Sky & Telescope - May 2022 - 13

ssance
way, University of London), though, there hasn't actually
been a drought. " The attitude is: 'We haven't had a mission
since Magellan, nothing's happened,' " he says. " Like, hang
on, there has been Venus Express, there has been Akatsuki
at Venus. They were atmosphere-focused and not surfacefocused,
but they have been doing surface science. "
The European Space Agency's Venus Express studied Venus
from 2006 to 2014; Japan's Akatsuki arrived in 2015 and is
still operating. Despite being devoted to the planet's cloud
decks, their results have overturned prevailing attitudes
about the history of Venus's barren landscape. " Out of the
Magellan mission came this paradigm that Venus had catastrophic
resurfacing and then quiescence, " says Smrekar. " It
was a cool idea, but I think it's wrong. "
Instead, Venus Express produced abundant (though
inconclusive) evidence for recent - and even continuing
- volcanism. Both it and Akatsuki have shown
Venus's atmosphere to be much more dynamic,
and much more connected to the rocky surface,
than we realized. Those discoveries have laid the
foundation for thrilling new Venus missions in
the 2030s.
Hot Wind, Acid Clouds
We've known the fundamental facts about
Venus's atmosphere since Mariner 2 performed
the first-ever planetary flyby in
1962; probes, balloons, and landers from
the Soviet and American space agencies
filled in much of the rest. Very nearly the
same size as Earth and only a little closer
to the Sun, Venus rotates backwards, but
slowly. The retrograde rotation counteracts
its orbital motion, so its sidereal days
(243 Earth days long) are longer than its
years (225 Earth days).
Venus's surface is shrouded by an utterly
opaque layer of clouds, more than 20 kilometers
thick. The clouds are 75% pure sulfuric
acid droplets, but they also contain a mysterious
" ultraviolet absorber " that creates dark
streaks in ultraviolet-filter images. Fortuitously,
CLOUDS
Clouds most commonly form at or above an
atmospheric pressure of around 1 bar, or what
we have at sea level on Earth. On worlds where
the pressure is much higher than that - Venus, for
example - clouds cover the entire planet, all the
time. In places where the pressure is much lower
than 1 bar, such as Mars, clouds are rare and thin.
But Earth can have thick clouds in some places and
none in other places.
sk yand tele scope .o r g * MAY 2022 13
CLOUD ICONS: KUSDARTI / THE NOUN PROJECT

Sky & Telescope - May 2022

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

Contents
Sky & Telescope - May 2022 - Cover1
Sky & Telescope - May 2022 - Cover2
Sky & Telescope - May 2022 - 1
Sky & Telescope - May 2022 - Contents
Sky & Telescope - May 2022 - 3
Sky & Telescope - May 2022 - 4
Sky & Telescope - May 2022 - 5
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Sky & Telescope - May 2022 - 7
Sky & Telescope - May 2022 - 8
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Sky & Telescope - May 2022 - 84
Sky & Telescope - May 2022 - Cover3
Sky & Telescope - May 2022 - Cover4
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