Beneath its swirling clouds, Venus is a
world of relentless heat, crushing
pressure, and volcanic planes stretching
for hundreds of kilome. A planet
reshaped by cataclysmic eruptions and
alien geology. Aside from a few
haunting, grainy photos from the
surface, Venus kept its secrets hidden
for centuries. No one had truly seen
what lay beneath the veil until Mellin.
On the 4th of May 1989, Space Shuttle
Atlantis launched its third flight from
the Kennedy Space Center. On board, it
carried a very special payload, the
first deep space probe launched by a
space shuttle, a probe bound for Venus
that was about to make history. For 4
years, the Mellan spacecraft ambitiously
studied our nearest neighbor, mapping
98% of its surface to a resolution of up
to 100 m. The images it sent back
shattered our assumptions of Venus
forever. And that's what I'm going to
show you today.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we explore the
stunning images of Venus. NASA's Mellan
mission sent back, the surprises they
revealed about Venus's violent past, and
the mysteries that still linger
unanswered to this day.
Mariner 10 snapped some of the first
pictures of Venus in 1974,
capturing Venus's dense cloud formations
on its way to Mercury. A year later, the
Soviet Union's Venera program landed a
spacecraft on the rocky planet, sending
back the first and only images from
Venus's surface. They show a desolate,
eerie landscape. But these images only
captured data from tiny portions of the
planet's surface. The lander's cameras
could only see a few meters in any
direction and were destroyed within
hours by Venus's crushing pressures.
In the 1970s, the Pioneer Venus Orbiter,
also known as Pioneer Venus 1 or Pioneer
12, provided some radar mapping data,
but its resolution was low and its
images incomplete.
Imagine trying to map the Earth, but
Google Maps didn't let you zoom in
further than 75 km.
New York City would just be one pixel,
so pretty hard to make an accurate map.
Additionally, Pioneer 12 didn't map the
northern and southernmost parts of
Venus. That's like a map of Earth with
most of the Arctic and Antarctic circles
missing.
NASA decided they could do better. They
wanted to see it all. Landforms,
tectonics, impact, and chemical
processes, erosion, and even get to know
Venus's interior. So they mounted an
ambitious mission to capture the entire
surface of the planet in ultra high
detail along with a gravitational map
that would give insights into what lies
beneath. That mission was Mellin.
Now before I show you Mellin's photos,
you need to understand three key
engineering innovations that made me
Mellin's mission so groundbreaking.
First, to penetrate Venus's dense
atmosphere, Mellin improved on Pioneer's
basic radar ultimatry.
Engineers used a 3.7 m high gain Voyager
antenna and components from other past
missions to create a synthetic aperture
radar that collected multiple readings
of each area from different orbital
positions. These combined readings
simulated observations from a much
larger antenna, revealing unprecedented
surface details.
Second, Mellin followed a polar orbital
path, scanning Venus in north south
strips during each of its 3-hour
15-minute orbits. In total, it completed
six 243-day
mapping cycles. Cycles 1 to three mapped
the planet surface and cycles four to
six captured gravitational field data.
By the end of its first cycle on the
15th of May 1991, Mellin exceeded its
70% mapping goal, covering 83.7%.
By the end of cycle 3, it had mapped 98%
of Venus at 100 to 250 m resolution. The
probe ended up sending home more data
than all of NASA's previous planetary
missions combined, a total of 150 GB. By
today's standard, it admittedly isn't
that impressive. Your phone probably has
more storage capacity, but for the
early9s, it was quite something.
Finally, after its third mapping cycle
in September 1992, Mellin transmitted a
continuous radio signal to NASA's deep
space network. Based on how the probe's
acceleration changed as it orbited the
planet, this would produce a change to
the radio signal via the Doppler effect,
allowing scientists to decipher Venus's
gravity field. This revealed information
about the planet's interior structure
and density distribution.
The images I'm about to show you are 10
times sharper than any previous radar
images taken from Earth or orbiting
spacecraft at the time and 250 times
sharper than Pioneer 12's data. For the
first time, we actually got to see what
was lurking under those thick, noxious
clouds. Let's take a look.
[Music]
Where previous missions had only shown
vague outlines, Mellin revealed a world
in exquisite detail, revealing for the
first time the surface characteristics
of our next door neighbor. This mosaic
took a decade to put together, with the
bulk of the radar data coming from
Mellin's readings. Let's zoom in even
further and take a little tour.
When you approach Venus, you immediately
notice the lack of craters. Compared
with the moon or Mars, it's pretty
untouched with Mellin only identifying
940 impact craters across the entire
planet. Many small impact craters are
missing because their meteors burn up in
Venus's atmosphere. And the other
craters we did find didn't look as
expected.
Take these three craters for example.
How danalova and Aleon. On impact,
debris from the surface is ejected and
forms the pale yellow blanket-like
formations around each crater. Crater
ejector leave behind distinctive marks
and shapes that help scientists
determine the angle and energy of impact
and how long ago it happened, the
composition of surface and subsurface
materials, and much more. What's
interesting about these crater ejector
is they all show sineuous flows in a
flower-shaped pattern, not unlike lava
flows. They are made of molten rock and
remain this way for way longer than
expected due to Venus's high surface
temperatures.
The Adivar Crater is another great
example of Venus's unique ejector
patterns. On airless worlds like the
moon, ejected material from the impact
follows an arked ballistic path. But on
Venus, the ejected debris interacts with
the planet's dense atmosphere, creating
powerful winds that sweep the material
outward in groundhugging flows. This
creates unusual streaks like the
horseshoe shaped one we see here, which
are only found on Venus. Finally, the 90
km wide Adams crater has a 600 km
outflow tail likely made of impact melt
or magma which can remain in its liquid
form for much longer due to the high
temperature and pressure on Venus.
The scarcity of these craters suggests
Venus's surface is actually quite young.
Indeed, gravity data collected by Mellin
supports the hypothesis that Venus
underwent a global resurfacing event
approximately 300 to 500 million years
ago. So, what could have caused such a
dramatic event?
Volcanoes. Lots and lots of volcanoes.
We knew Venus had volcanic features
before Mellin, but we had no idea that a
staggering 85% of the planet is covered
in volcanic flows. Like these pancake
domes 65 km wide with broad flat tops
less than 1 km tall. They likely formed
from highly viscous lava which later
cooled and withdrew leading to the
cracks and pits you can see in the
image. or these sprawling lava flows
stretching for hundreds of kilometers
over the fractured plains beneath two
large shield volcanoes, Sapasmons and
Martmons.
By studying the varying shapes and
patterns of these volcanic planes,
scientists can identify different
volcanic formation processes from
localized shield volcano eruptions to
massive regional lava flooding events.
Speaking of Martmons, let's take a
closer look. Towering at a dizzying
8,000 m tall, it's almost as large as
Mount Everest. It's also a shield
volcano characterized by its broad,
gently sloping sides. They are typically
formed by fluid lava flows like the
Mount Aaloa in Hawaii.
description below. Now, back to the volcanoes.
Shield volcanoes are not the only kind
of volcano you'll see on Venus. Small
volcanic domes like these are also very
common features on the planet's surface.
Unlike shield volcanoes, volcanic domes
are formed by small bulbous masses of
lava too thick to flow very far. As it
slowly exits the vent, the lava piles up
and cools on the sides. This cluster of
volcanoes sits between rough lava flows
in the east and smooth lava flows in the
west, indicating two different types of
lava overlapping. Though the exact
process remains unknown, the abundance
of lava flows and volcanic features on
Venus confirmed that volcanism played a
dominant role in shaping Venus's surface
and gave rise to the theory that the
planet might still be volcanically
active to this day. In 2024, researchers
who were revisiting Mellan's archival
data found that two volcanoes actually
erupted during the prob's watch in the
early 1990s. This supported a historic
finding from the previous year that
Martmon's had also erupted in 1991.
So what's going on beneath the surface?
What is Venus's mantle like?
[Music]
A hint to those answers lies in the
surface corona like this 500 kilometer
wide Yavin corona.
When hot upwelling magma from the depths
of a planet's mantle reaches the surface
or the lithosphere, it leaves its mark.
On Earth, our tectonic plates shift over
this magma hot spot, creating volcanic
chains like Hawaii or flood bassults.
But Venus only has one single tectonic
plate. So mantle plume activity pushes
the surface upward before collapsing as
the magma cools. The result, these
corona.
Despite being hundreds of millions of
years old, many corona appear well
preserved. There are around 500 of them
widely distributed across the planet in
patterns inconsistent with plate
boundaries and their characteristics
suggest a lithosphere that is too thick
or strong to break into mobile plates
like Earth's. All this evidence suggests
a unique style of lithospheric
deformation where the crust stays
largely in place but is pushed, pulled,
and deformed by forces below. This
stagnant lid planet model might also
play a role in Venus's runaway
greenhouse effect. On Earth, our
tectonic plates carry out vital
processes like burying oceanic carbon.
When it rains, atmospheric carbon
interacts with mountain rocks to create
new minerals which slowly make their way
to the oceans and eventually find
themselves stored in seabed sediment.
This sediment is then subducted when an
oceanic plate sinks the seabed back into
Earth's magma layer, a process that
regulates Earth's temperatures and the
concentration of carbon dioxide in our
atmosphere.
Since Venus's crust is stagnant and
devoid of tectonic activity, this
regulatory process can't take place.
Instead, heat builds up beneath the
surface and greenhouse gases are not
effectively removed from the atmosphere.
The hotter the interior becomes, the
more unstable the system until the whole
lithosphere overturns in a global
resurfacing event and the cycle begins
again.
We aren't exactly sure when the last
resurfacing event occurred on Venus, but
NASA's technical report following Mellin
suggests it happened about 300 million
years ago.
Another curious symptom of Venus's
unique tectonics and mantle activity are
the tesseray that we can see in the
highland regions of the planet. They are
distinct geological features
characterized by highly deformed terrain
with a tilelike appearance. They cover
about 8% of Venus's surface and are
primarily found in the highland regions
as some of the oldest visible surface
features on Venus. They date back about
750 million years. The USSR's Venera 15
and 16 missions first identified these
formations in the 80s, but Mellin
brought them to life in spectacular
detail, like this photo of Alpha Regio,
one of the most prominent tesser on
Venus.
Scientists still aren't sure exactly how
tesseray form, but the two leading
theories indicate they are likely made
of volcanic rocks or they are part of
Venus's continental crust deformed
through compression or expansion. If so,
they'd be gateways into Venus's
geological past and possibly even show
us what the climate was like billions of
years ago.
Fascinatingly, Mellin actually managed
to capture the first evidence of active
tectonics occurring on another planet in
the solar system in Venus's Aphroditi
Terror, a continental area roughly the
size of Africa. The image on the left
was taken in late November of 1990
during Mellin's first trip around Venus.
The image on the right was taken 8
months later as the spacecraft flew over
the region for the second time. See the
bright flow-like area that appeared?
It's likely the result of a landslide
which was possibly triggered by a Venus
quake.
On the 13th of October 1994, after
completing one of the most successful
deep space missions ever, the probe made
its final descent into the atmosphere of
the planet it had studied so devoutly
over the last 4 years. As it plunged
towards the surface, it continued to
transmit data about Venus's upper
atmosphere until it was consumed by the
intense heat and pressure.
Over 30 years later, Mellin is still our
primary source of information on Venus.
And as any good mission, it raised as
many questions as it answered. Was there
ever water on Venus? If there was, would
Venus have been habitable?
How has the planet evolved through time?
Is Venus still volcanically active
today? Together, NASA's upcoming Veritas
and Da Vinci missions will set out to
answer them and many more. Set to launch
in 2028 to 2030, they will revolutionize
our understanding of Venus once again.
Da Vinci Plus will study Venus's clouds
during two Gravitas flybys and also send
a descent probe deep into Venus's
atmosphere to get a better understanding
of its gases, chemistry, and water
history.
Even though it isn't expected to survive
the landing, the probe will collect
valuable data and images on its
hour-long descent to the planet's
scorched surface. Meanwhile, the Veritas
spacecraft will be a Venus orbiter,
similar to Maven, currently orbiting
Mars. Over the three Earth years it
spends circling our neighbor, its job
will be to search for evidence of
ongoing volcanism and tectonic activity
by measuring heat coming from the
surface and analyzing the composition of
Venus's tesseray.
These findings will help us understand
just how different or similar Venus and
Earth are. Could our neighbor really be
a window into our future? or is it more
like our hot evil twin?
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