(Bill Yenne, "The Atlas of the Solar System," Brompton Books Corp., Greenwich, 1987, p. 33.)
* Venus was spoken of by the Greek poet Homer and the Romans who named it for their goddess of beauty, Venus.
* It was the Astronometer Giovanni Cassini (1625-1712) who sketched the first known drawing of Venus' surface features in 1667. Of course these features would quickly change as he was only seeing clouds which moved.
* In the early 1900s most astronomers believed Venus' surface features were obscured by cloud cover.
* Mariner 2 passed within 21,600 miles of Venus in December of 1962 and discovered much about Venus' atmosphere and the planet's surface temperature.
(Bevan M. French and Stephen P. Maran, eds., "A Meeting with the Universe," NASA EP-177, U.S. Government Printing Office, 1981.)
* Venus ground-based radar measurements in the early and mid-1960s showed that the rotation period of Venus is about 240 days and that the rotation is retrograde, so that it spins in the opposite sense with respect to the Earth.
* The 1962 flyby of Venus by Mariner 2 led to an accurate determination of the planet's mass. This spacecraft, and ground-based observations, also measured high temperatures, around 300° C, in the atmosphere of Venus.
* Ground-based observations detected various minor components of the Venus atmosphere, including the gases hydrochloric and hydrofluoric acid (1967), carbon monoxide (1968), water (1972), and sulfuric acid (1978). In 1973, it was found that the upper cloud layer is composed of sulfuric acid droplets.
* From the USSR's Venera 7 in 1970, it was found that the atmosphere is largely carbon dioxide, with a pressure at the planetary surface about 100 times that of the Earth's atmosphere. Venera 7 also measured a surface temperature of about 500° C.
* Mariner 10 flew past Venus in 1974. Among the results were
* Venus has no significant magnetic field.
* A notable disturbance in the solar wind is produced as it flows past Venus.
* Venus is closer to a perfect sphere than the Earth.
* Ultraviolet images of the atmosphere revealed streamline and circulation patterns, including Y- and C-shaped structures.
* The upper atmosphere was found to rotate much more rapidly (once in about 4 Earth days) than Venus itself, a result also suggested by ground-based measurements.
* Hydrogen and helium were detected in the atmosphere.
*In 1975, the Venera 9 and 10 lander spacecraft found that the surface of the planet is firm and rocky. Their other results included
* The measured surface winds had velocities of about 3 to 13 kilometers per hour (2 to 8 miles per hour).
* A significant amount of sunlight reaches the surface.
* The surface rocks vary in radioactivity and have compositions resembling those of granite and basalt.
* The 1978 Pioneer Venus mission included both atmospheric probes and an orbiting spacecraft. Among the results were
* The atmosphere was found to circulate in large planetwide systems, much simpler than the circulation patterns on the Earth.
* A collar of polar clouds was discovered, which may be part of a large atmospheric circulation vortex.
* At least four distinct cloud and haze layers were found at different altitudes.
* The haze layers contain small aerosol particles, perhaps sulfuric acid droplets.
* Accurate measurements of the atmospheric composition showed that it was about 96 percent carbon dioxide, 4 percent nitrogen, with small amounts of water, oxygen, and sulfur compounds. Rare gases such as argon and neon detected in the atmosphere suggest that Venus is richer in volatile elements than the Earth or Mars.
* The surface of Venus was found to be generally smooth, much less irregular than that of the Earth.
* Radar measurements from the Pioneer Venus Orbiter and from ground-based observatories revealed the presence of two broad plateaus as well as apparent volcanic structures, craters, and canyons.
*Lightning and thunder are present on Venus, according to results from the Venera 11 and 12 1anders in 1978.
(The following is from "The Solar System" NASA/ASEP, 1989, p. 3.)
* Venus is the Roman goddess of love and beauty.
* This is the second planet from the Sun.
* Venus is covered by clouds.
* These clouds move three times faster than hurricane winds.
* These clouds move east and west.
* Venus' surface temperature is 900° F.
* The atmospheric pressure of Venus is 97 times that of Earth.
* Venus' upper clouds contain sulfuric acid.
* Because Venus rotates "backward," the Sun rises in the West.
* Venus' orbit is near circular.
* There is evidence of two major activity volcanic areas on Venus' surface.
* The concentration of lightning over the volcanic regions suggests frequent volcanic activity.
* Venus has nickel-iron core.
* No magnetic field is found on Venus.
* Venus circles the Sun every 224.7 Earth days.
* One Venus day would equal 243 Earth days.
* Venus' gravity is .91 of Earth's gravity.
* The diameter of Venus is 7,502 miles.
* Venus probably had seas at one time.
* There have been 17 space missions to Venus‹12 Russian and 5 American.
(NASA, Jet Propulsion Laboratory, "Our Solar System at a Glance," NASA Information Summaries, PMS 010-A (JPL), June 1991.)
Veiled by dense cloud cover, Venus, our nearest planetary neighbor, was the first planet to be explored. The Mariner 2 spacecraft, launched on August 27, 1962, was the first of more than a dozen successful American and Soviet missions to study the mysterious planet. As spacecraft flew by or orbited Venus, plunged into the atmosphere or gently landed on Venus' surface, romantic myths and speculations about our neighbor were laid to rest.
On December 14, 1962, Mariner 2 passed within 34,839 kilometers (21,648 miles) of Venus and became the first spacecraft to scan another planet; on-board instruments measured Venus for 42 minutes. Mariner 5 launched in June 1967, flew much closer to the planet. Passing within 4,094 kilometers (2,544 miles) of Venus on the second American flyby, Mariner 5's instruments measured the planet's magnetic field, ionosphere, radiation belts and temperatures. On its way to Mercury, Mariner 10 flew by Venus and transmitted ultraviolet pictures to Earth showing cloud circulation patterns in the Venusian atmosphere.
In the spring and summer of 1978, two spacecraft were launched to further unravel the mysteries of Venus. On December 4 of the same year, one of these travelers‹the Pioneer Venus Orbiter‹became the first spacecraft placed in orbit around the planet.
Five days later, the five separate components making up the second spacecraft‹the Pioneer Venus Multiprobe‹entered the Venusian atmosphere at different locations above the planet. The four small, independent probes and the main body radioed atmospheric data back to Earth during their descent toward the surface. Although designed to examine the atmosphere, one of the probes survived its impact with the surface and continued to transmit data for another hour.
Venus resembles Earth in size, physical composition and density more closely than any other known planet. However, spacecraft have discovered significant differences as well. For example, Venus' rotation (east to west) is retrograde (backward) compared to the west-to-east spin of Earth and most of the other planets.
Approximately 96.5 percent of Venus' atmosphere (95 times as dense as Earth's) is carbon dioxide. The principal constituent of Earth's atmosphere is nitrogen. Venus' atmosphere acts like a greenhouse, permitting solar radiation to reach the surface but trapping the heat that would ordinarily be radiated back into space. As a result, the planet's average surface temperature is 482 degrees Celsius (900 degrees Fahrenheit), hot enough to melt lead.
A radio altimeter on the Pioneer Venus Orbiter provided the first means of seeing through the planet's dense cloud cover and determining surface features over almost the entire planet. NASA's Magellan spacecraft, launched on May 5, 1989, has orbited Venus since August 10, 1990. The spacecraft uses radar-mapping techniques to provide ultrahigh-resolution images of the surface.
Magellan has revealed a landscape dominated by volcanic features, faults and impact craters. Huge areas of the surface show evidence of multiple periods of lava flooding with flows lying on top of previous ones. An elevated region named Ishtar Terra is a lava-filled basin as large as the United States. At one end of this plateau sits Maxwell Montes, a mountain the size of Mount Everest. Scarring the mountain's flank is a 100-kilometer (62-mile) wide, 2.5-kilometer (1.5-mile) deep impact crater named Cleopatra. (Almost all features on Venus are named for women; Maxwell Montes, Alpha Regio and Beta Regio are the exceptions.) Craters survive on Venus for perhaps 400 million years because there is no water and very little wind erosion.
Extensive fault-line networks cover the planet, probably the result of the same crustal flexing that produces plate tectonics on Earth. But on Venus the surface temperature is sufficient to weaken the rock, which cracks just about everywhere, preventing the formation of major plates and large earthquake faults like the San Andreas Fault in California.
Venus' predominant weather pattern is a high-altitude, high-speed circulation of clouds that contain sulfuric acid.