Solar system mysteries: What happened to Venus?
By Mika McKinnon It may sometimes be called Earth’s twin, but the relationship between our home and its nearest planetary neighbour is more Jekyll and Hyde. “Early on we believe Venus had oceans and quite possibly life,” says David Grinspoon of the University of Denver in Colorado. That makes sense; Venus is the same size and composition as Earth, and gets roughly the same amount of sunlight. It is technically inside the solar system’s habitable zone where liquid water can exist. So how did it become so inhospitable? We are still not entirely sure. That seems odd, considering we have been sending probes to Venus since the dawn of the space age. But our attempts to peer at the planet have been thwarted by its opaque sulphuric acid clouds, impenetrable to early orbiters. Of the craft we have sent to investigate the surface, less than half survived the trip, the rest collapsing under the punishing pressures Venus’s atmosphere generates. The few survivors didn’t last long. Between them, they amassed less than a single day of ground observations. What they saw could have been painted by Salvador Dali: a dim, desolate wasteland pitted by endless sulphuric acid rain and scoured by syrupy winds whose speeds are dictated by the time – fast at dawn and dusk but slowing in the heat of the day. If the choking, largely carbon dioxide atmosphere doesn’t kill you, the heat – a lead-melting 460 °C – surely will. These scenes support the standard explanation for Venus’s predicament: