In January 2023, NASA's Curiosity rover captured images of noctilucent clouds during a Martian sunset, including a rare category of iridescent bright noctilucent clouds that appear feather-shaped and glow in the Martian sky.
Curiosity captured images over 16 minutes of sunlight and atmospheric ice crystals interacting in the Martian twilight. The images reveal iridescent clouds that resemble a giant feather in the Martian skies, appearing slightly colored after sunlight scatters during sunset and shimmering in hues of red, green, and pearlescent white as they float high above the Martian surface.
This marked the fourth Martian year in which Curiosity observed these noctilucent clouds. Mark Lemmon, an atmospheric scientist at the Space Science Institute in Colorado, remarked on the growing pattern of iridescent clouds. "I'll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact. 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," said Lemmon, according to Universe Today.
Noctilucent clouds on Mars are composed of ice crystals of carbon dioxide (dry ice) and only form over certain regions, while Earth's noctilucent clouds are composed of water ice and are only visible during twilight. These Martian clouds form at altitudes of around 60 to 80 kilometers, classified as mesospheric clouds. Clouds on Mars, made of either water ice or carbon dioxide ice, are rare in the planet's thin, dry atmosphere but occasionally appear in the equatorial zone when temperatures drop, forming only in early Martian fall and only in the southern hemisphere.
When clouds are both noctilucent and iridescent, they're called nacreous clouds, and under the right conditions, noctilucent clouds can take on an iridescent, mother-of-pearl quality. The iridescence of the clouds is due to the scattering of sunlight and uniform particle size, indicating that the clouds had a brief evolution in a uniform environment, a phenomenon similar to the rainbow on Earth.
One possibility for the formation of noctilucent clouds is that gravity waves might be causing carbon dioxide to condense into ice in the southern latitudes of Mars, according to dailygalaxy.com. Studying these clouds could provide insights into seasonal changes and climate evolution on Mars.
Lemmon noted that the seasonal recurrence of these clouds has allowed researchers to predict their appearance and plan observations in advance, according to Mashable.
The article was written with the assistance of a news analysis system.