M-class asteroids are a relatively rare type of asteroid in the main asteroid belt, located between the orbits of Mars and Jupiter. For many years, planetary scientists have thought that they were the remnants of small protoplanets that were shattered in the violent early days of the solar system, leaving only an exposed metal core behind. Unfortunately, determining whether an asteroid is mostly metallic is very difficult with traditional optical telescopes. For the past decade, we have used the Arecibo Planetary Radar to probe these objects, for only a radar telescope can give an unambiguous indication of a metallic composition. Read More

Though not visible to the naked eye or even with binoculars, the green-tailed Comet 45P/Honda-Mrkos-Pajdusakova (HMP) did not escape the gaze of the world-renowned Arecibo Observatory. Scientists from the University of Arizona’s Lunar and Planetary Laboratory (LPL) and the Universities Space Research Association (USRA) at Arecibo Observatory have been studying the comet with radar to better understand its solid nucleus and the dusty coma that surrounds it.

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E. G. Rivera-Valentin, P. A. Taylor, A. Virkki, and B. Aponte-Hernandez report that Arecibo (2380 MHz, 12.6 cm) delay-Doppler radar images obtained on 2017 January 20 and 23 reveal near-Earth asteroid (163693) Atira is a binary system. Visible range extents of the components in images with 150 m/pixel resolution suggest a primary up to 4.8 ± 0.5 km in diameter and a secondary 1.0 ± 0.3 km in diameter.

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