Venus: Hellish planet belies lovely name
By Amanda Jermyn

Venus, our closest planetary neighbor, is about the same size as Earth and has roughly the same gravity. Like Earth it is a rocky, or terrestrial planet, but that is about where the resemblance ends. While Venus is named for the Roman goddess of love, there is nothing romantic about conditions on this planet. With an average temperature of 863 degrees Fahrenheit it is by far the hottest planet in the entire Solar System, despite being nearly twice as far from the Sun as Mercury, which averages only 332 degrees F. Venus has the densest atmosphere of the four terrestrial planets, consisting of 95.5% carbon dioxide and 3.5% nitrogen, with atmospheric pressure on its surface about 92 times that of Earth. This hellish planet is covered by opaque clouds of sulfuric acid. It has many more volcanoes than Earth, and is thought to be currently volcanically active.

However, conditions on Venus were not always like this. Billions of years ago it was cooler and had a more Earth-like atmosphere, possibly with large amounts of liquid water on its surface. As gases accumulated in the atmosphere, its temperature rose, causing a runaway greenhouse effect, and vaporizing any water on the planet. With greenhouse gases currently raising temperatures on Earth, this should serve as a cautionary tale.

Venus has many other odd features. It orbits the Sun every 224.7 Earth days. However, one day on Venus (one rotation on its axis) lasts 243 Earth days, so its day is longer than its year! Also, Venus orbits the Sun in the opposite direction from all the other planets, and rotates on its axis in the opposite direction from most other planets. So to an observer on Venus, the Sun would rise in the west and set in the east. Unlike Earth, Venus has no moon, no plate tectonics, and only a minimal magnetic field, so it has almost no protection from cosmic radiation. Temperatures on Venus donít vary much between night and day, nor between the equator and the poles. The clouds of sulfuric acid covering the planet reflect about 90% of sunlight back into space, so the area beneath the cloud is dimly lit.

From here on Earth, Venus appears brighter than any star in the night sky and is bright enough to be seen with the unaided eye in a clear sky during the day. However, exploring the planet in detail close up has proved far more difficult as its thick cloud cover cannot be penetrated by visible light, and the intense heat and high pressure at its surface present a challenge for spacecraft attempting to land there. Beginning in the early 1960ís the Soviet Venera and US Mariner programs sent a series of probes to Venus, some more successful than others. While Earth-based radar gleaned some basic information about its surface, radar measurements from spacecraft have provided far greater detail. The United States Magellan probe, launched in 1989, mapped over 98% of the surface of Venus, obtaining high-resolution radar images comparable to photographs taken of other planets in visible light. Currently, the European Space Agencyís Venus Express probe is orbiting Venus, studying its atmosphere, clouds, surface characteristics and temperature. It discovered a huge double atmospheric vortex, or large-scale hurricane, at the planetís south pole.

In August of this year NASAís Geoffrey Landis announced plans to put a wind- and solar-powered rover on the surface of Venus. Named Zephyr, for one of the Greek wind gods, the rover would be powered by a 23-foot tall sail covered in solar cells so that any electric power could be used for the radio and scientific instruments. It has been designed to withstand Venusís high temperatures, crushing pressures and corrosive atmosphere. Landis envisions the rover spending a month on Venus, traveling about 15 minutes a day. While Zephyr wouldnít be the first rover to land on Venus it would be the first to last longer than two hours, the record so far for survival in this hostile environment.

Despite the challenges of successfully landing and maintaining a rover on Venus, with so many unanswered questions, the potential rewards are huge. What caused the planetís dense atmosphere? Were conditions ever right for life to take root? Shrouded in clouds and mystery, Venus keeps her secrets close.

While there is no public Stars Club meeting in December, please watch out for next yearís exciting line-up of talks and events.