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Ken Tapping, April 29, 2009
In the sky this week...
> Look for Mercury, the closest planet to the Sun low in the west after sunset.
> Saturn still dominates the southern sky during the evening. Jupiter rises about 4 a.m., Venus and Mars about 5a.m.
> The Moon will reach First Quarter on May 1.
Here in Southern British Columbia we are surrounded by solidified lava, thousands of cubic kilometres of it. Fortunately the last eruptions took place around a million years ago. Lava is a melted mixture of minerals, such as olivine, feldspar, silica and many others. All these melt at more than a thousand degrees Celsius, so by definition lava is very hot stuff.
How about very cold planets where ice is as permanent a rock mineral as the other minerals? Imagine grains of other minerals trapped in a huge mass of ice. Provided the planet remains cold enough, that ice rock will be as permanent as any rock here on Earth. However, if that rock is trapped underground and subjected to heat, it will become molten at about zero degrees Celsius, with the grains of other minerals floating around in it, and then erupt out of volcanoes as a stream of mud. This would cool and solidify on the surface to make mountains looking just like the ones around here in BC. It might sound far-fetched, but the possibility fits at least two places in our Solar System.
Titan is Saturn's largest Moon. Thanks to the Cassini and Huygens spacecraft, we've seen Titan's surface close up. Photographs show a landscape with lakes rather like what we see on the Canadian Shield, but without the trees. It is a lot colder. At Titan's large distance from the Sun, it receives little solar heat; most of its meagre supply of warmth comes from the kneading it gets from Saturn's gravity. It is still a very cold place, roughly -180 Celsius, and those lakes are liquid hydrocarbons. On Titan water is just another mineral, or so we thought. However there is now evidence that the heating Saturn provides to Titan's interior is enough to melt water, and there are volcanoes that erupt the result - mud - in huge flows that solidify to form the same lava features as those we see here on Earth.
With Saturn continually kneading Titan and producing heat, we can see how Titan might have mud volcanoes. However, how can we have mud volcanoes on Mars? So far three "squirts" of muddy "lava" have been detected on Mars, emerging as a fizzy mixture loaded with methane. The first big question is where is that methane coming from? Here on Earth this gas is produced by many forms of life, ranging from bacteria to us, and on to cows, elephants and whales. Is this evidence of things living underground on Mars? Secondly, with nothing nearby to knead the planet and make it warmer, where is Mars getting the heat from? This suggests that whether or not Mars is still molten inside, it is still warm enough deep underground to melt water to drive the mud volcanoes. In addition, a layer of warm, liquid water, loaded with various chemicals, could be just what we need for Martian life to exist, and to produce all that methane.
Here on Earth lava is hot enough to kill everything, and to wreak great destruction. Mud lava would be highly preferable. However if we were beings living on Titan's surface, the muddy flows from local volcanoes would probably be as deadly.
Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,