The planet with the second largest number of moons now has two more. The U.S. Cassini spacecraft discovered them around Saturn, bringing the giant ringed planet's known total to 33.
Cassini used the sharpest cameras ever aimed at Saturn to discover the smallest bodies ever seen circling it. It took the pictures on June 1 as it was approaching the giant gas planet for a four-year orbit, but the U.S. space agency NASA released them Monday, August 16, two-and-a-half months later.
It has taken that long for a member of the photo analysis team at the University of Paris to recognize them as moons. They are mere specks on the photographs, measuring only three and four kilometers across. The smallest moons known previously are about 20 kilometers in diameter.
One of the new moons may have been spotted 23 years ago in a single image taken by NASA's Voyager spacecraft, which only flew past Saturn. Scientists are comparing the two sets of images to be sure.
Finding more bodies around Saturn is one of the goals of the Cassini mission. It is also studying established moons, the planet's rings, and its magnetic field.
NASA says the two moons were found in an unexpected location. Cassini scientists had thought there might be tiny bodies within gaps between the planet's rings, so they were surprised to discover this pair further away, approximately 200,000 kilometers from the center of Saturn between two major moons, Mimas and Enceladus.
Why would moons be expected between the rings? One theory suggests that if small comets the size of a house are numerous in the outer solar system, they would collide frequently with inner moons and break them apart. The pulverized moons would then form rings, which would eventually come back together into moons within the ring system.
However, the fact that the moons were discovered well beyond Saturn's rings could mean that small comets are rarer than thought in the outer solar system and that these moons survived intact since the solar system's early days.
NASA says that knowing this is essential for understanding the region beyond the planet Neptune where comets are thought to be in abundance and for understanding the histories of the craters of the giant planets' moons.
Cassini scientists are still looking for more moons between Saturn's rings, but they are also eager to get a closer look at the new moons if it is possible to retarget Cassini from its scheduled observations.