Observational Evidence for an Impact on the Main-Belt Asteroid (596) Scheila

Ishiguro, Masateru; Hanayama, H.; Hasegawa, Susumu; Sarugaku, Yuki; Watanabe, J.; Fujiwara, Hideaki; Terada, Hiroshi; Hsieh, Henry H.; Vaubaillon, Jérémie; Kawai, N.; Yanagisawa, K.; Kuroda, D.; Miyaji, Takeshi; Fukushima, Hideo; Ohta, Kouji; Hamanowa, Hiromi; Kim, Junhan; Pyo, Jeonghyun; Nakamura, Akiko

doi:10.1088/2041-8205/740/1/l11

Cited by 63 publications

(63 citation statements)

References 16 publications

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“…We thus conclude that the radius of an impactor would have been of the order of meters in size. The ejecta mass is comparable to estimates of the ejected mass around P/2010 A2 (3.7 × 10 7 kg, Snodgrass et al 2010; 5 × 10 7 kg, Moreno et al 2010;6-60 × 10 7 kg, Jewitt et al 2010) and 596 (Scheila) (3 × 10 7 kg, Hsieh et al 2012a; 4 × 10 7 kg, Jewitt et al 2011;1.5-4.9 × 10 8 kg, Ishiguro et al 2011; 6 × 10 8 kg, Bodewits et al 2011; 2 × 10 10 kg, Moreno et al 2011b), both of which are suspected to have undergone collisions in the main belt. With so few examples, it is difficult to know if the similarity of the ejecta masses is coincidence or intrinsic to the nature of main belt asteroidal collisions.…”

Section: Discussionsupporting

confidence: 72%

Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid

Stevenson¹,

Kramer²,

Bauer³

et al. 2012

ApJ

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In this work, we characterize the recently discovered active main belt object P/2012 F5 (Gibbs), which was discovered with a dust trail >7 in length in the outer main belt, 7 months prior to aphelion. We use optical imaging obtained on UT 2012 March 27 to analyze the central condensation and the long trail. We find B-band and R-band apparent magnitudes of 20.96 ± 0.04 mag and 19.93 ± 0.02 mag, respectively, which give an upper limit on the radius of the nucleus of 2.1 km. The geometric scattering cross-section of material in the trail was ∼4 × 10 8 m 2 , corresponding to a mass of ∼5 × 10 7 kg. Analysis of infrared images taken by the Wide-field Infrared Survey Explorer in 2010 September reveals that the object was below the detection limit, suggesting that it was less active than it was during 2012, or possibly inactive, just six months after it passed through perihelion. We set a 1σ upper limit on its radius during this time of 2.9 km. P/2012 F5 (Gibbs) is dynamically stable in the outer main belt on timescales of ∼1 Gyr, pointing toward an asteroidal origin. We find that the morphology of the ejected dust is consistent with it being produced by a single event that occurred on UT 2011 July 7 ± 20 days, possibly as the result of a collision with a small impactor.Key words: comets: individual (P/2012 F5 (Gibbs)) -minor planets, asteroids: individual (P/2012 F5)

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Section: Discussionsupporting

confidence: 72%

Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid

Stevenson¹,

Kramer²,

Bauer³

et al. 2012

ApJ

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“…The impact ejecta observed on main belt asteroid (596) Scheila during the impact in 2010 (Ishiguro et al 2011) produced an average brightness change of ∼5% over a 10,000 km 2 area. If we use the crater-size scaling law (Housen & Schmidt 1983) with an exponent parameter of 0.7, based on an escape velocity of 55 m s −1 for Scheila (as calculated by Ishiguro et al 2011) and 0.5 km s −1 for Ceres, the same impact on Ceres could produce an ejecta field that is 10 4 smaller, or ∼1 km 2 .…”

Section: Discussionmentioning

confidence: 99%

“…If we use the crater-size scaling law (Housen & Schmidt 1983) with an exponent parameter of 0.7, based on an escape velocity of 55 m s −1 for Scheila (as calculated by Ishiguro et al 2011) and 0.5 km s −1 for Ceres, the same impact on Ceres could produce an ejecta field that is 10 4 smaller, or ∼1 km 2 . Scaling with albedo and size shows that such an impact is still too small to produce any albedo change on Ceres detectable by our analysis.…”

Section: Discussionmentioning

confidence: 99%

Surface Albedo and Spectral Variability of Ceres

Reddy

Nathues

et al. 2016

ApJL

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Previous observations suggested that Ceres has active, but possibly sporadic, water outgassing as well as possibly varying spectral characteristics over a timescale of months. We used all available data of Ceres collected in the past three decades from the ground and the Hubble Space Telescope, as well as the newly acquired images by the Dawn Framing Camera, to search for spectral and albedo variability on Ceres, on both a global scale and in local regions, particularly the bright spots inside the Occator crater, over timescales of a few months to decades. Our analysis has placed an upper limit on the possible temporal albedo variation on Ceres. Sporadic water vapor venting, or any possibly ongoing activity on Ceres, is not significant enough to change the albedo or the area of the bright features in the Occator crater by >15%, or the global albedo by >3% over the various timescales that we searched. Recently reported spectral slope variations can be explained by changing Sun-Ceres-Earth geometry. The active area on Ceres is less than 1 km 2 , too small to cause global albedo and spectral variations detectable in our data. Impact ejecta due to impacting projectiles of tens of meters in size like those known to cause observable changes to the surface albedo on Asteroid Scheila cannot cause detectable albedo change on Ceres due to its relatively large size and strong gravity. The water vapor activity on Ceres is independent of Ceres' heliocentric distance, ruling out the possibility of the comet-like sublimation process as a possible mechanism driving the activity.

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“…P/2010 A2 (LINEAR), (596) Scheila, and P/2012 F5 (Gibbs) were all observed to exhibit comet-like dust features which were later determined to in fact be ejecta clouds produced by recent impacts Snodgrass et al 2010;Bodewits et al 2011;Ishiguro et al 2011a,b, Stevenson et al 2012. As such, despite the observationally comet-like morphologies of these objects, we do not consider them to be "true" MBCs, and instead prefer the term "disrupted asteroids" (e.g., Hsieh et al 2012a), where the general term "active asteroids" has been suggested to encompass both true MBCs and disrupted asteroids (Jewitt 2012).…”

Section: Are They Actually Icy?mentioning

confidence: 99%

Main-Belt Comets as Tracers of Ice in the Inner Solar System

Hsieh

2012

Proc. IAU

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Abstract. As a recently recognized class of objects exhibiting apparently cometary (sublimationdriven) activity yet orbiting completely within the main asteroid belt, main-belt comets (MBCs) have revealed the existence of present-day ice in small bodies in the inner solar system and offer an opportunity to better understand the thermal and compositional history of our solar system, and by extension, those of other planetary systems as well. Achieving these overall goals, however, will require meeting various intermediate research objectives, including discovering many more MBCs than the currently known seven objects in order to ascertain the population's true abundance and distribution, confirming that water ice sublimation is in fact the driver of activity in these objects, and improving our understanding of the physical, dynamical, and thermal evolutionary processes that have acted on this population over the age of the solar system.

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Observational Evidence for an Impact on the Main-Belt Asteroid (596) Scheila

Cited by 63 publications

References 16 publications

Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid

Characterization of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid

Surface Albedo and Spectral Variability of Ceres

Main-Belt Comets as Tracers of Ice in the Inner Solar System

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