New Satellites of Uranus Discovered in 2003

Figure 1: Discovery images of one of the newly found Uranus satellites S/2003 U3 showing its motion relative to background stars and galaxies. Click on the image to learn more.

Scott S. Sheppard and David Jewitt at the University of Hawaii have discovered 2 new outer satellites of Uranus designated S/2001 U2 (now named Ferdinand) and S/2003 U3 (now named Margaret). The discovery images were obtained from the Subaru 8.3m telescope atop Mauna Kea in Hawaii on August 29, 2003. Further observations by the Hawaii team using the Gemini 8.2m telescope allowed Brian Marsden at the Minor Planet Center to link the satellites to independent discovery observations obtained in 2001 by a group lead by Matt Holman and JJ Kavelaars. The 2001 observations were not enough to determine if the objects were satellites of Uranus and no reliable orbits were found. They were than lost until discovery in 2003 by the Hawaii team.

The new Uranus satellite S/2001 U2 (Ferdinand) was announced by the International Astronomical Union on October 1 ( IAU Circular 8213 ) and S/2003 U3 (Margaret) on October 9 ( IAU Circular 8217 ). The new satellites are about 12 and 11 kilometers in diameter respectively. S/2001 U2 (Ferdinand) has an orbital period of about 8 years and is in a retrograde orbit. S/2003 U3 (Margaret) has an orbital period of just over 4 years and is the first prograde irregular satellite discovered around Uranus. All the giant planets now have known prograde and retrograde irregular satellites.

Uranus now has 27 known satellites of which 9 have irregular orbits.

See a table of Uranus' known satellites .

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For more information about satellites in our Solar System visit The satellites page.