Looking Up – Bob Eklund

Venus_southern_hemisphere_mediumAfter eight years in orbit, the European Space Agency’s Venus Express has completed routine science observations and is preparing for a daring plunge into the planet’s hostile atmosphere.

Venus Express was launched on a Soyuz-Fregat from the Russian Baikonur Cosmodrome in Kazakhstan on 9 November 2005, and arrived at Venus on 11 April 2006.

It has been orbiting Venus in an elliptical 24-hour loop that takes it from a distant 66,000 km over the south pole—affording incredible global views—to an altitude of around 250 km above the surface at the north pole, close to the top of the planet’s atmosphere.

With a suite of seven instruments, the spacecraft has provided a comprehensive study of the ionosphere, atmosphere and surface of Venus.

“Venus Express has taught us just how variable the planet is on all timescales and, furthermore, has given us clues as to how it might have changed since its formation 4.6 billion years ago,” says Håkan Svedhem, ESA’s project scientist. “This information is helping us decipher how Earth and Venus came to lead such dramatically different lives, but we’ve also noticed that there are some fundamental similarities.”

Venus has a surface temperature of over 450°C, far hotter than a normal kitchen oven, and an extremely dense, choking mixture of noxious gases for an atmosphere. But from the mission’s infrared survey of the chemical composition of the rocky surface, we have learned that Venus might have once had a plate tectonics system like Earth, and even an ocean of water.

Just like Earth, Venus is losing parts of its upper atmosphere to space and Venus Express measured twice as many hydrogen atoms escaping out of the atmosphere than oxygen. Because water is made of two hydrogen atoms and one oxygen atom, the observed escape indicates that water is being broken up in the atmosphere.

Today, the total amount of water on Earth is 100,000 times that on Venus. But because the two planets are about the same size and formed at the same time, both may have had similar amounts of the precious liquid in their early years.

Studies of the planet’s ‘super-rotating’ atmosphere—it whips around the planet in just four Earth-days, much faster than the 243 days the planet takes to complete one rotation about its axis—also turned up some intriguing surprises. In one study, average wind speeds were found to have increased from roughly 300 km/h to 400 km/h over a period of six Earth years.

Conversely, a separate study found that the rotation of the planet had slowed by 6.5 minutes since NASA’s Magellan, which completed its 5-year mission at Venus 20 years ago, measured it.

However, it remains unknown if there is a relationship between the increasing wind speeds and the slowing rotation.

Now, after eight years in orbit, the fuel supplies necessary to maintain the elliptical orbit are running low and will soon be exhausted. Thus, routine science operations concluded this week, and the spacecraft is being prepared for one final mission: to make a controlled plunge deeper into the atmosphere than ever before attempted.

 

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