An enormous, mysteriously stationary structure high over the surface of Venus may be the largest gravity wave in the Solar System, according to Japanese astronomers.
In 2015, cameras onboard the Japan Aerospace Exploration Agency (JAXA) spacecraft Akatsuki captured images of a humungous boomerang-shaped bulge measuring more than 10,000km (6,214mi) across the cloud-tops of Venus, at 65km (40mi) in altitude. Scientists have been studying the strange erection, which is just weirdly hanging there in the planet's atmosphere, and published their findings in Nature Geoscience this week.
We're told that huge features spotted over Venus's surface typically move slightly faster or slower than the alien world's remorseless wind. However, over several days of observation, the mystery structure hardly budges from its position as the planet’s fast-moving background winds billow by. Essentially, it remains in place, just floating way up high ominously covering nearly the diameter of Venus, despite the high-speed winds screaming past it.
While named after the goddess of love, Venus is no angel: its miserable hellscape is shrouded in thick sulphur dioxide clouds peppered with drops of sulphuric acid. Its upper atmosphere rotates faster than the planet, causing the clouds to shift westwards as they are blown away by a background wind that moves at approximately 100 metres per second (223 miles per hour).
Numerical simulations of Venus’s atmosphere, using observations from the Akatsuki craft, suggest that the bow-shaped structure may have resulted from a stationary gravity wave produced near the mountain ranges below the clouds, before it spread upwards. Exactly how the stationary wave is produced continues to baffle boffins, but it's believed the mountains are key.
“The formation and propagation of a mountain gravity wave, [however], remain difficult to reconcile with assumed near-surface conditions on Venus,” the researchers admit.
The Japanese probe's long-wave infrared camera detected the bow-shaped formation as an unusually warm shape between the high-temperature regions at the northern and southern poles.
Bow structures aren’t uncommon on Venus: previous sightings have been spotted in ultraviolet images, but they have always moved at the same speed of the planet’s surface winds and were not as large. Researchers hope to produce more detailed simulations to explore the idea of a stationary gravity wave.
“Since gravity waves transfer momentum, mountain-induced waves may be important for the climatology of Venus,” the team's paper states.
JAXA’s mission to study Venus was initially shaky. Akatsuki failed to enter the planet’s orbit in December 2010, and made a second successful orbital burn to get the spacecraft out of the Sun’s orbit and into Venus’s five years later. ®