What is THAT?!

Mind Bending | November 2, 2023
Mars Sunset

Image credit: NASA/JPL/Texas A&M/Cornell
By Dr. Teri Gee, Director, Barlow Planetarium

Look at this picture. It might look fake, but it’s not! It’s a real photo.

Can you guess what it is? It’s a sunset! Now, you might be thinking that the Sun is way too small and this looks nothing like a sunset. That would be true… if it were taken on Earth.

But it wasn’t! This is a photo taken of a sunset on Mars. The NASA rover called Spirit took this photo on May 9, 2005. The Sun looks so small because Mars is a lot farther away from the Sun than the Earth is. The Earth is about 93 million miles from the Sun while Mars is about 149 million miles from the Sun.

What about the color?

This might seem strange. Mars is often called the Red Planet, but here, we have a bluish hue to the sky as the Sun sinks below the horizon. Why would this be?

First, why is Mars called the Red Planet in the first place?

Well, it’s because it looks red. But why does it look red? This is because Mars has high amounts of iron oxide in its soil. What is iron oxide? It’s rust! So Mars is rusty and there’s so much rust in its soil that even from the Earth, Mars has a distinctly red-orange color to it.

Okay, so Mars is red, but why is its sunset blue?

Interestingly enough, this is because of that same dust only aloft in the atmosphere. On Earth, when the Sun sets, light is scattered through more of the atmosphere. Compared to Mars, the Earth has a thick atmosphere and when the Sun passes through more of it, the blue light is scattered away and the red and orange light is left. When there’s more dust in the atmosphere, the red and orange colors can be even more vibrant.

On Mars, with its much thinner atmosphere, there is less gas to scatter the light, but there’s a lot of dust and those particles of dust are very, very small, so small that when the light hits them the blue color isn’t scattered as much as it is on Earth. When the Sun is setting on Mars, the light hits those tiny dust particles and in the direction of the Sun, we see the blue color.

As we head into winter, the Sun will set earlier and earlier. Next time you watch a sunset and enjoy the orange and red colors here on Earth, think about that blue sunset on Mars!

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