What Color Is Mars?
QUICK ANSWER
Mars appears red because its surface is covered in iron oxide (rust). Up close, the actual color is more of a reddish-brown or butterscotch rather than the bright red of, say, a tomato. The Martian sky is butterscotch yellow during the day, but sunsets appear blue, the opposite of Earth.
Mars's red color is the most famous thing about it. The color is real, but the cause is surprisingly mundane: Mars is rusty. Up close, the actual appearance is more interesting than the postcard version, including a sky that does exactly the opposite of Earth's at sunset.
Why is Mars red?
Mars's red color comes from iron oxide, also known as rust. According to NASA, Mars's surface is covered in dust that contains a high concentration of iron-rich minerals that have been chemically oxidized over billions of years. The same chemical process that turns iron tools rusty on Earth has slowly turned the entire planet into a rusted-out landscape. The thin Martian atmosphere also kicks dust into the sky regularly, giving the planet a uniformly red appearance from space.
What does Mars look like up close?
Less vivid than telescope images suggest. From orbit, Mars appears bright red because the dust is uniformly distributed across the planet and the atmosphere accentuates the color. On the surface, the actual rock and soil look more like reddish-brown or butterscotch, with darker basaltic patches mixed in. Photos from rovers like Curiosity and Perseverance show a landscape that's earthy and dusty rather than fire-engine red. The colors vary slightly by region, with some areas appearing more orange and others more grayish.
Why are Mars sunsets blue?
Because Mars's atmosphere scatters light differently than Earth's. On Earth, the atmosphere scatters short-wavelength blue light, which is why the sky looks blue during the day and sunsets look red and orange. On Mars, the atmosphere is full of fine dust that scatters red and orange light, leaving the blue wavelengths to pass through near the Sun. The result is a butterscotch-colored daytime sky with blue sunsets, opposite to what we see on Earth.
Was Mars always red?
Probably not. Billions of years ago, Mars likely had a thicker atmosphere, liquid water on the surface, and a much less oxidized appearance. The rusting happened over time as iron-bearing minerals were exposed to small amounts of oxygen and water in the atmosphere. The bright red we see today is essentially the result of billions of years of slow weathering, after Mars lost most of its atmosphere and water. The current color is the chemical signature of a planet that has been drying out for ages.
Mars is red because it's rusty, and the rust is the residue of billions of years of slow chemical weathering. The actual color up close is closer to butterscotch than fire-engine red, and the sky does the opposite of Earth's at sunset. Mars is more visually nuanced than its reputation suggests.
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