Mohawk Valley Astronomical Society

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Volcano Worlds Part 1 of 2: Volcanoes of Fire

by Perry Pezzolanella

Volcanoes are an essential part in the evolution of a world. They create new land, alter the landscape with the release of lava and bring to the surface many minerals and compounds that would otherwise be trapped far below the surface. Volcanoes also release gases that can create an atmosphere if the world has sufficient gravity to retain it; this can play a role in the climate and the evolution of life. Volcanoes release huge amounts of carbon dioxide that can help warm a world as this gas helps to trap the heat from the Sun. Ash released high into the atmosphere can reflect sunlight and cool the world for several years. Released sulfur compounds can form acids that break down compounds and cause chemical reactions, which create new compounds vital for life. Volcanoes also release water vapor, the key ingredient for life. Earth is not the only volcanic world; several other worlds have a history of volcanic eruptions, some of which are active to this very day.

Mercury and the Moon were shaped by volcanic eruptions, although not by the classical towering mountains of belching lava and smoke. Vast plains cover both worlds where huge amounts of magma erupted from beneath the surface, usually when an asteroid or comet impacted and punctured the crust. The resulting crater flooded with molten lava and solidified into smooth plains. These areas on the Moon are visible today as dark mare and give the Moon its face. Mercury also experienced vast plains flooded by lava, but as Mercury cooled it shrank causing the crust to crack, which created numerous scarps along the surface. Several irregular pits have been discovered by the MESSENGER spacecraft that hint at volcanic outgassing in the recent past. The gravity of Mercury and the Moon is too weak for them to retain any of the gases that were emitted from the eruptions as an atmosphere. All of the worlds in the Solar System obtained their heat when massive objects collided together to create them. Heavier elements then differentiated, or sank toward the core, releasing more heat. Radioactivity also contributed to their internal heat along with tidal friction among the planets and moons.

Mars appears to be volcanically dead, but huge volcanoes dot the planet, the biggest being Olympus Mons, which towers over 16 miles high. The great Tharsis bulge with three massive volcanoes gives proof that Mars was once a volcanically active world. Mars has no plate tectonics to move the crust around, therefore a hot spot stays in the same area and the volcano is able to build up to incredible heights. These volcanoes released huge amounts of carbon dioxide and water vapor into the air creating a thicker, warmer atmosphere during that era. Rain may have fallen and pooled on the surface. Once the volcanoes died, Mars’ weak gravity was not able to hold onto much of the atmosphere so it grew thinner, drier, and colder.

Venus is a planet where volcanoes rule. About 500 million years ago the entire surface may have been flooded in one huge volcanic upheaval. The surface is unusually young with very little cratering. Radar images from the Magellan orbiter during 1990-94 reveal lava flows everywhere. Dried lava riverbeds up to 4000 miles long were detected along with flooded basins. There are huge, frozen lava flows down mountains, damned up against ridges, and even breaching ridges. It is uncertain if Venus is volcanically active today, but the Pioneer Venus Orbiter detected lightning around several of the peaks during 1977-92 and Venus Express confirmed lightning a few years ago. Ash clouds generate static electricity because they are so dry and turbulent resulting in numerous flashes of lightning on Earth and this would also apply to any volcano on another world with an atmosphere capable of supporting a turbulent plume. Venus also had a surge in sulfur dioxide in its atmosphere in 1977 that dropped and leveled off a few years later. This is a common gas from volcanoes and strongly hints that Venus is still volcanically active to this day. The average surface temperature is 870ºF, but there are spots suspected to be as hot as 1300º that are in need of verification. Venus Express has detected that Idunn Mons has an unusually warm peak. This volcanic mountain rises about 1.5 miles above the torrid plains, and there is strong evidence that it may be active today. Thick clouds completely cover Venus and prohibit any direct view, therefore confirmation of active volcanoes may have to wait until exploration below the clouds with balloons and landers becomes more frequent.

Volcanoes on Earth may have helped create life by warming the atmosphere with carbon dioxide, releasing water vapor, and creating vital compounds, but volcanoes have destroyed Venus. The huge amounts of carbon dioxide and sulfur dioxide that were released, coupled with its closer proximity to the Sun, have turned Venus into a toxic, pressurized inferno. Any water was lost or combined with sulfur dioxide to create a sulfuric acid mist that readily destroys anything it touches. If life ever got started on Venus, it was savagely destroyed and sterilized.

Io is the icon of volcanic worlds as it is peppered with huge, powerful volcanoes. The plumes from these volcanoes tower over 200 miles above the surface and the lava is the hottest known anywhere in the Solar System as it reaches 3000ºF, about 1000ºF hotter than Earth’s lava! The lava is made of sulfur, a major component of Io besides silicates, and gives it a colorful surface. The warmer lava flows and warm ash deposits are orange and red while the hot lava lakes and calderas are black. Cool and cold sulfur deposits are yellow and white. Io’s volcanoes are powered by tidal flexing from giant Jupiter and the three large moons: Europa, Ganymede, and Callisto. These tides flex the surface as much as 300 feet, which heats the interior to enormous temperatures. The pressure within builds and when it is released, there is no doubt about the power of these volcanoes. Areas as large as Arizona are flooded with molten sulfur and covered with ash. Io’s gravity is too weak for the volcanoes to create an atmosphere, but the eruptions are so powerful that many sulfur particles escape Io and go into orbit around Jupiter. They become ionized by Jupiter’s powerful magnetic field. Thanks to the influx of these particles from Io, the volcanoes may be responsible for generating the most intense and deadliest radiation belt in the Solar System. Io is immersed in this radiation belt and in this case volcanoes can be credited with sterilizing it.

Volcanoes may conjure up images of lava and fire, but beyond Jupiter are worlds so cold that the volcanoes are not fiery. They erupt and behave in ways that are far more exotic than what is known on warmer Earth. In the next edition of Telescopic Topics the worlds of icy volcanism will be explored.