Since Venus is the closest planet to Earth, it is very convenient to observe it. However, with all this, the "morning star" is fraught with a lot of mysteries. No, there’s definitely no life on it. Scientists are particularly interested in the rapidly rotating atmosphere of Venus. This is one of the unsolved mysteries of the solar system, which raises such strong winds in the atmosphere of Venus that one wind can fly around the planet in four days. Recent data from the Venus Express satellite has shown that winds are getting faster.
Being close to Earth in size, Venus is covered in a very dense poisonous atmosphere, rich in carbon dioxide. The surface of the planet is completely covered by a veil of soft yellowish clouds. Only ultraviolet waves (and to a lesser extent infrared waves) penetrate through the clouds, and even then they are lost in them due to an unknown ultraviolet absorber into the clouds. By tracking the movement of these clouds, observers were able to measure super-hurricane winds that circle above the surface of the planet, at about 70 km above the sultry volcanic plains.
Despite dozens of years of observations from Earth and onboard spacecraft, a number of secrets remain unsolved. What causes the incredible rotation of the atmosphere of Venus? Winds move 50 times faster than the planet itself rotates. How do winds change with latitude and longitude? How do they change over time?
Some of these questions are currently being answered with instruments on board Venus Express, such as the Venus Monitoring Camera (VMC), which has been monitoring the atmosphere for ten Venusian years, equivalent to six Earth years. VMC takes snapshots of Venus in the ultraviolet and near infrared ranges. Simultaneous visualization of these two ranges allows you to identify the features of clouds, and thus obtain data on winds at two different levels - 70 and 60 kilometers above the surface.
Venus Express orbits 24 hours, approaches approximately 250 km to the North Pole, and then moves 66,000 km to the South Pole. Such an elliptical trajectory provides good monitoring conditions for the entire southern hemisphere and allows you to take high-resolution images. These factors, coupled with VMC photographs, made it possible for the first time to draw up a detailed map of winds, with temperature and directions, over five years.
Recent analyzes of the movement of Venus clouds and wind speeds based on VMC data were made by two independent groups - one from Russia (under the leadership of Khatuntsev) and the Japanese team (Kouyama). Painstakingly measuring the movement of clouds from VMC images, the two groups revealed new patterns in the rotation of the planet.
“We analyzed images obtained during 127 orbital flights by manual observation and tracking, as well as 600 orbits by digital correlation,” said Igor Khatuntsev from the Space Research Institute in Moscow in an article in the journal Ikarus. “More than 45,000 functions were tracked through human visual comparisons and more than 350,000 functions were automatically observed using a computer program.”
A manual method of measuring wind speed is to track the movements of high-contrast clouds from several pictures taken at different times. This approach made it possible to compose better patterns of cloud movement and more accurate than those obtained by the digital method at middle and high latitudes, where clouds, as a rule, line up in rows or where there is low contrast. The only negative of this method is that it takes a lot of time.
On the other hand, the digital tracking technique is able to streamline image processing and produces 10 times more wind vectors. Both methods are good for studying low latitudes (below 40 degrees), but digital is preferred when studying flows at an average speed.
The Japanese-Swedish team relied solely on its automated tracking method, outputting data from several snapshots taken an hour apart at latitudes between 55 and 70. A specially developed mathematical formula was supposed to reduce the number of errors in image analysis. An analysis of this team was published in the journal Geophysical Research .
A detailed analysis made it possible to establish the average atmospheric circulation, long-term and diurnal trends, variations from orbit to orbit, and frequency.
At low latitudes of the middle zone (east-west), the wind moves at a speed of approximately 94 m / s (338 km / h) in a retrograde direction. (The surface of Venus and the atmosphere moves in a retrograde direction, i.e. clockwise from the north pole, in the opposite direction of motion of other planets). The zonal wind speed reaches a peak at 40-50 degrees S and reaches 102 m / s in mid-latitude flows. From 50 degrees towards the pole, the zonal wind sharply loses speed. This means that the winds of the upper cloud cover go around the planet at the equator in five days, and only three in mid-latitudes.
The average meridional wind (from the equator to the pole) slowly rises from zero at the equator to 10 m / s at 50 degrees S. At higher latitudes, the meridional wind gradually slows down, reaching zero speed when approaching the rapidly moving eye of a global vortex located at the pole.
Perhaps the biggest discovery is a constant increase in the upper bar of wind speed of the average cloud cover from 300 km / h to almost 400 km / h from 2006 to 2013.
“This is a huge increase in the already high speed of rotation of the atmosphere,” commented Igor Khatuntsev. “Such a wide scatter has never been seen on Venus before, and we don’t understand why it happened.”
Both works also showed that wind speed exhibits short-term and long-term fluctuations. This includes regular changes related to local time of day and the height of the sun above the horizon.
Other changes in wind speed are even more difficult to explain. According to some observations, the zonal wind slows down slowly from 100-110 m / s at the equator to less than 50 m / s in the polar region, while according to other observations, the wind speed was constant at 40 degrees S. with slight acceleration at 50 degrees.
“We detected a peak that occurs every 238 days, but it could be a mistake,” says Khatuntsev. “It can be associated with periods when the VMC could make observations on the day side of the planet.”
“Our analysis of the daily cloud speed, based on VMC imagery, showed that the average zonal speed constantly varies between 20 m / s every 255 days,” said Toru Kouyama of the Ibaraki Research Institute in Japan.
“These documents have increased the number of questions that we need to answer and which are related to the atmospheric super-rotation of Venus. This is one of the biggest inexplicable secrets of the solar system, ”said Hakan Sweden , a scientist at Venus Express. “Further studies of the spatial structure of the wind are necessary in order to explain what drives the atmospheric circulation pattern. Meanwhile, Venus Express continues to amaze us with its observations of this dynamic and ever-changing planet. ”
The first European mission to Venus began with the launch of Venus Express from the Baikonur Cosmodrome on November 9, 2005 at the Soyuz-Frigate launcher. The device entered the orbit of Venus on April 11, 2006. The payload of the satellite includes various spectrometers, spectrophotographic cameras and cameras taking images in the range from ultraviolet to thermal infrared; there is also a plasma analyzer and magnetometer on board.
Admire the gallery: 50 years of exploration of the solar system.
The article is based on materials .
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