Martian sunsets are blue

Blue Sunsets have you ever saw or heard about them?
You wouldn’t know it, not right away, but there is something strange about this picture. It’s a sunset, yes, but notice the blush of color right above the sun. It’s blue. And as you look up, the blue fades into a faint rose or pink.

Now think about the sunsets you’ve seen, how often the sky can turn golden, or orange, sometimes pink, red, but when you look up, away from the setting sun, those colors fade back to a pale, twilight blue? It’s rare to see a sunset dipped in blue.

So this photo is a puzzle: it’s blue where the red should be and red where the blue should be. Why?

Martian sunsets are blue

Because we’re not on Earth. This is a Martian sunset. On May 19, 2005, the camera on NASA’s little robot, the rover named Spirit, took this picture while sitting in the Gusev crater on Mars. NASA snapped the photo, says the press release, “around 6:07 in the evening of the Rover’s 489th Martian day.”

Apparently, Mars has blue sunsets all the time. Earth doesn’t.

NASA admits that there’s a color filter on Spirit’s camera that exaggerates the colors slightly, but they say the blues you see here “are similar to what a human would see” on Mars. Not so much the pinks. Pinks are slightly more pronounced in these photos, but the blues are true colors.

So here’s our question: Why are Martian sunsets blue?

The Air On Mars Is Different From The Air On Earth

Martian sunsets are blue

On Earth, the air is mostly nitrogen and oxygen. We’ve also got moisture, dust particles, smoke, aerosols, pollen, salt from the ocean. The atmosphere on Earth is denser — meaning there are more molecules per cubic inch in our air.

Martian air, by contrast, is much, much thinner, about 1percent the density of air on Earth, plus the gasses are different: they’ve got CO2, nitrogen and argon, but most important, says Mark Lemmon, associate professor of planetary sciences at Texas A&M University, air on Mars is rich with teeny, teeny particles of dust. Their dust is smaller than our dust, and they’ve got more of it in the Martian sky. Dust is the key to why the two sunsets look different, so we’ll be keeping our eye on Martian dust.

According to Professor Lemmon, when sunshine hits Martian dust, the blue light doesn’t bounce far. It sticks near the dust, pingponging around at close range. That’s why if there’s a dust storm on the horizon, (and that’s what seems to be happening in the video), the area around the sun traps a lot of blue light, and the sun seems to glow blue.

Red light, as we’ve said, ricochets much farther off, so in the video, the reddish patches are some distance from the sun, the blue is tucked in close.

The point being, if you happen to be camping out on Mars and see an intense blue sunset like the one in the video, make sure the wind isn’t blowing in your direction, because a few hours from now, that sandstorm might blow your tent down. (You did remember to bring a tent, no?)