Photometric survey of the very small near-Earth asteroids  with the SALT telescope

Kwiatkowski, T.

doi:10.1051/0004-6361/200913153

Cited by 11 publications

(7 citation statements)

References 27 publications

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“…The amplitude of the light curve informs the axial ratio of the particle. The relationship between the light curve amplitude and axial ratio (Kwiatkowski et al, 2010) is

Axial Ratio ((), normalb / normala) \geq \frac{1}{10^{0.4 A (normalα) / (1 + sα)}}

where A(a) is the observed light curve amplitude in magnitudes, s is the slope of the increase in light curve amplitude with phase angle, and a is the average phase angle of the observations (93° for P252). For s , we use 0.015 magnitude per degree of phase angle as determined by Zappala et al (1990) for carbonaceous asteroids.…”

Section: Resultsmentioning

confidence: 99%

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Hergenrother

Maleszewski

et al. 2020

JGR Planets

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Near‐Earth asteroid (101955) Bennu is an active asteroid experiencing mass loss in the form of ejection events emitting up to hundreds of millimeter‐ to centimeter‐scale particles. The close proximity of the Origins, Spectral Interpretations, Resource Identification, and Security–Regolith Explorer spacecraft enabled monitoring of particles for a 10‐month period encompassing Bennu's perihelion and aphelion. We found 18 multiparticle ejection events, with masses ranging from near zero to hundreds of grams (or thousands with uncertainties) and translational kinetic energies ranging from near zero to tens of millijoules (or hundreds with uncertainties). We estimate that Bennu ejects ~104 g per orbit. The largest event took place on 6 January 2019 and consisted of ~200 particles. The observed mass and translational kinetic energy of the event were between 459 and 528 g and 62 and 77 mJ, respectively. Hundreds of particles not associated with the multiparticle ejections were also observed. Photometry of the best‐observed particles, measured at phase angles between ~70° and 120°, was used to derive a linear phase coefficient of 0.013 ± 0.005 magnitudes per degree of phase angle. Ground‐based data back to 1999 show no evidence of past activity for Bennu; however, the currently observed activity is orders of magnitude lower than observed at other active asteroids and too low be observed remotely. There appears to be a gentle decrease in activity with distance from the Sun, suggestive of ejection processes such as meteoroid impacts and thermal fracturing, although observational bias may be a factor.

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“…The amplitude of the light curve informs the axial ratio of the particle. The relationship between the light curve amplitude and axial ratio (Kwiatkowski et al, 2010) is

Axial Ratio ((), normalb / normala) \geq \frac{1}{10^{0.4 A (normalα) / (1 + sα)}}

Section: Resultsmentioning

confidence: 99%

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Hergenrother

Maleszewski

et al. 2020

JGR Planets

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“…Using their results they identify prediction trends and the twelve most suitable asteroids to look for orbital drift in future observations. Inspired by the works of Rossi, Marzari & Scheeres (2009), Kwiatkowski (2010), and Nugent et al (2012a), a simple Monte Carlo method to estimate the strength and detectability of the YORP-rotational-acceleration of an asteroid without knowing its shape is developed in Section 2. The method utilises either a direct diameter measurement of the asteroid or the asteroid's absolute magnitude value; hereafter referred to as diameter-based and absolutemagnitude-based method variants/predictions respectively.…”

Section: Estimating the Yorp Effect Detectabilitymentioning

confidence: 99%

The strength and detectability of the YORP effect in near-Earth asteroids: a statistical approach

Rozitis

Green

2013

Monthly Notices of the Royal Astronomical Society

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In addition to collisions and gravitational forces, it is now becoming widely acknowledged that photon recoil forces and torques from the asymmetric reflection and thermal re-radiation of sunlight are primary mechanisms that govern the rotational evolution of an asteroid. The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect causes changes in the rotation rate and pole direction of an irregularly shaped asteroid. We present a simple Monte Carlo method to estimate the range of YORP-rotational-accelerations acting on a near-Earth asteroid (NEA) without knowledge of its detailed shape, and to estimate its detectability using light-curve observations. The method requires knowledge of an asteroid's orbital properties and size, and assumes that the future observational circumstances of an asteroid have already been thought through. It is verified by application to the observational circumstances of the seven YORP-investigated asteroids, and is then applied to 540 NEAs with NEOWISE and/or other diameter measurements, and to all NEAs using MPCORB absolute magnitudes. The YORP-detectability is found to be a strong function of the combined asteroid orbital and diameter properties, and is independent of the rotation period for NEAs that don't have very fast or slow rotation rates. The median and 1-sigma spread of YORP-rotational-acceleration expected to be acting on a particular NEA (dω/dt in rad yr -2 ) can be estimated from its semimajor axis (a in AU), eccentricity (e), and diameter (D in km) by using

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“…This naturally also explains the apparent spin-size barrier found for asteroids with diameters larger than 150 m, that are found not to have periods shorter than 2.2 hours (Pravec et al 2002a;Kwiatkowski 2010). …”

Section: The Spin -Size Barrier Of Asteroidsmentioning

confidence: 83%

Hyper-Velocity Impacts on Rubble Pile Asteroids

Deller¹

2017

Springer Theses

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SummaryMost asteroids in the size range of approximately 100 m to 100 km are rubble piles, aggregates of rocky material held together mainly by gravitational forces, and only weak cohesion. They contain high macroporosities, indicating a large amount of void space in their interiors. How these voids are distributed is not yet known, as in-situ measurements are still outstanding.In this work, a model to create rubble pile asteroid simulants for use in SPH impact simulations is presented. Rubble pile asteroids are modelled as gravitational re-aggregating remnant fragments of a catastrophically disrupted parent body, which are represented by spherical pebbles. It is shown that this approach allows to explicitly follow the internal restructuring of rubble pile asteroids during impact events, while preserving the expected properties of the bulk asteroid as known from observations and experiments. The bulk behaviour of asteroid simulants, as characterized by the stability against disruption and fragment size distribution, follows the expected behaviour and is not sensitive to the exact distribution of voids in the interior structure, but rather to the void fraction as the amount of consolidated void space in between the constituent fragment pebbles. No exact a priory knowledge of the fragment size distribution inside the body is therefore needed to use this model in impact simulations.Modelling the behaviour of the large-scale rubble pile constituents during impact events is used as a tool to infer the internal structure of asteroids by linking surface features like hills or pits to the creation of sub-catastrophic craters.In this work, the small rubble pile asteroid (2867) Šteins is analysed. The flyby of the Rosetta spacecraft at Šteins has revealed several interesting features: the large crater Diamond close to the southern pole, a hill like feature almost opposite to the crater, and a catena of crater pits extending radially from the rim of the crater.A possible link between these two structures and the cratering event is investigated in a series of impact simulations varying the interior of a plausible shape of Šteins prior to the event that formed crater Diamond. A connection between the cratering event and the hill is shown to be highly unlikely. Therefore, the hill is most likely a remnant of the formation of Šteins. Its size therefore helps to infer the initial size distribution of fragments forming the asteroid.The formation of a fracture radially from the crater can be observed for rubble pile simulants with highly collimated voids. This fracture could plausibly form the catena of pits observed on Šteins. This can therefore serve as a link between observable surface features and Šteins internal structure. The interior of Šteins is most likely an aggregate of fragments that themselves are only lightly fractured, and large void spaces might be found inside the asteroid. As Šteins seems to be a good example of a YORPoid, an asteroid that has been evolved to a top-like shape by radiative forces due to the YORP ...

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Photometric survey of the very small near-Earth asteroids  with the SALT telescope

Cited by 11 publications

References 27 publications

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

The strength and detectability of the YORP effect in near-Earth asteroids: a statistical approach

Hyper-Velocity Impacts on Rubble Pile Asteroids

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Photometric survey of the very small near-Earth asteroids with the SALT telescope

Cited by 11 publications

References 27 publications

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

The strength and detectability of the YORP effect in near-Earth asteroids: a statistical approach

Hyper-Velocity Impacts on Rubble Pile Asteroids

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Product

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Photometric survey of the very small near-Earth asteroids  with the SALT telescope