Something strange is going on in the atmosphere of Venus, where what looks like a massive wave was spotted among the planet's clouds. The Japanese Akatsuki spacecraft in orbit around our neighbor observed the baffling bow-shaped bright region stretching for 10,000 km (6,214 miles) across the tops of the clouds.

The discovery is surprising because the upper atmosphere of Venus is thick, with fast-moving clouds of sulfuric acid that speed by at 100 meters per second (328 feet per second) while the surface below rotates at a crawl – a day on Venus actually takes longer than a trip around the sun on the planet.

The orbiter observed the structure for several days before it disappeared, during which time it remained essentially fixed in place despite the speedy clouds surrounding it.

"We suggest that the bow-shaped structure is the result of an atmospheric gravity wave generated in the lower atmosphere by mountain topography that then propagated upwards," writes Makoto Taguchi of Tokyo's Rikkyo University and colleagues in a paper on the phenomenon published in the most recent issue of Nature Geoscience.

The researchers report that computer models support the idea of a vast mountain range basically creating a continent-spanning, stationary gravity wave. They also say that the center of the bow seems to be situated above a massive highland known as Aphrodite Terra.

Just to be clear, we're talking about waves caused by gravity similar to what we see on Earth in our own oceans or when mountains push streams of air upward, and not to be confused with gravitational waves, the recently verified ripples in space time that validated Einstein's theory of general relativity.

The big wave on top of Venus' clouds doesn't quite jive with what scientists presume it must be like near the planet's surface though, leading Taguchi's team to suggest that winds in the lower atmosphere may be much more variable than previously thought.

"Although smaller scale gravity waves have been seen near to ground level on Venus before, the scale of this new feature seems to be extremely large, probably the largest in the solar system," writes University College London physics professor Andrew Coates, who did not participate in the research, in The Conversation.

Coates also points out that Venus was once believed to support life underneath dense, water-rich clouds before the space age. Now that we're finally getting a closer look at our neighbor, it appears there's still plenty more to learn.

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