Venus is sometimes called Earth's twin, as it is roughly the same size as Earth, occupies the orbital lane adjacent to ours, and has a problem with greenhouse gases (namely carbon dioxide) in its atmosphere. Yet the similarities between the two worlds end quickly: The greenhouse effect spiraled out of control on Venus, meaning it is a toasty 900 degrees Fahrenheit at the surface — hot enough to melt lead. Beyond carbon dioxide, its atmosphere is, unlike Earth's, filled with churning yellow clouds composed of malodorous sulfuric acid. And its geology is very, very weird compared to our planet's: while Earth's surface is comprised of continental "plates" that slowly drift across the crust over millions of years, Venus has no plate tectonics and a completely different geology.
One of Venus' lingering geologic mysteries involves the innumerable volcanoes which pepper the planet's surface. Astronomers and planetary scientists were unsure if and how many were active, and what their relationship was to the planet's evolution. This is particularly a mystery because in other ways, Venus is so similar to Earth, even on the inside. Hence, the notion that it would have such alien geology seems peculiar indeed.
Now, thanks to a recent study in the journal Science Magazine, astronomers are closer to answering their burning questions about Venus' evolution. After analyzing eight months worth of images of the Venusian surface as captured by the Magellan spacecraft in the early 1990s, researchers from the University of Alaska Fairbanks and the California Institute of Technology found changes which they believe reveal ongoing volcanic activity — meaning the planet could join the small club of solar system bodies with active volcanoes, which currently counts only two members (Earth and Io).
"The upcoming missions are going to provide radar images that will be much more equivalent to seeing the big island of Hawaii erupting as you fly over in an airplane."
What the researchers found specifically wasn't quite a smoking gun — nor a smoldering, lava-spewing one — but rather a volcanic vent that is roughly 2.2 square kilometers. During the eight-month observation period, that vent changed shape, suggesting active volcanism.
Similarly, researchers discovered volcanic flows downhill from that vent which were visible in later images, although these may have been present before and were simply missed.
Regardless, the potential implications of the new study are massive.
"I think all planetary scientists agreed that Venus is still volcanically active in the sense that we knew future eruptions would occur, but we did not know whether the times between eruptions, or when the next eruption would be, was going to be months, years, decades, or thousands of years, all of which would have been acceptable with the data we had before," explained Dr. Robert Herrick, a study co-author who works the University of Alaska Fairbanks' Geophysical Institute, in an email to Salon.
Herrick noted that it is theoretically possible (though unlikely) that this is the only active volcanic activity to occur on Venus in millions of years, and that they therefore coincidentally happened to capture an image of during it during an eight-month span three decades ago. Herrick added that he feels this is unlikely.
"Realistically seeing a volcano change after searching a small fraction of the planet over an eight-month period means that eruptions probably occur every handful of months or so," Herrick argued.
Dr. Scott Hensley, who works at the Jet Propulsion Laboratory at the California Institute of Technology and also co-authored the study, elaborated that this revelation about likely volcanic activity raises many provocative questions. For one thing, astronomers have long speculated about how rocky planets evolve; in Earth's case, the surface breaks out into mountains and other landmarks based on ever-shifting masses beneath our feet known as tectonic plates. The tensions between these plates as they move to and fro causes everything from earthquakes to volcanic eruptions to the slow reshaping of continents.
Yet Venus, unlike Earth, does not have plate tectonics, so Hensley and other scientists want to know how its surface evolved, and whether its geologic evolution is unusual among rocky planets — or, perhaps, if Earth is the weird world. Hensley offered the possibility that Venus' behavior could be due to "episodic volcanism where periods of intense activity, and interspersed with periods of dormancy whereas another has steady rate of volcanism." This theory suggests that Venus undergoes a cycle in which it is relatively calm for millions of years, followed by sudden, planet-wide volcanic activity that resurfaces much of the planet.
Herrick shed further light on how active volcanoes might exist without plate tectonics. He added that because planet formation produces heat and radioactive elements (which, in turn, supply a long-term heat source), planets themselves are actually much hotter than outer space.
"Volcanism, and plate tectonics on Earth, is literally bringing hot material up to the surface and cooling it off," Herrick explained. "Smaller planetary bodies generally cool more quickly than large ones (sort of like a cup of soup cools more quickly than a large pot of soup), so the smaller bodies like the moon have had volcanism in the past even though they had no plate tectonics."
Taking off the hat of jargon-citing scientist for a moment, Herrick seemed compelled to the elaborate on the "coolness factor" of the upcoming Venus-based missions.
"The change we see is a change that is a couple of miles in scale, but Magellan resolution only gives us several dozen fuzzy pixels to see it," Herrick gushed. "The upcoming missions are going to provide radar images that will be much more equivalent to seeing the big island of Hawaii erupting as you fly over in an airplane."
These upcoming missions, known as VERITAS and EnVision, "will almost certainly map many new examples of activity on Venus and thus enabling us to understand how Earth and Venus evolved so differently," Henley told Salon. Yet even if those missions prove to be a wash, one thing is indisputable thanks to the new analysis of the Magellan images: In Henley's own words, "Our research has shown Venus is volcanically active today and is not in dormant state. Thus Venus joins Earth and Io as being volcanically active rocky bodies in our solar system."
In other words, the volcanism club has expanded its membership roll.
