Radar and Optical Observations of Equal-Mass Binary Near-Earth Asteroid 2017 YE5
Abstract
Radar observations with the 70-m Goldstone, 305-m Arecibo, and 100-m Green Bank radio telescopes between 2018 June 21 and 26 find that near-Earth asteroid 2017 YE5 is, in fact, two asteroids of similar size in mutual orbit about each other. 2017 YE5 is only the fourth equal-mass binary asteroid system identified among the near-Earth asteroid population, following (69230) Hermes (Margot et al., 2003; IAUC 8227), 1994 CJ1 (Taylor et al., 2014; DPS 46, #409.03), and (190166) 2005 UP156 (Taylor et al., 2017; DPS 49, #204.02). Equal-mass binaries make up less than 1% of radar-observed near-Earth objects larger than 200 meters in diameter compared to roughly 15% for bilobate (peanut-shaped) asteroids and roughly 15% for binaries with more disparate sizes. Both components in the 2017 YE5 system are approximately 900 m in diameter, implying a very dark optical albedo of less than 3% for an absolute magnitude of 19.2. When combined with their relatively close approach to Earth, within about 16 lunar distances (6 million km), the radar images of 2017 YE5, with resolution as fine as 7.5 m per pixel, are the best yet of an equal-mass binary system. The radar images suggest the components have somewhat different shapes and possibly different radar-scattering properties. Variation in the radar images from day to day suggests the system was initially viewed far from edge on and that the mutual orbit has a separation of about four component radii and a period of roughly one day. Analysis of optical lightcurves, including possible mutual events, collected between late June and late July from the Center for Solar System Studies (CS3; United States), Observatorio Astronomico do Sertao de Itaparica (OASI; Brazil), and Blue Mountains Observatory (BMO; Australia) is ongoing. Constraints on the spin states, shapes, scattering properties, and mutual orbit will be presented and placed into context with the other three known, equal-mass, near-Earth binary systems.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5050807T