Scientists Reveal Mysteries on the Night Side of VenusPopular Mechanics
Jay Bennett September 15, 2017
Photo credit: NASA/JPLVenus is a strange world. About as inhospitable as can be-with temperatures pushing 900 degrees Fahrenheit, sulphuric acid rains, and surface pressures equivalent to the depths of Earth's oceans-Venus is unique in the solar system for another reason as well. A day on Venus is longer than a year on Venus, as the planet takes about 225 days to orbit the sun and 243 days to rotate on its axis. Earth's sister planet also rotates in the opposite direction of its orbit around the sun, the only planet in the solar system to do so.
As a result, one half of Venus receives an enormous amount of sunlight before it finally rotates over to the night side. A team of international scientists using data from the European Space Agency's Venus Express spacecraft recently discovered that there are large discrepancies between the daytime and nighttime sides of Venus. The night side was documented in detail for the very first time, and cloud structures and atmospheric conditions were seen on the night side that had never been spotted before.
"While the atmospheric circulation on the planet's dayside has been extensively explored, there was still much to discover about the night side," said Javier Peralta of the Japan Aerospace Exploration Agency (JAXA), and lead author of the
study recently published in the journal Nature Astronomy. "We found that the cloud patterns there are different to those on the dayside, and influenced by Venus' topography."
Although the planet Venus rotates at a snail's pace, strong winds in the high Venusian atmosphere blow at speeds up to 60 times faster than the surface of the planet below, a phenomenon known as "super-rotation." The clouds of Venus are carried by these intense winds, traveling fastest in the high reaches of the atmosphere at an altitude of 65 to 72 km (213,00 to 236,000 feet).
Photo credit: ESA/JAXA/J. Peralta and R. HuesoThe night side of Venus has been notoriously difficult to observe. "We focused on the night side because it had been poorly explored; we can see the upper clouds on the planet's night side via their thermal emission, but it's been difficult to observe them properly because the contrast in our infrared images was too low to pick up enough detail," said Peralta. Hundreds of infrared images in different wavelengths were taken with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on Venus Express, allowing researches to resolve the clouds on the night side of Venus for the first time.
Previous models of Venus suggested the planet's super-rotation occurs on the night and day sides in a uniform way. However, the new study found that the night side of Venus has its own distinct cloud formations and morphologies. Wavy filaments of cloud were spotted that are not found on the day side of the planet, and mysterious upwelling movement was documented in the night-side atmosphere, apparently independent of the atmospheric movement of Venus, known as stationary waves.
Photo credit: ESA/S. Naito/R. Hueso/J. Peralta"Stationary waves are probably what we'd call gravity waves–in other words, rising waves generated lower in Venus' atmosphere that appear not to move with the planet's rotation," said co-author Agustin Sánchez-Lavega of University del País Vasco in Bilbao, Spain. "These waves are concentrated over steep, mountainous areas of Venus; this suggests that the planet's topography is affecting what happens way up above in the clouds."
These mysterious stationary waves were modeled in 3D using VIRTIS data as well as radio data from the Venus Radio Science experiment (VeRa) on Venus Express. The phenomenon was thought to be the result of winds passing over topographic features on the surface, a process that has been documented on the day side of Venus. However, past Russian landers on the planet briefly measured wind speeds that might not be strong enough to be the source. What's more, the southern hemisphere of the planet, where Venus Express took the readings, is devoid of significant surface features.
Ever more baffling is the fact that the stationary waves are absent in the middle and lower cloud levels of Venus, not appearing until roughly 50 km above the surface (164,000 feet). Where these waves of upwelling energy come from, researchers still don't know for sure.
"It was an exciting moment when we realised that some of the cloud features in the VIRTIS images didn't move along with the atmosphere," said Peralta. "We had a long debate about whether the results were real–until we realized that another team, led by co-author Dr. Kouyama, had also independently discovered stationary clouds on the night side using NASA's Infrared Telescope Facility (IRTF) in Hawaii. Our findings were confirmed when JAXA's Akatsuki spacecraft was inserted into orbit around Venus and immediately spotted the biggest stationary wave ever observed in the Solar System on Venus' dayside."
These stationary waves, and the general behavior of the atmosphere on the night side of Venus, have planetary scientists tossing old models of Venus out the window and going back to the drawing board. "Our models of Venus remain unable to reproduce this super-rotation, which clearly indicates that we might be missing some pieces of this puzzle," said Peralta.
Source:
ESAhttps://www.yahoo.com/news/scientists-reveal-mysteries-night-side-173706834.html
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