Shape model and spin-state analysis of PHA contact binary (85990) 1999 JV6 from combined radar and optical observations

Rozek, A.; Lowry, S. C.; Nolan, M. C.; Taylor, P. A.; Benner, L. A. M.; Fitzsimmons, A.; Zegmott, T. J.; Weissman, P. R.; Green, Simon; Rozitis, Benjamin; Snodgrass, Colin; Smythe, W. D.; Hicks, M. D.; Howell, E. S.; Virkki, A. K.; Aponte-Hernandez, B.; Rivera-Valentin, E. G.; Rodriguez-Ford, L. A.; Zambrano-Marin, L. F.; Brozovic, M.; Naidu, S. P.; Giorgini, J. D.; Snedeker, L. G.; Jao, J. S. and Ghigo, F. D. (2019). Shape model and spin-state analysis of PHA contact binary (85990) 1999 JV6 from combined radar and optical observations. Astronomy & Astrophysics, 631, article no. A149.



Context. The potentially hazardous asteroid (85990)1999 JV6 has been a target of previously published thermal-infrared observations and optical photometry. It has been identified as a promising candidate for possible Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect detection.
Aims. The YORP effect is a small thermal-radiation torque considered to be a key factor in spin-state evolution of small Solar System bodies. In order to detect YORP on 1999 JV6 we developed a detailed shape model and analysed the spin-state using both optical and radar observations.
Methods. For 1999 JV6, we collected optical photometry between 2007 and 2016. Additionally, we obtained radar echo-power spectra and imaging observations with Arecibo and Goldstone planetary radar facilities in 2015, 2016, and 2017. We combined our data with published optical photometry to develop a robust physical model.
Results. We determine that the rotation pole resides at negative latitudes in an area with a 5◦ radius close to the south ecliptic pole. The refined sidereal rotation period is 6.536787±0.000007 h. The radar images are best reproduced with a bilobed shape model. Both lobes of 1999 JV6 can be represented as oblate ellipsoids with a smaller, more spherical component resting at the end of a larger, more elongated component. While contact binaries appear to be abundant in the near-Earth population, there are only a few published shape models for asteroids in this particular configuration. By combining the radar-derived shape model with optical light curves we determine a constant-period solution that fits all available data well. Using light-curve data alone we determine an upper limit for YORP of 8.5×10−8 rad day−2.
Conclusions. The bifurcated shape of 1999 JV6 might be a result of two ellipsoidal components gently merging with each other, or a deformation of a rubble pile with a weak-tensile-strength core due to spin-up. The physical model of 1999 JV6 presented here will enable future studies of contact binary asteroid formation and evolution.

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