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Skywatching

Exploring Venus, the volcano planet

Volcanic eruptions on Venus

Venus has often been referred to as the Earth's twin.

It is the second planet out from the Sun. We live on the third. It is around the same size as Earth, with a diameter of 12,104 kilometres, compared to our world's 12,756 kilometres.

Our world is hot inside, due to residual heat from its formation some 4.5 billion years ago, and from the decay of radioactive elements. Venus was formed at the same time, and made of more-or-less the same stuff, so we would expect it too to be hot and at least partially molten inside.

The resemblance ends there. Venus has a corrosive atmosphere, is permanently enveloped in a thick layer of cloud, and has a surface temperature hot enough to melt lead and tin.

The first real look at the surface of Venus was provided by the Magellan spacecraft, which used radar to map the planet's surface. Radio waves are unaffected by the clouds.

The world Magellan revealed was a surface with hundreds of volcanoes, some much larger than any on Earth. As one might expect, there were no signs of oceans or living things.

What was odd was that none of those volcanoes were seen to be erupting. We would expect the interior of Venus to be more or less as hot as the inside of our world. The Venusian volcanoes are large, dome-shaped structures—like the volcanoes forming the islands of Hawaii—not the steep, cone-shaped volcanoes like Vesuvius or Mount Saint Helens.

On Earth, we have two main classes of volcanoes—those associated with subduction zones and those lying over hot spots in the Earth's mantle. There is a subduction zone just off the West Coast of British Columbia, where the seabed of the Pacific Ocean is being pushed down and under the continent.

This mixture of rock, sediment and seawater melts and bubbles up forming volcanoes, like Mount St Helens. The upwelling magma forms a sticky lava that tends to plug up the volcano's plumbing. Pressurized with superheated steam, the volcanoes erupt explosively. These volcanoes form the familiar sharp cones, which periodically blow themselves up and reform.

The Hawaiian Islands are formed from the other type of volcano. A hot spot in the mantle produces upwelling magma that breaks through to the surface. The lava is mostly melted basaltic rock, which runs freely. These volcanoes rarely explode, and since the lava flows so easily, it forms flat dome-shaped volcanoes, like thick pancakes. The lava can flow many kilometres, covering huge areas.

Although the Magellan space mission is long over, scientists continue to analyze the data. Recently, evidence was found of a volcanic eruption. The volcano Maat Mons had a side vent that recently filled with lava, which overflowed down the side of the volcano onto the surrounding land. The surprising thing is only this one example has been found so far, although the surface of Venus is the result of continuing volcanic activity.

The Moon is covered with impact craters. That is because it has been geologically dead for billions of years, and its surface has been unchanged for a long time, apart from the accumulated effect of countless meteoric impacts.

Telescopes or binoculars will reveal countless craters. On the other hand, the Earth, which is at least as old, shows less than 200 impact craters. That is because the surface of our world is being continuously recycled by erosion and plate tectonics.

Venus has few craters, so its surface is geologically young. There are no signs of plate tectonics, but frequent outflowings of lava from the numerous volcanoes would bury the craters, renewing the surface.

It is likely our not seeing this volcanic activity is mainly due to the difficulty we have in observing our planet's twin.

•••

• Venus lies low in the dawn glow.

• Jupiter shines high in the south after sunset.

• Saturn is getting hard to see, as it sinks into the sunset glow.

•The Moon will be new on Feb. 9.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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