Astronomers Discover Moon Orbiting Asteroid

Press Release Text

(Images in various formats are available here.)


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The above infrared image is a composite of 5 detections of the new moon (taken -- clockwise from top -- on the nights of 1998 Nov 6,7,9,10 and 1). The green dashed line shows the orbit of the moon around the primary asteroid (45)Eugenia. The period of the orbit is 4.7 days. The moon travels in a closewise direction in this view. The radius of the nearly circular orbit is about 1200 km. The orbit is tilted about 45 degrees with respect to our line-of-sight, so it appears as an oval. The main asteroid is about 215 km in diameter and we estimate the moon's diameter to be 13 km. The moon is 300 times fainter than the asteroid. The large "cross" is a common artifact caused by stray light in the telescope, and is not a real object. Utilizing a new technology, called adaptive optics, we have been able to achieve images 6 times sharper than could otherwise have been obtained from the Earth's surface. Adaptive optics detects and removes the blurring caused by the Earth's atmosphere. Images are obtained at the Canada-France-Hawaii Telescope located on Mauna Kea, Hawaii. Photo credit: Laird Close (European Southern Observatory, Munich, Germany), Bill Merline (Southwest Research Institute, Boulder, CO USA)

Moon Orbit


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The above infrared image (1.6 microns) is a superposition of 5 detections of the new moon (taken --clockwise from top-- on the nights of Nov 1998, 6, 7, 9, 10, and 1 UT). The blue dashed line shows the orbit of the moon around the primary asteroid (45) Eugenia. The period of the orbit is 4.7 days. The moon travels in a clockwise direction (with North up and East to the left). The radius of the orbit is 1190 km. The main asteroid's diameter is close to 215 km (depicted here as a central white circle) and we estimate the moon's size is 13 km in diameter. The moon is 285 times fainter than the main asteroid and is very close to the main asteroid (just over 5 asteroid diameters away, or 0.77 arcseconds on the sky). Image processing (deconvolution) was used to increase the contrast between the moon and the main asteroid. The apparent variations in the moon's brightness and size are artificially produced due to changes in the atmospheric clarity from night to night.

Utilizing adaptive optics this image (resolution of approximately 185 km or 0.12 arcseconds on the sky) is 6 times sharper than could have been otherwise obtained from the ground. Images taken with the PUEO adaptive optics system of the Canada-France-Hawaii Telescope located on Mauna Kea, Hawaii.

Photo Credit: Laird Close (European Southern Observatory, Munich, Germany), Bill Merline (Southwest Research Institute, Boulder, CO, USA)

Discovery Image


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Above is the unprocessed, "raw" image from which the discovery was made on Nov 1, 1998. This shows the primary asteroid, with the satellite (white blob to upper left at about 10:30 position).

Moon Orbit Movie


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Investigators

Contact Information
Dr. William J. Merline  merline@boulder.swri.edu
                        Southwest Research Institute
                        Boulder CO USA

Dr. Laird Close         lclose@eso.org
                        European Southern Observatory
                        Munich, Germany

Dr. Christophe Dumas    dumas@hokulewa.jpl.nasa.gov
                        Jet Propulsion Laboratory
                        Pasadena, CA USA 

Dr. Clark R. Chapman    cchapman@boulder.swri.edu
                        Southwest Research Institute
                        Boulder, CO USA

Dr. Francois Roddier    roddier@ifa.hawaii.edu
                        Institute for Astronomy
                        University of Hawaii
                        Honolulu, HI  USA

Dr. Francois Menard     menard@cfht.hawaii.edu
                        Canada-France-Hawaii Telescope Corp.
                        Kamuela, HI USA

Dr. David Slater        dslater@swri.edu
                        Southwest Research Institute
                        San Antonio, TX  USA

Dr. Gilles Duvert       duvert@obs.ujf-grenoble.fr
                        Laboratoire d'Astrophysique de Grenoble
                        Grenoble, France

Dr. Chris Shelton       cshelton@keck.hawaii.edu
                        W.M. Keck Observatory
                        Kamuela, HI  USA

Dr. Tom Morgan          tmorgan@hq.nasa.gov
                        NASA Headquarters
                        Washington, DC  USA

Bill Merline  merline@boulder.swri.edu
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Last updated 06-Oct-1999 by Will Colwell