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First evidence of water frost on the tallest volcanoes of Mars


A new study reveals for the first time the presence of water frost on the peak of Martian volcanoes near the equator. This discovery was published in a recent Nature Geoscience paper, with contributions from researchers of the Royal Observatory of Belgium (ROB) and the Royal Belgian Institute for Space Aeronomy (BIRA-IASB).

The presence of frost was observed independently by:

  • the Colour and Stereo Surface Imaging System (CaSSIS) and the Nadir and Occultation for Mars Discovery (NOMAD) instruments onboard the European Space Agency’s (ESA) ExoMars Trace Gas Orbiter (TGO) spacecraft
  • the High Resolution Stereo Camera (HRSC) from ESA's Mars Express mission.

Scientists from ROB analysed data from the TGO-NOMAD instrument. NOMAD, led by BIRA-IASB, consists of three distinct spectrometers that observe the Martian atmosphere and surface across various wavelengths and in different observation modes. Specifically, the Limb Nadir and Occultation (LNO) spectrometer of NOMAD, originally designed to measure absorptions by the Mars atmosphere of infrared sunlight reflected from the surface, detected an absorption by ice deposits at the summit of Olympus Mons, located at an altitude of 20 km above the surrounding area.

The weather conditions at these high altitudes were simulated by the researchers at ROB in order to assess spacecraft observations within a consistent theoretical framework and to better identify the frost composition. Modelling of Martian air circulation at the summit of the caldera, the large depression at the peak of ancient volcanoes, revealed that moist air can indeed condense into water frost at the bottom of the caldera floor during the night and early morning, similar to what can be observed on the Earth.

This discovery provides new insights into Martian climate dynamics, highlighting the importance of ongoing research to understand the Martian water cycle and prepare for future Mars missions and possible human exploration.

Frost is observed in the caldera of Olympus Mons on Mars
This early morning wide-angle image of Olympus Mons (LST = 7:20 a.m., Ls = 346.7°, lat = 18.2°N,
lon = -133.2°E) taken by the Mars Express High Resolution Stereo Camera (MEX-HRSC) reveals for
the first time the presence of frost on the summit of the volcano, the tallest one on Mars and in the
entire Solar System. © ESA/DLR/FU Berlin


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Karolien Lefever
Email : Karolien (dot) Lefever (at) aeronomie (dot) be

Newfound frost atop Olympus Mons
This rectangular slice of Mars shows the terrain atop Mars’s volcano Olympus Mons. Rippled, uneven, stepped terrain can be seen, with different illuminations. The right-hand side of the image is blue-toned, representing the newly discovered water ice frost.


News image 1
News image legend 1
This simulated perspective oblique view shows Olympus Mons, the tallest volcano not only on Mars but in the entire Solar System. The volcano measures some 600 km across and lies 20 km above the surrounding area.

These data were obtained by the High Resolution Stereo Camera aboard ESA’s Mars Express, and the oblique perspective angle subsequently created using a Digital Elevation Model (DEM). The data were gathered as part of new research revealing water frost for the first time near Mars’s equator (a part of the planet where it was thought improbable for frost to exist). The vertical scale is exaggerated by a factor of five.

Credit: ESA/DLR/FU Berlin (A. Valantinas)
News image 2
News image legend 2
This image shows frost on the caldera floor of the Ceraunius Tholus volcano. The frost is shown in blue. This blue colour is due to the way in which CaSSIS constructs its images, using both near-infrared and visible channels – a so-called ‘NPB’ image, as opposed to a typical RGB (red-green-blue) image.

This combines the instrument's near-infrared (N), panchromatic (P) and blue (B) filters. This provides more information on a feature’s spectral diversity in a large range of wavelengths invisible to the human eye.