快猫短视频

AFTER a 14-year search the Hubble Space Telescope has found two tiny moons
orbiting Uranus only previously seen by a planetary probe. The find supports a
theory that the moons鈥攐ne inside Uranus鈥檚 main ring and one
outside鈥攁ct as 鈥渟hepherds鈥�, keeping the ring from dispersing.

The Voyager 2 spacecraft discovered the moons, named Cordelia and Ophelia, as
it whizzed passed the planet in January 1986. But researchers could not get a
precise fix on their orbits. Even though astronomers immediately began training
their telescopes on Uranus, light from the main ring blotted out the moons.

However, Philip Nicholson of Cornell University in New York State and Richard
French of Wellesley College in Massachusetts began analysing images of Uranus
from a range of different telescopes. They watched the ring pass in front of
distant stars and spotted what looked like ripples produced by the moons,
prompting the theory that the moons were keeping the ring in line.

Last month, Erich Karkoschka of the University of Arizona searched Hubble
pictures again for the moons. He spotted Ophelia by electronically stacking
dozens of Hubble images. 鈥淚f you look at any one image, you cannot be convinced
it鈥檚 there,鈥� he says, but when the images are combined, 鈥渢hen you can see it.鈥�
The study of the images showed that Ophelia was close to the position that
French had predicted from 16 years of observing ring ripples.

French encouraged Karkoschka to look again for Cordelia, giving him fresh
predictions of its location. They proved to be bang on target: Karkoschka
spotted Cordelia when he aligned the right images. He says that finding the
second moon at the predicted spot was 鈥渁 big day for celestial mechanics,鈥� and
confirming their positions either side of the ring supports the idea of their
shepherding role.