Comparing Earth with Mars, Venus, exoplanets, and other worlds reveals both shared processes and important differences. These studies clarify planetary formation, atmospheres, surfaces, climates, and the conditions associated with habitability.
Venus completes one orbit around the Sun in about 224.7 Earth days, but its solid surface needs approximately 243 Earth days to rotate once relative to the distant stars. By that definition, a Venusian day is longer than a Venusian year. The comparison is accurate, although it uses the sidereal day...
Ancient Mars left two records that appear to tell consecutive parts of the same story. Magnetized crust shows that the young planet once generated a global magnetic field. Dry valleys, deltas, lake deposits, and water-formed minerals show that it also supported environments unlike its cold,...
Venus is often called Earth’s twin because the two planets are close in size, mass, density, and basic composition. The resemblance ends at the surface. Venus has an atmosphere more than 90 times as massive as Earth’s, temperatures near 465°C, and clouds made largely of sulfuric acid droplets. It is...