Video

This false-color animation shows the movement of the atmosphere over the southern hemisphere of Venus over a period of one Earth-week. The images, taken by the European Space Agency’s Venus Express spacecraft, show blue areas as coldest; yellow, warmest.

ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA

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Great quantities of positively charged hydrogen and oxygen ions are escaping the turbid atmosphere of Venus into space, a finding that might help explain how the planet may have lost an ancient body of water.

R. Hueso, Grupo de Ciencias Planetarias, Univ. del País Vasco, Spain

Oxygen Glow This false-color image, taken by the European Space Agency’s Venus Express spacecraft, shows patterns of oxygen atoms released by photodissociation of CO₂ in Venus’ upper atmosphere during the daytime (left). The atmospheric currents shuttle the atoms to the night side of the planet, where they combine to form O₂, generating an infrared airglow (right).

This discovery is just one in a slew of results from the European Space Agency’s Venus Express spacecraft that were announced at a press conference in Paris on Nov. 28. The results are also published in nine papers in the same issue of Nature (2007, 450, 629, 633, 637, 641, 646, 650, 654, 657, and 661).

With similar mass and density and about the same amount of CO₂ as Earth, Venus is in many ways Earth’s twin. But whereas Earth’s CO₂ is sequestered in its crust, most of Venus’ CO₂ is in the atmosphere. And whereas Earth is covered in oceans, Venus is dry as a bone—an uninhabitable place with surface temperatures of about 450°C and a wild, turbulent atmosphere with pressure 100 times that of Earth. Scientists believe the two planets started out similarly but aren’t sure why they ended up being so different.

Numerous spacecraft have explored Venus, starting with the U.S.’s Mariner 2 in 1962. The last mission dedicated to the study of Venus was NASA’s Magellan, which ended in 1994. Venus Express was launched two years ago, and its suite of instruments has been mapping the planet in unprecedented detail since last April.

“We’ve come back to a new era in Venus research,” Håkan Svedhem, a Venus Express Project scientist, said at the news conference.

Venus Express has sent back detailed measurements of H⁺, O⁺, and He⁺ escaping Venus’ atmosphere. O⁺ is escaping at half the rate of H⁺, suggesting that this is a way Venus may be losing water. The planet may have lost oceans’ worth of water over billions of years.

The spacecraft also has traced the transport of oxygen and other species around the planet. On the day side of Venus, the dissociation of CO₂ produces atomic oxygen; the turbulent atmospheric currents then shuttle oxygen atoms to the planet’s night side, where they recombine to form O₂ and generate an infrared glow.

In addition, Venus Express sent back the first confirmation of lightning on Venus. Lightning, which produces ozone and nitrogen oxides on Earth, undoubtedly also affects the chemistry of the Venutian atmosphere, a fact that will have to be included in future atmospheric models of the planet, noted Venus Express Interdisciplinary Scientist David Grinspoon.

“The next pictures [of Venus’ atmosphere] in textbooks will have to have a lightning flash,” Grinspoon said.