Observing the Night Side of Venus is Actually Pretty Tricky

Observing the dark side of planets is hard. In the visible spectrum, they are almost unobservable, while in the infrared some heat signatures may come through, but not enough to help see what is going on in a planet’s atmosphere.  Now a team from the University of Tokyo think they’ve developed a way to monitor weather patterns on the night side of one of the most difficult planets of all – Venus.

Venus is well known for its turbulent atmosphere and hellish temperatures.  But on the night side of the planet it is not clear what effect the cooling associated with being out of the sun has on the “weather” of the planet.  Venus’ weather itself can be thought of as the continual movement of clouds in the dense planetary atmosphere.  But on the night side, the resolution of infrared images that might be able to provide insight into that weather hasn’t been high enough to be useful.

UT discussion of the formation of Venus.

So Professor Takeshi Imamura from the University of Tokyo turned to Venus Climate Orbiter Akatsuki.  It is the first ever Japanese probe to orbit another planet, and has been providing images of Venus’ atmosphere since shortly after its launch in 2010.  In that time, it has managed to collect some data on the night side of the planet, but trying to resolve small cloud patterns against the overall background of noise in the nighttime Venusian atmosphere proved difficult.  

Adding to that difficulty were fierce winds that whip the atmosphere around at speeds exceeding hurricane-force winds on Earth.  Known as a “super-rotation”, this phenomenon is specific to the atmosphere of Venus.  Forcing weather patterns rapidly from east to west, it makes tracking those weather patterns particularly difficult.  But not too difficult for graduate student Kiichi Fukuya.  He developed a methodology that allows researchers to account for the super-rotation in their data, and isolate small scale cloud movements that lie therein.

Directional lines of wind action on the different sides of Venus.
Directional lines of wind action on the different sides of Venus.
Credit – JAXA / Imamura et al.

One dramatic outcome from the newfound ability to correct for the super-rotation is finding that the north-south winds that drive some of the atmosphere’s circulation switch direction on the night side of the planet.  The full consequences of such an abrupt change are sure to be huge, but Dr. Imamura and his team have not yet parsed them out.  

Doing so might help upgrade models of not only Venusian weather, but also Earth weather too, as the two planets have many similarities.  Dr. Imamura and his team will have plenty of other data to help with their studies soon.  Three new missions to Venus, two from NASA, one from ESA, are expected to launch in the coming years.  With their improved instrumentation, and the new data correction techniques, humanity should soon have a much clearer picture of the weather taking place on our nearest neighbor.

Learn More:
University of Tokyo – The weather forecast for Venus
Nature – The nightside cloud-top circulation of the atmosphere of Venus
Space.com – Nighttime weather on Venus revealed for the 1st time
UT – Venus Express Probe Reveals the Planet’s Mysterious Night Side

Lead Image:
Thermal signature of clouds on the night side of Venus collected by Akatsuki.
Credit – JAXA / Imamura et al.