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1980 occultation observation of a satellite of asteroid (216)

Gene A. Lucas


Observations of a satellite of asteroid (216) Kleopatra made 30 years ago by SJAA members, Gerry Rattley and Bill Cooke, have now been substantiated professionally.

At the recent American Astronomical Society meeting in Pasadena on October 6, 2010, a presentation was made by Dr. Franck Marchis (SETI Institute, UC-Berkeley) on “Characteristics of Known Triple Asteroids in the Main Belt”. One point made during Dr. Marchis’ AAS talk was that the visual observations made by Gerry Rattley and Bill Cooke during the October 10, 1980 stellar occultation by (216) Kleopatra (near Loma Prieta, CA; reported to IOTA), were now deemed not only plausible, but very probable. The results for (216) Kleopatra were included with further results for five other asteroids that show duplicity and/or satellites.

(216) Kleopatra is a relatively large asteroid, measuring 217 x 94 x 81 km. It is believed to be a loosely packed metallic object, based on its radar albedo. Kleopatra is 217 km (135 miles) long, give or take 25% – about the size of the state of New Jersey. The irregular, bi-lobate (“dumbbell’) elongated shape has been strongly confirmed by teams of IOTA occultation observers on several occasions (1980, 1991, 2008, and 2009).

In 2008, Marchis’ team imaged (216) Kleopatra with the Keck II telescope adaptive optics, definitely showing the irregular “peanut” shape of the asteroid, along with two nearby satellites. Other researchers have previously imaged Kleopatra with the large radar dishes at Goldstone and Arecibo, producing a 3-D map of its shape and orientation. Now, Marchis and his team have plotted the orbits for two satellites of the asteroid, which strongly confirms likelihood of the visual occultation observations of a satellite by Rattley and Cooke, made in October, 1980.

This marks a distinct turning point – for now, 30 years later, professionals have at last recognized the value of such occultation observations by amateurs. For since that time, those observations have been either largely ignored, or denigrated completely by the professionals – For many years, the thought of the existence of satellites of asteroids was held to be implausible, if not impossible – just as the concept of irregular shapes for the asteroids was also held in contempt by many theoreticians previously. Of course, direct images from spacecraft have confirmed what was previously suggested by many ground-based occultation observations. (This is also true for several of the comet nuclei which have been imaged, including recent radar results for Comet 103P Hartley.)

The details of the story are explained in an article published on the internet by Kelly Beatty, a columnist for Sky and Telescope magazine, who was in the audience at the October AAS meeting in Pasadena: The complete PPT presentation by Dr. Marchis and his team may be downloaded here: And an abstract for their forthcoming paper, submitted for publication in the professional journal ICARUS, is here:

Gerry Rattley served as an SJAA officer and Board Member during the 1980s, and was a recipient of the A.B Gregory Award in 1982. He has continued to be an active occultation observer and member of the International Occultation Timing Association (IOTA). Since moving to Gilbert, Arizona in July, 1982, Gerry has been active in the Saguaro Astronomy Club and more recently, the East Valley Astronomy Club. Presently he is an active volunteer telescope operator at the Gilbert Rotary Centennial Observatory (GRCO) in Gilbert, AZ.


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