A sharply defined cloud front on Venus, stretching about 6,000 kilometers across, has puzzled planetary scientists since Japan’s Akatsuki spacecraft spotted it sweeping around the planet’s equator. The feature looked too large, too persistent, and too strange to fit neatly into existing models of Venusian weather. Now a team that included the University of Tokyo says it has pinned down the cause: the largest known hydraulic jump in the solar system. That phrase may sound exotic, but the basic effect is familiar. It happens when a fast, shallow flow suddenly slows and deepens. In a kitchen sink, you can watch water spread thinly from the faucet before it abruptly thickens into a raised ring. On Venus, researchers say, something similar happens in the atmosphere. However, it occurs on a planetary scale and inside a world wrapped in sulfuric acid clouds. “We identified the phenomena, but for years we couldn’t understand it,” said Professor Takeshi Imamura of the University of Tokyo’s Graduate School of Frontier Sciences. “However, thanks to this research, we’re now able to show …