Astronomy

The Reasons it is so Difficult to Land Probes on the Surface of Venus



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Venus presents many barriers to remote artificial exploration, not least among them its hellish temperature gradients and its opaque atmosphere filled with acid.  Data from short-lived probes that have landed there reveal that even metal machines find survival difficult on volcanic landscapes tortured into nightmarish, jumbled heaps of irregular size and shape.


The planet Venus is known to many laymen for its brightness in the early morning skies.  Since it is the second planet from the Sun, it will frequently be spotted in close proximity to that radiant body just before sunrise on Earth, the third planet from the Sun.  It is also called the Morning Star, since its brilliance can be seen with the naked eye.


It has been said that beauty is only skin deep.  Perhaps a scientist will see this beauty despite the following descriptions; there is little chance that the interest in hard-to-get Venus will wane.


Atmospheric opacity


The atmosphere of Venus is chemically active.  It is filled with aerosol droplets of sulfuric acid, lending enough optical opacity to block visual inspection of anything deeper than its uppermost layers.  In addition, more than 96 percent of the atmosphere is carbon dioxide, and this contributes to the runaway greenhouse effect that keeps the planet’s surface hotter than any desert on Earth.


Burning-hot temperatures


The surface temperature on Venus is very hot, hovering near the melting point of lead.  Much of the surface is covered with active volcanoes or pockmarked by the remains of old ones.  Lava flows cover much of the remaining surface of the planet.  “The entire planet was resurfaced by volcanic flows between 300 and 500 million years ago.”


Air pressure extremes


Atmospheric pressure at the surface of Venus approaches 92 times that measured on Earth, that is, more than 1,250 pounds per square inch.


The Soviet Venera 4 probe landed uncomfortably on this inhospitable planet.  Unfortunately, its batteries were exhausted by the heat of the atmosphere during its long descent to the ground.  To make matters more difficult for mission controllers, two other probes almost reached the ground, but were crushed at about 20 kilometers height. 


Unfriendly alien topography


Space agencies prefer to have some idea of the surface topography before they send half-billion-dollar craft to land on it.  The Venusian atmosphere works against them in this respect, since optical inspection is impossible.  It is possible that radar mapping could reveal those few possible landing areas, away from the corona structures that also appear on Venus – “ringlike structures that range from roughly 95 to 360 miles (155 to 580 kilometers) wide.”  There are other barriers to smooth landings by anything less than an intelligent pilot or a very capable artificial intelligence:  tesserae, “raised areas in which many ridges and valleys have formed in different directions.”

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