The plausibility of the geology of Char

Char is (according to StarCraft Wiki) a planet orbiting a binary star-system in the Koprulu sector. Its dimensions are comparable to earth with a diameter slightly smaller of 10.521 km to the 12.756 km of earth, gravity is also comparable with 91% of earth. Char possess two small moons with a diameter under 1.000 km named Eris and Ate in a planet-near orbit.

Fig.1. Char as imagined by jahim-myess 2009 ©

The surface is dominated entirely by a volcanic landscape, according to the sparse information recovered from a geological survey by the Confederacy and the Kel-Morian Combine more than 52 calderas, 18 mountain ranges with active volcanoes, 38 lava-lakes and 5 lava-oceans of varying extent were recognized, small temporally pockets of liquid water were also spotted on the surface, feed probably by the rare rain events. The remaining large plains are covered with dark lava and ash-layers. Thermal scans of the surface showed temperatures ranging from 48°C to 800°C - the last values reached in large pyroclastic flows travelling down from the volcanoes. The atmosphere consists mainly of oxygen with great amounts of sulphur and ash derived from the volcanic exhalations, water vapour is present but most of the time in very small quantities - only periodically and locally clouds supersaturated of water vapour form and rain occurs. Despite the hostile environment and the resemblances to hell the planet was soon colonized to gain access to his rich mineral deposits, especially heavy metals - Char is one of the richest resource nodes in the sector and was hotly contested by the Terrans, the Protoss and finally the Zerg. From all the colonized planets Char is characterized by a quite unique tectonic, intense phases of tectonic storms and magmatic activity occur periodically, melting entire areas of the surface and sparing only temporary islands that drift like a raft on an immense ocean of fire. According to the videogame StarCraft this is the fictive description of one of the last battlefields in a future war between three alien races, however science-fiction stories tend to be at last inspired by real science - so how plausible is such a planet? Until 1995, with the first detection of an exosolar planet in the 51 Pegasi system, many speculation were proposed about the existence of planets or even inhabited worlds orbiting other stars. Most time these worlds resembled surprisingly earth - with landscapes that would not be to unfamiliar to us and only the advent of space probes in the 20th century showed us that the exotic worlds can possess an exotic landscape with a own exogeology. With its pronounced eccentric orbit Char is apparently a common example in space - research showed that exoplanets can have a wide range of eccentricities and that our solar system is quite unusual with it's close to circular orbits. The research confirmed also that planets can form and persist in such gravitationally and dynamically active systems that are multiple star systems, 25% of the discovered planets until today occur in a binary-planetary system with two stars. Two types of binary-planetary systems can be distinguished - the planet can be bound by the gravitation of just one star (S-Typ Orbit) or orbit the mass centre of both the star-partners (P-Typ Orbit). Models show that probably only planets orbiting the primary star have dynamically stable orbits for long periods - so these planets are better suited to host a stable environment and support life. Char apparently possess a typical P-Typ Orbit and hosted no primary life forms; the only recent signs of life found on the burned surface are introduced neobiota by humans (ragnasaurs, some mushroom-like fungi and small rodents) and 10 billions of Zergs. In the videogame two main geomorphologic units can be distinguished on the surface of Char:

-UNIT 1: Extended smooth plains of dark rocks forming the low- and the highlands, only occasionally broken open by lava-lakes, seem to be the results of episodic large scale effusion of very fluid lava, in outcrops various superimposed layers are recognizable, comparable to the landscape formed by the terrestrial Deccan traps.

Fig.2. Lava-lake on Char with steep cliffs showing layered mafic rocks of unit 1, SCV for scale, note also the degassing of volcanic gases in a vespene geyser field - a resource unknown on earth. -UNIT 2: The second unit composed also of dark (mafic?) rocks is characterized by a wrinkled aspect, randomly distributed circular depressions and large crystals-like features are recognizable. This unit can be found only on the lowlands of the first unit. Fig.3. Contact of unit 1 to unit 2, SCV for scale, in the upper corner creep of the Zerg-infestation on Char is recognizable. The circular depressions are an interesting detail, three possible explanations are possible - the crater-like features could be maars (proposed by reynardo), formed by the explosive reaction between groundwater and magma, they could be craters of a more explosive volcanism (signs of a chance in the chemistry of the magma?) or finally impact craters, implying that these areas are older than the surrounding smooth plains (if we assume that the Char systems followed a similar evolution to our solar system, where impacts decreased over geologic time). The cartoonish crystal-like features could be formed only by slow crystallization of circulating fluids or cooling magma, and subsequently liberated by erosion from the surrounding lava sheets (or crystallised dikes as proposed by reynardo). The largest crystals found on earth formed underground in very peculiar conditions over millions of years - in a cave precipitating from an aqueous solution in the mine of Naica or in pegmatite intrusions - time that due the tectonic activity of Char apparently is not available. Also the erosion on Char, with little water in the atmosphere, should be practically inexistent or very slow. The unusual planetary tectonics of Char is explained in the videogame by its eccentric orbit and varying gravitational pull of the two stars on the planet - the kinetic energy is transformed by friction in heat, melting the entire crust when Char approaches its two suns. In our solar system there is an example that maybe inspired this idea. Io is one of the larger moon of the gas giant Jupiter, and the most active body in the solar system. Io is too small to produce or store enough heat inside, the energy to feed the intense volcanism, based on sulphur (melt temperature 115°C) , is provided by tidal heating on the slightly eccentrically orbit around Jupiter. However this orbit is stabilized only by the presence of the other moons of Jupiter, without them Io would approach a circular orbit and soon cool down. That Char would remain or survive long enough on such an extreme orbit that produces as much energy to melt mafic rocks (with melt temperature of over 1.000°C) is therefore doubtful. There could be however a second model to explain the tectonics of Char. Venus possess a similar diameter (12.104 km) and bulk density to earth, also the heat generated inside the two planets should be similar. On earth this energy is released by upwelling and ascending currents of the mantle, the creeping material crashes the outermost insolating crust and heat is dissipated along convergent and divergent plate boundaries. Signs of strain like mountain belts, thrust systems and rifts are mostly concentrated at these boundaries. The surface of Venus is in contrast surprisingly smooth, there are less than 1.000 craters known randomly distributed and 80% of the topography consist of plains, elevations are concentrated in two large "bumps" - Ishtar and Aphrodite-Terra. Fig.3. Simplified version of the topographic map provided by the Pioneer Venus Orbiter released in 1980 by NASA. There are however unique tectonic landforms and terrains on Venus, divided into five classes: plains, volcanic rises, crustal plateaus, tesserae, coronae, and chasmata - the last three features are associated with strain on Venus crust: tesserae are areas of ridges or fractures (resembling the unit 2 on Char), coronae are circular to elliptical altitudes and chasmate are large graben-like structures. These features resemble nothing on earth and it is therefore improbable that Venus release its inner heat in the same manner as earth trough plate boundaries. Fig.4. Tessera terrain in Ovda Regio. Broad ridges, assumed to be open folds, trend ENE. The ridges are cut by grabens trending NNW, and they are embayed by radar-dark material that fills topographic lows. The "eye-shaped" pattern in the western part of the image suggests that some of the deformation of this tessera terrain was ductile. G = grabens; R = broad ridges(after WATTERS & SCHULTZ 2010). According to one model for Venus, the stagnant-lid model, the lithosphere insulates the mantle until the growing heat reaches the melting temperature of the crust, causing increased volcanism and possibly reshaping the entire crust. This model would also explain the lack of impact craters (like on unit 1 on Char) of the surface - the Venusian crust was apparently mostly reshaped by an intense volcanism 300 to 500 million years ago. And there is the problem with this model to apply it on Char - the periodic partial melting of the crust would occur in geologic periods, not so often as proposed in the videogame. Char is a imaginary world, however the discoveries on the planets of our solar system and the discovery of exoplantes shows that there are exotic worlds with their own exotic geology (at least for geo-based -logists). Bibliography: MASON; J.W. (2008): Exoplanets Detection, Formation, Properties, Habitability. Springer: 314 WATTERS, T.R. & SCHULTZ, R.A. (2010): Planetary Tectonics. Cambridge University Press: 518 Online Resources: HAMILTON, C.J. (2002): Planetscapes. (Accessed 05.05.2011) USGS (05.08.2003): Solar System Geology - Venus. (Accessed 05.05.2011) USGS (05.11.2010): Maps of Venus Published by the U.S. Geological Survey. (Accessed 05.05.2011)