Hot lava flows suggest volcanoes are active on Venus
Sen—Volcanoes appear still to be active on the surface of Earth’s neighbouring planet Venus, space scientists have discovered.
Results from the European Space Agency’s now defunct Venus Express suggest that hot spots on the Venusian terrain are due to fresh flows of lava from volcanic eruptions.
Because Venus is permanently shrouded by dense clouds, Venus Express was unable to image these eruptions directly, so the evidence has come from the spacecraft’s Venus Monitoring Camera (VMC) which mapped thermal emission—or heat—from the surface.
Observing through a near-infrared, transparent spectral window in the planet’s atmosphere, the VMC allowed an international team of planetary scientists to spot localised changes in surface brightness over just a few days.
Venus’s surface is thought to be relatively young, laid down by a flood of lava around 500 million years ago. NASA’s Magellan spacecraft used radar to map this surface in the early 1990s, and revealed that it was covered with volcanoes, but no one could tell whether they were active or not.
Then Venus Express made readings, reported in 2010, that showed infrared radiation from three volcanic regions was different from surrounding areas, leading scientists to conclude that it was due to lava flows that were less that 2.5 million years old.
Another piece of the jigsaw came in 2012 when it was shown that there had been a sharp rise in the sulphur dioxide content of Venus’s upper atmosphere in 2006 and 2007, followed by a gradual fall. This provided more clues that active volcanoes might be injecting vast amounts of the gas into the air.
The latest findings were made by a team led by Eugene Shalygin from the Max Planck Institute for Solar System Research (MPS) in Germany. The team found emission from what seem to be flows of hot lava along along a rift zone, or fracture in the surface crust, called Ganiki Chasma, close to the volcanoes Ozza Mons and Maat Mons. It is thought an upwelling of magma below the crust can bring hot material through the fractures to the surface.
A radar map of the Venusian volcano Ozza Mons, shown in red at the centre, is surrounded by thousands of kilometers of rift zones, coloured in purple. Data from Venus Express spacecraft suggests there are active lava flows in hotspots along the rifts. Image credit: Ivanov/Head/Dickson/Brown University
The Ganiki Chasma had already been considered to be one of Venus’s most recently geologically active regions, and now it appears it is still active today. One of the hotspots, known as Object A, is calculated to be only about one square kilometer in size. Venus’s average surface temperature is known to be 480° C, or more than twice the maximum in a domestic oven, but Object A showed a temperature of 830° C.
Shalygin, whose findings are published in the journal Geophysical Research Letters, said in a statement: “We have now seen several events where a spot on the surface suddenly gets much hotter, and then cools down again. These four ‘hotspots’ are located in what are known from radar imagery to be tectonic rift zones, but this is the first time we have detected that they are hot and changing in temperature from day to day. It is the most tantalising evidence yet for active volcanism.”
Geologist James W Head, of Brown University, at Providence, Rhode Island, who was part of the team, said in a statement: “We knew that Ganiki Chasma was the result of volcanism that had occurred fairly recently in geological terms, but we didn't know if it formed yesterday or was a billion years old. The active anomalies detected by Venus Express fall exactly where we had mapped these relatively young deposits and suggest ongoing activity.”
Venus Express Science Operations Co-ordinator Colin Wilson, of the University of Oxford, told Sen: “It is really exciting because we’ve known for the last 20 years that Venus is covered with volcanoes, thanks to the Magellan radar map, but no one knew whether they were active or dormant. We always suspected that Venus’s surface is relatively young, but now this new result actually suggests that the volcanoes are active today on Venus.
“This raises a whole new question of how unusual is the Earth’s volcanism and tectonism? If we find it on Earth and our nearest Earth-sized planet then does that mean that all Earth-sized planets are likely to have active volcanism and tectonism?”
So how many volcanoes might be active on Venus? Wilson told us: “It is a very good question, but for the current study, they concentrated their search on the flanks of known volcanoes. They found not just one hotspot, but a number which change temperature in this one system of rift zones. Clearly the next stage would be to try to do more statistical research to see how prevalent this is.”
He added: “It is almost magical that we can see the surface of Venus at all because of its thick layers of cloud. But there are wavelengths where we can see thermal emissions from the surface and measure the surface temperature. Very much central to the goals of Venus Express was to try to exploit these wavelength windows to look at the surface.”
Venus Express's eight-year mission ended in December, 2014, after its fuel ran out, contact was lost and it began descending into the planet's atmosphere.