Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the Early Solar System

Sierks, H.; Lamy, P.; Barbieri, C.; Koschny, D.; Rickman, H.; Rodrigo, R.; A’Hearn, M. F.; Angrilli, Francesco; Barucci, Maria Antonella; Bertaux, J. L.; Bertini, Ivano; Besse, S.; Carry, B.; Cremonese, G.; Deppo, Vania Da; Davidsson, B.; Debei, S.; Cecco, M. De; León, J. de; Ferri, F.; Fornasier, S.; Fulle, M.; Hviid, S. F.; Gaskell, R. W.; Groussin, O.; Gutierrez, P.; Ip, Wing-Huen; Jordá, L.; Kaasalainen, M.; Keller, H. U.; Knollenberg, J.; Kramm, R.; Kührt, Ekkehard; Küppers, M.; Lara, L. M.; Lazzarin, M.; Leyrat, C.; Moreno, J. J. Lopez; Magrin, S.; Marchi, S.; Marzari, F.; Massironi, Matteo; Michalik, H.; Moissl, R.; Naletto, G.; Preusker, Frank; Sabau, L.; Sabolo, W.; Scholten, F.; Snodgrass, C.; Thomas, N.; Tubiana, C.; Vernazza, Pierre; Vincent, J. B.; Wenzel, K. P.; Andert, T. P.; Pätzold, M.; Weiss, B. P.

doi:10.1126/science.1207325

Cited by 189 publications

(149 citation statements)

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“…Most of the data have been acquired at relatively small phase angles, thus we have a good sampling of the opposition surge. If we fit a straight line for the radiance factor of facets observed with phase angle larger than 20 • , we measure a increase of the radiance factor of 0.11 due to the non-linear enhancement, which is ∼ 50% of the albedo at zero phase angle (0.19 ± 0.02, the geometric albedo according to Sierks et al, 2011). The spread of points is due to geometric condition only, the so-called disk profile (Shkuratov et al, 2011), were facets close to limb are obscured in the extreme values of incidence and emergence angles.…”

Section: Then It Providesmentioning

confidence: 99%

“…The rotational period of 8.168 hours and direction of the pole axis were improved (Carry et al, 2010). The global shape with principal axes dimensions of 121 ± 1 km × 101 ± 1 km × 75 ± 13 km was determined (Sierks et al, 2011), even if a large fraction of the asteroid's southern hemisphere was not visible during the fly-by and consequently the shortest semi-major dimension is not well constrained. From the shape model, an estimation of volume of (5.0 ± 0.4) · 10 5 km 3 has been derived and combining it with the mass obtained by the Radio science investigation 1.7 · 10 18 kg ± 1 by Pätzold et al (2011) a bulk density of 3.4 ± 0.3g · cm −3 has been computed.…”

Section: Introductionmentioning

confidence: 99%

“…The OSIRIS camera systems (Keller et al, 2007) composed of two cameras (NAC, Narrow Angle Camera and WAC, Wide Angle Camera) observed the asteroid (Sierks et al, 2011) in 21 broad and narrow band filters covering more than 50% of the surface with spatial scales up to 60 m/pixel. The rotational period of 8.168 hours and direction of the pole axis were improved (Carry et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Asteroid (21) Lutetia: Disk-resolved photometric analysis of Baetica region

Hasselmann

Fornasier

Leyrat

et al. 2016

Icarus

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ABSTRACT. (21) Lutetia has been visited by Rosetta mission on July 2010 and observed with a phase angle ranging from 0.15 to 156.8 degrees. The Baetica region, located at the north pole has been extensively observed by OSIRIS cameras system. Baetica encompass a region called North Pole Crater Cluster (NPCC), shows a cluster of superposed craters which presents signs of variegation at the small phase angle images. For studying the location, we used 187 images distributed throughout 14 filter recorded by the NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) of the OSIRIS system on-board Rosetta taken during the fly-by. Then, we photometrically modeled the region using Minnaert diskfunction and Akimov phase function to obtain a resolved spectral slope map at phase angles of 5 • and 20 • . We observed a dicothomy between Gallicum and Danuvius-Sarnus Labes in the NPCC, but no significant phase reddening (−0.04 ± 0.045% · microns −1 deg −1 ). In the next step, we applied the Hapke (2008Hapke ( ,2012 model for the NAC F82+F22 (649.2 nm), WAC F13 (375 nm) and WAC F17 (631.6 nm) and we obtained normal albedo maps and Hapke parameter maps for NAC F82+F22. On Baetica, at 649.2 nm, the geometric albedo is 0.205 ± 0.005, the average single-scattering albedo is 0.181 ± 0.005, the average asymmetric factor is −0.342 ± 0.003, the average shadow-hiding opposition effect amplitude and width are 0.824 ± 0.002 and 0.040 ± 0.0007, the average roughness slope is 11.45 • ± 3 • and the average porosity is 0.85 ± 0.002. We are unable to confirm the presence of coherent-backscattering mechanism. In the NPCC, the normal albedo variegation among the craters walls reach 8% brighter for Gallicum Labes and 2% fainter for Danuvius Labes. The Hapke parameter maps also show a dicothomy at the opposition effect coefficients, single-scattering albedo and asymmetric factor, that may be attributed to the maturation degree of the regolith or to compositonal variation. In addition, we compared the Hapke (2008Hapke ( , 2012 and Hapke (1993) parameters with laboratory samples and other small-solar system bodies visited by space missions.

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Section: Then It Providesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Asteroid (21) Lutetia: Disk-resolved photometric analysis of Baetica region

Hasselmann

Fornasier

Leyrat

et al. 2016

Icarus

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“…Rosetta encounter with main-belt asteroid (21) Lutetia has demonstrated that not all M-type asteroids are metal-rich 17 . Indeed, the low radar albedo 8 of 1950 DA is very similar to that of Lutetia, suggesting a similar composition.…”

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confidence: 99%

“…Indeed, the low radar albedo 8 of 1950 DA is very similar to that of Lutetia, suggesting a similar composition. The best meteorite analog for Lutetia is an enstatite chondrite 17 , which has a grain density of 3.55 g cm -3 . Taking the same meteorite analog and grain density for 1950 DA implies a macro-porosity of 51 ± 19 % and indicates that it is a rubble pile asteroid (Fig.…”

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confidence: 99%

Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA

Rozitis

MacLennan

Emery

2014

Nature

177

137

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Space missions 1 and ground-based observations 2 have shown that some asteroids are loose collections of rubble rather than solid bodies. The physical behavior of such 'rubble pile' asteroids has been traditionally described using only gravitational and frictional forces within a granular material 3 . Cohesive forces in the form of small van der Waals forces between constituent grains have been recently predicted to be important for small rubble piles (10-kilometer-sized or smaller), and can potentially explain fast rotation rates in the small asteroid population 4-6 . Hitherto, the strongest evidence came from an analysis of the rotational breakup of main belt comet P/2013 R3 (ref. 7), although that was indirect and poorly constrained by present observations. Here we report that the kilometer-sized asteroid (29075) 1950 DA 8 is a rubble pile that is rotating faster than that allowed by gravity and friction. We find that cohesive forces are required to prevent surface mass shedding and structural failure, and that the strength of the forces are comparable to, though somewhat less than, that of lunar regolith.It is possible to infer the existence of cohesive forces within an asteroid by determining if it is a rubble pile with insufficient self-gravity to prevent rotational breakup by centrifugal forces. One of the largest known candidates is near-Earth asteroid 1950 DA (mean diameter of 1.3 km; ref.8), as it has a rotation period of 2.1216 hr that is just beyond the critical spin limit of ~2.2 hr estimated for a cohesionless asteroid 9 . A rubble pile structure and the degree of self-gravity can be determined by a bulk density measurement, which can be acquired through model-tomeasurement comparisons of Yarkovsky orbital drift 10 . This drift arises on a rotating asteroid with non-zero thermal inertia, and is caused by the delayed thermal emission of absorbed sunlight, which applies a small propulsion force to the asteroid's afternoon side. Thermalinfrared observations can constrain the thermal inertia value 11 , and precise astrometric position measurements conducted over several years can constrain the degree of Yarkovsky orbital drift 2 . Recently, the orbital semimajor axis of 1950 DA has been observed to be decreasing at a rate of 44.1 ± 8.5 m yr -1 because of the Yarkovsky effect 12 , which indicates that the asteroid's sense of rotation must be retrograde. Using the Advanced Thermophysical Model 13,14 , in combination with the retrograde radar shape model 8 , archival WISE thermal-infrared data 15 (Extended Data Table 1, and Extended Data Figs 1 and 2), and orbital state 12 , we determine the thermal inertia and bulk density of 1950 DA (Methods). The thermal inertia value is found to be remarkably low at 24 +20 / -14 J m -2 K -1 s -1/2 , which gives a corresponding bulk density of 1.7 ± 0.7 g cm -3 ( Fig. 1 and Extended Data Fig. 3). This bulk density is much lower than the minimum value of 3.5 g cm -3 required to prevent loss of surface material by centrifugal forces (Fig. 2).Spectral observations of 1950...

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On the Way to Comet 67P/Churyumov‐Gerasimenko

2014

Comets and Their Origin

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Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the Early Solar System

Cited by 189 publications

References 32 publications

Asteroid (21) Lutetia: Disk-resolved photometric analysis of Baetica region

Asteroid (21) Lutetia: Disk-resolved photometric analysis of Baetica region

Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA

On the Way to Comet 67P/Churyumov‐Gerasimenko

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