And now for something completely different: NASA’s Curiosity rover captured a feather-shaped cloud glowing in the Martian sky shortly after sunset on the Red Planet.
It dates back to January 2023, but NASA recently featured the image in an agency spotlight highlighting the rover’s investigation of the planet’s skies conducted last month.
In that investigation, Curiosity captured images over the course of 16 minutes on January 17, or Sol 4426 on Mars. The images show reddish-green clouds in the Martian twilight. The clouds are noctilucent (or “night shining”) clouds, caused by the way the Sun’s light scatters in the dusty Martian atmosphere.
According to a NASA release, Martian clouds are made of either water ice or carbon dioxide ice. Only the latter group—which occur at higher altitudes and lower temperatures than water ice clouds—shine in the way shown above. Noctilucent clouds occur on Mars at altitudes between roughly 37 and 50 miles (60 and 80 kilometers) above the surface. When the clouds drift much lower (below about 31 miles, or 50 kilometers up) they evaporate due to rising temperatures in the atmosphere.
Noctilucent clouds are not merely an extraterrestrial phenomenon. Rocket launches on Earth can cause the glowing clouds in Earth’s upper atmosphere, which are only visible shortly after sunset or before sunrise—otherwise it is too bright to see them.
Mars’ clouds come in many shapes and sizes. In 2022, ESA scientists spotted clouds not unlike those that form on Earth in the Red Planet’s skies. The following year, the Perseverance rover was greeted with heavy cloud cover—a sign of the overcast days to come on the dusty, not-too-distant world. The recently imaged iridescent clouds are not a newly discovered phenomenon but are still mesmerizing to behold—and still require plenty of scrutiny.
The twilight clouds were first seen on Mars by NASA’s Pathfinder mission in 1997. Curiosity didn’t repeat the trick until 2017, and last month’s sighting is the fourth Mars year the rover has spotted the clouds.
Late last year, NASA researchers published a study in the Geophysical Research Letters describing how the iridescent effect reveals how ice forms and grows in Mars’ atmosphere.
“I’ll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact,” said Mark Lemmon, an atmospheric scientist at the Space Science Institute in Colorado and the study’s lead author, in a NASA release. “Now it’s become so predictable that we can plan our shots in advance; the clouds show up at exactly the same time of year.”
The release notes that these clouds have not been seen by rovers in other parts of Mars. It may be that the region Curiosity roves—on Gale Crater’s Mount Sharp—may be predisposed to hosting the clouds.
