Venus has a second wind. Not only do winds whip around our planetary neighbour鈥檚 equator, they also blow from the equator toward the poles, something never conclusively observed before. Their existence could help solve the biggest mystery about the planet鈥檚 atmosphere: how it rotates so quickly.
Venus rotates once every 243 Earth days, but its atmosphere does so every four days, with wind speeds in excess of 400 kilometres per hour parallel to the equator. Energy from sunlight is needed to maintain this frenzy. But with more sunlight hitting near the equator than at the poles, it wasn鈥檛 clear how enough energy could arrive where it was needed.
The newly detected meridional winds, blowing at a relatively leisurely 80 kilometres per hour, could pull some of that energy away from the equatorial regions, spreading it more evenly throughout the atmosphere.
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鈥淚t was difficult to understand how the atmosphere could maintain these speeds at high latitudes,鈥� says Pedro Machado at the Astronomical Observatory of Lisbon, Portugal. 鈥淏ut with these meridional winds, we have energy and momentum transported from equatorial regions to higher latitudes.鈥�
You measured that?
Machado and his colleagues were able to 鈥渟ee鈥� the wind using the Doppler effect. Just as a siren鈥檚 sound changes pitch as it moves toward or away from you, light waves reflected off Venus鈥檚 atmosphere are compressed or elongated depending on the atmosphere鈥檚 motion.
But the Doppler shift is tiny in the case of Venus鈥檚 winds. To observe it, the team studied sunlight reflected from Venus鈥檚 clouds, which are being dragged along by those winds. We already know how different atoms and molecules absorb light in different ways, leaving a distinctive signature. To detect the clouds鈥� motion, and hence the associated wind, Machado and colleagues compared the Doppler-shifted light they were seeing with that known signature.
鈥淚t is amazingly hard to make these kinds of measurements,鈥� says at NASA鈥檚 Goddard Space Flight Center in Greenbelt, Maryland. 鈥淚 just read the paper and thought, holy smoke, you measured that?鈥�
We already had hints of meridional circulation from the , but its orbit only allowed it to study winds in Venus鈥檚 southern hemisphere. Using the in Hawaii, Machado and his team were able to measure the winds in both hemispheres, finding them to be symmetrical.
鈥淭his is very important, because we don鈥檛 know how the atmosphere of Venus works,鈥� says at the University of the Basque Country in Bilbao, Spain. 鈥淯nderstanding meridional circulation is one of the key elements to solving this problem.鈥�
With the Doppler method attaining precision close to what spacecraft can achieve, without leaving Earth, Machado hopes to use it to probe the atmospheres of other nearby worlds like Saturn and its hazy moon Titan.
Icarus
