Iridescent Clouds on Mars Seen by Curiosity

Laying on a grassy field staring at the cloud formations in the sky and coming up with harebrained ideas about their shapes is a common feature in childhood summers – at least as they’re portrayed in media.  Someday that image might translate to a child laying on a sandy or rocky outcropping, looking up at the sky seeing iridescent, shimmering clouds in the sky.  The biggest differences would be that the child would be looking through a visor, and those clouds would be on Mars.  And Curiosity recently released some stunning images of what they might look like.

Curiosity’s project scientists were caught a little bit off guard one Martian year ago when clouds started to form earlier in the year than they expected.  This year they were ready with the rover’s Mastcam and black-and-white navigational cameras, and not only did they capture some breathtaking images, they collected some interesting scientific data as well.

Some of the data collect was on cloud height – the clouds the cameras saw formed much higher up than they originally expected.. Usually, Martian clouds form around a height of 60km, but these appeared much higher than that.  It can be hard to calculate altitude without a second reference point to triangulate from, but the clouds were visible at sunset, so the scientists were able to track how long they were illuminated once the sun had receded behind the Martian surface and thereby calculate their height.  

Clouds at that height most likely aren’t formed of the water ice crystals that are so common in Earth-bound clouds.  Frigid temperatures in the Martian atmosphere meant that the clouds were more likely formed by CO2, or dry ice crystals.  There is other data that will need collecting before that hypothesis is confirmed, but most likely Curiosity saw clouds of both water and carbon dioxide.  

More clouds captured by Curiosity - these ones over a rock outcropping.
More clouds captured by Curiosity – these ones over a rock outcropping.
Credit – NASA / JPL-Caltech / MSSS

While the clouds were relatively easy to see in the black-and-white images from the navigational cameras, the truly spectacular pictures came from the Mastcam.  The color images show two types of clouds that were particularly stunning.

In a beautiful turn of naming, the first type of clouds are known as “noctilucent”, or “night shining” in Latin.  They burst with brightness as the atmosphere cools around sunset, causing more crystals to from in the cloud, and then fade from view after the sun dips below the horizon.  

UT Video discussing the Martian atmosphere, or lack thereof.

Even more striking are the “mother of pearl” clouds that are wispy but iridescent clouds that are one of the only splashes of certain color in the Martian landscape.  Wisps of red, yellow, and blue can be seen in the Curiosity images, and scientists predict that a person would have been able to see the colorful display unaided if they happened to be standing next to the rover.

These displays are surely not the last time a Martian rover will encounter clouds, nor will it be anytime soon before a person can be there to observe them first hand.  In the meantime, maybe some kids sitting on a grassy hill in the summertime back on Earth can imagine what the scene in the sky would look like on a different planet.

Learn More:
JPL – NASA’s Curiosity Rover Captures Shining Clouds on Mars
UT – There’s One Cloud on Mars That’s Over 1800 km Long
UT – High Altitude Clouds on Mars
UT – Martian Clouds Might Start with Meteor Trails Through the Atmosphere

Lead Image:
Mother of pearl clouds captured by Curiosity’s Mastcam on March 5 2021.
Credit: NASA / JPL-Caltech / MSSS