We tend to think of Mars resembling Earth, and in many ways it is true. It is relatively small and rocky. It has an atmosphere and recognizable geological features. We can identify the composition of its rocks, study its weather patterns and detect seismic activity.
But Mars is also very unlike Earth. And this is never clearer than when looking at photos of the red planet taken by its rovers and orbits. What we take for granted on earth can be transformed into breathtaking alien phenomenon just a planet away.
Here are some of our favorite photos that capture the planet’s wild weirdness next door.
A crater full of ice
This is the Korolev crater, not far from Mars’ northern Polish ice cap, which was depicted by the European Space Agency’s Mars Express orbit. It is 81.4 kilometers (50.6 miles) across, and is filled with water ice year-round.
As the air moves over the ice, it cools and sinks, resulting in a layer of cold air that sits directly above the ice. Since air is a poor thermal conductor, this cold layer acts as an insulator that protects the ice from warmer air and thus prevents it from melting.
The ice dome is 1.8 km (1.1 km) thick and up to 60 km (37.3 miles) in diameter, with a volume of approximately 2,200 cubic kilometers (528 cubic miles). It’s not much compared to, say, Antarctica, but it’s more than you might expect from a planet as dry as Mars.
Partial eclipse of the moons
On earth we have an unusual coincidence. The distance relationship between the earth and the moon versus the earth and the sun is almost exactly the same as the size relationship between the moon and the sun. This means that when the moon passes in front of the sun for a total eclipse, it completely covers the sun.
That is not the case on Mars. When one of the Mars moons passes in front of the sun for an eclipse in Mars, it is much smaller. The passage is more correctly called a transit. NASA’s Curiosity rover has observed many such transits from Mars’s two moons, Phobos and Deimos, and they are more like shadows floating across the sky.
Starfleet on Mars
This photograph went viral last year for its obvious link to the Star Trek Starfleet logo, but Mars’ Hellas Planitia is dotted with hundreds of these chevron-shaped formations. They are actually known as “ghost dunes”, formed by ancient lava flows.
Long ago, when this lava ran freely over the Martian surface, the landscape was surrounded by sand dunes. The lava flowed around these dunes and sat in that shape. When the sand blew away in the wind, only the lava remained, surrounded by the impression of sand dunes that were no longer there.
The strange hole
Also on Mars, this property is special: what appears to be a conical mountain, with a hole at the top … but completely hollowed out. Located on the side of a giant shield volcano, this is what is called a skylight with lava tubes, and it is hollow because sometimes the lava flows can solidify on the surface while the flow continues below. Then the flowing lava can drain away and leave the lava caves behind. Some of the surface can then collapse and open a skylight in the tunnel below.
It is much larger than any such lava tube found on the earth, and the conical shape of the skylight is also extremely strange. How and why it became so is a mystery.
Compared to Earth, Mars is a veritable crater party. Its thin atmosphere does not provide nearly the protection that the earth does, and a much larger proportion of space rocks rain down on the surface. This spectacular impact happened sometime between September 2016 and February 2019, and it’s like nothing on earth.
The color has been slightly improved to reveal the impact wave, where the impact has blown the surface dust away to reveal the dark layer below. The crater itself is relatively small, only 15 to 16 feet wide (49 feet to 53 feet), which means the object must have been only about 1.5 feet (5 feet) across and very dense. Such an object would burn up and disintegrate in the earth’s atmosphere before we hit our own planet.
Sunset on Mars
We are relatively used to the brownish hue of the Martian sky, as seen in many images captured by Mars rovers. But when the sun rises and sets on Mars, something strange happens – rather than the well-known blazing red from the sunset of the earth, the Martian sky becomes a beautiful blue.
This phenomenon has to do with particles in the atmosphere. On Earth, the smaller gas particles in the atmosphere spread blue light more efficiently.
When the sun is above this, the effect is that the sky appears blue, but at sunrise and sunset, when the light has a longer distance to travel across the atmosphere to reach our eyes, only the red wavelengths can travel so far, making the sky appear yellow, orange and red.
On Mars, the atmosphere is filled with dust particles. These are fine, but much larger than gas particles, and they spread the red wavelengths rather than the blue ones. As a consequence, the colors of the sky are reversed.
This incredible image shows the complex terrain of Juventae Chasma, a weather-beaten 250-kilometer (155-mile) square carved into the Martian surface.
In it you can see distinct craters, but a lot of other interesting features too, including what can be inverted power channels – left as the area around low-lying land erodes away, so the channel is now taller.
There are also holes and divots that reveal distinct layers, which you can find in sedimentary rock on earth, revealed by wind erosion. We are not sure which process created the layers on Mars, but they are quite common on Mars over different terrain types.
Raindrops of sand
It’s been a long time since it’s rained on Mars … and ironically, that’s why so many of these raindrop-shaped dunes dot the Copernicus crater. They are rich in a mineral called olivine, a magnesium iron silicate found in rich rock and the most common mineral in the Earth’s mantle.
However, not much olivine is found on the surface of the earth, as it weathers rapidly, especially in the presence of moisture, and turns to clay. Because Mars is so dry, these olive pads can hang around the surface for a very long time.