Mars

Rust and water

Mars is the fourth planet from the Sun and is often called the Red planet due to its reddish, rusty appearance. This colour is, in fact, rust—or more technically iron oxide—on its surface. Rust normally forms when iron comes in contact with water as a liquid, or in the atmosphere. Today, the atmosphere of Mars is incredibly thin, stripped by the solar wind over millions of years to be 100 times thinner than Earth's. And there are no oceans.

But long ago, Mars, like Earth today, was partially covered in oceans of water, which may have caused the rocks to redden. This history is why the search for life outside of our planet has focused on this amazing dusty ball.

Scientists have found lots of evidence that ancient seas and rivers once existed on Mars! One of the biggest clues is Valles Marineris, a giant canyon system over 4,000 kilometers long and 7 kilometers deep—10 times longer and 4 times deeper than Earth's Grand Canyon. Valles Marineris likely formed due to the planet's crust stretching and cracking, which allowed water to flow and carve out the deep valleys. Other features like outflow channels and dried-up riverbeds suggest that ancient rivers once flowed across Mars' surface. These channels are huge and look like they were made by massive floods, showing that Mars had a lot of water long ago.

So where did all this water go? Mars also has highly visible polar ice caps of frozen water and carbon dioxide. Additionally, radar data from orbiters show that lakes of liquid water could be hidden beneath the ice caps' surface. Scientists have also spotted dark streaks on the sides of craters and hills that seem to come and go with the seasons. These streaks might be caused by salty water flowing down the slopes. And where there is liquid water, there may be life.

As no humans have set foot on Mars, the search for life has been led by an incredible array of probes and rovers (robots with wheels or tracks that can move around), sent over several years to trundle around the surface and sample the Martian soil. The latest Mars rovers, such as Curiosity and Perseverance, can show if the environment was once suitable for life by sampling the minerals and chemicals in the rocks, taking pictures, and drilling into the soil.

Volcanic past

Though Mars is quiet today, it was once very volcanically active, but not in the same way as on Earth. Earth’s volcanism is almost entirely controlled by the location of tectonic plates that constantly create and recycle rocks. Volcanoes typically form along the margins of these tectonic plates, are numerous, and are constantly active as new crust is created and old crust is remelted.

By contrast, Mars formed no tectonic plates, so the magma systems that fed the volcanoes were stuck in the same position for a long time. This resulted in some truly enormous volcanoes on Mars! The largest and most famous is Olympus Mons, the largest volcano in the Solar System. At around 22 km high, it is nearly three times the height of Mount Everest, and at 600 km in diameter, it covers an area almost the same as Poland.

Key Stats

Mars has a few things in common with the Earth, but it is also very different.

Seasons:

A year on Mars, the time it takes to orbit the Sun, is about 687 Earth days long, nearly twice as long as a year on Earth. This longer year results in longer seasons. Each Martian season lasts for about six Earth months.

Mars' axis is also tilted at about 25 degrees, similar to Earth's 23.5 degrees, which means it experiences similar seasonal changes, including summer, fall, winter, and spring. One interesting aspect of the seasons on Mars is the planet's elliptical orbit, which causes more extreme differences between its hemispheres. For instance, the southern hemisphere experiences shorter, warmer summers and longer, colder winters compared to the northern hemisphere.

Moons

Mars has not one but two small moons: Phobos and Deimos. Unlike Earth's moon, the moons or Mars are irregularly shaped and much smaller.

Phobos is the larger of the two, about 22 kilometers (14 miles) in diameter, and has an orbit very close to Mars—so close that it completes an orbit in just 7.7 hours.

Deimos is smaller, with a diameter of around 12 kilometers (7.5 miles), and takes about 30.3 hours to orbit Mars. Both moons are thought to be captured asteroids from the nearby asteroid belt, which is why they have irregular shapes and compositions similar to asteroids.

Dust storms

Martian dust storms are one of the planet's most dramatic and fascinating weather phenomena. These storms can range from small dust devils to massive planet-wide events that cover the entire surface of Mars. They form due to the planet's thin atmosphere and abundant fine dust particles on the surface.

Solar heating of Mars' surface causes temperature differences that create strong winds, lifting dust into the atmosphere. Martian storms can be much larger and longer-lasting than Earth's dust storms. While Earth's storms are limited in size and typically last a few days, Martian storms can cover the whole planet and persist for weeks or even months, significantly reducing sunlight and affecting surface temperatures.

geckzilla, CC BY 2.0, via Wikimedia Commons

geckzilla, CC BY 2.0, via Wikimedia Commons

en:Mars Reconnaissance Orbiter, en:NASA . Image Credit: NASA/JPL-Caltech/Univ. of Arizona, Public domain, via Wikimedia Commons

The same (but different)

Mars is one of the five planets visible to the naked eye from Earth — it appears as a bright red "star" in the night sky.

• Naked eye: Mars can be seen without any equipment. It appears as a bright, reddish point of light. The best times to observe Mars are during opposition, when Mars is closest to Earth and directly opposite the Sun in the sky.

• Binoculars: Using binoculars, you can see Mars as a small disc. It will still appear reddish in colour, but will be brighter and more detailed than with the naked eye.

• Small telescope: A small telescope allows you to see surface features such as polar ice caps and large dark areas on Mars. During opposition, you can observe these features more clearly.

How to see Mars from Earth