* Astronomy

Blobrana · L

RE: asteroid (162173) 1999 JU3

Blobrana · L

Title: Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition
Authors: M.-J. Kim, Y.-J. Choi, H.-K. Moon, M. Ishiguro, S. Mottola, M. Kaplan, D. Kuroda, D. S. Warjurkar, J. Takahashi, Y.-I. Byun

Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid sample return missions, not only because of its accessibility but also because of the first C-type asteroid for exploration missions. The lightcurve-related physical properties of this object were investigated during the 2011-2012 apparition. We aim to confirm the physical parameters useful for JAXA's Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase function. Our data complement previous studies that did not cover low phase angles. With optical imagers and 1-2 m class telescopes, we acquired the photometric data at different phase angles. We independently derived the rotational lightcurve and the phase curve of the asteroid. We have analysed the lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of 7.625 ± 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R = 18.69 ± 0.07 mag and the phase slope of G = -0.09 ± 0.03 were also obtained based on the observations made during the 2011-2012 apparition.

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Blobrana · L

(162173) 1999 JU3 is an Apollo asteroid. It is the proposed target of the Japanese space probe Hayabusa 2.
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Blobrana · L

Title: Spitzer Observations of Spacecraft Target 162173 (1999 JU3)
Authors: H. Campins, J. P. Emery, M. Kelley, Y. Fernandez, J. Licandro, M. Delbo, A. Barucci, E. Dotto

Near-Earth asteroid 162173 (1999 JU3) is the primary target of the Hayabusa-2 sample return mission, and a potential target of the Marco Polo sample return mission. Earth-based studies of this object are fundamental to these missions. We present a mid-infrared spectrum (5-38 microns) of 1999 JU3 obtained with NASA's Spitzer Space Telescope in May 2008. These observations place new constraints on the surface properties of this asteroid. To fit our spectrum we used the near-Earth asteroid thermal model (NEATM) and the more complex thermophysical model (TPM). However, the position of the spin-pole, which is uncertain, is a crucial input parameter for constraining the thermal inertia with the TPM; hence, we consider two pole orientations. In the extreme case of an equatorial retrograde geometry we derive a lower limit to the thermal inertia of 150 J/m² /K/s^0.5. If we adopt the pole orientation of Abe et al. (2008a) our best-fit thermal model yields a value for the thermal inertia of 700±200 J/m² /K/s^0.5 and even higher values are allowed by the uncertainty in the spectral shape due to the absolute flux calibration. The lower limit to the thermal inertia, which is unlikely but possible, would be consistent with a fine regolith similar to what is found for asteroid 433 Eros. However, the thermal inertia is expected to be higher, possibly similar to or greater than that on asteroid 25143 Itokawa. Accurately determining the spin-pole of asteroid 162173 will narrow the range of possible values for its thermal inertia.

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