Opposition Effect of Asteroids

Belskaya, I. N.

doi:10.1006/icar.2000.6410

Cited by 175 publications

(180 citation statements)

References 45 publications

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“…A weighted least-squares fit to the data in Figure 2 (dashed line) shows that in the 5 12 phase-angle range, the phase darkening is well represented by a linear coefficient = 0.043 AE 0.014 mag deg À1 . The magnitude of is inversely related to the albedo (Belskaya & Shevchenko 2000): the large value found for 143P/Kowal-Mrkos suggests a low-albedo surface. The measured phase darkening falls within the range of other published values, namely, for P/Tempel 2 ( = 0.04 AE 0.01 mag deg À1 ; Jewitt & Luu 1989), P/Encke ( = 0.05 AE 0.02 mag deg À1 ; Fernández et al 2000), and P/Neujmin 1 ( = 0.025 AE 0.006 mag deg À1 ; Delahodde et al 2001).…”

Section: Observational Resultsmentioning

confidence: 97%

143P/Kowal-Mrkos and the Shapes of Cometary Nuclei

Jewitt¹,

Sheppard²,

Fernández³

2003

Astron J

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We add 143P/Kowal-Mrkos to the small but growing sample of well-observed cometary nuclei. Photometric observations from 3.4 to 4.0 AU heliocentric distance reveal a pointlike object with no detectable outgassing. Periodic modulation of the scattered light (Dm R = 0.45 AE 0.05) is attributed to rotation of the bare nucleus with a double-peaked period 17.21 AE 0.10 hr and a projected ratio of the shortest to longest axis of about 0.67/1. We also measured the phase coefficient (0.043 AE 0.014 mag deg À1 ), the BVRI colors (VÀR = 0.58 AE 0.02), and the absolute red magnitude [m R (1, 1, 0) = 13.49 AE 0.20]. The effective circular radius is 5.7 AE 0.6 km (geometric albedo 0.04 assumed). We study the properties of 11 well-observed Jupiterfamily comet (JFC) nuclei. On average, the nuclei are systematically more elongated (average photometric range Dm R = 0.54 AE 0.07) than main-belt asteroids of comparable size (Dm R = 0.32 AE 0.05) and more elongated than fragments produced in laboratory impact experiments. We attribute the elongation of the nuclei to an evolutionary effect, most likely driven by sublimation-induced mass loss. However, we find no evidence for any relation between the nucleus shape and the sublimation timescale. This may be because the timescale for evolution of the nucleus shape is very short compared with the dynamical timescale for the JFCs, meaning that most nuclei in our sample are already highly physically evolved.

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Section: Observational Resultsmentioning

confidence: 97%

143P/Kowal-Mrkos and the Shapes of Cometary Nuclei

Jewitt¹,

Sheppard²,

Fernández³

2003

Astron J

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“…Belskaya & Shevchenko 2000). The large suggests (but does not prove) that EP has a low-albedo, possibly porous surface.…”

Section: Rotation and Sizementioning

confidence: 93%

The Strange Case of 133P/Elst-Pizarro: A Comet among the Asteroids

2004

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We present a new investigation of the comet-asteroid transition object 133P/(7968) Elst-Pizarro. We find mean optical colors (BÀV = 0.69 AE 0.02, VÀR = 0.42 AE 0.03, RÀI = 0.27 AE 0.03) and a phase-darkening coefficient ( = 0.044 AE 0.007 mag deg À1 ) that are comparable both to other comet nuclei and to C-type asteroids. As in 1996, when this object's comet-like activity was first noted, data from 2002 show a long, narrow dust trail in the projected orbit of the object. Observations over several months reveal changes in the structure and brightness of this trail, showing that it is actively generated over long periods of time. Finson-Probstein modeling is used to constrain the parameters of the dust trail. We find optically dominant dust particle sizes of a d $ 10 m released with low ejection velocities (v g % 1.5 m s À1 ) over a period of activity lasting at least 5 months in 2002. The doublepeaked light curve of the nucleus indicates an aspherical shape (axis ratio a/b ! 1.45 AE 0.07) and rapid rotation (period P rot = 3.471 AE 0.001 hr). The practical identification of 133P/Elst-Pizarro as a comet (i.e., a mass-losing body) is not in doubt, but the origin of the mass loss is unclear. The 1996 trail has been previously explained as debris released by a chance impact, but our discovery of recurrent activity renders this interpretation implausible. We consider two hypotheses for the activity in 133P/ Elst-Pizarro. The ejection of particles is naturally explained if the object is a barely active Jupiter-family comet that has evolved into an asteroid-like orbit, perhaps under the prolonged action of nongravitational forces due to asymmetric mass loss. In this case, the orbital similarity to the Themis family must be considered coincidental. Alternatively, 133P/ Elst-Pizarro could be a true member of the Themis family on which buried ice has been recently excavated by impact.

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“…Both the opposition effect amplitude and the value of the phase slope are consistent with a moderate-albedo surface. Based on the empirical correlation between phase coefficient and albedo (Belskaya & Shevchenko 2000), an average albedo in the range of 0.12-0.20 is expected for Lutetia's surface.…”

Section: Photometrymentioning

confidence: 99%

Puzzling asteroid 21 Lutetia: our knowledge prior to the Rosetta fly-by

Belskaya

Fornasier

Krugly

et al. 2010

A&A

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Aims. A wide observational campaign was carried out in [2004][2005][2006][2007][2008][2009] that aimed to complete the ground-based investigation of Lutetia prior to the Rosetta fly-by in July 2010. Methods. We obtained BVRI photometric and V-band polarimetric measurements over a wide range of phase angles, and visible and infrared spectra in the 0.4-2.4 μm range. We analyze them with previously published data to retrieve information about Lutetia's surface properties.Results. Values of lightcurve amplitudes, absolute magnitude, opposition effect, phase coefficient, and BVRI colors of Lutetia surface seen at near pole-on aspect are determined. We define more precisely parameters of polarization phase curve and show their distinct deviation from any other moderate-albedo asteroid. An indication of possible variations in both polarization and spectral data across the asteroid surface are found. To explain features found by different techniques, we propose that (i) Lutetia has a non-convex shape, probably due to a large crater, and heterogeneous surface properties probably related to surface morphology; (ii) at least part of the surface is covered by a fine-grained regolith of particle size smaller than 20 μm; (iii) the closest meteorite analogues of Lutetia's surface composition are particular types of carbonaceous chondrites, or Lutetia has specific surface composition that is not representative among studied meteorites.

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Opposition Effect of Asteroids

Cited by 175 publications

References 45 publications

143P/Kowal-Mrkos and the Shapes of Cometary Nuclei

143P/Kowal-Mrkos and the Shapes of Cometary Nuclei

The Strange Case of 133P/Elst-Pizarro: A Comet among the Asteroids

Puzzling asteroid 21 Lutetia: our knowledge prior to the Rosetta fly-by

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