Mars Odyssey data may explain mystery behind Martian surface frost

Data from NASA's Mars Odyssey orbiter, the agency's longest-lived Mars mission, may explain why Martian frost, made up largely of carbon dioxide, can be invisible to the naked eye and why dust avalanches, which are reshaping the planet, appear on some slopes.

Last year, while studying images captured by the Mars Odyssey orbiter, researchers used visible light - perceptible to the human eye - to look at the Martian surface and they could see ghostly, blue-white morning frost illuminated by the rising Sun. However, when they used the orbiter's heat-sensitive camera, the frost appeared more widely, including in areas where none was visible.

In a new study published in the Journal of Geophysical Research: Planets, the researchers have proposed a surprising answer that may also explain how dust avalanches are triggered after sunrise.

According to the authors, Mars has so little atmosphere, hence the Sun quickly warms frost that builds up overnight. Instead of melting, dry ice vaporizes into the atmosphere within minutes. The study authors propose that they were seeing “dirty frost” – dry ice frost mixed with fine grains of dust that obscured it in visible light but not in infrared images.

Scientists believe that dust avalanches on Mars probably look something like a ground-hugging river of dust releasing a trail of fluffy material behind. As the dust travels downhill over several hours, it exposes streaks of darker material underneath - called dark streaks or slope streaks.

For this study, the authors mapped the slopes streaks and found that they tend to appear in places with morning frost. They propose the streaks resulted from the vaporizing frost, creating just enough pressure to loosen the dust grains, causing an avalanche.

The mystery of frost on Mars. Mars Odyssey data may explain why CO2 frost on Mars can be invisible to the naked eye & why dust avalanches appear on slopes. The orbiter's infrared, temp-sensitive camera provides a one-of-a-kind view of the Martian surface. https://t.co/dsga4kxIUI pic.twitter.com/XW2K26Jdg7

— NASA JPL (@NASAJPL) May 5, 2022