Is it true that, as we follow the planets outward from the sun, the distances become about double each time? Does that mean that Venus is closer to Earth than Mars is?
Yes, it is true that there is somewhat of a pattern to the distances of the planets from the Sun. Venus is 1.8 times as far from the Sun as Mercury, and Earth is about 1.4 times as far from the sun as Venus. Mars is 1.5 times farther than Earth. This seems to be a pattern - each planet could be between 1.4 and 1.8 times farther from the sun than its "inside" neighbor. Then comes the problem - Jupiter is 3.4 times farther from the sun than Mars. This is where the pattern falls apart, although some say that the asteroid belt, which is in between Jupiter and Mars, could count as a substitute for a planet. Then Saturn is 1.8 times farther than Jupiter, Uranus is 2 times farther than Saturn, and Neptune is 1.6 times farther from the Sun than Uranus. Pluto doesn't fit this pattern at all. So there seems to be some sort of pattern to this, but there's no real theory that explains why the planets ended up at the distances they did, so it could also be a complete coincidence that they're somewhat evenly spaced.
So the "doubling" rule does work, but only approximately. This means that yes, the difference between the average orbital distance of Mars from the Sun to the average orbital distance of Earth from the Sun is greater (about 78 million km) than the difference between the Earth's average orbital distance from the Sun to Venus' average orbital distance from the Sun (41 million km). However, since the distance between the Earth and other planets depends not only on the size of their orbits but also on where they are in their orbits relative to each other, Venus is not always closer to Earth than Mars is.
This page was last updated on July 18, 2015.