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Mars, the planet we know best, has interesting surface features including evidence for running water.

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"Ladies and gentlemen, I have a grave announcement to make...

...Incredible as it may seem, strange beings who landed in New Jersey tonight are the vanguard of an invading army from Mars." — Orson Welles, "The War of the Worlds" radio broadcast, October 30, 1938.

Orson Welles caused a panic when some people took his news bulletins, meant to be a radio drama anthology, as the truth. No evidence of life has been found on Mars. Would people believe it if he broadcasted this today? Would you?


Mars is the fourth planet from the Sun, and the first planet beyond Earth’s orbit (Figure below). Mars is a quite different from Earth and yet more similar than any other planet. Mars is smaller, colder, drier, and appears to have no life, but volcanoes are common to both planets and Mars has many.

Mars is easy to observe, so Mars has been studied more thoroughly than any other extraterrestrial planet. Space probes, rovers, and orbiting satellites have all yielded information to planetary geologists. Although no humans have ever set foot on Mars, both NASA and the European Space Agency have set goals of sending people to Mars sometime between 2030 and 2040.

Picture of Mars

This image of Mars, taken by the Hubble Space Telescope in October, 2005, shows the planet’s red color, a small ice cap on the south pole, and a dust storm.

A Red Planet

Viewed from Earth, Mars is reddish in color. The ancient Greeks and Romans named the planet after the god of war. The surface is not red from blood but from large amounts of iron oxide in the soil.

The Martian atmosphere is very thin relative to Earth’s and has much lower atmospheric pressure. Although the atmosphere is made up mostly of carbon dioxide, the planet has only a weak greenhouse effect, so temperatures are only slightly higher than if the planet had no atmosphere.

Surface Features

Mars has mountains, canyons, and other features similar to Earth. Some of these surface features are amazing for their size! Olympus Mons is a shield volcano, similar to the volcanoes that make up the Hawaiian Islands. But Olympus Mons is also the largest mountain in the solar system (Figure below).

Picture of Olympus Mons

Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the Martian surface, more than three times taller than Mount Everest. The volcano’s base is about the size of the state of Arizona.

Mars also has the largest canyon in the solar system, Valles Marineris (Figure below).

The largest canyon in the solar system, Valles Marineris

Valles Marineris is 4,000 km (2,500 mi) long, as long as Europe is wide, and one-fifth the circumference of Mars. The canyon is 7 km (4.3 mi) deep. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and about 2 km (1.2 mi) deep.

Is There Water on Mars?

It was previously believed that water cannot stay in liquid form on Mars because the atmospheric pressure is too low. However, there is a lot of water in the form of ice and even prominent ice caps (Figure below). Scientists also think that there is a lot of ice present just under the Martian surface. This ice can melt when volcanoes erupt, and water can flow across the surface.

In late 2015, NASA confirmed the presence of water on Mars.  

The north polar ice cap on Mars

The north polar ice cap on Mars.

Scientists think that water once flowed over the Martian surface because there are surface features that look like water-eroded canyons. The presence of water on Mars suggests that it might have been possible for life to exist on Mars in the past.

Two Martian Moons

Mars has two very small moons that are irregular rocky bodies (Figure below). Phobos and Deimos are named after characters in Greek mythology — the two sons of Ares, who followed their father into war. Ares is equivalent to the Roman god Mars.

Phobos and Deimos, both of Mars' moons

Mars has two small moons, Phobos (left) and Deimos (right). Both were discovered in 1877 and are thought to be captured asteroids.

The Mars Science Laboratory was launched on November 26, 2011 and will search for any evidence that the Red Planet was once capable of supporting life. Curiosity is a car-sized rover that will scour the red planet for clues after it lands in August 2012.


  • Mars is the easiest planet to study because it doesn't have thick clouds obscuring its surface.
  • The surface of Mars has volcanoes and channels that were once filled with water.
  • Mars has two moons that are thought to be captured asteroids.


  1. Why is Mars red?
  2. Why doesn't Mars have liquid water now? What evidence is there that Mars once had liquid water?
  3. Is the surface of Mars young, like the surface of Venus? How would you know?

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