Venus is unique among the planets in rotating in a retrograde sense about an axis that is almost normal to the ecliptic (Table 1.1). Like Mercury, it has a high Earth - like density ( 5243 kg m-3 ). On the basis of its density together with gravity estimates from Magellan's orbit, it is though that the interior of Venus may be similar to that of Earth, with a rocky mantle surrounding an iron core about 3000 km in radius, that is possibly at least party molten. However, in contrast to the Earth, Venus has no detectable magnetic field.