Astronomers discovered 11 small moons orbiting Jupiter, bringing the giant planet's total to 28.

Only Saturn has more, with a total that rose to 30 in October. However, some of the newly discovered objects around both planets will need to be confirmed by other observations.

Jupiter's newly found moons, spotted late last year and announced Friday, are all estimated to be less than 5 miles (8 kilometers) wide, though astronomers stressed that the estimates were crude, based on the brightness of the objects.

The discoveries were made using the University of Hawaii's 88-inch (2.2-meter) telescope atop Mauna Kea. To find such tiny objects, Scott Sheppard, David Jewitt, Yan Fernandez and Gene Magnier produced three images of various patches of the sky, then looked for objects that moved against the background of stars, which sit relatively still.

Jupiter's system of moons is dominated by the four largest, Io, Europa, Ganymede and Callisto. These "Galilean" moons, named after their discoverer, are all visible with a small telescope or binoculars. The newly found satellites are part of Jupiter's outer "irregular" satellite system, doubling the number of moons in that region.

Each has an orbit that is highly "eccentric," or non-circular. Their orbits are also "inclined," meaning that they are not in the same plane as Jupiter's equator. The most distant one orbits about 13.3 million miles (21.4 million kilometers) from the planet.

Nine orbit in the opposite direction of Jupiter's rotation, a motion known as retrograde. Of the previously discovered satellites, five also travel in a retrograde orbit.

Retrograde satellites are thought to be space rocks that wandered near Jupiter from elsewhere in the solar system and were captured into orbit. Scientist don't know exactly how this might have happened, but one theory suggests that a young Jupiter had a bloated atmosphere that would have slowed the objects down, causing them to settle into orbit.

Other moons, which orbit in the same direction as the planet spins, are often thought to have formed as a byproduct of planet formation.

Some of the newly found satellites orbit in groups, and the discoverers said it's possible that a larger object broke up while being captured, forming several small moons that now orbit in a huddle.