For the first time, a huge, bow-shaped wave was seen in the Venusian atmosphere’s highest regions, another source of wonder for astronomers and fresh insights into what lies below.
The planet is enveloped in a thick cloud layer, stretching some 40 miles above the surface. The atmosphere shields Venus from view and makes it difficult to understand it. However, an image captured by the Japan Aerospace Exploration Agency caught the mysterious structure when the Akatsuki spacecraft arrived there in December 2015.
Through infrared and ultraviolet imaging, the team found a prominent curved wave in the upper atmosphere, where winds blow in excess of 200 miles per hour, and any feature in the vicinity should easily get carried along. The wave, however, remained firmly planted and lasted for at least four days.
Gravity Waves?
The wave is described to cover over 6,000 miles, stretching almost from pole to pole and accompanied by a bit warmer air in the upper atmosphere of Venus some 40 miles above the surface. It is fairly common to find such a huge feature, but it is practically unheard of for it to not move.
The atmosphere on the planet is in super-rotation, which means it outpaces the planet itself. Compare this to Earth, where winds move only up to 20 percent the speed of the planet.
This led researchers, discussing their findings in the journal Nature Geoscience, to deem the massive structure a result of “gravity waves,” which are a phenomenon in a planetary atmosphere caused by winds that collide with features on the surface. Note, however, that these are not the elusive gravitational waves or distortions in space-time that are likely produced by the most extreme events, such as the collision of black holes or two huge celestial bodies.
In Venus, the mountainous characteristics on the surface are potentially forcing winds into the upper atmosphere, a place where they slow down to form a persistent wave. The bulge is in fact located above the continent-sized highland region called Aphrodite Terra.
Astounding Size And Immobility
The bow wave disappeared a month later when researchers revisited the mission, but scientists have previously observed gravity waves in the same upper atmosphere, where the Venus Express of ESA discovered similar cloud shapes over the Ishtar Terra in 2014. This wave, however, is far more humungous than those ones.
“But because Venus Express had a different orbit where it got lots of images of the poles but not of the low latitudes, it never saw a feature like this,” said atmospheric scientist Colin Wilson, who worked on Venus Express data, in a Christian Science Monitor interview. “It never got these beautiful images which this Japanese spacecraft has now revealed.”
For Makoto Taguchi, a coauthor of the recent Japanese paper, these Y-shaped structures sometimes resembling a bow are always spotted and imaged, but all move with the background westward wind.
"This is the first evidence of gravity wave propagation from the lower atmosphere to the middle atmosphere,” Taguchi said, explaining that lower atmospheric conditions may impact the higher atmosphere’s dynamics “by momentum transfer” of such waves.
Given these findings, scientists can potentially prove the lower and middle Venusian atmosphere through a look at the cloud tops — a piece of the puzzle that is Venus and its thick atmosphere.
The Japanese orbiter was expected to enter the planet’s orbit back in December 2010, but glitches involving one of its thrusters led it to orbit the sun for five years before finally entering the planet’s orbit. The spacecraft has started beaming data to JAXA.
