TY - JOUR
T1 - Goldstone and Arecibo radar observations of (99942) Apophis in 2012–2013
AU - Brozović, Marina
AU - Benner, Lance A.M.
AU - McMichael, Joseph G.
AU - Giorgini, Jon D.
AU - Pravec, Petr
AU - Scheirich, Petr
AU - Magri, Christopher
AU - Busch, Michael W.
AU - Jao, Joseph S.
AU - Lee, Clement G.
AU - Snedeker, Lawrence G.
AU - Silva, Marc A.
AU - Slade, Martin A.
AU - Semenov, Boris
AU - Nolan, Michael C.
AU - Taylor, Patrick A.
AU - Howell, Ellen S.
AU - Lawrence, Kenneth J.
N1 - Funding Information:
We thank the Goldstone and Arecibo technical and support staffs for help with the radar observations. This work was performed at the Jet Propulsion Laboratory , California Institute of Technology , under contract with the National Aeronautics and Space Administration ( NASA ). This material is based in part upon work supported by NASA under the Science Mission Directorate Research and Analysis Programs and the Human Exploration and Operations Mission Directorate Advanced Exploration Systems Program. The work by P.P. and P.S. was supported by the Grant Agency of the Czech Republic , Grant 17-00774S . We would like to thank Davide Farnocchia, Steve Chesley, and Paul Chodas for a valuable discussion on the orbit of Apophis. We also thank two anonymous reviewers.
Publisher Copyright:
© 2017 Elsevier Inc.
PY - 2018/1/15
Y1 - 2018/1/15
N2 - We report radar observations of Apophis obtained during the 2012−2013 apparition. We observed Apophis on fourteen days at Goldstone (8560 MHz, 3.5 cm) and on five days at Arecibo (2380 MHz, 12.3 cm) between 2012 December 21 to 2013 March 16. Closest approach occurred on January 9 at a distance of 0.097 au. We obtained relatively weak echo power spectra and delay-Doppler images. The highest range resolution was achieved at Goldstone, 0.125 µs or ∼20 m/px. The data suggest that Apophis is an elongated, asymmetric, and possibly bifurcated object. The images place a lower bound on the long axis of 450 m. We used the Pravec et al. (2014) lightcurve-derived shape and spin state model of Apophis to test for short axis mode (SAM) non-principal axis rotation (NPA) and to estimate the asteroid's dimensions. The radar data are consistent with the NPA spin state and they constrain the equivalent diameter to be D = 0.34 ± 0.04 km (1σ bound). This is slightly smaller than the most recent IR observation estimates of 375(−10) (+14)m and 380–393 m, reported by Müller et al. (2014) and Licandro et al. (2016) respectively. We estimated a radar albedo of 0.25 ± 0.11 based on Goldstone data, and an optical albedo, pV, of 0.35 ± 0.10. Licandro et al. (2016) reported pV in the range of 0.24–0.33. The radar astrometry has been updated using a 3-D shape model. The Yarkovsky acceleration has not been detected in the current orbital fit, but if the position error during the 2021 encounter exceeds 8–12 km, this could signal a detection of the Yarkovsky effect.
AB - We report radar observations of Apophis obtained during the 2012−2013 apparition. We observed Apophis on fourteen days at Goldstone (8560 MHz, 3.5 cm) and on five days at Arecibo (2380 MHz, 12.3 cm) between 2012 December 21 to 2013 March 16. Closest approach occurred on January 9 at a distance of 0.097 au. We obtained relatively weak echo power spectra and delay-Doppler images. The highest range resolution was achieved at Goldstone, 0.125 µs or ∼20 m/px. The data suggest that Apophis is an elongated, asymmetric, and possibly bifurcated object. The images place a lower bound on the long axis of 450 m. We used the Pravec et al. (2014) lightcurve-derived shape and spin state model of Apophis to test for short axis mode (SAM) non-principal axis rotation (NPA) and to estimate the asteroid's dimensions. The radar data are consistent with the NPA spin state and they constrain the equivalent diameter to be D = 0.34 ± 0.04 km (1σ bound). This is slightly smaller than the most recent IR observation estimates of 375(−10) (+14)m and 380–393 m, reported by Müller et al. (2014) and Licandro et al. (2016) respectively. We estimated a radar albedo of 0.25 ± 0.11 based on Goldstone data, and an optical albedo, pV, of 0.35 ± 0.10. Licandro et al. (2016) reported pV in the range of 0.24–0.33. The radar astrometry has been updated using a 3-D shape model. The Yarkovsky acceleration has not been detected in the current orbital fit, but if the position error during the 2021 encounter exceeds 8–12 km, this could signal a detection of the Yarkovsky effect.
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U2 - 10.1016/j.icarus.2017.08.032
DO - 10.1016/j.icarus.2017.08.032
M3 - Article
AN - SCOPUS:85033691774
VL - 300
SP - 115
EP - 128
JO - Icarus
JF - Icarus
SN - 0019-1035
ER -