This high-resolution image shows newly discovered frost at the top of Olympus Mons, the tallest volcano not only on Mars but in the entire Solar System. The frost appears blue on the floor of the volcano’s caldera and around its northern rim. It is absent on the well-lit steep slopes seen on the left of this image. Credit: ESA/TGO/CaSSIS
“We thought it was impossible for frost to form around Mars’s equator, as the mix of sunshine and thin atmosphere keeps temperatures relatively high at both surface and mountaintop – unlike what we see on Earth, where you might expect to see frosty peaks,” says lead author Adomas Valantinas, who made the discovery as a PhD student atPerspective view of Olympus Mons from Mars Express, with frost in the cauldron-like hollow.
These volcanoes have calderas, large hollows, at their summits, caused as magma chambers emptied during past eruptions. The researchers propose that air circulates in a peculiar way above Tharsis; this creates a unique microclimate within the calderas of the volcanoes there that allows patches of frost to form.
“There are a few reasons: firstly, we need an orbit that lets us observe a location in the early morning. While ESA’s two Mars orbiters – Mars Express and TGO – have such orbits and can observe at all times of day, many from other agencies are instead“Secondly, frost deposition is linked to colder Martian seasons, making the window for spotting it even narrower. In short, we have to know where and when to look for ephemeral frost.
Discovering the frost relied upon collaboration between two of ESA’s orbiting Mars explorers: ExoMars TGO and Mars Express.