Scientists from Rikkyo University in Tokyo have reported finding a huge structure in the atmosphere of Venus, using Japan’s Akatsuki spacecraft. The findings are published today in Nature Geoscience.
The mammoth structure is believed to be a stationary wave spread over a vast region, stretching for 10,000 kilometers (6,200 miles) in the cloud tops of Venus’ upper atmosphere. Interestingly, the wave did not move over several days, but instead remained stationary over a mountainous region on the planet’s surface.
The structure was visible in infrared images from Akatsuki taken between December 7 and 11, 2015. The spacecraft entered orbit around Venus on December 7, 2015, after a five-year hiatus when it failed to orbit in 2010. This observation was made, therefore, on the first day it entered orbit.
At the moment, the exact properties of the wave aren’t clear. But the most likely explanation is that this was some sort of wave generated as air flowed over a mountain nearby, from high to low temperature. This is more commonly known as a gravity wave (not to be confused with a gravitational wave), where two regions try to balance out in equilibrium – like how a wave propagates over an ocean.
“This is the first evidence of gravity wave propagation from the lower atmosphere to the middle atmosphere [of Venus],” Makoto Taguchi from Rikkyo University, one of the study’s authors, told IFLScience. He noted, though, that 15 other bow-shaped regions had been found before, but usually they move with the background wind on Venus; this region stayed stationary for four days.
Images taken over four days from Akatsuki showed the wave staying in roughly the same place. ©Planet-C
On Venus, a westerly wind blows up to 60 times faster than the planet’s rotation, reaching speeds of more than 360 kilometers per hour (225 miles per hour). So Taguchi said it was “surprising” that the wave managed to stay in the same position, suggesting the process may be similar to how a stone in a shallow river can prevent the smooth flow of water.
“There may exist a mechanism of gravity wave generation like a mountain wave or a thermal tide, which are found in the terrestrial atmosphere,” he said. “To answer this question we need more data that covers all local times and longitudes.”
Venus has an extremely thick atmosphere, which means it is difficult to directly see its surface or lower atmosphere. This observation suggests the lower atmosphere affects the upper atmosphere, though – so studying the latter could reveal secrets about the former.
As for Akatsuki, well, there’s plenty more to come. The spacecraft’s flagship infrared camera has been used to study the atmosphere in fine detail, while a second camera that can actually see the surface in infrared has been looking for active volcanoes. A third camera has begun searching for lightning on the planet, with results expected in the next few years.