It's getting harder and harder to find new moons in our solar system -- the easy ones are all discovered
First posted 2:40 p.m, October 2, 2002
It's getting harder and harder to find new moons in our solar system -- the easy ones are all discovered.
So the discovery of a previously unknown moon around the planet Uranus took, as one can imagine, a lot of time and effort. It also took multiple telescopes and the expertise of roughly a dozen astronomers.
The newfound moon, called S/2001, was announced Monday by the International Astronomical Union. The planet is known to have more than 20 satellites.
The latest discovery was led by Matthew Holman of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. The satellite, probably one of many small undiscovered moons, is estimated to be 9 to 12 miles (15 to 20 kilometers) wide, Holman told SPACE.com. It is the smallest Uranian satellite found so far.
Uranus has 10 so-called "regular" moons that carve orderly paths around the planet all in pretty much the same plane. There are also six irregular satellites, including S/2001. These objects take odd courses around the planet and are thought to be the remnants of a collision between a comet and some other large object that had been orbiting Uranus.
"Tracking irregular satellites is an enormous undertaking," Holman said. Candidates are sometimes spotted but then lost. If not re-observed within about two months, he said, they must be rediscovered and a new observational campaign begun.
The initial discovery of S/2001 was made last summer by Holman, J.J. Kavelaars of the Dominion Astrophysical Observatory in British Columbia, and Dan Milisavljevic of McMaster University in Ontario.
Several long-exposure images were analyzed together, and the moon shows up in distinct locations, whereas background stars are seen as long smudges.
But that first sighting, made with the Canada-France-Hawaii Telescope and the Cerro-Tololo Inter-American Observatory in Chile, was not publicly announced. Ten other researchers helped with other observations used to pin down the path of the object and then to calculate its orbit during several months of tracking.
Jupiter has 39 known satellites, the most of any planet in the solar system. Saturn has 30. Astronomers expect both totals to go higher as more and finer observations are made. The same will likely hold true for Uranus.
"The number of fainter [Uranian satellites] suggests that we will find many more when we use bigger telescopes to improve our searches," Holman said.
Editor's Note: This story originally put the tally of Uranian moons at 16. Peter Brown of the University of Canberra kindly corrected us. The true tally is at least 22, other astronomers say, with uncertainty due to the fact that newfound small moons sometimes are not immediately confirmed. This story also now includes a revised size estimate of the newfound moon from the study's lead scientist.
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