Mars orbits the Sun at an average distance of 228 million kilometers (about 142 million miles), completing one full trip every 687 Earth days. That makes a Martian year nearly twice as long as ours. But what makes Mars’s orbit especially interesting is its shape: it’s noticeably more elliptical than Earth’s, which creates big swings in distance, speed, and even seasonal weather on the planet.
Shape and Size of the Orbit
Mars follows an elliptical path around the Sun, meaning it’s not a perfect circle. At its closest approach to the Sun (perihelion), Mars sits about 206.7 million km away, or 1.38 AU. At its farthest point (aphelion), that distance stretches to 249.2 million km, or 1.666 AU. One astronomical unit (AU) equals the average Earth-Sun distance, so Mars ranges from about 1.4 to 1.7 times farther from the Sun than we are.
That gap of roughly 42.5 million km between the closest and farthest points matters. Mars’s orbital eccentricity, a measure of how stretched out an orbit is, runs more than five times higher than Earth’s. Earth’s orbit is close to circular, so the difference between our nearest and farthest points from the Sun is relatively small. Mars, by contrast, experiences a significant difference in solar energy depending on where it is in its orbit.
How Long a Martian Year Lasts
A single orbit takes Mars 686.98 Earth days, commonly rounded to 687. In Martian solar days, called sols (each about 24 hours and 39 minutes), that works out to 668.6 sols per Martian year. If you lived on Mars, you’d wait almost two Earth years between birthdays.
Mars also moves more slowly through space than Earth does. Its average orbital velocity is about 86,677 km/h (roughly 24.1 km/s), compared to Earth’s 107,000 km/h. The farther a planet sits from the Sun, the slower it needs to travel to maintain a stable orbit, which is why Mars takes longer to complete each lap.
How Eccentricity Shapes the Seasons
Mars has an axial tilt similar to Earth’s (about 25 degrees), so it does experience seasons. But the stretched orbit adds a layer of complexity that Earth doesn’t really have. Mars reaches perihelion, its closest point to the Sun, during southern hemisphere summer. That means the southern hemisphere gets significantly more intense solar heating during its summer than the northern hemisphere gets during its own summer.
The practical result: southern summers on Mars are shorter and hotter, while northern summers are longer and milder. This asymmetry drives real differences in weather. Global dust storms, one of Mars’s most dramatic phenomena, tend to kick off during southern summer when solar heating peaks. The timing is so consistent that planetary scientists track Martian seasons using a coordinate called solar longitude, and the onset of major dust storms clusters around the same orbital position year after year.
Over much longer timescales (tens of thousands of years), Mars’s eccentricity and axial tilt both fluctuate. When the tilt drops to around 15 degrees, models suggest the atmosphere thins dramatically, thick carbon dioxide ice caps form at both poles, and dust storms largely cease. When the tilt climbs to 35 degrees, polar temperatures rise enough that water ice caps can become unstable, and dust storms may rage during summer in both hemispheres. These slow orbital shifts are thought to have carved the layered terrain visible in Mars’s polar ice caps today, with alternating bands of ice and dust recording climate cycles stretching back millions of years.
Mars and Earth: The Opposition Cycle
Because Earth orbits closer to the Sun and moves faster, it periodically catches up to Mars and passes between Mars and the Sun. This alignment is called opposition, and it happens roughly every 26 months (the precise average is 779.94 days). Opposition is when Mars appears brightest in Earth’s sky and when the two planets are closest together.
Not all oppositions are equal, though. Because of Mars’s eccentric orbit, the distance between the two planets at opposition varies considerably. When opposition happens while Mars is near perihelion, the two worlds can close to less than 56 million km. The most famous recent example was August 2003, when Mars came within 55.76 million km of Earth, the closest approach in nearly 60,000 years. When opposition falls near Mars’s aphelion instead, the gap can be over 100 million km.
These close perihelic oppositions follow a rough pattern. After seven oppositions (about 15 Earth years), the geometry nearly repeats, with the seventh opposition landing about 19 degrees behind the first in its position along the orbit. A longer cycle of 15 oppositions over about 32 Earth years brings the alignment back to within about 11 degrees of the starting point. For anyone hoping to spot Mars through a telescope or binoculars, perihelic oppositions offer the best views, and they cluster around late summer in the northern hemisphere because of where Mars’s perihelion falls relative to the geometry of the two orbits.
Why the Orbit Matters for Space Missions
Every Mars mission ever launched has been timed around the orbital relationship between the two planets. The most fuel-efficient transfer, called a Hohmann transfer orbit, requires launching when Earth and Mars are positioned so the spacecraft arrives just as Mars catches up to it. This launch window opens roughly every 26 months, coinciding with the opposition cycle. Miss it, and you wait over two years for the next chance.
The eccentricity of Mars’s orbit also means travel times and distances vary from window to window. A mission launched during a close approach deals with a shorter trip and lower energy requirements than one aimed at a more distant alignment. Once a spacecraft arrives, the elliptical orbit affects surface operations too: solar-powered rovers and landers receive noticeably less sunlight when Mars is near aphelion, reducing the energy available for driving, drilling, and transmitting data back to Earth.