Why Did Venus Turn Inside Out?
Venus is unmistakable in our sky. Never straying terribly far from the Sun, it blazes brilliantly either in the evening or morning. But along with its brilliance, Venus hides a secret.
Size comparison of Venus with Earth
Many inner planets and moons preserve a great record of ancient impacts from objects that struck them in the early history of the Solar System, right on down to the present. But planetary scientists have found that Venus underwent a colossal resurfacing event, a volcanic cataclysm, some three-quarters of a billion y ears ago.
This means that most of the craters and other surface features we find on Venus are relatively young. But what could have caused such a huge, relatively recent global resurfacing? As on planetary scientist put it, “We are in the unenviable place of having to explain a planet that inexplicably threw up all over itself!”
For as yet unknown reasons, Venus seems to have stored enormous amounts of energy deep inside for a long time after the planet’s formation. Scientists know that the better part of a billion years ago, a huge amount of this banked energy was released. But no one yet knows what triggered this event or why it happened exactly when it did.
Instabilities deep within Venus conspired –through physical evolution, the laws of physics, and interplay between countless atoms—to let loose and re-cover our “sister planet” in a large way.
 David J. Eicher, from Astronomy