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May 28, 2010 Vol. 3, Issue 5

 

The Pioneer Venus Orbiter mission, launched on May 20, 1978, is one of only a handful of missions to study Venus.

Global view of Venus created from composite data from Magellan, Pioneer, and Venera

Global view of Venus created from the composite data from Magellan, Pioneer, and Venera data. Credit: NASA

Scientists once thought Venus to be Earth’s twin, only slightly warmer, but early exploration missions showed otherwise. Venus is similar to Earth in size, mass, density, composition, and gravitational pull. However, a thick atmosphere consisting largely consisting of carbon dioxide surrounds Venus, making it impossible to observe the planet’s surface at visible wavelengths. The atmosphere traps the sun’s rays, generating surface temperatures of 880 degrees Fahrenheit (hot enough to melt lead) and pressures 90 times that of Earth. Scientists are hoping to better understand Earth’s greenhouse mechanism by studying this extreme effect on Venus.

The Venus Orbiter delivered a number of findings, including novel measurements of Venus’s gravitational field, more complete morphological and geological maps (e.g. volcanoes, valleys, and mountains), extensive atmospheric observations, and evidence of a strong greenhouse mechanism. The Orbiter also detected electrical signals indicative of lightning and the unexpected finding that Venus experiences ultraviolet emissions from oxygen in the atmosphere, better known as aurora borealis.

Fewer than three months after Orbiter launched, its sister spacecraft, the Pioneer Venus Multiprobe, embarked on its journey on August 9, 1978. Its mission goals were to relay data on climate, chemical makeup, and atmospheric conditions of the planet. The Multiprobe carried four probes called Sounder, North, Day and Night. The spacecraft bus functioned as the probe transporter and carried two science experiments.

To date, the United States has never landed on Venus. Russia has successfully accomplished this feat multiple times, beginning with Venera 7 in 1970. Lander missions are difficult, as the spacecrafts do not last more than a couple of hours due to the intense temperatures and pressures on the planet’s surface.

In early April this year, ESA’s Venus Express, which launched on November 9, 2005, returned data suggesting volcanic activity on the surface of Venus. If the data from Venus are confirmed, the planet would join the ranks of Earth and Jupiter’s moon Io as the only planets known to be geologically active in our solar system. On May 21, the Japanese Aerospace Exploration Agency (JAXA) is scheduled to launch the Venus Climate Orbiter Akatsuki, which will provide the most in-depth look at the planet’s atmosphere to date.

The Venus Orbiter, the twelfth of the Pioneer missions, was designed to last eight months, but extended its mission in excess of fourteen years. On October 8, 1992, the Orbiter entered the Venusian atmosphere after it ran out of fuel, and was destroyed upon atmospheric entry.

Read Pioneering Venus: A Planet Unveiled by Richard O. Fimmel, Lawrence Colin, and Eric Burgess.

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