This video looks at the characteristics of the outer planets, dwarf planets, moons and comets. To see the review of the inner planets, watch this video. The common feature of the outer planets is that they are all gas giants. They have no solid surface. What we observe is a ball of gas or vapor so we cannot land on them. There is a lot to take in, so you may want to pause the video to have a good read. Which of the gas giants has rings? Pause the video while you think of an answer. The answer is that all four of them have rings, but only those of Saturn are visible from the Earth. Until 2006, a verse to recall the planetary order could have been, my very elegant mother always jumps sideways underneath pillows. In that year, it was decided that Pluto was not a true planet, and so was reclassified as a dwarf planet. Poor Pluto. There are certain rules to be a planet. Firstly, you must be in orbit around the sun. Secondly, you must be heavy enough to be almost spherical in shape. And thirdly, you have cleared your neighbourhood of rocks and debris. Pluto joined other named dwarf planets, which are bodies that orbit a star and have a stable shape, but have not cleared their orbits of other debris. The large asteroid, Seris, is another example of a dwarf planet and others well beyond Pluto are being discovered. A moon is a natural satellite. It's a body which orbits a planet, and so of course is part of the solar system. As you will have seen, some of the planets have a large number of moons, and some none at all. Stop the video if you want to go back and look. Earth is unusual, as our moon, the moon, is large when compared to the planet in orbits. It is thought that the moon was created very early on in the life of the Earth after a significant interplanetary collision which ejected rock which was then captured in orbit. There are other objects that are part of our solar system we rarely see. Comments People once thought the appearance of a comet in the night sky was a warning of a tragic event about to happen. Comments are similar to large dirty snowballs, a few tens of kilometres across. That follow a huge elliptical path around the sun that may take decades, centuries, or longer to complete one orbit. It was Sir Edmund Haley who was first to successfully predict a return of a comet that now bears his name. It returns every 75 years, and was last seen in 1986. You do the maths. These ancient objects only become visible when their orbit brings them near to the sun. That's when a huge tale of vaporised material is lit up by sunlight. Notice that the tail always points away from the sun as it passes by, showing the effect of the invisible solar wind leaving the surface of the star. Before you go, did you remember the verse to recall the order of the planets?