Bob the Alien's Tour of the Solar System
Bob the Alien's Tour of the Solar System

Welcome to Mars

Mars as seen from the Viking 1 Orbiter in 1980 (image credit: NASA)

Mars is the fourth planet from the Sun and the last of the four Inner Planets. Mercury, Venus and Earth are the other Inner Planets. It is the second closest planet to Earth. The closest planet to Earth is Venus. Mars is the second smallest planet in the Solar System with only Mercury being smaller than it. It is about half the size of Earth. Mars is often known as the Red Planet as it is red in colour. In mythology, Mars was the Roman god of War, a name probably inspired by the planet's colour as it represents blood. Its Greek name is Ares.

The length of a day on Mars is not much longer than a day on Earth. It takes 24 hours and 37 minutes for Mars to spin once on its axis, compared to 23 hours and 56 minutes for Earth to do the same. A Martian day is often called a Sol. To complete a full journey around the Sun, Mars takes 687 days. Therefore, a Martian year is 687 days long.

Deimos and Phobos (Image credit: NASA/JPL-Caltech/University of Arizona)

Mars has two small moons - Phobos and Deimos. These moons are very different from the Moon orbiting Earth. They are irregularly-shaped, not round like Earth's Moon, and are possibly captured asteroids. They orbit Mars quite closely and travel around the planet quickly. Phobos is 9,377 kilometres (5,827 miles) away from Mars and orbits it every 7 hours, 39 minutes. Deimos is 23,460 kilometres (14,580 miles) away and completes an orbit in just over 30 hours.

The surface of Mars as imaged by the Curiosity rover in 2012

Mars' surface is covered in ancient craters, thought to have been formed by meteorite impacts over billions of years. Countless rocks of all shapes and sizes are scattered across the surface of the planet, covered in a dusty layer of rust (iron oxide). This is what gives Mars its red colour. The planet was once volcanically active and is home to the largest volcano in the Solar System - Olympus Mons. Olympus Mons is 27 kilometres (17 miles) high. In comparison, Earth's highest mountain, Mount Everest, is 8.8 kilometres (5.5 miles) high. Another feature of Mars' surface is Valles Marineris, a 4,000 kilometres (2485 miles) long canyon which stretches almost a quarter of the way around the planet. It is the largest known surface canyon in the Solar System.

Scientists believe that water was once abundant on the surface of Mars and quite possibly plentiful enough to form oceans similar to those on Earth. Nowadays, Mars is a dry planet with only small signs of the present existence of water. So where did all of the water go? Nobody knows for certain, but scientists certainly aim to find out through missions to Mars. For almost half a century, a number of space craft have visited Mars. Some have simply flown past it to take pictures, others spend years orbiting the planet to collect data, and some have even landed on its surface to take in its sights and sounds, probe its soil and poke its rocks. Even now, there are rovers on Mars travelling very slowly across its surface and making discoveries.

The main reason for visiting Mars, apart from the fact that it is fairly easy to get to, is that there is a small chance that the planet could have supported life at some point in its long history. There's even a remote possibility that it could support life in some form today. The presence of water is a key factor in this which is why scientists get quite excited whenever they find some there. So far, all missions to Mars have been unmanned, and all discoveries have been made by robots. However, at some point in the not-too-distant future (hopefully), people will travel to Mars. Who knows what they'll find when they get there?

Mars is the 4th planet from the Sun.
Mars takes 687 days to orbit the Sun.
A days on Mars is 24 hours, 37 minutes.
Mars has two moon, Phobos and Deimos
Mars is the final of the four Inner Planets.
Mars is the second smallest planet in the Solar System.
Average distance from Sun227,936,640 km
141,633,260 miles
1.52 A.U.
Closest distance to Sun (Perihelion)206,600,000 km
128,400,000 miles
1.38 A.U.
Farthest Distance from the Sun (Aphelion)249,200,000 km
154,900,000 miles
1.67 A.U.
Diameter across equator6,794 km
4,222 miles
Circumference around equator21,344 km
13,263 miles
Bob the Alien's Tour of the Solar System
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