Venus Express Plunging Into The Atmosphere

Credit: ESA

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.

This video includes interviews in English with Håkan Svedhem, ESA mission scientist and Patrick Martin, ESA Venus Express mission manager

“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.”

SEPARATED AT BIRTH?

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.

Credit: ESA/VIRTIS-VenusX IASF-INAF, Observatoire de Paris (R.Hueso, Univ. Bilbao)

Today, the total amount of water on Earth is100 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.

Meanwhile, the spacecraft’s cameras have tracked thousands of features in the cloud tops some70 km above the planet’s surface, including an enormous swirling vortex at the planet’s south pole that shares similarities with hurricanes on Earth. The spacecraft also recorded bursts of lightning – identified by their electromagnetic signature – generated in clouds of sulphuric acid.

  Credit: ESA/AOES medialab

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.

Magellan’s radar survey of the planet revealed that its surface was heavily altered in the past by a large number of volcanoes. But Venus Express has provided tantalising hints that the planet may well be still geologically active today. One study found numerous lava flows that must have been created no more than 2.5 million years ago, just yesterday on geological timescales, and perhaps much more recently.

Indeed, measurements of sulphur dioxide in the upper atmosphere have shown large variations over the course of the mission. Although peculiarities in the atmospheric circulation may produce a similar result, it is the most convincing argument to date of present-day active volcanism.

FINAL SWANSONG

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.

Venus Express aerobraking.

Credit: ESA – C. Carreau

“We have performed previous short ‘aerodrag’ campaigns where we’ve skimmed the thin upper layers of the atmosphere at about 165 km, but we want to go deeper, perhaps as deep as 130 km, maybe even lower,” says Patrick Martin, Venus Express mission manager.

“It is only by carrying out daring operations like these that we can gain new insights, not only about usually inaccessible regions of the planet’s atmosphere, but also how the spacecraft and its components respond to such a hostile environment.”

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