Francisco (moon)

Francisco, also called Uranus XXII and previously known as S/2001 U 3, is one of the smallest moons of the planet Uranus. It was found on August 13, 2001, by scientists John J. Kavelaars, Matthew J. Holman, Dan Milisavljevic, and Tommy Grav using a big telescope in Chile. They used the 4.0-meter Víctor M. Blanco Telescope at the Cerro Tololo Observatory to spot it.

Francisco orbits Uranus in the opposite direction of most of the planet's other moons. It stays about 4.3 million kilometers (2.7 million miles) away from Uranus and takes around 267 days—almost three-quarters of a year—to go around the planet once. Scientists think Francisco might be about 22 kilometers (14 miles) wide, but there is still a lot they do not know about its size and other features. The moon was named after a character named Francisco, who is a lord in William Shakespeare’s play The Tempest.

Discovery

Francisco was discovered on 13 August 2001 by a group of astronomers: John J. Kavelaars, Matthew J. Holman, Dan Milisavljevic, and Tommy Grav. They were looking for distant moons of Uranus using the 4.0-meter Víctor M. Blanco Telescope at Cerro Tololo Observatory in Chile. They found Francisco and three other moons of Uranus—Trinculo, Ferdinand, and Margaret—by using a special computer method to spot the faint moons.

To learn more about Francisco’s path around Uranus, the team kept watching it from different telescopes, including the 200-inch Hale Telescope at Palomar Observatory and the 8.2-meter Very Large Telescope at Paranal Observatory. These observations continued until 5 September 2002. The discovery of Francisco was announced by the Minor Planet Center on 6 October 2003.

Name

When Francisco was discovered, it was called S/2001 U 3 by the Minor Planet Center. Later, on 29 December 2005, it was named Uranus XXII by a group of experts from the International Astronomical Union. The moon is named after a character named Francisco from William Shakespeare’s play, The Tempest. In the story, Francisco is a lord who gets shipwrecked with King Alonso and others.

Orbit

Francisco is an irregular moon of Uranus. These moons have wide, stretched-out paths as they travel around the planet, unlike the closer, more circular paths of Uranus's regular moons. Scientists think moons like Francisco may have once been asteroids that got pulled into Uranus's orbit long ago.

Francisco orbits Uranus in the opposite direction from the way Uranus travels around the Sun, which is called a retrograde orbit. It is the closest known irregular moon to Uranus. Its path changes a little over time because of the pull of the Sun and other planets, but scientists can still describe its average path over many thousands of years.

Physical characteristics

Francisco is a very faint moon, with an average brightness that can only be seen using special cameras on large telescopes. Scientists think its surface is dark and made of frozen water, minerals, and other natural materials, much like other unusual moons. By looking at how bright it is, they guess Francisco’s size to be somewhere between 11 to 17 kilometers (7 to 11 miles) across, though some experts believe it might be a bit larger, around 22 kilometers (14 miles).

Exploration

Francisco has not been seen up close by a space probe, but Voyager 2 passed by it in 1986 when it flew by Uranus. Scientists hope to learn more about Francisco and other moons of Uranus with a planned mission called the Uranus Orbiter and Probe. This mission will watch how the moons' brightness changes to learn about their shapes and how they spin. However, because Francisco's orbit is positioned differently, the mission might not be able to get very close to it.