Local Manifestations of Cometary Activity

Vincent, Jean‐Baptiste; Farnham, T. L.; Kührt, Ekkehard; Skorov, Yu. V.; Marschall, Raphael; Oklay, N.; El‐Maarry, M. R.; Keller, H. U.

doi:10.1007/s11214-019-0596-8

Cited by 27 publications

(20 citation statements)

References 95 publications

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“…Dust ejection is a common phenomenon in comets and active asteroids. Even for well-studied comets such as 67P/Churyumov-Gerasimenko, substantial uncertainty exists as to the physical mechanism through which particles are released from the surface (21). We consider multiple hypotheses for the particle ejection mechanism, evaluating their respective strengths and weaknesses.…”

Section: Possible Ejection Mechanismsmentioning

confidence: 99%

Episodes of particle ejection from the surface of the active asteroid (101955) Bennu

Лауретта

Hergenrother

Chesley

et al. 2019

Science

151

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Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts.

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Section: Possible Ejection Mechanismsmentioning

confidence: 99%

Episodes of particle ejection from the surface of the active asteroid (101955) Bennu

Лауретта

Hergenrother

Chesley

et al. 2019

Science

151

187

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“…Even during high-cadence imaging, observation biases affect our characterization of ejection events. Unlike a strongly collimated cometary jet (Vincent et al, 2019), Bennu ejection events have a broad azimuthal launch cone (Leonard et al, 2020, this collection) resulting in some fraction of ejected material being 10.1029/2020JE006381 Journal of Geophysical Research: Planets unobservable due to interference from the asteroid (e.g., particles in front of the sunlit hemisphere, behind the asteroid, or in shadow) or motion away from the spacecraft.…”

Section: Observation Biasmentioning

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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“…( 2019 ) and the local manifestations of activity as described in this book in Vincent et al. ( 2019 ) is therefore of particular interest. Even though understanding this link of the coma to the surface is of vital importance to understanding cometary activity on a more basic level this has turned out to be immensely challenging, even with a large data set as provided by the in-situ and remote sensing instruments.…”

Section: Introduction and Historical Contextmentioning

confidence: 94%

“…For more details and ways out of this paradox as well as our state of knowledge about the physical properties of the surface we refer to Vincent et al. ( 2019 ) as well as Groussin et al. ( 2019 ) in this book.…”

Section: The Physics Of Developing Cometary Comaementioning

confidence: 99%

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Cometary Comae-Surface Links

et al. 2020

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A comet is a highly dynamic object, undergoing a permanent state of change. These changes have to be carefully classified and considered according to their intrinsic temporal and spatial scales. The Rosetta mission has, through its contiguous in-situ and remote sensing coverage of comet 67P/Churyumov-Gerasimenko (hereafter 67P) over the time span of August 2014 to September 2016, monitored the emergence, culmination, and winding down of the gas and dust comae. This provided an unprecedented data set and has spurred a large effort to connect in-situ and remote sensing measurements to the surface. In this review, we address our current understanding of cometary activity and the challenges involved when linking comae data to the surface. We give the current state of research by describing what we know about the physical processes involved from the surface to a few tens of kilometres above it with respect to the gas and dust emission from cometary nuclei. Further, we describe how complex multidimensional cometary gas and dust models have developed from the Halley encounter of 1986 to today. This includes the study of inhomogeneous outgassing and determination of the gas and dust production rates. Additionally, the different approaches used and results obtained to link coma data to the surface will be discussed. We discuss forward and inversion models and we describe the limitations of the respective approaches. The current literature suggests that there does not seem to be a single uniform process behind cometary activity. Rather, activity seems to be the consequence of a variety of erosion processes, including the sublimation of both water ice and more volatile material, but possibly also more exotic processes such as fracture and cliff erosion under thermal and mechanical stress, sub-surface heat storage, and a complex interplay of these processes. Seasons and the nucleus shape are key factors for the distribution and temporal evolution of activity and imply that the heliocentric evolution of activity can be highly individual for every comet, and generalisations can be misleading.

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Local Manifestations of Cometary Activity

Cited by 27 publications

References 95 publications

Episodes of particle ejection from the surface of the active asteroid (101955) Bennu

Episodes of particle ejection from the surface of the active asteroid (101955) Bennu

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Cometary Comae-Surface Links

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