Sky & Telescope - July 2022 - 57

Pro-Am Conjunction by Diana Hannikainen
Cytherean
Secrets
Here's a project for you
if Venus's atmosphere
intrigues you.
V
enus has enthralled humanity since
the dawn of time with its brilliant
presence in the twilit sky. And yet the
second planet from the Sun jealously
guards its secrets under a roiling,
cloud-enshrouded atmosphere. Renewed
interest in the planet next door is bubbling,
with several new missions on the
horizon (S&T: May 2022, p. 12). But
the Japan Aerospace Exploration Agency
(JAXA) orbiter Akatsuki ( " Dawn " in
Japanese) is already there now.
Venus's notorious sulfuric clouds
occupy altitudes between about 48 and
70 kilometers (30 to 43 miles) above the
planet's surface. The clouds are further
subdivided into upper, middle, and lower
levels. Below 56.5 kilometers, the clouds
contribute to the infamous greenhouse
effect that keeps the Venusian surface
permanently out of view. Above that,
there's a whole other phenomenon: The
top cloud layer rotates at around 100
meters per second (more than 200 mph),
which is some 60 times faster than the
solid planet below it! We've known about
this superrotation for more than a century
now, but its origin still eludes us.
Odder still, in 2016 Javier Peralta
(JAXA) and collaborators found in
Akatsuki data an occasional disruption
in the mid-level clouds that propagates
at the equator even faster than the
superrotating winds above it. This cloud
discontinuity catalyzes changes in the
properties of the clouds as it roars across
the planet. Peralta notes this recurring
phenomenon is present in archival data
going back to the 1980s, though it has
never been reported. Maybe it's time we
started paying closer attention to Venus.
And that's exactly what Emmanuel
Kardasis did.
PROBING VENUS'S
ATMOSPHERE
The cloud discontinuity is
visible as a dark feature
stretching vertically across
the dayside face of the
planet. Scientists suggest
that this feature may be
transporting energy from
lower (deeper) altitudes
to the upper clouds of
Venus, feeding the as-yetunexplained
superrotation.
This pseudocolor image
combines infrared and
ultraviolet data.
An amateur takes the lead. An avid
planetary observer, Kardasis began dabbling
in near-infrared imaging of Jupiter
in 2009 and within a few years was
pointing his scope at the more challenging
Venus. Eventually, he presented his
observations at the European Planetary
Science Congress in 2017, where he first
met Peralta.
After their encounter, Kardasis
embarked on his own investigation of
the cloud discontinuity, by observing
Venus himself and by trawling through
the archives. On March 11, 2020, he
noticed in his own data that the discontinuity
had reappeared after an absence
of four years. He immediately called on
the amateur community for concerted
near-infrared monitoring of Venus.
He and Peralta teamed up and analyzed
the data from Akatsuki alongside
those of the amateurs. They confirmed
that the discontinuity is confined to the
middle cloud level; its absence in the
upper clouds suggests that the disruption
dissipates at a certain altitude,
giving clues to its origin. Kardasis published
the team's findings in the February
2022 issue of Atmosphere (https://
is.gd/kardasis_atmosphere).
Amateurs' coverage of Venus in the
near-infrared was essential to the success
of the project. Long-term monitoring
of Venus's daytime mid-level
clouds is otherwise sparse at best, in
part because Akatsuki's near-infrared
cameras aren't operational anymore.
" Having observers spread out increased
chances of witnessing the passage of
the discontinuity, especially during the
period when Venus's daytime side was
smaller, " Kardasis mentions.
Gear up. There's more to be done.
If, like Kardasis, you're keen to investigate
the clouds of Venus, you'll need an
8-inch or larger telescope, a planetary
camera, and infrared filters, as well as
image-capturing software and a dataprocessing
package. Once you're happy
with your images, you can upload them
to the Planetary Virtual Observatory &
Laboratory database (https://is.gd/planetary_vol;
or you can go to the ALPO or
ALPO-Japan websites). Don't forget to
carefully log all your observing details:
date and time, location, and equipment.
Ongoing amateur observations of
Venus's dayside mid-level clouds should
help crack several conundrums. For
example, along with professional observatories'
data of the nightside lower
clouds, they'll probe the cloud discontinuity
as it passes from the planet's
dayside to the nightside and back. And
amateurs' exploration of the superrotation
phenomenon at multiple vertical
levels will continue to yield exciting outcomes.
Venus might not be able to hold
onto its secrets so jealously anymore.
¢ Observing Editor DIANA HANNIKAINEN
is indeed enthralled with brilliant Venus.
sk yand tele scope .o r g * JULY 2022 57
EMMANUEL KARDASIS
https://www.is.gd/plan-etary_vol https://www.is.gd/plan-etary_vol https://is.gd/kardasis_atmosphere https://is.gd/kardasis_atmosphere http://www.skyandtelescope.com
Sky & Telescope - July 2022

Table of Contents for the Digital Edition of Sky & Telescope - July 2022
