Solar System

Four rocky globes and four gas giants with no solid surface, almost mini stars. At least 140 moons, one of which, Ganymede, is bigger than planet Mercury. All planets except Mercury have some sort of atmosphere, as do some of the moons. Europa, a moon of Jupiter may even have liquid water, whereas some are just lumps of rock and ice. Some moons have volcanic activity, often caused by gravitational flexing as they circle their host planet.
Jupiter has at least 63 moons, and Saturn, 33. The four gas giants (Jupiter, Saturn, Uranus and Neptune) all have a ring system, possibly associated with electro-magnetic and volcanic interactions with their moons.
The temperature on Mars sometimes gets above zero degrees C, whereas Triton, a moon of Neptune, is the coldest object in the solar system at a shivery minus 235 degrees C.
Neptune was discovered by mathematical calculation after unexplained fluctuations were discovered in the orbit of Uranus. Pluto, the only planet discovered in the 20th century and the only one discovered by photographic survey, is now described as a "dwarf planet". The Somerset Space Walk alongside the Taunton and Bridgwater Canal has a scale model of the solar system. The model of Pluto, in Taunton, is the size of a pea, and 6.8 miles from the model of the sun at Maunsell Lock. Try seeing that with the naked eye!