A new theory to explain superrotation on Venus
One of the mysteries in our Solar System is superrotation, a phenomenon known since the late 1960s, in which the winds on Venus blow faster than the planet rotates. Scientists have proposed a number of theories, but none have been completely satisfactory. Now scientists in Mexico have for the first time suggested a viable mechanism by which a faster wind higher above the planet is driving the superrotation.
A complete rotation of the planet Venus takes 243 Earth days, but the atmosphere, traveling at speeds of around 200 m/s, takes only four Earth days to go all the way around. Scientists have been studying the supersonic-speed winds in the ionosphere 150-800 kilometers above the surface. The winds, known as the “transterminator” flow, travel at several kilometers per second and are thought to be driven by interaction with the solar wind.
The team propose that the transterminator flow in the cryosphere could transfer flow momentum to the atmosphere below in the form of pressure waves as they dissipate. The interaction on the night side between the flow on the dawn side and the flow on the dusk side generates waves because they flow at different speeds, with the dusk side flow being much faster.
The waves travel down from the ionosphere, and through the thermosphere and mesosphere to the troposphere depositing most of the momentum and dissipating in the cloud layer, moving the atmosphere in a retrograde direction and driving the superrotation. There is enough energy in the transterminator flow to overcome the viscosity and drive superrotation. The produce 84 dB on the night side, enough to maintain a roar in the clouds on the planet’s night side “similar to a symphony orchestra playing ‘fortissimo’.”
The Akatsuki extraterrestrial weather satellite, which was launched from Japan last Friday, should arrive at Venus in December, when it may shed some light on the issue.
Venus, Mercury, and Moon
Credit & Copyright: Pete Lawrence (Digital-Astronomy)
Explanation: Earlier this month, Venus and Mercury climbed into the western twilight, entertaining skygazers around planet Earth in a lovely conjunction of evening stars. Combining 8 images spanning April 4 through April 15, this composite tracks their progress through skies above Portsmouth, UK. Each individual image was captured at 19:50 UT. The sequential path for both bright planets begins low and to the left. But while Venus continues to swing away from the setting Sun, moving higher above the western horizon, Mercury first rises then falls. Its highest point is from the image taken on April 11. Of course on April 15, Venus and Mercury were joined by a young crescent Moon.
First Photos of Another Planet’s Surface: Venus
Photograph NSSDC/GSFC/NASA (via nationalgeographic.com)
“From June to October 1975, Russian space probe Venera 9 became the first craft to orbit, land on, and photograph Venus. Venera 9 consisted of two main parts that separated in orbit, an orbiter and a lander. The 5,070-pound (2,300-kilogram) orbiter relayed communication and photographed the planet in ultraviolet light. The lander entered the Venusian atmosphere using a series of parachutes and employed a special panoramic photometer to produce 180-degree panoramic photos of the surface of the planet.”
Vénus par Galileo
Voici 20 ans jour pour jour, la sonde américaine Galileo en route vers Jupiter survolait Vénus, s’en approchant au plus près à 16 000 km. La photo ci-dessus, qui détaille les épais nuages de ce monde surchauffé (400 °C à la surface !), a été prise quelques jours plus tard, le 14 février.
Crédit : NASA/JPL
Venus by Galileo
20 years ago to the day, the American probe Galileo flew past Venus, getting as close as 16,000 km, on its way to Jupiter. The above photograph, showing the thick clouds of this overheated world (400°C on its surface!), was taken a few days later on 14 February.
Galileo mission (NASA)
Direction Vénus et Halley
Le 15 décembre 1984, voici 25 ans jour pour jour, une fusée russe Proton envoyait dans l’espace la sonde Vega-1. En juin 1985, ce programme ambitieux déposa à la surface de Vénus un atterrisseur et déploya dans son atmosphère un ballon qui dériva au gré des vents. Un an plus tard, l’engin porteur passa à 8 890 km du noyau de la comète de Halley et participa ainsi à son observation avec la sonde européenne Giotto. Le 21 décembre, Vega-2 était lancée à son tour, accomplissant avec succès la même triple mission (atterrisseur sur Vénus, ballon dans l’atmosphère de cette planète et survol de la comète de Halley).
Crédit : DR
Les missions Vega-1 et 2 sur le site de Don P. Mitchell
Venus & Halley here we come
25 years ago today, on 15 December 1984, a Russian Proton rocket sent the Vega-1 probe into space. In June 1985, this ambitious programme landed a lander on the surface of Venus and released a balloon which was to drift at the mercy of the winds into its atmosphere. A year later, the carrier spacecraft passed the nucleus of Halley’s Comet at a distance of 8,890 km and therefore took part in its observation, together with the European probe Giotto. Vega-2 was launched, in turn, on 21 December, and successfully accomplished the same triple mission (lander on Venus, balloon in the planet’s atmosphere and flyby of Halley’s Comet).
Vega-1 and 2 missions on Don P. Mitchell’s website