Ostro, S. J., D. B. Campbell, A. A. Hine, I. I. Shapiro, J. F. Chandler, C. L. Werner, and K. D. Rosema (1990). Astron. J. 99, 2012-2018.
Radar echoes from the near-earth asteroid 1627 Ivar, whose orbit crosses the Earth's, reveal it to be about twice as long as it is wide, with a maximum dimension no less than 7 km and probably within 20% of 12 km. The surface is fairly smooth at centimeter-to-meter scales but appears irregular and nonconvex at kilometer scales.