Spacecraft Eyes Venus for Active Volcanoes

Venus may harbor active volcanoes that produce the high amounts of sulfur dioxide in its atmosphere.

Scientists debate whether the sulfur dioxide detected by the European Space Agency's Venus Express comes from recent volcanic eruptions, or simply lingers on from eruptions that happened as far back as 10 million years ago.

?Volcanoes are a key part of a climate system,? said Fred Taylor, a Venus Express scientist from Oxford University.

Sulfur compounds don't stay long in Earth's atmosphere because they eventually react with the planetary surface, but they may take longer to react with surface rocks on Venus.

Venus Express used spectroscopy to analyze how the Venusian atmosphere absorbs starlight and sunlight, which indicates the type of atoms and molecules in the atmosphere. The spacecraft watched as the sulfur dioxide in the upper atmosphere dropped by two-thirds over several days.

?I am very skeptical about the volcanic hypothesis,? said Jean-Loup Bertaux, a Venus Express principal investigator from the French Aeronomy Service. ?However, I must admit that we don?t understand yet why there is so much SO2 [sulfur dioxide] at high altitudes, where it should be destroyed rapidly by solar light, and why it is varying so wildly.?

That dramatic change in sulfur dioxide levels was smaller in the lower atmosphere, where Venus Express gauged sulfur dioxide levels by how much infrared radiation that they absorbed. A stronger infrared signature seen by VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) means more sulfur dioxide.

"With VIRTIS, we monitor sulfur dioxide at an altitude of 35-40 kilometers (21-24 miles), and we have seen no change larger than forty percent on a global scale over the last two years,? said Giuseppe Piccioni, VIRTIS co-principal investigator in Rome.

Scientists hope they can confirm or disprove active volcanoes on Venus, either by looking for local plumes of gas rising from volcanoes or finding hot spots on the surface that suggest fresh lava flows. That only adds up to more work ahead for Venus Express.

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