The Venus Express spacecraft has found convincing evidence that Earth is not the only geologically active planet in the solar system.

Infrared emissions from lava flows on the surface of Venus indicate that they are relatively young, which means the planet may still be capable of volcanic eruptions.

"The solidified lava flows, which radiate heat from the surface, seem hardly weathered. So we can conclude that they are younger than 2.5 million years old – and the majority are probably younger than 250,000 years," Jörn Helbert of the DLR Institute of Planetary Research in Germany, co-author of a study published April 8 in Science, said in a press release. "In geological terms, this means that they are practically from the present day."

The results could explain why there are fewer asteroid impacts than expected on the planet's surface. Volcanism has been the prime suspect, because lava flows can fill in and obscure craters. But scientists were unsure whether a major episode of volcanic activity resurfaced much of the planet all at once in the past, or if intermittent activity has slowly filled in craters over time. The existence of a recent flow suggests the latter is more likely, and that volcanism may be ongoing.

Venus is shrouded in a thick cloud cover which obscures the visible light emissions form the surface. So a team led by Suzanne Smrekar of NASA's Jet Propulsion Laboratory studied the thermal emissions of the surface using the Visible and Infrared Thermal Imaging Spectrometer on the Venus Express orbiter. Older surfaces tend to be smoothed by weathering over time, while younger surfaces are more rough and have higher thermal emissions.

Several areas on the surface had been identified as potential volcanic centers by radar imagery data from the Magellan mission, which ended in 1994 when the spacecraft was intentionally crashed into the surface. Smrekar's team targeted three of these areas and found they had higher thermal emissions than the surrounding areas.

“Now we have strong evidence right at the surface for recent eruptions,” Smrekar said in a press release.

Because Venus is similar in size and internal structure to Earth, comparisons between the two planets can help scientists understand our own planet's evolution. If volcanism on Venus is also similar to Earth, as the new study indicates, that narrows the factors that could have sent the planets on such different paths that ended with Earth being habitable and Venus being bone dry and hellishly hot.

In order to determine what the young rock is made of, Helbert plans to build a lab that can heat various rock types to around 900 degrees Fahrenheit, the planet's surface temperature, and study their thermal emission signatures to compare to the Venus Express readings.

Images: 1) 3-D radar image of Maat Mons volcano./DLR. 2) Thermal emission signature of Venutian volcano. Red is higher emissivity./NASA/JPL/ESA.

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