Astronomers observed other weird artifacts on the planet’s surface, in addition to many substantial volcanoes that suggest an active geology in the recent past. These include coronae (crown-shaped surface features), tesserae (crunched features where the planet’s crust is pushed together and buckles), and arachnoids (circular or oval features filled with concentric rings) — so named because they are spider-like in appearance. Moreover, scientists found trace signs of erosion and tectonic shifts on our sister planet.
As scientists looked more carefully at the body of data returned from Magellan, it became clearer that this was a planet that had, somehow, turned itself inside out. Dating various features on the planet’s surface subsequently revealed Venus must have undergone a cataclysmic upheaval about 750 million years ago, very recently in geologic terms. At about that time, Venus’ surface seems to have been completely wiped clean.
Planetary scientists believe strongly in the gradual, slow, methodical workings of nature. Venus’ geology placed them in an awkward position because a huge catastrophic event apparently attacked the planet suddenly.
Nonetheless, in 1992, Gerald Schaber of the U.S. Geological Survey wrote that what was observed on the planet may have resulted from a “global resurfacing event or events.” Don Turcotte of Cornell University followed a year later, proposing the venusian crust may have grown so thick over time that it trapped the planet’s heat inside, which eventually flooded the planet with molten lava. Turcotte described the process as cyclical, suggesting that the event of several hundred million years ago may have been just one in a series.
Others have suggested that low-level volcanism may be responsible for coating the planet’s surface over time without a need for any global catastrophes. The European Venus Express spacecraft, which orbited the planet between 2006 and 2014, found the best evidence to date that Venus has been volcanically active in the recent geological past. “All the geologists agree,” says Schaber, “something very strange happened.” However scientists still have work to do before they can pinpoint the exact mechanisms that caused Venus to undergo a makeover.