Here we are looking down on the inner solar system as the planets orbit the Sun. The orbits of Earth and Mars are shown. The planet Venus is labeled, and Mercury is also seen orbiting closer to the Sun.

The first thing to note is that Earth’s orbit is very close to circular. We stay about the same distance from the Sun, only changing by about 3.4 percent over the course of a year. Surprisingly, we are closer to the Sun in early January than at any other time—right in the middle of winter!

The orbit of Mars is much more elliptical (oval-shaped), so Mars varies its distance from the Sun by over 20 percent. In August of 2003, the planets will approach each other when Mars is at its closest to the Sun. At that point, we'll be only 55,755,126 km (34,644,564 mi) from the Red Planet, the closest we’ve been since 57,617 BC! We won't be this close again until the year 2287.

Mars and the Earth approach each other every 2.133 years, but they don’t often meet when Mars is at its closest to the Sun. That happens about every 15 to 17 years. In 2003, however, Earth and Mars are at their closest when Mars is only three days from its closest approach to the Sun (shown with a tick-mark on Mars’ orbit).