Most people are familiar with Earth's orbital pattern, so it is easiest to discuss Mars's orbit as it relates to Earth's. Mars and Earth share many similarities in their orbits. They are both elliptical patterns and are held on a similar axial tilt. Mars's orbit has a more eccentric pattern than Earth, which introduces some differences in weather patterns between the two planets.
If viewed from above, both Earth and Mars appears to orbit the sun in a counterclockwise direction and are nearly on the same plane. An Astronomical Unit is a measurement of approximately 150 million km, or the distance from Earth to the Sun. Earth's orbit is therefore 1 Astronomical Unit (AU), while Mars averages 143 million miles (230 million km) or 1.5 AU. It takes Earth one year to orbit the sun, while a Mars orbit clocks in at about 687 Earth days or 1.88 times as long as an Earth year. A Mars day is slightly longer than an Earth day, averaging about 24 hours, 39 minutes, and 35 seconds.
Eccentricity is used to define the shape of any planetary orbit. A perfect circle has an eccentricity of zero. Ellipses have an eccentricity between 0 and 1, while parabolas have an exact measurement of 1. Mars's orbit has an eccentricity of 0.09, which makes it the second most eccentric orbit of all the planets. Only Mercury has a greater one.
This eccentricity means that there is a big difference in distances from when it is closest to the Sun, or its perihelion, and when it is furthest away, the aphelion. The perihelion on the Mars orbit is approximately 1.38 AU or 129 million miles (207 million km.) The aphelion is about 1.66 AU or 155 million miles (249 million km.)
Mars's axial tilt is 25.19 degrees. Since this is very similar to the Earth's tilt of 23.45 degrees, Mars's seasons are very similar to those on Earth in that there are four. Each season lasts nearly twice as long as an Earth season since the Mars year is longer. They also tend to be much more extreme since the aphelion and perihelion are so drastically different. Summers are hotter since Mars's orbit comes closer to the sun, while winters are harsher in its furthers reaches.
It is presumed that many years ago, Mars's orbit was much less eccentric. It is estimated to have been closer to 0.002 about 1.35 million Earth years ago. The gravitational forces created by the other planets have been slowly pulling Mars into a greater elliptical pattern.
