Radar images of Comet 209P/LINEAR: Constraints on shape and rotation

Comet 209P/LINEAR passed within 0.06 AU from Earth 23-27 May 2014, and we obtained images of the nucleus using the Arecibo and Goldstone planetary radar systems. The Arecibo images range from 75-m to 15-m resolution, and reveal an elongated nucleus about 2.5x3km in size. We did not detectevidence of large (few cm) grains in the coma, which have been detected in several other comets (e.g. Harmon et al. 2011). These images alone may not be sufficient to determine a detailed shape model, but they do constrain the size and rotation characteristics. Hergenrother observed the comet using the 1.8m VATT telescope and finds the rotation rate to be either 10.9 or 21.9 hours, however the radar data rule out the longer period. The highest resolution (15m) images show unusual surface features, unlike radar images of similar-sized asteroids. The six comet nuclei imaged by spacecraft to date, show great diversity in surface structure, texture and distribution of volatiles. More examples are needed in order to understand the formation and evolution of comets. Interpretation of the radar surface features of 209P/LINEAR and comparison to other comet nuclei will be presented.