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Veiled Venus

October 8, 2014

While visible markings were apparent on Mars when viewed through better quality telescopes, Venus was always a mystery. The thick atmosphere of Venus cloaked its surface features. It wasn't until the emergence of radar imaging, first from Earth, then later by orbiting spacecraft, that the topography of Venus was revealed.

Statue of the Roman goddess, VenusVenus Unveiled

Venus should be the goddess of wardrobe malfunction.

The Roman goddess, Diana, who was the goddess of the hunt, was often described as being nuda genu; that is, bare at the knee. That's because she wore a short skirt that wouldn't impede her movements. Venus, however, as the goddess of love, was not adverse to going full monty.

This might be the reason why Venus is depicted so often in art.

(Vénus genitrix, photo by Gautier Poupeau, Paris, France, via Wikimedia Commons.)

Before that time, science fiction authors wrote about a hot and humid Venus, somewhat like Earth in its Carboniferous period. The scientific justification for this came from no less than a Nobel laureate. As Svante Arrhenius, who was awarded the 1903 Nobel Prize in Chemistry, wrote in "The Destinies of the Stars,"

"A very great part of the surface of Venus is no doubt covered with swamps, corresponding to those on the Earth in which the coal deposits were formed, except that they are about 30 C (54° F.) warmer."[1]

That idea became untenable in 1922 when astronomers showed that the spectroscopic signatures of water and oxygen were absent in the atmosphere of Venus.[2] Speculation then morphed Venus into a dry, desert planet. Further research showed that the atmosphere of Venus is quite a bit different from Earth's. The atmosphere is mostly carbon dioxide (96.5%) and nitrogen (3.5%), with a considerable quantity of sulfur dioxide (150 ppm). The surface pressure is 93 bar; that is, nearly a hundred times that of the Earth. The surface temperature is about 450°C.

As they say, a picture is worth a thousand words, and the Soviet Venera 9 spacecraft landed on Venus in 1975 and survived long enough to transmit back to Earth the first image of the surface of Venus (see figure). This was the first image returned from the surface of another planet.

Processed Venera 9 image, Copyright 2003, Don P. Mitchell
The Venera 9 image of the surface of Venus. The location of the lander was at 32° S, 291° E, and the image was taken with the Sun near zenith on October 22, 1975. (Processed Venera 9 image, used with the permission of Don P. Mitchell. Copyright 2003, Don P. Mitchell, all rights reserved.)

Since the atmosphere of Venus prevents optical mapping of its surface features, there have been several spacecraft sent to Venus with radar mapping capability. In 1978, the Pioneer Venus Orbiter, also known as Pioneer 12, arrived at Venus for mapping with a 20 Watt S-band (1.757 GHz) radar capable of resolving 23 x 7 kilometer patches of the planet. This spacecraft provided useful data through 1992.

The Soviet Venera 15 and Venera 16 spacecraft reached Venus within a day of each other in 1983. These spacecraft were equipped with synthetic aperture radar, and they imaged about 25% of the surface in eight months of operation. As technology advanced, so did the radar mapping capability of spacecraft. 1989 saw the launch of the very successful Magellan mission to Venus.

Magellan was unconventionally launched from a Space Shuttle with an assist from an Inertial Upper Stage booster. The spacecraft used aerobraking (a technique dramatically depicted in the film, 2010: The Year We Make Contact) to circularize its Venus orbit. The Magellan synthetic aperture radar produced a very complete mapping of Venus, as shown in the figure.

Full globe radar map of Venus by the Magellan spacecraft
Full globe radar map of Venus by the Magellan spacecraft. The colors are not the colors of Venus; rather, they are a color representation of altitude. (Via Wikimedia Commons.)

Computer image processing has allowed some spectacular representations of some Venus surface features, such as Maat Mons, the highest volcano and the second highest mountain, as shown in the figure. This mountain (mons) is named after Maat, the Egyptian Goddess of truth and justice.

Venus, Maat Mons, 3D perspectiveMaat Mons, the highest volcano and the second highest mountain on Venus, shown from processed radar data.

The vertical scale in this representation has been exaggerated by a factor of ten.

(Via Wikimedia Commons.)

Research on the atmosphere of Venus continues, and data from the European Space Agency Venus Express may have explained mysterious holes found decades ago in its nightside ionosphere. Analysis by NASA scientists at the Goddard Space Flight Center reveals that the Sun's magnetic field lines may be penetrating into the crust of Venus, as the location of the holes indicates.[3-5] Says NASA scientist and research team leader, Glyn Collinson,
"This work all started with a mystery from 1978... When Pioneer Venus Orbiter moved into orbit around Venus, it noticed something very, very weird – a hole in the planet's ionosphere. It was a region where the density just dropped out, and no one has seen another one of these things for 30 years."[3]
The solar wind, when it reaches Venus, creates a plasma and a thin magnetosphere, much smaller than Earth's. The structure of this magnetosphere is apparently responsible for the creation of two long cylinders of low density material on the side of the planet away from the Sun (see figure). Says Collinson, "The lines go right through down to the planet's surface and some ways into the planet."[3]

Figure caption
Trailing plasma holes in the solar wind behind Venus. (Still image from a YouTube video by NASA's Goddard Space Flight Center/G. Duberstein.)[4]

References:

  1. Svante Arrhenius, "The Destinies of the Stars," Joens Elias Fries, Translator, G.P. Putnam's Sons, New York & London, 1918, pp. 251f.
  2. Chas E. St. John and Seth B. Nicholson, "The Physical Constituents of the Atmosphere of Venus," Phys. Rev., vol. 19 (April 1, 1922), pp. 444ff.
  3. Karen C. Fox, "NASA Research Helps Unravel Mysteries Of The Venusian Atmosphere," NASA Goddard Space Flight Center Press Release, September 11, 2014.
  4. The Mysterious Holes in the Atmosphere on Venus, NASA YouTube video, September 11, 2014. Available for download, here.
  5. ESA Venus Express website .

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