there is a small planet so near the Sun
that it is scarcely visited in a bright
glare of our star like an elusive ghost
it was best observed from Earth in the
Twilight when the Sun is gone from the
sky the ancient Romans gave it its name
mercury so little was known about the
planet the scientists could only guess
at its origin and evolution
like the planet Mars it could have had
violent volcanoes deep canyons scarred
by violent wings or like our own moon
its surface might be pitted with craters
a record of ancient events written on a
planet's surface the best photographs of
mercury added little to our knowledge
but when man learn to travel in school
the electronic cameras of the spacecraft
called Mariner 10 revealed the planet in
startling detail
in June of 1975 scientists from five
nations assembled at the California
Institute of Technology to exchange the
information they had gained from the
exploration of the planet Mercury by the
spacecraft Mariner 10 included in the
group for scientists representing many
techniques of exploration including the
detection of various forms of radiation
the study of gases in a planet's
atmosphere and the powerful scientific
tool photography of the surface of a
planet
welcome to Pasadena we are convened the
photographic exploration of mercury was
led by dr. Bruce Murray from the
California Institute of Technology the
objective I have is to present a
relatively simple interpretation of
history of mercury and to draw some
conclusions about the other terrestrial
planet the work that dr. Murray and his
colleagues are engrossed in goes beyond
the exploration of a single planet
mercury they are afraid of they are
seeking insights into the history of our
entire inner solar system the search for
new information began with the launch of
Mary
these photographs appear were taken to
test the cameras that were to photograph
both venus and mercury for the first
time after leaving the gravitational
field of Earth Mariner 10 began its long
voyage to mercury the spacecraft's
flight path was carefully chosen to skim
past the planet orbiting between Earth
and Mercury cloud covered beings the
Mariner 10 cameras at close range were
to show us a startling new Venus of
Venus we couldn't see from Earth Venus
has been a real frustration to
photograph from the ground because in
the visible it's perfectly featureless
there is occasionally a little bit of
indentation along the Terminator and
occasionally one can see a little
structure around the limb but basically
appears from the earth to be obscured by
an incredible haze and the ultraviolet
however that's the wavelength beyond the
blue that the eye cannot see but
photographic film can respond to very
faint markings have been observed and it
was those faint markings in the
ultraviolet that persuaded us to make a
maximum effort to photograph Venus in
the ultraviolet up close the Mariner 10
cameras photographed Venus in
high-resolution section
each photograph covered only a small
portion of the planet the frames were
then pieced together into mosaics to
give a detailed picture of the entire
planet the results of the Mariner 10
photography in the ultraviolet are
really good fact much much better than
we had hoped because as you can see
looking at first of a picture of Venus
indivisible that was taken by Mariner 10
and then when we switch to one that was
taken in the ultraviolet and has been
enhanced with a computer to bring up the
details there's a tremendous pattern of
organization of markings let's take a
look at what's in these pictures the
most prominent thing one can see is a
very bright south polar cap probably a
great vortex almost like a huge cyclone
and there are dark streaks that come
into this as though they're winding up
like taffy so the whole series of
mosaics is like a series of snapshots of
Venus in time and from those mosaics it
was possible to create a time-lapse
movie of the rotation of the Venus
atmosphere during the period of time
Mirror can flew by and flew away from
the planet so the pattern of rotation of
features on Venus and the upper happens
here way up high by our standards is
remarkable in that the atmosphere on
Venus rotates faster than a surface in
the case of the earth the atmosphere
tends to drag behind a little bit as one
might imagine case of Venus the
atmosphere rotates all the way around
the planet once every four days the
surface rotates once every 243 days so
the atmosphere is rotating almost 60
times as fast at the top anyway as a
planet itself
the gravitational field of Venus was
used to bend the flight path of Mariner
10 inwards towards mercury and the
gravity of the Sun pulled Mariner
towards its first encounter with the
planet in March of 1974 Mariner 10 flew
past mercury during the next year that
would perform two more flyby Mariner 10
returned almost 3,000 pictures of the
surface of mercury these pictures reveal
craters and other features which were
formed very early in the history of
mercury and may refer to events that
affected the entire inner solar system
Mars Earth Moon and Venus as well as
mercury the pictures of mercury revealed
craters and many other features and to
the geologist these features and these
pictures are like the pages of a history
book and the entry book for mercury may
go back almost to the formation of the
solar system itself
five million years ago a bath cloud of
gas and dust floated through the galaxy
we call the Milky Way the ghostly
remains of a great star that had died in
a gigantic explosion the gas and dust is
twisted and shaped by magnetic forces
electrical currents and the subtle pull
of gravity as it swirls around a
thickening core the huge cloud gradually
flattens into a disk dust and gas
gravitates slowly inwards and Eddie's
begin to form in the cloud
particles of matter cluster into solid
box
the larger bodies continue to grow
sweeping up particles and dust that they
orbit the convincing core of the disk
and begin to heat under the increasing
gravitational pressures
in the central core of the disk
incredible heat is being generated
hotter and hotter until it reaches
critical temperatures and then billions
of years ago a nuclear reaction occurred
and our Sun was ignited
the intense radiation repelled the
surrounding gas rust the increasing
interest in time has formed them in from
molten spheres mercury like the other
inner planets is continuously bombarded
by debris that formed craters on its
surface in the final stages of its
formation mercury flowed from internal
heat hot lava was forced to a surface
being torn by collisions with masses of
rock that were shaping the planet but
seeing heat that triggered the lava
flows also melted rock and metals in the
interior of mercury a heavy iron
concentrated at Mercury's center to form
a dense core which was overlain by a pen
shell of lighter material brought to the
surface by lava flows again the surface
was gouged and pitted by a great series
of impacts leaving huge craters on the
surface the Mariner 10 photographs have
revealed these early craters to
scientists for the first time
one of these craters was formed by a
massive rock perhaps a small planet that
crashed into mercury in the Mariner 10
photographs half of this huge crater was
hidden on the night side of the planet
today this huge crater is called Cologne
the impact spewed millions of tons of
debris across the surface of mercury
creating a ring of mountain ranges over
a mile high the floor of this base will
split by great surface cracks wide and
people as the surface continued to form
deep inside the Train it's heavy iron
core began to contract the surface
bucket cracked and great section
hundreds of miles wide were split 'old
leaving immense mile-high walls of rock
called scarfs again there was a great
flow of lava covering many of the large
craters and leaving smooth flat plains
this set the stage for the final episode
in the history of mercury a period of
light crater is the great point
in this time
mercury died the internal heat that
triggered many of the events in the
planet's history turned off and for
three and a half billion years mercury
has remained as we see it today
before Mariner 10 there were a multitude
of possible Mercury's now there's only
one the mystery of craters and basins
and planes which illustrates how
photography can be an exploratory tool
it displays features which were perhaps
never even anticipated and and sometimes
could not even be imagined before the
experiment was flown in a sense it
provides answers to questions that were
not even asked this was true at Mars
when Mariner 4 returned pictures of what
appeared to be a moon like surface it
had been expected that Mars might be
very much like the earth the folded
mountain ranges and many other
earth-like features instead it looked
like the moon and that was a big shock
and it was even bigger shock when
Mariner 9 in 1971 visited Mars again and
found huge volcanoes and even some
peculiar sinuous channels that looked
like they might have been formed by
flowing water at some point in Martha's
history now Viking has transported man's
vision to the actual surface the fantasy
of science fiction has been replaced by
the strange lonely reality of the
Martian landscape when Mariner 10 flew
by Venus it discovered an unexpectedly
well-organized set of cloud motions and
the unexpected would certainly
encountered the case of mercury which
turned out to exhibit not only moonlight
features on its surface but a sequence
of events there that seemed to be very
similar to those of the moon and that's
extraordinary
because mercury is very different inside
compared to the moon and that means it
must have had a different history of
heating and modification of the surface
from the inside and furthermore it lives
in a very different part of the solar
system much closer to the Sun
and therefore it must have experienced a
different exterior history as well and
yet a picture show that victory has a
surface history very similar to that of
the moon and to me that extraordinary a
comparison of the craters on the moon
Mercury and Mars shows that these inner
planets were subjected to cratering at
the same time before Mariner tenant
would believe that the source of
cratering of the inner solar system was
the asteroid belt orbiting beyond Mars
because of the difference in distance
from the belt it was assumed that no two
planets would be cratered the same those
planets farther from the asteroid belt
like mercury would have fewer craters
but a careful count of the craters on
mercury and a comparison with those on
the Moon and Mars showed them all to be
roughly equal if the crater count is
equal then the source could not be the
asteroid belt but must have come from
elsewhere in the solar system
one strong possibility is the planet
Jupiter with a gravitational attraction
second only to the Sun it is possible
that on two occasions Jupiter literally
hurled millions of tons of rock inwards
towards the Sun to impact the planets of
the inner solar system including mercury
this cratered record on Mercury was read
three times because of a fortunate
coincidence Mercury's orbit around the
Sun is 88 Earth days Mariner tens orbit
was twice as long or a hundred
seventy-six days these synchronous
orbits
allowed Mariner 10 to fly past mercury a
second and third time
the path of the first flyby was on the
dark side of mercury the second
encounter sent the spacecraft past the
light side of the planet specifically
for photography after another six-month
journey around the Sun Mariner 10 made
its third and final encounter to look
again at a major discovery made during
the first flyby the presence of a
magnetic field around mercury similar to
earth a bow shock wave blocks the solar
wind from the Sun and deflects it around
the planet creating an environment
similar to the magnetic field around
Earth this discovery was a surprise
because mercury slow rotation about once
every 57 Earth days had led scientists
to believe that the planet could not
generate a magnetic field it is believed
that Earth's magnetic field is generated
by an interaction between the planets
faster rotation and its molten core Mary
Norton's discovery may change theories
on how these fields are formed and has
given scientists their first opportunity
to compare two magnetic fields in the
inner solar system there were other
measurements made at Mercury by Mariner
10 infrared showed that Mercury's
surface ranges in temperature from 700
degrees Fahrenheit to 300 degrees below
zero the widest temperature range of any
planet the ultraviolet experiment
revealed that mercury has a very thin
atmosphere of helium sensors measured
the invisible cosmic rays which flood
our solar system at tremendous speeds
penetrate any surface and are unaffected
by gravitational forces their source is
unknown exploration is an adaptive
process each new piece of information
adds the value of others that were
accumulated earlier we had the results
of the Apollo program on the moon it
helped us understand the timescales and
to some extent the processes we were
seeing when we look at Mars with Mariner
9
now that Mariner 10 has looked at
mercury we can begin to compare it with
the Moon and Mars and begin to realize
that there is a common solar system
history which has been recorded on these
planets whose early services have not
been erased by erosion and other
atmospheric processes that same common
history affected the earth too and so by
looking at these services reading those
records were in fact looking back into
the Earth's history into a heretofore
unexplored domain of time our own
history on the earth now we can begin to
compare and contrast to look for
similarities and differences and try to
recognize our family relationships among
the terrestrial planets are we cousins
or brothers or all of us those are
strangers it happened inhabit the same
portion of the solar system that's the
task of comparative planetology that's
where we go from here
in future planetary flights Venus will
be explored once again the probes of one
pioneer spacecraft will penetrate its
thick atmosphere while a second pioneer
orbits the planet
- Mariner class spacecraft will explore
the planet Jupiter and then by Albert
Street Saturn one of the Mariners may be
sent onto the planet Uranus over a
billion and a half miles from the Sun
and someday in our future we will send
intelligent machines robots to explore
the hostile surface of Mars and perhaps
even the ancient moons of Jupiter and
Saturn
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