Astronomers studied the dark side of Venus—the side that experiences long nights—for the first time at a detailed global scale. What they found was surprising.
The clouds of Venus [Image by NASA]
Venus is perhaps one of the strangest planets in our solar system. For one thing, it has no natural satellites. It rotates in the opposite direction to most of our neighboring planets. It also has the longest rotation period of all the planets in the solar system. The planet spins once every 243 Earth days, with days and nights lasting that long. In fact, a single day on Venus lasts longer than an entire Venusian year. Earth and Venus are sometimes called “sister planets” because they are similar in size, mass, and composition, but in most other ways, Venus is worlds apart from Earth.
Scientists haven't studied the night side of Venus all that much. Recently, however, they found out that Venus's swirling clouds and mighty winds are much more chaotic when night falls.
A model of how clouds move as Venus rotates [Image by ESA/JAXA/J. Peralta and R. Hueso]
"While the atmospheric circulation on the planet's day side has been extensively explored, there was still much to discover about the night side," said Javier Peralta lead author of the study on the dark side of Venus.
However, scientists have been having a very difficult time observing the night side of the planet. This is because the infrared images don't have enough contrast to provide much detail that indicate what goes on when night falls on Venus. Thus, researchers took hundreds of photographs in varying wavelengths with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS). As a result, the researchers were able to study nighttime Venusian clouds in detail for the first time.
According to the findings, the night side has its own cloud formations distinct from those on the day side. Researchers found wavy cloud filaments on the night side, as well as a phenomenon called stationary waves. These stationary waves appeared as a strange upwelling in the atmosphere. The researchers said that stationary waves are clouds that formed lower in the atmosphere and did not appear to move along with the planet's rotation.
Of course, as is almost always the case with scientific research, these answers brought up even more questions.
Stationary waves [Image by ESA, S. Naito, R. Hueso and J. Peralta]
Researchers created 3D models of the waves with the data from VIRTIS as well as data from the Venus Radio Science experiment (VeRa). Initially, the researchers thought that the waves were winds that pass over the topographical features on Venus's surface. However, previous findings show that the winds may not be strong enough to produce the waves. There are also no significant topographical features on the southern hemisphere of the planet.
Even more strangely, the waves don't appear in the lower and middle cloud regions of Venus. They appear quite high up, at about 50 kilometers from the surface. Taking all this information into account, the researchers aren't actually sure what's causing the waves.
This discovery is quite significant. As of now, it's making scientists reevaluate what they know about our sister planet. Peralta says that they're “missing some pieces of this puzzle”, but they may be able to find those pieces with more examinations of the dark side of Venus.
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