Dust moves through the atmosphere.
Winds reshape dunes.
Seasonal changes alter the distribution of carbon dioxide.
Frost forms.
Ice appears and disappears.
Clouds drift through the sky.
And under the right circumstances, those clouds can even shimmer with multiple colors.
The colorful clouds therefore offer a different way of seeing Mars.
The planet is not simply a dead-looking landscape beneath an empty sky.
It has an atmosphere capable of producing subtle and sometimes spectacular phenomena.
The View From Another World
Imagine standing beside Curiosity as the Sun disappears below the Martian horizon.
The rocks around you would be fading into twilight.
The sky would remain dominated by the familiar dusty tones of Mars.
And high above, barely visible at first, a thin cloud would catch the last sunlight.
Tiny ice particles would scatter that light.
Instead of a plain white cloud, faint hints of red, green, blue and purple would appear.
The colors would be subtle.
The cloud would be enormous compared with anything a human could create.
And the material making it possible could be frozen carbon dioxide — the same gas that makes up most of Mars' atmosphere.
It would be an extraordinary sight.
And yet it would be completely natural.
A Rainbow Without Rain
Calling the phenomenon a “rainbow” is poetic rather than technically precise.
There is no rain falling through the Martian sky and no conventional rainbow arching across the horizon.
The colors are produced by iridescence, a different optical phenomenon involving the interaction of light with small, similarly sized particles.
That difference is important.
Still, the visual effect can be remarkably rainbow-like.
NASA itself has described these clouds as producing a rainbow of colors and refers to them as “mother-of-pearl” clouds because of their shimmering appearance.
So while Mars does not have an Earth-style rainbow hanging over its surface, it has something arguably just as fascinating.
A cloud can become a palette of colors.
What Curiosity Has Taught Us
Curiosity's primary mission is much broader than photographing beautiful clouds.
The rover was designed to investigate whether Gale Crater ever had environmental conditions capable of supporting microbial life.
Since landing in 2012, it has studied rocks, minerals, sediments and ancient geological environments.
Its observations have helped scientists reconstruct parts of Mars' environmental history.
The cloud observations are another piece of that larger scientific puzzle.
By studying the present-day atmosphere, scientists can better understand how Mars functions today.
That knowledge can also help researchers interpret the planet's past.
The Red Planet was not always the cold, dry world we see now.
Evidence collected by Curiosity and other missions indicates that ancient Mars once had environments involving liquid water and conditions that could have supported microbial life. NASA continues to use Curiosity's observations to investigate how the planet evolved from those ancient conditions into the world it is today.
Even a delicate cloud can therefore become part of a much bigger story.