Mohawk Valley Astronomical Society

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Planet of Fire: Venus

by Perry Pezzolanella, MVAS

Another long day is breaking on Venus as the sun rises in the west at the Soviet Venera 9 Lander site on the slope of a huge shield volcano known as Theia Mons in a vast uplifted region known as Beta Regio. The weather forecast for the 58.5 Earth days of daylight ahead is the same as any other day: mostly cloudy with a hint of hazy sun and a slight breeze laced with an occasional sulfuric acid mist with a high of 865° F after an overnight low of 865° F. It is autumn 1978 back on Earth and the U.S. fears another severe winter. For the Venera 9 spacecraft this is all irrelevant for it died within an hour of landing on October 22, 1975. It transmitted its data including one stunning picture from the surface making it the first spacecraft to transmit an image from the surface of another planet. Then it rapidly succumbed due to the combination of a carbon dioxide atmosphere up to 90 times Earth's laced with sulfuric acid, and blistering heat that approached 900° F. It was doomed to sit forever silently on that hillside strewn with sizzling, red-glowing rocks slowly frying and eroding. Suddenly, there is a huge blast far away upslope shaking the ground beneath Venera 9. A huge volcano erupts at Theia Mons unleashing a huge cloud of ash and dust crackling with almost continuous lightning. Fiery lava flows downhill far past Venera 9 and tons of sulfur dioxide and ash pour high into the dense atmosphere perpetuating the gloomy skies overhead.

As the world celebrated Christmas 1978, Venus came under intense scrutiny by an armada of spacecraft the likes of which it has never seen. The U.S. launched the Pioneer Venus Orbiter on May 20, 1978 and also the Pioneer Venus Multiprobe on August 8, 1978. All totaled, five probes from the U.S. entered the atmosphere of Venus that December and studied the chemistry of the clouds and hazes, and detected huge amounts of sulfur dioxide too large to be explained by chemistry alone. Something was creating an excess of sulfur dioxide. The Pioneer Venus Orbiter arrived that same month and eventually discovered that the concentration of sulfur dioxide was decreasing over time. It also monitored lightning and found a high number of flashes clustered around several of the highest peaks with the highest concentration clustered around Beta Regio, particularly at the peak of Theia Mons.

The Pioneer Venus Orbiter monitored Venus closely as it mapped its surface crudely with radar until October 1992. During its 14-year life it detected a steady decrease of sulfur dioxide in the atmosphere reaching a stable level by the early 1980's, as well as decreasing intensity of lightning flashes. When Galileo flew past Venus in 1990 on its way to Jupiter and Cassini flew past it in 1999 on its way to Saturn, neither spacecraft could find any indication of lightning. A few days before Christmas Day 1978, a Soviet lander, Venera 11, plunged towards the broiling surface followed by Venera 12 on Christmas Day. Both detected almost continuous lightning and one of them heard thunder. Unfortunately neither transmitted pictures from the surface as the lens cap failed to jettison from the camera and rapidly melted in place thereby ruining any chance of a surface photo. During the early 1990's the U.S. Magellan spacecraft orbited Venus and radar mapped the surface with unprecedented detail. Magellan's thermal mapper detected small hot spots on the surface as hot as 1300° F. It was not long before there was a stunning revelation.

With decreasing atmospheric sulfur dioxide and lightning activity, lightning clustered around mountain peaks, and hot spots dotting the surface, the obvious conclusion was that Venus has volcanoes that may be active even today. Venus may have experienced a huge eruption in 1977 or 1978 that increased the sulfur dioxide concentration rapidly in the atmosphere, and caused lightning as the dry ash in the plume produced huge amounts of static discharge, often common in Earth's volcanic eruptions. For Venera 9 it would have been the perfect scenery of Hell as it experienced all of this in nearly 900° F heat. If only it were still functioning back then, it would have been able to record the chemistry, take photographs of the changes in the landscape and record the quality of light.

Magellan revealed volcanic landforms covering nearly 90% of the surface of Venus! Many of the landforms are similar to Earth's: steep-sided towering volcanoes, wider and flatter shield volcanoes, and lava domes, but Venus also has volcanic features so strange that there are nothing like them on Earth. Vast low-lying areas are covered by smooth flows of lava similar to the basalt flows in the western U.S. and the smooth mare on the Moon. The plains of Venus are peppered with volcanoes of all shapes and sizes, often in clusters. Many of the smaller volcanoes are no more than ten miles across and are built by runny lava. There are a few huge volcanoes that tower up to five miles above the plains and are over 100 miles across. They are covered with overlapping lava flows and may be active today. This is convincing evidence that huge masses of hot, upwelling material exist beneath the surface. In varying stages of upwelling, there can be bulges, domes, shields, fractures and even collapses, complete with lava dams and rivers of runny lava that can flow up to 4000 miles across the surface and down into the lowlands. Flowing lava, usually about 2000° F, is still chilled in the intense heat by the dense atmosphere, which enhances the cooling power even at 900° F.

Venus has clusters of pancake domes with steep sides that are formed by thick lava unlike any on Earth and far larger, being up to 40 miles across. Coronae are another volcanic feature unique to Venus. These are surrounded by a concentric ring of ridges and fractures usually surrounded by a trough complete with a mound or sometimes a depression if the magma chamber collapses. All coronae appear to be caused by upwelling of hot material from below, but perhaps pushing up into a thinner crust that has an easier tendency to buckle and wrinkle. Some coronae suffer landslides that have scalloped the outer flanks that give them the appearance of spiders, ticks, and anemones when seen from above with radar.

All six Soviet Venera Landers 9-14 determined that the surface is basalt, which is a common volcanic material. The paucity of craters indicates that the surface of Venus might be quite new, possibly created by a massive global eruption of volcanic overturning that wiped out the older craters perhaps as recent as 600 million years ago (the age of the Solar System is about 4.5 billion years old).

The view from the surface of Venus would be spectacular if it were not for the hellish conditions. In spite of the fierce heat which would otherwise cause landforms to slump, the lack of water in the rocks gives them strength and rigidity. This makes Venus a world of steep-sided cliffs, towering mountains, and deep canyons, even though nearly 70% of the planet is considered gently rolling uplands.

It is hard to imagine Venus being any hotter than it already is, but during periods of intense volcanic activity, such as was suspected around 600 million years ago, the increase in carbon and sulfur dioxide from the volcanic gases may have increased the surface temperature to as high as 1200° F. At that temperature the ground would glow dull reddish even more than it does today and would alter the atmosphere. The clouds and haze would clear and the Sun would blaze down upon the fiery landscape. At night the stars would sparkle above the vast field of red-glowing rocks and the Milky Way might actually be visible in areas where ground glow is not too intense. Anyone looking at Venus from Earth would, for a brief time, see the bare surface before it cooled back down below 1000° F and clouded over again. Venus is truly a world born of fire, evolved by fire, shaped by fire, and ultimately, as the Sun dies and swells up, to die by fire.