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

A Rozek, S. C. Lowry, M C Nolan, P. A. Taylor, L A M Benner, A. Fitzsimmons, T. J. Zegmott, P R Weissman, S. F. Green, B Rozitis, Colin Snodgrass, W D Smythe, M D Hicks, E S Howell, A K Virkki, B Aponte-Hernandez, Edgard G. Rivera-Valentin, L A Rodriguez-Ford, L F Zambrano-Marin, M BrozovicS P Naidu, J D Giorgini, L G Snedeker, J S Jao, F D Ghigo

Research output: Contribution to journalArticlepeer-review


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 eect 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 6:5367870:000007 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 x 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.
Original languageEnglish
Article numberA149
Number of pages28
JournalAstronomy & Astrophysics
Publication statusPublished - 13 Nov 2019


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