Meet the moons: planetary satellites in pictures

The most distant moon yet to be seen in close-up is Triton, the largest moon of Neptune. It has a thin, nitrogen atmosphere and seasonal polar caps of nitrogen ice. Only the south polar cap is visible in this shot, because the northern one was in seasonal darkness. Beyond the polar cap is a richly textured surface formed largely by icy volcanism Photograph: USGS/JPL/NASA

The most volcanically active body in the solar system is Jupiter’s moon Io. It is a fraction bigger than our moon and is the only other large moon to have a rocky, rather than icy, surface. It is coloured yellow by sulfur compounds. These two views were recorded by Nasa’s Galileo orbiter in April and September 1997. The large orange ring is fallout from a previous eruption of the volcano Pele Patera. The grey deposit to its right erupted from the volcano Pillan Patera after the first image was taken Photograph: University of Arizona/JPL/NASA

Saturn’s rings are made of brick-sized lumps of ice, individually too small to be regarded as moons. This image, however – captured by the Cassini orbiter in 2013 – shows Pan, a 28km-long ‘shepherd moon’ whose orbit lies in a gap between the rings. The gravity of shepherd moons maintains the sharply defined edge of planetary rings Photograph: Space Science Institute/JPL-Caltech/NASA

This image was taken by the Cassini orbiter in 2009, looking south onto Saturn’s rings when the plane of the planet's rings was almost exactly edge-on to the sun. It shows the 86km-long moon Prometheus and its elongated shadow cast onto the rings on one side (the faint thin line crossing the wide grey ring about halfway up the image on the right). On the other side, you can see disturbances in a narrow ring caused by the gravitational attraction of Prometheus, which is orbiting anticlockwise, faster than the particles in the ring. Photograph: Space Science Institute/JPL/NASA

Some moons periodically swap orbits. These are two of Saturn's moons, Janus (right) and Epimetheus (left), imaged in 2006 by the Cassini orbiter. One orbits slightly closer to Saturn than the other, but about every four years they swap over Photograph: Space Science Institute/JPL/NASA

This is a close-up colour view of Epimetheus taken by the Cassini orbiter from a range of 74 600km. The large crater, called Hilairea, is 33km across. Photograph: Space Science Institute/JPL/NASA

This is a Cassini image looking at the night side of Enceladus. Jets of ice particles spouting from cracks near the moon’s south pole catch the sunlight Photograph: Space Science Institute/JPL-Caltech/NASA

At 5,151km in diameter, Titan is Saturn’s largest moon and is the only moon in the solar system to have a dense atmosphere. This natural-colour image taken by the Cassini orbiter shows its orange hydrocarbon smog with a blue haze above. A vortex pattern sits over the south pole. To see the surface of Titan, filters can be used to block wavelengths of light reflected by the smog, or radar can be used to penetrate it Photograph: Space Science Institute/JPL-Caltech/NASA

A radar view through Titan’s blue haze shows a rugged terrain made of water ice with what appear to be rivers of liquid methane draining into lakes. This one, named Ligeia Mare, is in Titan’s north polar region Photograph: Cornell/ASI/JPL-Caltech/NASA

Cassini recorded this image of Titan's surface using a narrow-band near-infrared filter to accept only light at 938 nanometres wavelength, which is just about able to penetrate the haze. The dark patch near the north is a large lake called Kraken Mare that has been imaged by radar. The equatorial dark patches may be dry seabeds Photograph: Space Science Institute/JPL/NASA

This is Iapetus, Saturn’s outermost large satellite which was discovered in 1671 by Giovanni Domenico Cassini (after whom the Cassini orbiter spacecraft is named). All Cassini could see of Iapetus through his telescope was a tiny speck of light, but he noted that it is always much fainter when on one side of Saturn than the other. From this simple observation, he correctly surmised that Iapetus keeps the same face towards Saturn throughout its orbit and that its leading hemisphere must be much darker than its trailing hemisphere. Most moons keep the same face towards the object they are orbiting. However, Iapetus’ asymmetric brightness is unusual. The side that always faces forward as Iapetus orbits (its leading hemisphere) has become coated in dark, reddish dust collected from space. The other side is highly reflective ice Photograph: Space Science Institute/JPL/NASA

Jupiter's moon Europa is arguably the place in the solar system, apart from Earth, most likely to host life. It is only slightly smaller than our own moon and probably made of similar stuff except that it has an outer layer of ice. The way the icy surface has become cracked with pieces shunting around suggests that there is a liquid water layer between the solid icy shell and the rocky interior. These images were recorded by Nasa’s Galileo orbiter in 1996 and 1997 Photograph: University of Arizona/JPL/NASA

This is Phobos, the larger of the two small moons of Mars, in a picture taken by Nasa's Mars Reconnaissance Orbiter. It is only 22km long and is almost certainly an asteroid that was 'captured' by Mars. The grooves are thought to be the trails made when Phobos passed through hails of debris thrown up by impacts on Mars, only about 6,000km away Photograph: University of Arizona/JPL-Caltech/NASA