Little is known about the weather at night on Venus as the absence of
sunlight makes imaging difficult. Now, researchers have devised a way to use
infrared sensors on board the Venus orbiter Akatsuki to reveal the first
details of the nighttime weather of our nearest neighbor. Their analytical
methods could be used to study other planets including Mars and gas giants
as well. Furthermore, the study of Venusian weather granted by their methods
could allow researchers to learn more about the mechanisms underpinning
Earth’s weather systems.
Earth and Venus share a lot in common. They are similar in size and mass,
they’re both within the same orbital region known as the habitable zone
(thought to support liquid water, and possibly life), they both have a solid
surface, and both have a narrow atmosphere that experiences weather.
Therefore, the study of the weather on Venus can actually aid researchers in
their quest to better understand the weather on Earth too. To do this,
researchers need to observe cloud motion on Venus day and night at certain
wavelengths of infrared light. However, until now only the weather on the
daylight-facing side was easily accessible. Previously some limited infrared
observations were possible of the nighttime weather, but these were too
limited to paint a clear picture of the overall weather on Venus.
Enter the Venus Climate Orbiter Akatsuki. Launched in 2010, it is the first
Japanese probe to orbit another planet. Its mission is to observe Venus and
its weather system using a variety of onboard instruments. Akatsuki carried
an infrared imager which does not rely on illumination from the sun to see.
However, even this cannot directly resolve details on the nightside of
Venus, but it did give researchers the data they needed to see things
indirectly.
“Small-scale cloud patterns in the direct images are faint and frequently
indistinguishable from background noise,” said Professor Takeshi Imamura
from the Graduate School of Frontier Sciences at the University of Tokyo.
“To see details, we needed to supress the noise. In astronomy and planetary
science, it is common to combine images to do this, as real features within
a stack of similar images quickly hide the noise. However, Venus is a
special case as the entire weather system rotates very quickly, so we had to
compensate for this movement, known as super-rotation, in order to highlight
interesting formations for study. Graduate student Kiichi Fukuya, developed
a technique to overcome this difficulty.”
Super-rotation is one significant meteorological phenomenon that,
thankfully, we do not get down here on Earth. It is the ferocious east-west
circulation of the entire weather system around the equator of the planet,
and it dwarfs any extreme winds we might experience at home. Imamura and his
team explore mechanisms that sustain this super-rotation and believe that
characteristics of Venusian weather at night might help explain it.
“We are finally able to observe the north-south winds, known as meridional
circulation, at night. What’s surprising is these run in the opposite
direction to their daytime counterparts,” said Imamura. “Such a dramatic
change cannot occur without significant consequences. This observation could
help us build more accurate models of the Venusian weather system which will
hopefully resolve some long-standing, unanswered questions about Venusian
weather and probably Earth weather too.”
U.S. space agency NASA recently announced two new missions to explore Venus
with probes named DaVinci+ and Veritas, and the European Space Agency also
announced a new Venus mission named EnVision. Combined with the
observational capacity of Akatsuki, Imamura and his team hope they will soon
be able to explore the Venusian climate not just in its present form but
also over its geological history.
Reference:
Fukuya, K., Imamura, T., Taguchi, M. et al.
The nightside cloud-top circulation of the atmosphere of Venus.
Nature 595, 511–515 (2021). DOI:
10.1038/s41586-021-03636-7
Tags:
Space & Astrophysics