Volcanic double-whammy says Venus still spews

Venus’s namesake may be the goddess of love, but the planet looks more angry than passionate. Two studies that reveal recently solidified lava and what appears to be the largest volcano in the solar system raise the possibility that huge fiery outpourings could still happen there today.

Many planetary scientists had thought Venus was geologically dead, making the Earth the only rocky planet with active volcanism.

Suzanne Smrekar of NASA’s Jet Propulsion Laboratory in Pasadena, California, and her colleagues have found signs of relatively recent volcanism by measuring the infrared “glow” of solidified lava.

Hot rocks

Since the Venusian surface is nearly 480 °C, it emits infrared radiation. Older volcanic rocks tend to emit less infrared, say the researchers, because carbon dioxide and sulphur dioxide in the planet’s atmosphere weather the rocks and change their composition.

Smrekar and colleagues used an instrument on the European Space Agency’s Venus Express spacecraft, which is in orbit around Venus, to monitor infrared radiation at a specific wavelength that penetrates the planet’s perpetual cloud cover.

They targeted three areas in Venus’s southern hemisphere that radar and gravity observations by NASA’s Magellan spacecraft in the 1990s suggested are “hotspot” volcanic deposits, like Hawaii: the Imdr, Themis and Dione regiones. They found all three areas are especially “bright” at the infrared wavelength that their instrument could see, which means the rocks there formed more recently.

In the act

Pinning down the exact age of the rocks is tricky, though. It is not clear how quickly the surface is weathered by the atmosphere of Venus. They are no more than 2.5 million years old, Smrekar says, but they could be as young as mere hundreds of years.

“I think this is way cool,” says Mark Bullock at the Southwest Research Institute in Boulder, Colorado, who was not involved in the study. The evidence for recent volcanism “changes our understanding in the sense that now we will probably start focusing on catching Venus in the act of erupting”. Such eruptions would affect the planet’s atmosphere, clouds and climate, he says.

Big mountain

In another study, which will appear in the May edition of Geology, a map based on radar observations by NASA’s Magellan spacecraft in the 1990s reveals that a previously known feature on Venus could actually be the largest known volcanic structure in the solar system.

Vicki Hansen of the University of Minnesota in Duluth re-analysed the area, which includes an oval tectonic feature called Artemis.

Earlier maps of Venus showed Artemis as a raised feature surrounded by a deep ringed trough, 2400 kilometres across in total.

Hansen and colleagues found evidence of lava and a volcanic structure extending well beyond the ring. “Wrinkle ridges” caused by the cooling and contraction of lava extend across an oval 13,000 kilometres wide. Radial fractures, associated with upwelling lava, span 12,000 kilometres.

The structure covers up to one-third of the planet’s surface. The researchers believe that makes Artemis the largest volcanic feature yet identified in the solar system. It may have been caused by “a plume with a much bigger effect on the surface than anyone had envisioned”, she says. “It’s so big it must have come from the core-mantle boundary.”

When the eruption occurred remains unknown, and the volcano is thought to be inactive today.

Journal reference: Science, DOI: 10.1126/science.1186785 (Smrekar et al); Geology, in press (Hansen et al)