NEW YORK — Evidence of recently active volcano hotspots on Venus like those that created the Hawaiian Islands has been found in new observations by a European spacecraft.
These relatively young and potentially active surface features could give scientists clues to how the planet has resurfaced over the last billion years, which in turn could help them better understand the interior dynamics of Venus, as well as climate change on Earth’s nearest neighbor and on Earth itself.
The hotspots on Venus’ surface were first recognized by NASA’s Magellan spacecraft, which entered into orbit around the planet in 1990. These hotspots stood out because they had a distinctive rise in topography, volcanic centers and telltale gravity signatures.
The sites were the most likely candidates for recent volcanic activity on the surface of Venus — the question of whether or not Venus’ surface is geologically active has been a major one in studies of the planet — but just how young the features were was unclear.
“We were getting warm there, but not actually hot,” said Suzanne Smrekar of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and a member of the team that analyzed the new observations by Venus Express, a probe launched by the European Space Agency (ESA) in 2005.
An instrument aboard Venus Express, ESA’s first probe to Venus, mapped thermal emissions from the southern hemisphere of Venus, which indicate differences in the composition of the surface. Unusually high emissions patterns were seen around the only three of nine known hotspots that Venus Express could image: Imdr, Themis and Dione Regiones.
Surface regions that are old would be expected to have low emissivity patterns because of long exposure to weathering from Venus’ harsh atmosphere.
So the high emissivity of these hotspots and the evidence from Magellan “all point to the fact that these are recent [volcanic lava] flows,” Smrekar said.
Exactly how young the features are is hard to pin down because of limited information about the environment at Venus’ surface and the composition of its lower atmosphere, but Smrekar and her colleagues estimate that the lava flows are younger than 2.5 million years old, possibly even as young as a few hundred to tens of thousands of years old.
To pin down the age of the flows would likely take a lander to the venusian surface, last visited by the Soviet Venera probes in the early 1980s, to get better measurements of conditions there.
The young age of the hotspots has implications for understanding how Venus might have been resurfaced.
Magellan data showed that the surface of Venus had few craters. Since it is known that the solar system has undergone periods of heavy bombardment that are still visible on ancient unchanged surfaces, such as that of Earth’s Moon, the evidence suggested that Venus had been resurfaced since then.
One possible cause of the resurfacing is a catastrophic event that would have buried the planet’s surface under about 1.6 kilometers of lava, perhaps triggered by unknown, exotic interior processes unlike those that operate within the Earth.
Another explanation is a more gradual, small-scale process that would imply that volcanism was still happening today and that Venus had an interior more like Earth’s, though Venus would still lack Earth’s surface-reshaping plate tectonics.
The estimated young age of the hotspots suggests that the latter is the case on Venus and that the planet “doesn’t have to have had this exotic resurfacing event,” Smrekar said.
A volcanic eruption was put forward as a possible explanation to a strange bright spot seen in the atmosphere of Venus last year. Smrekar and several of her colleagues are following up on this event to see if a volcanic eruption from one of these hotspots coincides with the spot and could feasibly explain it. If it does and can, then that link could be even more evidence that Venus’ volcanoes are still active.
“We’re kind of going from warm, warmer, warmest to maybe really hot,” Smrekar said.
Determining whether Venus is still active and what kind of processes govern its interior could also help scientists better understand what kinds of planets might be orbiting other stars.
“It’s a great laboratory for understanding terrestrial planets,” Smrekar said. “What’s really the anomaly [among these planets] — is it Venus, or is it the Earth?”
Understanding the processes at work on Venus, in particular volcanic eruptions, can also help scientists better understand climate change, both on Venus and on Earth, Smrekar said. Volcanoes spew gases that can change the composition of the atmosphere and affect the amount of sunlight that hits a planet’s surface, she said.
The new observations are detailed in the April 8 issue of the journal Science.
