Simultaneous Photometric and Polarimetric Observations of Asteroid 3 Juno

Takahashi, Shigeru; Yoshida, Fumi; Shinokawa, K.; Mukai, T.; Kawabata, Koji S.

doi:10.1088/0004-6256/138/3/951

Cited by 4 publications

(4 citation statements)

References 11 publications

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“…Infrared Space Observatory spectra of Juno show an 8-11.5 μm feature that is consistent with the laboratory measurements of the silicate minerals pyroxine and olivine (Dotto et al 2000). Evidence for surface features on Juno have been suggested by the variation as a function of rotation angle of its optical colors (Degewij et al 1979;Schroll et al 1981) and linear polarization (Shinokawa et al 2002;Takahashi et al 2009), and by a sequence of optical AO images, which suggested a large impact crater (Baliunas et al 2003). Somewhat surprisingly, there are no published images of Juno from the Hubble Space Telescope (Dotto et al 2002), and there have been no spacecraft encounters as of yet.…”

Section: Introductionsupporting

confidence: 74%

The 2014 Alma Long Baseline Campaign: Observations of Asteroid 3 Juno at 60 Kilometer Resolution

Partnership¹,

Hunter

Kneißl

et al. 2015

ApJ

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We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0. 042 ″ (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of 10 consecutive images reveals continuous changes in the asteroidʼs profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259 ± 4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215 ± 13 K, while the median over the whole surface is 197 ± 15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMAʼs potential to resolve thermal emission from the surface of main belt asteroids and to measure accurately their position, geometric shape, rotational period, and soil characteristics.

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Section: Introductionsupporting

confidence: 74%

The 2014 Alma Long Baseline Campaign: Observations of Asteroid 3 Juno at 60 Kilometer Resolution

Partnership¹,

Hunter

Kneißl

et al. 2015

ApJ

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“…A notable example is (4) Vesta (Dollfus et al 1989), which showed a 0.1% polarimetric variation, and the maximum of the polarization coincides with the lightcurve minimum, suggesting that albedo variation exists on the surface per the controlled polarization degree and visible magnitude. Similarly, (3) Juno, (9) Metis, and (216) Kleopatra showed rotational variations of 0.15-0.27 %, ∼0.1 %, and ∼0.2 %, respectively (Takahashi et al 2009;Nakayama et al 2000;Takahashi et al 2004). Although the measurement accuracy is too limited to detect such a small variations in the polarization degree, we suggest that Icarus has a quite homogeneous albedo in contrast with these asteroids because our measurement was made at a large phase angle, while these previous detections were made at a small phase angle where the polarization degree itself has small values (1/6∼1/10 of Icarus's |P r |, i.e., 0.5 |P r | 1.0%).…”

Section: Rotational Variation In P Rmentioning

confidence: 86%

Polarimetric Study of Near-Earth Asteroid (1566) Icarus

Ishiguro

Kuroda

Watanabe

et al. 2017

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We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles α= 57 • -141 • around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are P max =7.32±0.25 % at phase angles of α max =124 • ±8 • in the V -band and P max =7.04±0.21 % at α max =124 • ±6 • in the R C -band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of p V =0.25±0.02, which is in agreement with that of Q-type taxonomic asteroids. α max is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance q=0.187 au and a short rotational period of T rot =2.27 hours) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.

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“…As the data specify the rotation phase, we used the light-curve data acquired eight days before our observation (Vaduvescu et al 2017). Several large asteroids and the 5.8 km sized asteroid Phaethon have reported rotational variations of the degree of polarization smaller than 0.3% (Degewij et al 1979;Cellino et al 2016b;Nakayama et al 2000;Takahashi et al 2004Takahashi et al , 2009Belskaya et al 2010;Borisov et al 2018). However, our measurements are not accurate enough to assess this threshold.…”

Section: Degree Of Linear Polarization For Multibandsmentioning

confidence: 99%

(85989) 1999 JD₆: a first Barbarian asteroid detected by polarimetry in the NEA population

Kuroda

Ishiguro

Naito

et al. 2021

A&A

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Context. To investigate the physical properties of the surface layers of small Solar System objects, we take advantage of the phase-angle dependence of the linear polarization degree, which varies with albedo, composition, and other factors. In particular, the angle at which the positive and negative are reversed is a polarimetric parameter known as inversion angle. A group with large inversion angles (the so-called Barbarians) is unusual and is also noteworthy because of their association with meteorites. Aims. We identified an object with such a large inversion angle in the near-Earth asteroids and derived previously unknown parameters, including the maximum polarization degree. By comparing the polarimetric parameters and spectral properties of meteorites, we inferred the surface conditions based on the degree of polarization of the asteroid. Methods. We carried out multiband polarization imaging observations of an L-type near-Earth asteroid, (85989) 1999 JD6, at the Hokkaido University Observatory in 2015 and 2019, covering a wide range of phase angles 30°–105°. Of the polarimetric parameters, we derived the maximum value, inversion angle, and the slope at that angle from the phase angle-polarization degree curve. Results. We found that the inversion angle and the maximum polarization degree of 1999 JD6 are 27° and 13%. The inversion angle is significantly larger than those of the majority of all asteroids observed before, but is consistent with that of Barbarian asteroids. 1999 JD6 is the first example belonging to this group that is also among the near-Earth asteroids. Conclusions. We claim that 1999 JD6 is a member of the Barbarians and has rougher surface particles than lunar regolith.

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Simultaneous Photometric and Polarimetric Observations of Asteroid 3 Juno

Cited by 4 publications

References 11 publications

The 2014 Alma Long Baseline Campaign: Observations of Asteroid 3 Juno at 60 Kilometer Resolution

The 2014 Alma Long Baseline Campaign: Observations of Asteroid 3 Juno at 60 Kilometer Resolution

Polarimetric Study of Near-Earth Asteroid (1566) Icarus

(85989) 1999 JD₆: a first Barbarian asteroid detected by polarimetry in the NEA population

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Simultaneous Photometric and Polarimetric Observations of Asteroid 3 Juno

Cited by 4 publications

References 11 publications

The 2014 Alma Long Baseline Campaign: Observations of Asteroid 3 Juno at 60 Kilometer Resolution

The 2014 Alma Long Baseline Campaign: Observations of Asteroid 3 Juno at 60 Kilometer Resolution

Polarimetric Study of Near-Earth Asteroid (1566) Icarus

(85989) 1999 JD6: a first Barbarian asteroid detected by polarimetry in the NEA population

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(85989) 1999 JD₆: a first Barbarian asteroid detected by polarimetry in the NEA population