Transcript Venus Unveiled File

“Venus Unveiled”
The movie you are
about to watch today
is a little long for most
of my students, but
the material you will
see here is some
incredible stuff.
Here is a little
background for the
movie:
“Venus Unveiled”
From Earth-based
telescopes, Venus is
completely covered
with clouds, making it
impossible to know
what is underneath
unless we somehow
go there and drop
below those clouds.
“Venus Unveiled”
Therefore, the USSR sent a series of spacecraft called the
Venera missions. Those that successfully landed on the
surface took pictures like this.
“Venus Unveiled”
The US sent a
satellite called
Magellan. I
bounced radar
signals off the
surface and read
the echoes. The
result was a map
like you see to
the right … as if
the entire planet
was unveiled.
“Venus Unveiled”
One thing that was an odd discovery was the
apparently random distribution of volcanoes, and
yet all of the volcanoes are of the same variety.
“Venus Unveiled”
Earth’s uppermost layer (called the Crust) is cracked into huge plates
that are in constant motion. This motion is called Plate Tectonics.
When one plate dives underneath another, the friction of the sliding
rock melts, forms magma, and erupts as a volcano. Where plates are
colliding and sinking, volcanoes form, and the Ring of Fire is a huge
circle of volcanoes … but they are a special kind.
“Venus Unveiled”
Volcanoes that form from one plate diving under another
are called “pyroclastic” volcanoes because the explode
violently … like Mt. St Helens did. Rainier and the Alaska
volcano shown above center and right will also explode.
All of the volcanoes at plate boundaries are of this kind.
“Venus Unveiled”
So, the Aleutian Islands, Japan, Phillipines,
Andes, and Cascades in Washington are
explosive pyroclastic volcanoes.
“Venus Unveiled”
But a close look at Hawaii shows red
circles. If there are no plate boundaries,
then how can a volcano form there?
“Venus Unveiled”
It turns out that the Hawaiian Islands are a special class of volcanoes
called “shield volcanoes” because their shape is circular at the base,
and the tops are not pointy … making them look like giant shields.
The photograph is Mauna Loa, a huge volcano that makes up ½ of
the Big Island of Hawaii. Notice how it is shaped.
“Venus Unveiled”
Shield volcanoes erupt gently, as seen in the images above. The lava
fountain in the center is not a spectacular explosion, but a giant
“geyser” of gas and liquid rock. These volcanoes form from huge
magma chambers deep in the Earth that vent their lava upward,
regardless of plate movements. These volcanoes are found on Earth
only where magma flows move upward.
“Venus Unveiled”
The volcanoes on Venus (pictured above) are all like the Hawaiian
volcanoes. In fact, the volcanoes EVERYWHERE else in the Solar
System, planet or moon, are like the Hawaiian volcanoes … shield
volcanoes. Pyroclastic volcanoes are ONLY found on Earth because
only Earth has actively moving giant plates of crust.
“Venus Unveiled”
So, even though Earth (above left) and Venus
(above right) have identical topography of the
crust, there are no movements of plates on
Venus anywhere, so therefore no pyroclastic
volcanoes.
“Venus Unveiled”
Question? If there are no active plates on Venus, why are there so
many volcanic mountains across the surface? By the way, it appears
that all of them are dormant. Why are none of them active? When did
they stop? And, why are they all appearing to be the same age?
“Venus Unveiled”
Another even more odd
feature of Venus is the
completely random
distribution of craters,
and the apparent
similarity in age of them.
The possible cause of
this random distribution
of craters is the focus of
the movie you are about
to watch.
“Venus Unveiled”
The craters of Venus
all look similar …
nice round impact
basins with bright
ejecta blankets
around the rims. And
they all appear to be
“fresh,” meaning
relatively young.
“Venus Unveiled”
Why do ALL of the
craters of Venus
appear to be “fresh,”
as if they were
relatively recent
events and of the
same age? This is
the great question
the movie hopes to
answer.
“Venus Unveiled”
When this movie is completed, I hope
that you will know more about Magellan,
the history of thought regarding what is
under the clouds of Venus, and the two
leading theories that attempt to explain
the random distribution of a bunch of
similarly aged craters across the surface
of the planet. If time permits, perhaps
you can have a little class discussion
about the findings shown in the movie.
“Venus Unveiled”
PS … I know that I have just rushed through
some of the Earth processes involved in Plate
Tectonics, but believe me, there is so much
more to understand about volcanoes. I just had
to give you a little introduction to help you
better understand the terms used in the movie
and why the mystery of crater distribution
leads scientists like Turkot to think that some
major repeating catastrophe happens on
Venus, and perhaps nowhere else in the Solar
System. I can teach more on this when I get
home on Friday.