See How They Shine Trivia Quiz

The picture shows Callisto, the second largest moon of Jupiter. If the first thing you noticed was the large number of craters, you're on the right track as to what makes this moon special - it is the most heavily cratered object known in the Solar System, also because the surface is the oldest. Callisto contains a large amount of ice and thus never experienced geological processes such an volcanic activiy.

It is possible that the surface crust actually floats on a subsurface layer of liquid water.

This color picture of Pluto's moon Charon is actually a composite derived from several monochrome pictures taken at different wavelengths, but it does attempt to show the natural hues found on this satellite, although in reality, the brown is not as saturated as seen here. The images were captured by the New Horizons probe.

The brownish region, with its distinct color and topology, reminded scientists of Tolkien's Mordor, so it has informally been named Mordor Macula. Unlike Tolkien's Mordor, it would however be the most life-friendly area on this cold world: the color is caused by tholins - organic macromolecules.

Dactyl was a chance discovery - this tiny moon has a diameter of less than a mile (1.5 km) and orbits a body not that much larger - asteroid 243 Ida is an elongated rock with a mean radius of just under 16 kilometers. It was the first asteroid moon discovered and has, until 2023, not been photographed by any Earth-based telescope, but rather during the flyby of the Galileo probe. As might be expected for bodies so small, the orbital distance is very small, although the exact value is not known. The Galileo data suggests a distance of about 90 kilometers, but since it is not known whether Dactyl's orbit is circular or elongated, the mean distance could be as low as 65 kilometers or as high as several hundred.

Assuming the 90 kilometers figure as true, Dactyl would appear almost 20 times as large when viewed from Ida as the Moon is from the Earth - a rather massive presence!

If you thought the Ida-Dactyl system was tiny, you may be amazed that there is an even smaller one known: Didymos and its moon Dimorphos. Unlike Ida, which is located in the Asteroid Belt, Didymos is a near-Earth asteroid. Didymos is a mere 800 meters across and Dimorphos a lowly 150 meters - and the moon orbits its central body at just over 1100 meters distance. An astronaut would easily be able to jump from one of these bodies to the other, even in a spacesuit.

The reason we have such detailed images of this tiny body is that it was the target of the DART mission - an experiment designed to test the capability to possibly alter the orbit of an asteroid if it were found to pose a danger to Earth. Having a binary system allowed astronomers to immediately observe the small changes in orbital parameters. The picture is the last frame of video sent by the impactor probe just before it hit Dimorphos. The experiment was a full success - the orbital distance between Dimorphos and Didymos was changed by 60 meters. Even such a small deviation in orbital speeds, imposed on an asteroid a few years before it were to hit Earth, would ultimately mean the difference between a direct hit and a safe passage, should this ever be required.

Although far more than ten bodies in the Solar System have moons, only nine had any photos available to me where I could actually show the moon shine instead of just a speck of light, so Jupiter gets a second nod - the Galilean moons are quite recognizable.

This one is Io, the innermost of the four and known for its extreme volcanic activity. In fact, Io's surface appears yellow (the well-known reddish photographs are not true color) due to sulfur deposits - one could almost think this is a ball of cheese or one cut from a pineapple.

The extreme geological activity on Io is due to the fact that it is so close to Jupiter and its neighboring moons - the gravity of its neigbors is constantly tearing on it. The force is enough to cause Io to heat up internally, although it is not at risk of being torn apart.

Hopefully the picture angle did not fool you - this picture of Earth's moon is not quite the view you'd get from Earth - it is seen from above the ecliptic, with the Moon's North Pole being about a quarter down from the top, so the dark regions are not in the place you see them when looking up at night. Like many of the pictures in this quiz, this one was taken by the Galileo probe.

The bright spots in the left half, with the rays emanating from them, are not optical artifacts or reflections but rather the Kepler and Copernicus craters.

If you don't fancy the extreme heat of Mercury and Venus, Mars is the best planet to go to if you'd rather not have much moonlight shining on you - while it does have two moons, both of them are really small: Phobos (pictured) is about 22 kilometers across and Deimos even smaller at only about 13 kilometers. However, don't expect a featureless dot in the sky - Phobos is much closer to Mars than the Moon is to Earth. If you were to look up from Mars during a clear night, Phobos would appear about a quarter the diameter of Earth's Moon. It is expected that Phobos will last only 30 to 50 million years from now before either crashing into the planet or breaking apart. If the latter were to happen, Mars would gain a ring - at least for some time.

Phobos might become the next object astronauts set foot upon, even before Mars itself. Its small size and low gravity would lend itself to constructing a base from which the actual landing mission on the planet could be more easily completed than from a spaceship coming from Earth.

If you think this picture looks more like a planet than a moon - well, that's because Titan, Saturn's largest moon, has an atmosphere - one that, at the surface, is more dense than Earth's. Like Earth's atmosphere, it is mostly composed of nitrogen, with some methane and hydrogen making up the remainder. Methane is also the compound that forms most of Titan's clouds and some methane and ethane also falls as rain. Titan's surface supports several small seas of liquid methane, mostly around the polar regions. There is effecitvely no oxygen present in Titan's atmosphere, not even in compounds such as carbon dioxide, because the temperature is too low. However, solid oxygen-containing compounds, including water ice, can be found on the surface.

The photo of Titan shown here is not in actual color - a normal visible-light photograph just shows featureless orange haze caused by trace nitrogen-containing organic compounds.

Unlike the moons of Jupiter and Saturn, where several missions have brought back data and images, those of Uranus and Neptune have each only been visited and photographed by an Earth probe from a close distance once - both by Voyager 2. As such, we only know parts of their surface - in Titania's case, the existing images are centered almost exactly on the South Pole.

It will be a long time before we get to see a similar picture of the other hemisphere - just like Uranus itself, the system of its moons lies almost perpendicular to the ecliptic. Thus, each polar region faces the sun only every 84 years and the launch window for the North Pole solstice in 2028 has already passed, thus the first chance for mankind to see the other half of this Uranian moon in the same glory won't be before well into the 22nd century.

Neptune's fourteen known moons fall into two groups: seven inner, regular, moons orbit approximately at the plane of Neptune's equator, with the largest and outermost of those being Proteus, a 420 kilometer rock that looks more like a cube than a sphere. Beyond those, seven irregular, outer moons exist that have varied orbits, some of which are actually retrograde (opposite to the direction of Neptune's rotation). By far the largest of them is Triton (pictured).

It is thought that none of Neptune's current moons formed along with the planet. Triton is most likely a captured former dwarf planet and the smaller moons - even the regular ones - are probably fragments of an original moon that broke apart when Triton was captured. Like for Titania, only slightly less than half of Triton's surface has ever been photographed at high resolution, but seasons and day/night cycles on Triton are much shorter than for the Uranian moons, so a complete mapping mission could be launched at any time.