Arecibo radar observations of near-Earth asteroid (3200) Phaethon during the 2017 apparition

Taylor, Patrick A.; Rivera-Valentín, E. G.; Benner, L. A. M.; Marshall, Sean; Virkki, Anne; Venditti, Flaviane; Zambrano-Marín, Luisa F.; Bhiravarasu, S. S.; Aponte-Hernández, Betzaida; Sánchez-Vahamonde, Carolina Rodriguez; Giorgini, Jon D.

doi:10.1016/j.pss.2019.01.009

Cited by 58 publications

(51 citation statements)

References 28 publications

(65 reference statements)

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“…If we conservatively assume that the ejection process is roughly proportional in strength to the heliocentric distance (r −2 ), then normalizing Bennu's perihelion distance (0.895 au) to Phaethon's (0.140 au) produces activity (0.140 au/0.897 au) −2 or ~41 times stronger. If we normalize mass loss for larger surface area (D 2 ) of Phaethon (6.2 vs. 0.49 km diameter) (Taylor et al, 2019), then Bennu's activity would increase by an additional (6.2 km/0.49 km) 2 or ~150 times. If we scaled up the size of Bennu to match Phaethon and moved it to Phaethon's perihelion distance, its mass loss rate could increase to ~1 g s −1 which is within 0.1–1% of what is observed at Phaethon.…”

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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Section: Resultsmentioning

confidence: 99%

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Hergenrother

Maleszewski

et al. 2020

JGR Planets

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“…If this interpretation is correct, one might expect that all sungrazing objects are essentially spectrally homogenized within a few orbits. Another reason that we might expect Phaethon to be more varied is the complex, cratered shape of the object seen in radar 7 . Perhaps the material excavated by those craters was similar to that of the surface materials, and thus Phaethon has been extensively heated throughout, or perhaps the topography we see is old compared to the recent heating of the surface layers.…”

Section: Discussionmentioning

confidence: 99%

Near-infrared observations of active asteroid (3200) Phaethon reveal no evidence for hydration

et al. 2020

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Asteroid (3200) Phaethon is an active near-Earth asteroid and the parent body of the Geminid Meteor Shower. Because of its small perihelion distance, Phaethon's surface reaches temperatures sufficient to destabilize hydrated materials. We conducted rotationally resolved spectroscopic observations of this asteroid, mostly covering the northern hemisphere and the equatorial region, beyond 2.5-µm to search for evidence of hydration on its surface. Here we show that the observed part of Phaethon does not exhibit the 3-µm hydrated mineral absorption (within 2σ). These observations suggest that Phaethon's modern activity is not due to volatile sublimation or devolatilization of phyllosilicates on its surface. It is possible that the observed part of Phaethon was originally hydrated and has since lost volatiles from its surface via dehydration, supporting its connection to the Pallas family, or it was formed from anhydrous material.

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“…We consider that Phaethon has a mean equatorial diameter of 6.25 km and an oblateness (the ratio of semi-minor axis to semi-major axis) of 0.889, which is the same as Bennu's (Barnouin et al 2019). We note that Taylor et al (2019) did not specify the oblateness of Phaethon but implied that it would be similar to that of Bennu. For the oblateness, we do not account for the semi-intermediate axis to simplify the discussion.…”

Section: Semi-analytical Model For Structural Failure In a Top-shapedmentioning

confidence: 99%

“…Finally, We assumed that Phaethon currently has a top shape having Bennus oblateness, = 0.889, by following Taylor et al (2019). To check if this setting is consistent with other top-shaped asteroids, we consider six top-shaped near-earth asteroids: Ryugu (Watanabe et al 2019), 1994KW4 (Ostro et al 2006EV5 (Busch et al 2011), 1994CC (Brozović et al 2011), 2001SN263 (Becker et al 2015, and 2000 DP107 (Naidu et al 2015).…”

Section: Possible Source Of the Geminid Meteor Streammentioning

confidence: 99%

“…The examples of top-shaped asteroids are OSIRIS-RExs target (101955) Bennu (Lauretta et al 2019) and Hayabusa2s target (162173) Ryugu (Watanabe et al 2019;Sugita et al 2019;Kitazato et al 2019). Phaethon is currently spinning at a rotation period of 3.60 hr (Taylor et al 2019). The radar albedo is reported to be the lowest among the cataloged near-Earth asteroids (Taylor et al 2019), implying that its spectral type is consistent with a B-type (Taylor et al 2019), and thus the bulk density may be as low as ∼1.0 g/cm 3 (Scheeres et al 2019;Watanabe et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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Mass-shedding Activities of Asteroid (3200) Phaethon Enhanced by Its Rotation

Nakano

Hirabayashi

2020

ApJL

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Asteroid (3200) Phaethon, a B-type asteroid, has been active during its perihelion passages. This asteroid is considered to be a source of the Geminid meteor stream. It is reported that this asteroid is spinning at a rotation period of 3.60 hr and has a top shape (an oblate body with an equatorial ridge) with a mean equatorial diameter of 6.25 km. Here, we report that Phaethon's rotation state may be close to or above its critical rotation period when the bulk density is 0.5 − 1.5 g/cm 3 (a typical bulk density of a B-type asteroid). We found that in this condition, the structure of Phaethon is sensitive to failure unless the cohesive strength is ∼50 P a − ∼260 P a. This result implies that if there are some surface processes driven by, for example, thermal waves, large-scaled deformation may happen and cause mass shedding. From this interpretation, we propose the processes that produced the Geminid meteor stream in the past and dust tails recently. Phaethon initially rotated at a spin period shorter than the current period. The magnitude of structural deformation at this stage was higher than the present spin condition, and a large mass shedding event, i.e., the Geminid meteor stream, occurred. After this deformation process, the body became more oblate, and its spin slowed down. At this point, while the spin was high enough for the body to have mass shedding events, the magnitude of these events became small.

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Arecibo radar observations of near-Earth asteroid (3200) Phaethon during the 2017 apparition

Cited by 58 publications

References 28 publications

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Photometry of Particles Ejected From Active Asteroid (101955) Bennu

Near-infrared observations of active asteroid (3200) Phaethon reveal no evidence for hydration

Mass-shedding Activities of Asteroid (3200) Phaethon Enhanced by Its Rotation

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