Lightcurves of 26 Near-Earth Asteroids

Pravec, Petr; Wolf, M.; Šarounová, L.

doi:10.1006/icar.1998.5993

Cited by 67 publications

(75 citation statements)

References 25 publications

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“…EP's rotational period is less unusual among small asteroids. For example, in a study of 26 near-Earth objects (NEOs) with absolute magnitudes H V = 13.6-20.0 (effective radii approximately 0.2-4 km), Pravec, Wolf, & Š arounová (1998) found eight with P rot < 3.7 hr. Notably, 1943 Anteros, which with H R = 15.41 AE 0.13 is a reasonable size analog to EP (H R = 15.3 AE 0.1), was found to have P rot = 2.8695 AE 0.0002 hr.…”

Section: Rotation and Sizementioning

confidence: 99%

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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Section: Rotation and Sizementioning

confidence: 99%

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

2004

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“…We gathered a total of 55 dense-in-time light curves of Phaethon spanning 1994-2015, including 15 light curves from Ansdell et al (2014), 3 light curves from Pravec et al (1998), one light curve from Wisniewski et al (1997), and 7 light curves from Warner (2015). In addition, we obtained 29 new light curves with six different instruments.…”

Section: Optical Disk-integrated Photometrymentioning

confidence: 99%

Near-Earth asteroid (3200) Phaethon: Characterization of its orbit, spin state, and thermophysical parameters

Hanuš

Delbò

Vokrouhlický

et al. 2016

A&A

100

110

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Context. The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is at only 0.14 au and is associated with the Geminid meteor stream. Aims. We aim to use all available disk-integrated optical data to derive a reliable convex shape model of Phaethon. By interpreting the available space-and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo. Methods. We applied the convex inversion method to the new optical data obtained by six instruments and to previous observations. The convex shape model was then used as input for the thermophysical modeling. We also studied the long-term stability of Phaethon's orbit and spin axis with a numerical orbital and rotation-state integrator.Results. We present a new convex shape model and rotational state of Phaethon: a sidereal rotation period of 3.603958(2) h and ecliptic coordinates of the preferred pole orientation of (319 • , −39 • ) with a 5 • uncertainty. Moreover, we derive its size (D = 5.1 ± 0.2 km), thermal inertia (Γ = 600 ± 200 J m −2 s −1/2 K −1 ), geometric visible albedo (p V = 0.122 ± 0.008), and estimate the macroscopic surface roughness. We also find that the Sun illumination at the perihelion passage during the past several thousand years is not connected to a specific area on the surface, which implies non-preferential heating.

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“…Most of the data have been obtained by a few dedicated programs (see, e.g., Pravec et al 1998, Mottola et al 1995a, Krugly et al 2002 that placed a high priority within their observational strategies on suppressing selection effects against slow rotators as well as low amplitude objects, and on resolving complex lightcurves of tumblers and binaries among NEAs. Radar observations contributed to the rotation data 2 P. Pravec, A.W.…”

Section: Introductionmentioning

confidence: 99%

NEA rotations and binaries

2006

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Abstract. Of the nearly 3900 near-Earth asteroids (NEAs) known as of June 2006, 325 have estimated rotation periods, with most of those determined by lightcurve analysis led by a few dedicated programs. NEAs with diameters down to 10 meters have been sampled. Observed spin distribution shows a major changing point around diameter of 200 meters. Larger NEAs show a barrier against spins faster than 11 d −1 (period about 2.2 h) that shifts to slower rates (longer periods) with increasing lightcurve amplitude (i.e., with increasing equatorial elongation). The spin barrier is interpreted as a critical spin rate for bodies in a gravity regime; NEAs larger than 200 meters are predominantly bodies with tensile strength too low to withstand a centrifugal acceleration for rotation faster than the critical spin rate. The cohesionless spin barrier disappears at sizes less than 200 meters where most objects rotate too fast to be held together by self-gravitation only, so a cohesion is implied in the smaller NEAs.The distribution of NEA spin rates in the cohesionless size range (D > 0.2 km) is highly nonMaxwellian, suggesting that mechanisms other than just collisions have been at work. There is a pile up just in front of the barrier, at periods 2-3 h. It may be related to a spin up mechanism crowding asteroids to the barrier. An excess of slow rotators is observed at periods longer than 30 hours. A spin-down mechanism has no obvious lower limit on spin rate; periods as long as tens of days have been observed.Most NEAs appear to be in their basic spin states with rotation around principal axis with maximum moment of inertia. Tumbling objects (i.e., bodies in excited, non-principal axis rotation) are present and actually predominate among slow rotators with estimated damping timescales longer than the age of the solar system. A few tumblers observed among fast rotating coherent objects appear to be either more rigid or younger than the larger (cohesionless) tumblers.An abundant population of binary systems has been found among NEAs. The fraction of binaries among NEAs larger than 0.3 km has been estimated to be 15 ± 4%. Primaries of binary systems concentrate at fast spin rates (periods 2-3 h) and low amplitudes, i.e., they lie just below the cohesionless spin barrier. The total angular momentum content in binary systems suggests that they formed from parent bodies spinning at the critical rate. The fact that a very similar population of binaries has been found among small main belt asteroids suggests a binary formation mechanism that may not be related to close encounters with the terrestrial planets.

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Lightcurves of 26 Near-Earth Asteroids

Cited by 67 publications

References 25 publications

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

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

Near-Earth asteroid (3200) Phaethon: Characterization of its orbit, spin state, and thermophysical parameters

NEA rotations and binaries

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