Our knowledge of the Solar System has increased dramatically in the last 50 years by the use of spacecraft that have flown by, orbited and even landed on the planets, giving us high resolution images and detailed planetary data. This chapter will cover our Earth and its Moon and the planets Mercury, Venus and Mars, with the following two chapters covering the outer planets, highlighting aspects related to their properties, discovery and satellites. The material included is that which I have found of most interest and I can only hope that what I have found interesting, you will too.

Mercury

Mercury has only ever been visited by two spacecraft, Mariner 10, which made three flybys in the mid 1970s and, early in 2008, by the MESSENGER spacecraft, one of whose images is shown in Figure 4.1. Mercury looks very like the highland regions of the Moon.

In 1991, Mercury was observed by radar using the 70-metre Goldstone antenna with a half-million-watt transmitter. The radar reflections were received by the Very Large Array in NewMexico to provide high resolution radar images. To great surprise, a very strong reflectionwas received fromMercury’s north polar region, which closely resembled the strong radar echoes seen fromthe ice-rich polar caps of Mars. At very low temperatures water ice is a very effective radar reflector.