The readings were taken over a few days in December 2015, shortly after the orbiter arrived at Earth’s sister planet. The Japan Aerospace Exploration Agency (JAXA) scientists behind the discovery believe an “atmospheric gravity wave” caused the bow-shaped distortion.
Gravity waves happen when a fluid or gas is disturbed from its balanced state — or equilibrium — by external forces. In this case, the stationary wave was likely caused by wind pushing clouds in the lower atmosphere over a mountain range, the researchers reported. (Winds blast clouds around Venus at approximately 225 miles per hour.) The “wave” shape formed as gravity tugged at and settled the clouds back into their original equilibrium east of the mountains.
On Earth, a similar windy effect creates ocean waves at the beach and occurs with clouds on mountain ranges as well — though not to the gigantic extent as seen on Venus.
While the high winds and turbulent conditions of the planet’s upper atmosphere have been well documented, the lower atmosphere is less understood. Missions to the surface of Venus, such as the Soviet Venera probes, were only able to withstand the high pressure for an hour. The researchers propose that the huge wave started in the lower atmosphere and propagated to the upper clouds, where Akatsuki recorded it.
The findings suggest that the Venusian atmosphere is far more complex than previously thought. The researchers found that temperatures within the bow were much higher than outside. The team is uncertain whether this atmospheric feature is common or if it is unique to this set of Venusian mountains.
Akatsuki launched in 2010 from Tanegashima Space Center in Japan and is currently the only satellite orbiting Venus. The last orbiter, the European Space Agency’s Venus Express, ended its mission and fell gently into the planet in early 2015.