Neighbouring volcanoes: This image taken by Mars Express shows Ceraunius Tholus and the smaller Uranius Tholus, which were caused by meteor impacts
These stunning images of mist-capped volcanoes on Mars show how the northern hemisphere of the Red Planet was transformed by meteor impacts.
The collisions, which took place long after volcanic activity ceased, deposited ejected material over the lower flanks of the volcanoes, Ceraunius Tholus and the smaller Uranius Tholus.
Permanent and transient features are on display in the images, taken by Mars Express and just released by the European Space Agency (ESA).
These stunning images of mist-capped volcanoes on Mars show how the northern hemisphere of the Red Planet was transformed by meteor impacts.
The collisions, which took place long after volcanic activity ceased, deposited ejected material over the lower flanks of the volcanoes, Ceraunius Tholus and the smaller Uranius Tholus.
Permanent and transient features are on display in the images, taken by Mars Express and just released by the European Space Agency (ESA).
By the time the probe crossed again and took the final strip of data needed for this image, the clouds had long since dispersed and so there is a sharp line across them in the finished mosaic.
The Latin word 'tholus' means a conical dome and the base of Ceraunius Tholus is 80miles across, while the peak rises 3.4miles above the surrounding plains. At its summit is a large caldera that measures 15.5miles across.
Ceraunius Tholus is 80miles across and rises 3.4miles above its surroundings. At its summit is a large caldera that measures 15.5miles across
Lying 37miles to the north, Uranius Tholus is a smaller volcano with a base diameter of 38.5miles and a height of 2.8miles.
The flanks of Ceraunius Tholus are relatively steep and are etched with valleys that are deeply cut in many places. This suggests that soft and easily-eroded material, such as layers of ash, were deposited during the volcano’s eruptions.
The largest and deepest of these valleys is about 2.2miles wide and 300metres deep. It terminates inside an otherwise unrelated elongated impact crater that happens to lie between the two volcanoes, and has created a fascinating fan shape of deposits.
Although the source of the fan is still being debated in scientific circles, it may have been formed when material from a lava channel or tube was washed downwards by a melting ice cap on the volcano.
The summit crater - the caldera - is flat and smooth, so it may have contained a lake early in Mars’ history when the atmosphere was denser.
It is also possible that the water was produced when volcanic activity melted buried ice lenses. An ice lens forms when moisture seeps below the surface and forms a frozen layer between the top ‘soil’ and the rocky layer below.
Caused by an oblique impact by a meteorite, the elongated crater between the two volcanoes is called Rahe and measures 22miles by 11.2miles.
A smaller impact crater that measures 8 miles across can be seen to the west of Uranius Tholus.
This was also formed after all the volcanic activity ended and served to cover the lower flanks of the volcanoes with ejected material, with the result that only the upper regions of the original structures are now visible.

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