If I were to ask you what the largest known volcano in the solar system was, you’d probably answer Olympus Mons on Mars correct? I’ve recently discovered this is not exactly true. Although Olympus Mons is indeed tallest known volcano (at about 27 km) it is not the largest by area. Fortunately we don’t have far to go to find the true king — in fact we don’t even need to leave Mars. A scant (on a cosmic scale) 1750 km to the northeast lies Alba Patera.

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I “discovered” this feature while browsing Mars Orbiter Laser Altimeter (MOLA) data using JMARS (check it out — it’s very cool). I noticed a large caldera-like structure on a comparatively flat area of Mars. It looked to me like an Olympus Mons-type shield volcano that either never was, or had collapsed/slumped. Comparing the cratering of this feature to that of Olympus Mons led me to believe this was an older feature geologically. I immediately noted this “mystery volcano” covered a LOT more area than any of the Tharsis shields including Olympus Mons. At any rate it was armed with these suppositions that I began to search online for information about this feature.

Alba Patera (“patera” meaning “saucer” in Latin) has the largest diameter of any volcano in the solar system at over 1600 km (Olympus Mons is about 625 km across). Despite its size however, it is very flat — Alba Patera has a total height of only about 7 km. It lies directly north of the Tharsis bulge with it’s 100-km-diameter caldera right on 250ºE 40ºN. Most notably it is surrounded by a distinctive series of fractures oriented predominately north-south. Among these fractures are “chains” of crater-like features called collapse pits. In a volcanic enviroment collapse pits are formed when the roof of an evacuated lava tube collapses under its own weight. A great close-up of collapse pits from an area in the northeast region of the Alba Patera complex — taken by the Mars Odyssey Thermal Emission Imaging System (THEMIS) — can be seen here.

The following Terragen renders were done with bump and color maps obtained from Space-Graphics.com. Before overlaying the 3D render with the color map, I combined it with a grayscale MOLA image of the same region in order to enhance the surface detail. Although these renders aren’t as awe inspiring as Valles Marineris or as breathtaking as Planum Boreum, I learned many interesting facts about this region of Mars which had been — until this effort — unknown to me.

So the next time someone asks you about the largest volcano in the solar system, ask them if they mean “largest” or “tallest” — then set the record straight! 🙂

Welcome to Terragen Mars: Planum Boreum — the second installment of some visual explorations I’m creating using Terragen for Mac OS X.

Planum Boreum (North Plain) is the name of the area at the north pole of Mars. At about 1,200 km across, the martian polar cap is cut by canyons and troughs that dive as deep as 1 km beneath the surface. The largest of which is the Chasma Boreale (Northern Canyon) which nearly bisects the north polar cap by a third.

The ice cap contains layers of both light and dark material in a spiral pattern which is commonly agreed to be carved by wind and the evaporation of ices. During the Martian winter, the spiral polar cap bulks up with carbon dioxide ice, only to sublimate during the summer period exposing the plain and fairly permanent water-ice cap underneath. Elevation data from the Mars Observer Laser Altimeter (MOLA) instrument shows that large areas of the ice cap are quite smooth, with variations in elevation of only a meter or two over many kilometers.

The renders I have done were built from two main data sources, topographical data and an image overlay. The topography was generated from a bump map obtained at Space-Graphics.com based on MOLA data. My initial plan was to synthetically recreate the surface colors and I think I made a valiant attempt…

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Since the application of color in Terragen is primarily governed by altitude (min & max) and slope (min & max), I was unable to get the results I wanted. So it was back to the drawing board. Over the next few days I was poking around Mars images online and I came across an image of the north pole taken by the Mars Global Surveyor with the Mars Orbiter Camera (MOC) — specifically MGS MOC Release No. MOC2-231, 22 May 2000.

The MOC image covers the ice cap but it only partially covers region I am working with. So using a false-color image I generated from the grayscale bump map, I merged the two into this image covering the entire region. Although the topography remains accurate across this entire image, as you move away from the ice cap the coloration becomes synthesized. Not a bad trade-off though.

It was this image I overlaid onto the topography to achieve the results I was finally pleased with. Here is another render from a similar position and altitude as my first (poor) attempt.

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To be quite honest I was absolutely floored! It exceeded my wildest expectations. I hope you enjoy the rest of the views I rendered representing the Martian polar cap in early summer. The vertical relief has been doubled.

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Last but not least, I give you the Martian north pole in Quicktime VR from an altitude of approximately 35-40 km.

Click here to open the QTVR scene of Planum Boreum (north pole) in a new window

You’ll need Apple – QuickTime to view the file.

Where do we go next?