Mars: The Planet We Almost Recognise

Mars is the planet that feels like it should make sense. It has seasons. It has weather. Its days are almost exactly the same length as ours. Stand on the equator at noon and the ground beneath your feet could be a mild 20°C. For a moment, you could almost forget you are on another world. Then you look up at a thin, salmon-coloured sky, breathe nothing, and remember that Mars is a place where everything familiar has been taken away, one piece at a time, over billions of years.

A World Built on a Different Scale

Mars is roughly half the diameter of Earth, about 6,780 kilometres across, making it the second smallest planet in the solar system after Mercury. Its gravity is only 38% of ours. If you weigh 70 kilograms on Earth, you would weigh about 27 kilograms on Mars. You could jump roughly three times as high.

But what Mars lacks in size, it makes up for in geography. It is home to the tallest mountain in the solar system: Olympus Mons, a shield volcano that rises nearly 22 kilometres above the surrounding plains. That is roughly two and a half times the height of Everest. It is so wide, about 600 kilometres across, that if you stood at its base you would not be able to see the top. The curvature of the planet would hide it from you. And cutting across the Martian equator is Valles Marineris, a canyon system stretching more than 4,000 kilometres long and up to 7 kilometres deep. If you placed it on Earth, it would reach from London to beyond the Urals. The Grand Canyon could sit inside one of its side channels.

Mars does everything on an outsized scale for a planet this small. There is something almost defiant about that.

The Red Is Rust

The colour that gives Mars its nickname is iron oxide. The surface is rich in iron, and over billions of years that iron has reacted with trace amounts of oxygen to form rust. It coats the rocks, the dust, and even the fine particles that get swept up into the atmosphere, tinting the sky a faint pinkish hue during the day and, at sunset, turning it blue.

That last detail is worth pausing on. Sunsets on Mars are blue. On Earth, scattered light gives us red and orange sunsets. On Mars, fine dust particles in the atmosphere scatter the light differently, and the Sun sets in a cold, quiet blue. NASA's Curiosity rover photographed it, and the image is one of the most unexpectedly moving pictures ever taken on another planet.

Where the Water Went

Billions of years ago, Mars was a very different place. Evidence from orbiters and rovers shows that rivers once carved channels across its surface, lakes pooled in its craters, and it may have had an ocean covering much of its northern hemisphere. The atmosphere was thicker then, warm enough and dense enough to allow liquid water to persist on the surface.

Then Mars lost its global magnetic field. Without that invisible shield, the solar wind, a relentless stream of charged particles from the Sun, began stripping the atmosphere away, molecule by molecule, over hundreds of millions of years. As the atmosphere thinned, the temperature dropped. The water froze, evaporated, or seeped underground. What remains today is a world with an atmospheric pressure less than 1% of Earth's, too low for liquid water to survive on the surface for more than moments.

But the water did not vanish entirely. Both poles are capped with ice, a mix of water ice and frozen carbon dioxide. Beneath the surface, vast reserves of water ice are thought to extend across much of the planet. If all of it melted, some estimates suggest there would be enough to cover Mars in a shallow ocean more than 20 metres deep. The water is still there. It is just locked away.

The Planet of Robots

Mars is the only planet in the solar system inhabited entirely by robots. As of early 2026, NASA has five active missions at Mars, including the Curiosity rover, which has been exploring since 2012, and the Perseverance rover, which landed in Jezero Crater in February 2021.

Perseverance was sent to a specific place for a specific reason. Jezero Crater once held a lake fed by a river delta, exactly the kind of environment where, on Earth, microbial life thrives and leaves traces in the rock. The rover has been collecting core samples of Martian rock and sealing them in tubes, to be retrieved by a future mission and brought back to Earth for laboratory analysis.

In September 2025, the mission reported its most significant finding yet. A sample called Sapphire Canyon, drilled from a mudstone in an ancient riverbed, was found to contain organic carbon alongside unusual mineral textures, small features nicknamed "leopard spots" and "poppy seeds," that resemble patterns left behind by microbial activity on Earth. The team was careful to say they have not found proof of life. But they described the result as a potential biosignature, the closest anyone has come to evidence of past biology on Mars.

The sample is sealed in a tube, carried by the rover, waiting for a ride home.

Two Small Moons

Mars has two moons, Phobos and Deimos, both tiny and irregularly shaped. Phobos, the larger of the two, measures about 22 kilometres across. Deimos is roughly 12 kilometres. They are thought to be captured asteroids, though some models suggest they formed from debris blasted off Mars by an ancient impact.

Phobos orbits so close to Mars that it rises and sets twice in a single Martian day. It is also slowly spiralling inward. In roughly 50 million years, it will either crash into Mars or, more likely, break apart under gravitational stress and form a thin ring around the planet. Mars may one day join Saturn in having a ring, if only briefly by cosmic standards.

Dust Storms That Swallow the World

Mars has weather, and at times it is spectacular. Dust storms begin as local events but can grow to engulf the entire planet, lasting for weeks or even months. In 2018, a global dust storm darkened the sky so thoroughly that NASA's solar-powered Opportunity rover lost contact and never recovered. It had been operating for nearly fifteen years.

The storms happen because Mars's thin atmosphere heats unevenly. Temperature differences create strong winds that lift fine dust particles off the surface. Once airborne, the dust absorbs sunlight and heats the air further, which generates more wind, which lifts more dust. It is a feedback loop that can spiral quickly out of control. From orbit, the entire planet simply disappears beneath a blanket of ochre haze.

Talking About Mars With Your Kids

Mars is the easiest planet to get children excited about, because it already feels like somewhere they could go. It has ground they could stand on, a sky they could look at, and robots already driving around on its surface. That last fact alone is usually enough to start a conversation.

Start with the rovers. Tell your child that right now, at this very moment, there is a robot the size of a car driving around on Mars, picking up rocks and taking pictures. For a five-to-eight-year-old, that is not a science lesson. That is the beginning of an adventure story. If they want to see what Mars looks like, NASA publishes raw images from the rovers online. Scrolling through photos taken on the surface of another planet, together, is a surprisingly powerful experience.

Ask what they would pack. "If you were going to Mars, what would you bring?" is a question that tends to run for a while. It naturally leads to talking about what Mars does not have: no breathable air, no liquid water on the surface, no warmth at night. Children work out the problems of living on Mars faster than you would expect, and they enjoy doing it.

Let the scale blow their minds. Tell them Mars has a volcano so tall that if you stood at the bottom, you could not see the top because the planet curves away before you get there. Or that it has a canyon so long it would stretch across the whole of Europe. At this age, children are still building their sense of how big things can be. Mars is an excellent place to stretch it.

Once they are engaged, you can tell them that a robot on Mars found a rock that might, just might, contain signs of tiny creatures that lived billions of years ago. Scientists are not sure yet. The rock is sealed in a tube, sitting on the surface, waiting to be brought back to Earth so people can study it properly. That story, a discovery in a sealed tube on another planet waiting to be opened, has the structure of a fairy tale. Children feel it.

Mars is a planet children will come back to again and again. You do not need to cover everything in one go. A short conversation about the rovers today, the blue sunset next week, the life question whenever it comes up naturally. Let them set the pace. The curiosity will do the rest.