Ultraviolet image of Venus’ clouds as seen by the Pioneer Venus Orbiter (NASA)
That’s Venus, popping out at you after sunset. It’s the single brilliant star lowish in the west as twilight deepens. You can’t miss it. And in case you do, it’ll stick around, right there, the rest of the year. It hovers to the right of the crescent Moon on Thursday and Friday, July 11 and 12.
You probably already know that this nearest world to Earth is covered with shiny overcast clouds that brilliantly reflect the Sun. That’s what makes it the brightest “star” in the heavens. Maybe you also know that it’s the slowest-spinning object in the known universe. It barely rotates at all. One Venus day lasts as long as 243 of ours. You could walk faster than it spins.
And yet, for reasons no one understands, its winds are ferocious. The Venus atmosphere – a choking, unbreatheable blend of carbon dioxide with suspended droplets of sulfuric acid – sizzle at 850 degrees Fahrenheit. It has the hottest surface of any planet. Yet its superheated air races completely around that planet in just four Earth days: twice as fast as tornadoes blow. But why?
Even more bizarre, Venusian winds have been steadily growing faster. We know this because the Venus Express spacecraft, orbiting that world, has carefully monitored features in its cloud tops (some 44 miles above the surface) for the past six Earth years. Russian astronomers meticulously tracked more than 45,000 features by hand, and another 350,000 features automatically, using a computer program. In a separate simultaneous effort, a Japanese research group used an automated cloud-tracking method. All the results agree: When the spacecraft arrived there in 2006, the average wind speeds above the middle half of Venus enveloping its Equator – the equivalent latitude swath of Newfoundland to Argentina’s Patagonia – were a screaming category-5 hurricane, 186 miles per hour. These bewilderingly high winds have only grown since then. Nowadays they average 249 miles per hour.
Planetary astronomers are at a complete loss as to why this is happening. Håkan Svedhem, a European Space Agency Venus Express project scientist said, “The atmospheric super-rotation of Venus is one of the great unexplained mysteries of the solar system.” One more reason to pay it a look, the next clear evening during twilight.