January 17, 2017

Giant gravity wave seen in Venus atmosphere– What’s going on?

Shortly after coming into orbit around Venus in December 2015, the Japanese Akatsuki orbiter took a picture of an odd-looking phenomenon in the planet's atmosphere: a gravity wave in the upper cloud layer.

Quite common here on Earth, gravity waves are created when an atmosphere or body of water is disrupted, like when a tide washes over a sandbar. As gravity works to bring back equilibrium to the fluid, it overshoots, resulting in a wave effect.

venus gravity wave

Brightness temperature and UV brightness of the Venus disc. (Credit: Planet-C)

According to a new study on the bow-shaped wave recently published in the journal Nature Geoscience, the wave was imaged in the infrared and ultraviolet parts of the electromagnetic spectrum. The study team said that the structure extended 10,000 km (6,200 miles) through the planet’s atmosphere and lasted for a several days before disappearing.

"Over several days of observation, the bow-shaped structure remained relatively fixed in position above the highland on the slowly rotating surface, despite the background atmospheric super-rotation,” the study authors wrote in their report. “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."

Wave Caused From Surface Discrepancy

The gravity wave appears to have been caused by the contrast between Venus' rapidly spinning atmosphere and its more-slowly spinning terrain below. Of particular interest is a high area known as Aphrodite Terra, which is up to more than 3 miles high and the size of Africa near the equator. The structure juts into the quickly moving winds at the cloud level. This is a bit like water flowing over a stone in a stream.

While smaller scale gravity waves have been spotted close to ground level on Venus before, the size of this new feature appears to be quite large, most likely the biggest in the solar system, the study team said. It had been unclear if it is even possible for gravity waves to trigger such a massive effect.

The discovery shows that, while we can learn things about the thick, fast-moving upper atmosphere of Venus, it seems that low-altitude atmospheric mechanics are not fully comprehended yet. However, the planet's secrets are slowly being revealed in waves.


Image credit: JAXA