Europe鈥檚 Mars Express orbiter has stared down the throat of the Solar System鈥檚 largest volcano, Olympus Mons, to produce the best ever images of the giant peak.
The images, released on Wednesday, were taken with the orbiter鈥檚 High Resolution Stereo Camera (HRSC) from a height of 273 kilometres and reveal details as small as 12 metres across.
Geologists 鈥渃an now get their teeth into how similar the 3-D shapes of lava features are compared to Earth鈥檚 volcanoes,鈥� says Jan-Peter Muller, one of the camera鈥檚 co-investigators at University College London, UK.
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Olympus Mons rises 22 kilometres above the surface of Mars, making it nearly three times taller than Mount Everest. It is topped by a three-kilometre-deep caldera, which is the focus of the new images.
The overlapping circular pits visible were created after eruptions ceased and the magma within the volcano retreated, causing the peak to cave in. The largest pit occurred first, with the smaller ones sinking later. The concentric fractures also formed as the surface dropped.
Lava tubes
As good as the image is, crisper images are likely to follow, says another HRSC co-investigator, John Murray at the UK鈥檚 Open University. This is because the atmosphere was quite dusty when the images were taken.
Nonetheless, Murray has identified evidence of a tongue-shaped landslide inside the steep caldera wall, as well as flows from lava of different viscosities that probably arose in separate eruptions.
The strings of craters and the long, broken depression in the lower-right flank of the volcano may be exposed 鈥渓ava tubes鈥�, underground caverns formed when the lava inside them flowed away from the surface. Alternatively, they may be flank eruptions, when lava leaks from the side of a volcano.
鈥淚f they are flank vents, that suggests the same processes operated on Mars as on Earth,鈥� he says, pointing out that in 2003 lava erupted a kilometre below the summit of Italy鈥檚 Mount Etna.
鈥楳ajor headache鈥�
The image also shows that the HRSC team has overcome a major hurdle in its image processing techniques, says Muller. To produce a 3-D image, individual images from each of the stereoscopic cameras have to be matched up, but the steepness of the topography on Olympus Mons makes that a 鈥渕ajor headache鈥�, he says.
However, the large field of view of the new images 鈥� up to 102 kilometres across 鈥� shows the team is well on its way to overcoming the difficulties, Muller says.
The camera has had a few other minor setbacks. The exposure settings were off for the first couple of orbits, producing low-contrast images that showed a lot of sunlight reflected from atmospheric dust. Also, an entire orbit鈥檚 worth of images were also lost recently, possibly due to a storm that cut off the craft鈥檚 communication with an antenna in Australia.
But scientists are not complaining. 鈥淎t the moment, we鈥檙e drowning in data,鈥� says Muller. 鈥淚鈥檝e filled several hundred gigabytes already.鈥� Mars Express went into orbit around Mars on 25 December for a planned two-year mission. Its lander, Beagle 2, which was supposed to land on Mars the same day but has not been heard from, was declared officially lost on 6 February.