Venus is roughly the same size, mass, and density as Earth. Therefore it must generate heat in its interior (by the decay of radioactive elements) at the same rate as that of the Earth. On Earth, one of the main ways this heat escapes is through volcanic eruptions. During an average year, at least 50 volcanoes erupt.
But despite decades of searching, we haven’t seen clear signs of volcanic eruptions on Venus — until now. A new study of the geophysicist Robert Herrick from the University of Alaska, Fairbanks, which he reported this week at the Planetary and Lunar Science Conference in Houston and Published in the journal Sciencehas finally caught one of the planet’s volcanoes in the act.
The surface of Venus is not easy to study because it has a dense atmosphere including an unbroken cloud layer at an altitude of 45-65 km that is opaque to most wavelengths of radiation, including visible light. The only way to get a detailed view of the Earth from above the clouds is with radar pointing down from an orbiting spacecraft.
A technique known as aperture superimposition is used to create an image of a surface. This combines the varying strength of the radar echo back from Earth — including the time delay between transmission and reception, as well as slight frequency shifts corresponding to whether the spacecraft is getting closer to or away from the origin of a particular echo. The resulting image looks somewhat like a black and white photograph, except that brighter areas usually correspond to rough surfaces, and darker areas to smoother surfaces.
NASA’s Magellan probe orbited Venus from August 1990 to October 1994 and used this type of radar technology to map the planet’s surface with a spatial resolution of about a hundred meters at best. It showed that more than 80 percent of the surface is covered in pyroclastic flows, but how the smallest of them erupted recently, and whether any eruptions continued today, remained a mystery over the next three decades.