Stationary waves of unknown origin are formed in the atmosphere of Venus at night. An international group of astronomers came to this conclusion after analyzing images of the Venus Express spacecraft and NASA's IRTF infrared telescope in Hawaii.
Venus rotates slower than all other planets of the solar system, so the night and day on it are long: the Venusian night lasts almost 60 Earth days. Its atmosphere rotates much faster than the planet itself: this phenomenon, known as super-rotation, is especially characteristic of the upper boundary of the layer of sulfuric acid clouds (65-70 km from the surface), where atmospheric masses sometimes move 60 times faster than the underlying points on the surface. For comparison: the speed of the strongest earthly winds is five times less than the rotation speed of our planet.
Until now, super-rotation has not been simulated. Astronomers led by Javier Peralta of the Japan Aerospace Agency suggested that this would require studying the movement of the atmosphere on the planet's night side; all previous global models assumed that at night the winds on Venus blow the same way as during the day.
Peralta's team combined images taken in 2015 with NASA's IRTF infrared telescope in Hawaii and the Venus Express spectrometer from 2006 to 2008, and identified three cloud shapes on the night side of the planet that are not typical of the day side: wavy, uneven with torn edges and long filamentous or fusiform. Individual cloud ridges stretched for three thousand kilometers. In addition, many stationary waves (also called gravitational, or hydrodynamic) waves were discovered on the dark side of Venus - atmospheric disturbances that do not move with the atmosphere, but remain stationary relative to the surface.
The arrows indicate cloud shapes unique to the Venusian night. / ESA, JAXA, J. Peralta and R. Hueso
Stationary waves were recorded on Venus earlier; it is believed that they form above high mountains and rise from the lower layers of the atmosphere upward. But, as Peralta and his colleagues show, at night, standing waves arise over the southern part of the planet, where there are no large differences in altitude. In addition, nighttime stationary waves on Venus exist only in the upper layers of clouds, at an altitude of more than 50 kilometers, which contradicts the hypothesis of their origin at the surface. The origin of the night standing waves on Venus remains unclear.
The study is published in the journal Nature Astronomy.
Ksenia Malysheva
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