragments as well as to the boulders present on the surfaces of 25 143 Itokawa and 433 Eros asteroids. Consequently, this supports the interpretation that cometary boulders have different origins with respect to the impact-related asteroidal boulders.

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Section: Resultssupporting

confidence: 61%

Size-frequency distribution of boulders ≥10 m on comet 103P/Hartley 2

Pajola

Lucchetti

Bertini

et al. 2015

A&A

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“…A value close to -3.5 is significant because this is in agreement with the empirical value for the distribution of particle sizes resulting from a collision, and for a collisionally relaxed population (Dohnanyi 1969). The value for the dust in the tail of P/2010 A2 is slightly steeper than the size distribution measured with Hayabusa for the boulders larger than 5 m on the surface of (25 143) Itokawa, n = −3.1 (Michikami et al 2008).…”

Section: Quantity Of Dust In the Tailsupporting

confidence: 69%

P/2010 a2 Linear

Hainaut

Kleyna

Sarid

et al. 2012

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Comet P/2010 A2 LINEAR is an object on an asteroidal orbit within the inner main belt, therefore a good candidate for membership with the main belt comet family. It was observed with several telescopes (ESO New Technology Telescope, La Silla, Chile; Gemini North, Mauna Kea, Hawaii; University of Hawaii 2.2 m, Mauna Kea, Hawaii) from 14 Jan. until 19 Feb. 2010 in order to characterize and monitor it and its very unusual dust tail, which appears almost fully detached from the nucleus; the head of the tail includes two narrow arcs forming a cross. No evolution was observed during the span of the observations. Observations obtained during the Earth orbital plane crossing allowed an examination of the out-of-plane 3D structure of the tail. The immediate surroundings of the nucleus were found dust-free, which allowed an estimate of the nucleus radius of 80-90 m, assuming an albedo p = 0.11 and a phase correction with G = 0.15 (values typical for S-type asteroids). A model of the thermal evolution indicates that such a small nucleus could not maintain any ice content for more than a few million years on its current orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up and electrostatic dust levitations were also rejected, leaving an impact with a smaller body as the favoured hypothesis. This is further supported by the analysis of the tail structure. Finston-Probstein dynamical dust modelling indicates the tail was produced by a single burst of dust emission. More advanced models (described in detail in a companion paper), independently indicate that this burst populated a hollow cone with a half-opening angle α ∼ 40 • and with an ejection velocity v max ∼ 0.2 m s −1 , where the small dust grains fill the observed tail, while the arcs are foreshortened sections of the burst cone. The dust grains in the tail are measured to have radii between a = 1-20 mm, with a differential size distribution proportional to a −3.44±0.08 . The dust contained in the tail is estimated to at least 8 × 10 8 kg, which would form a sphere of 40 m radius (with a density ρ = 3000 kg m −3 and an albedo p = 0.11 typical of S-type asteroids). Analysing these results in the framework of crater physics, we conclude that a gravity-controlled crater would have grown up to ∼100 m radius, i.e. comparable to the size of the body. The non-disruption of the body suggest this was an oblique impact.

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“…The fitting regression line used to obtain the power-law index does not consider those points that are equally cumulatively repeated above 6 m because they represent a poor statistic that has not to be considered by the fit. This effect has previously been observed for larger boulder sizes as presented in Pajola et al (2015b) and Michikami et al (2008).…”

Section: On the Hatmehit Depression We Confirm The Results Ofmentioning

confidence: 62%

Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

Lucchetti

Cremonese

Jordá

et al. 2015

A&A

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Context. On 12 November 2014, the European mission Rosetta delivered the Philae lander on the nucleus of comet 67P/ChuryumovGerasimenko (67P). After the first touchdown, the lander bounced three times before finally landing at a site named Abydos. Aims. We provide a morphologically detailed analysis of the Abydos landing site to support Philae's measurements and to give context for the interpretation of the images coming from the Comet Infrared and Visible Analyser (CIVA) camera system onboard the lander. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 6 December 2014 to perform the analysis of the Abydos landing site, which provided the geomorphological map, the gravitational slope map, the size-frequency distribution of the boulders. We also computed the albedo and spectral reddening maps.Results. The morphological analysis of the region could suggest that Philae is located on a primordial terrain. The Abydos site is surrounded by two layered and fractured outcrops and presents a 0.02 km 2 talus deposit rich in boulders. The boulder size frequency distribution gives a cumulative power-law index of −4.0 + 0.3/−0.4, which is correlated with gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. The average value of the albedo is 5.8% at λ 1 = 480.7 nm and 7.4% at λ 2 = 649.2 nm, which is similar to the global albedos derived by OSIRIS and CIVA, respectively.

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Size-frequency statistics of boulders on global surface of asteroid 25143 Itokawa

Cited by 130 publications

References 18 publications

Size-frequency distribution of boulders ≥10 m on comet 103P/Hartley 2

Size-frequency distribution of boulders ≥10 m on comet 103P/Hartley 2

P/2010 a2 Linear

Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

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