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New moons make Uranus the champ

Science News, August 14, 1999 by R.C.

Astronomers have discovered two small bodies that are almost certainly moons of Uranus. If the discovery is confirmed, this distant planet would have 20 known moons--more than any other planet in the solar system. The former champion, Saturn, would become the runner-up, with 18 satellites.

J.J. Kavelaars of McMaster University in Hamilton, Ontario, and his colleagues announced their finding in a July 27 circular of the International Astronomical Union. The team used the 3.5-meter Canada-France-Hawaii Telescope atop Hawaii's Mauna Kea to spy objects in the outer solar system's reservoir of comets, the Kuiper belt, as well as to search the vicinity of Uranus. A search within 100 million kilometers of the planet revealed only the two bodies.

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There's a small possibility, says Kavelaars, that these small bodies are not satellites of Uranus but escapees from the Kuiper belt that are orbiting the sun. However, both the location and the speed of the faint objects--they lie near Uranus and appear to move with the planet--make that possibility remote, he says. The researchers estimate that each body has a diameter less than 20 km and resides several million kilometers from the planet.

Two years ago, using the 5-meter Hale Telescope on Palomar Mountain near Escondido, Calif., Kavelaars and his colleagues discovered the 16th and 17th moons of Uranus (SN: 12/6/97, p. 360). This past spring; Erich Karkoschka of the University of Arizona in Tucson, found an 18th moon in images taken by the Voyager 2 spacecraft as it flew past the planet.

The moons found by Kavelaars' team in 1997, as well as the objects announced in July, share an unusual trait. They are the only bodies with orbits inclined relative to the planet's equator.

Kavelaars suggests that soon after Uranus formed, two chunks of debris that resided near the planet collided and broke into fragments. The fragments then passed through gas in Uranus' young, bloated atmosphere that slowed them down until they were captured by the planet's gravitational field.

If the collision theory is correct, Uranus may have several more moons, but most would be too small and dim to detect, Kavelaars says.

Technology Industry

New moons make Uranus the champ

Science News, August 14, 1999 by R.C.

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