How Long Does Mars Take to Go Around the Sun?

Are you wondering how long Mars, the fourth planet in our solar system and our planetary neighbor, takes to orbit the Sun? 

Mars orbits—or completes one revolution—around the Sun every 686.98 Earth days, or once every 1.88 Earth years. While orbiting the Sun, Mars travels at an average speed of 53,979 miles per hour, which equates to 86,871 km per hour.

In the rest of the article, we will learn more about how long a Martian day lasts, the red planet‘s eccentricity, and why it only reaches conjunction with Earth every two years. 

Planet mars showing southern polar ice cap
Planet Mars (source)

Mars 101

Mars is the fourth planet from the Sun, both similar to and different from Earth. Like Earth, Mars is a terrestrial planet and is similar in shape but smaller in size. However, there are a few significant differences between these two planets.

Scientists believe that early in Mars’ history, it was very similar to Earth. But the loss of atmosphere caused it to lose its habitability, resulting in the barren world we see today.

One of those big differences, of course, is its distance from the Sun. Mars orbits the Sun at 142 million miles (228 million km), which is much, much farther away than Earth.

Due to its huge distance from the Sun, the time Mars takes to complete an orbit is vastly different from Earth.

How Long Does Mars Take to Orbit the Sun? 

Mars, like all other planets in our solar system, travels around the Sun in an elliptical orbit. A full year on Mars is constituted by one full revolution in its orbit.

The red planet moves at an average speed of 53,979 miles per hour (86,871 km per hour). At this speed, it takes Mars nearly 687 Earth days, or 1.88 Earth years to complete one year. That’s just about 23 months.

In addition to revolving, remember that Mars is also spinning about its own axis. One complete spin constitutes a Martian day. At Mars’ orbital speed of 24 km per second, it takes the planet 24 hours and 37 minutes to complete one rotation. That is just a little more than a day on Earth.

So, measured in Martian days (sols), it takes the Red Planet 669 sols to complete a single orbit of the sun.

Why Does Mars Only Reach Opposition Every Two Years?

While revolving around the Sun, Mars and Earth are in opposition once every 26 months. During this time, both planets are on the same side of the Sun, effectively at their closest distance to each other. 

Now, you might remember that the time Mars takes to orbit the Sun is 687 days, which is roughly 23 months. If Mars needs 23 months to make one revolution, why does it take 26 months to be in conjunction with Earth? 

Put simply, during those 23 months of Mars’s orbit, Earth has been moving around the sun too, and faster than Mars, so we are no longer aligned when Mars completes an orbit.

The extra three months needed to reach conjunction is the time it takes Earth to catch up to Mars once more. 

Orbital Eccentricity

Mars has an orbital eccentricity of 0.0935, one of the highest of all the planets in our system (Earth’s orbital eccentricity is just 0.0167).

The number represents the extent to which the planet’s orbit has deviated from being a perfect circle. This means that Mars’ orbit is more elliptical than Earth’s. The planet with the highest eccentricity is Mercury (0.21). 

The orbital eccentricity of a planet also suggests how far and near it can get to the Sun in the course of its orbit, which in turn dictates the severity and length of seasons. Like Earth, Mars has four seasons, but each is twice as long due to its longer orbit. 

When it is closest to the Sun at just 128 million miles (205 million km), the southern hemisphere that is tilted towards the Sun experiences higher temperatures, driving winds, storms, and other seasonal changes. 

When Mars is farthest from the Sun at 154 million miles (247 million km), the northern hemisphere faces the Sun. Polar caps that grow during winter disappear by summer.

How Long is a Day on Mars?

On Earth, scientists use Julian dates to keep track of events over long periods. On Mars, a system called the Mars Sols Date (MSD), which has been counted since December 29, 1873, is used to track time.

This is the local solar time in the Martian world, which scientists used to document events related to the planet and spacecraft. 

On average, a Martian ‘sol’ is 24 hours 39 minutes 35.2 seconds, which is roughly 40 minutes longer than an Earth day.  

Summary

So, we have seen how long Mars takes to orbit the Sun. While it might seem like a simple question at first, you see how and why the red planet takes 687 Earth days or 1.88 Earth years to complete one orbit. There were also a few other interesting points that we skimmed by. 

Although Mars around the Sun is 23 months, the orbit of Earth and Mars causes them to be in conjunction once every 26 months. 

In addition to moving around the Sun, Mars is also rotating about its axis, for which it takes 24 hours and 37 minutes

Mars is similar to Earth in many aspects: shape, size, and length of a day. After Mercury, Mars, the highest eccentricity of 0.0935 among all the planets in our system. Due to this, Martian seasons are extreme and last twice as long as our own.

A day on the Martian world is called a Sol, with each lasting 24 hours 39 minutes 35.2 seconds.

I think you will agree that Mars is a fascinating planet that is both similar to and different from Earth. I hope you’ll remember these points the next time you look at the red planet.


Written by Sharmila Kuthuner