Major Discoveries by Venus Express: 2006-2014
4. Super-rotation is speeding up
Venus is well known for its remarkable, super-rotating upper atmosphere, which sweeps around the planet once every four Earth days. This is in stark contrast to the rotation of the planet itself – the length of the day – which takes a comparatively laborious 243 Earth days.
After its arrival at the planet in 2006, Venus Express was able to conduct the most detailed survey of cloud motions in the atmosphere of Venus, with the surprising discovery that the planet's high level winds have become faster over time.
By tracking the movements of distinct cloud features in the cloud tops some 70 km above the planet's surface over a period of 10 Venusian years (6 Earth years), scientists were able to monitor patterns in the long-term global wind speeds.
In 2006, average cloud-top wind speeds between latitudes 50° on either side of the equator were clocked at roughly 300 km/h. However, detailed cloud tracking studies revealed that these already remarkably rapid winds are becoming even faster, increasing to 400 km/h over the course of the mission. The reason for this dramatic increase is unknown.
On top of this long-term increase in the average wind speed, studies have also revealed regular variations linked to the local time of day and the altitude of the Sun above the horizon, as well as the rotation period of Venus.
There have also been dramatic variations in the average wind speeds observed between consecutive orbits of Venus Express around the planet. In some cases, wind speeds at low latitudes varied such that clouds completed one journey around the planet in 3.9 days, while on other occasions they took 5.3 days.
This is one of the major discoveries made by Venus Express during the last eight years. Read more on the following pages: