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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