it's so close
for thousands of years man has found comfort in its presence
it's been a beacon for nocturnal travelers. a time keeper for farmers
and a location finder for sailors at sea for some cultures it's even been a god
it's the only cosmic body ever visited by human beings and today NASA is
planning a permanent outpost there but how did it get there in the first
place how did the moon come to be the answer is more astounding and
spectacular than most residents of Earth have ever imagined
at last count over 150 moons populate our solar system
Neptune claims 13 of them
Saturn has 48
and Jupiter hosts an astounding 62
earth on the other hand has just one
but it's a special one
our Moon oona as the Romans named it is remarkable in its size
it is by no means the largest moon in the solar system several others are
bigger one of Saturn's moons Titan for instance is twice the size but our moon
is the largest in relation to its host planet
it's 1/4 the size of yours it's really big compared to yours as you look
through a telescope at the euros from a distance you'd see the earth and this
other big thing you look at Jupiter or any other planet you got the big planet
and then little tiny moons right next to it so our moon is so much bigger and
it's the only one of the of the now eight planets that has that situation
the relative sizes of the two bodies are close enough that some astronomers go so
far as to refer to the Earth Moon system as a double planet the mean distance
from the earth to the moon is two hundred and thirty-four thousand miles a
three-day flight through space Luna's diameter is roughly one-quarter
the size of Earth's measuring 2,160 miles a single day on the moon is the
equivalent of 27.3 Earth days this is because one side of the Moon permanently
faces us oona is phase-locked with our planet so
the moon must fully orbit the earth in order to make one complete rotation on
its axis sort of like children in a game of ring-around-the-rosy they always face
inward as they hold hands and move in a circle
yet as closely related as the moon is to our earth it would only take a brief
visit to Luna to make it quite clear that it is in fact a very different
world from our planet
and an exceedingly dangerous place
there's no air of course so you need your spacesuit
indeed the moon has absolutely no atmosphere at all so there is nothing to
carry sound waves if you were standing on the moon with a friend and tried to
converse the person wouldn't be able to hear you except by radio no atmosphere
also means that there are no air molecules to scatter light from the Sun
so the sky is always black
and the landscape does little to help brighten the scene kind of monochromatic
you know not much color there the rocks are mostly gray brown colors it's maybe
a little warmer tone in one direction maybe toward the Sun and cooler tones
gray or tones looking in other directions but not so colourful extreme
temperatures would also add to the unpleasantness of a visit the swings
between hot and cold are brutal from 270 degrees above zero at midday to 240
degrees below zero at night
even the moon's low gravity just one-sixth of Earth's could present a
hazard to a tourist a reality the Apollo astronauts kept at the tops of their
minds during their many moon walks but they realized that beyond the thickness
of their visor in their spacesuit with death should they do something and fall
into a rock and lose their footing and fall to hit an outcrop this visor could
be cracked exposed to the lunar vacuum we would had a serious situation on our
hand
but while a spacesuit could protect owner tourists against the vacuum of
space a lack of oxygen temperature extremes and lethal solar radiation a
potential hazard a spacesuit would do little to protect against is
high-velocity micro meteoroids
they pummel the lunar surface frequently
tiny meteorites the little little ones that burn up in our atmosphere and make
shooting stars those there's no atmosphere on the moon they're coming
right down hitting the surface they pulverized the lunar surface generating
a dusty blanket of gravel light material called regolith dr. Amanda Hendrix
studies the moon at NASA's Jet Propulsion Laboratory
this plant here is kind of a regular Factory
it's ground up rock is what it is
the timescales at this gravel mill are a lot faster
here it's made in less than an hour but on the moon it is the result of more
than four billion years of bombardment by meteoroids and micro meteoroids
raining in on the surface and breaking up the rocket like the product of this
gravel mill lunar regolith has formed in a variety of grain sizes from large
rocks to fine dust this very fine dust is familiar to us from Apollo images
that were seen of astronauts footprints in the dust it's very fine and so fine
in fact that if astronauts had problems with it sticking to their spacesuits
getting into the equipment and it can end up causing a bit of a problem
really big meteorites have also hit the moment in the past
in fact these massive impacts are responsible for the dark circular
regions on the lunar surface the shapes the to many observers seem to be
arranged like the eyes nose and mouth of a human face they make up the
illusion of the man on the moon
they blasted huge basins in the moon's surface some of them are 700 miles
across
dark lava eventually burst through at the impact points and flooded the basins
today we call these dark regions Marya the Latin word for seas
this dates back to the 17th century when Renaissance era observers looked up at
the moon they speculated that the dark areas might be oceans and astronomers of
the time gave the many dark spots or seas whimsical names
the seas are all named after effects that were once attributed to the moon so
you have the sea of storms and the sea of crises and the Sea of Tranquility and
so forth some of the younger impact basins have had less time to erode so
their features are still relatively crisp one in particular is called Mar a
oriental a or the eastern sea it's some 600 miles across and the impact that
created it was so massive and direct the result looks very much like the bullseye
on a target this oriental a scar is kind of like a bullet shot into glass where
you see all the that sort of rings around it and fractures going out
people have often said if that had been on the side facing directly toward the
earth we might have had a whole different lithology about the moon
because it would have looked like a big eye staring at us
three concentric rings of mountain ranges surround mari orient all a and
some of the peaks rise to several thousand feet they're all effects of the
monster impact when we see mountain ranges on the earth they're mostly
caused first by the continents moving around crashing into each other very
slowly buckling up and creating mountain ranges which then erode into all the
spectacular shapes that we see the Matterhorn and so forth from water
erosion on the moon there are no continental plate tectonics the surface
is static yet you still have mountains on the moon and the reason is that those
big impact basins
that's a big explosion excavates app it throws material up on the outside so you
have these rings of mountains arcs of mountains that surround the impact sites
but their impact features and they're caused by the external forces not the
internal forces another notable impact crater much smaller than Mari oriental a
but every bit as spectacular is Tycho
named after a prominent 17th century Danish astronomer this impact feature is
located in the southwestern quadrant of the moon's near side it's in the bright
area you can almost see it with your naked eye and when that explosion
happened as with many other craters it shot out jets bright powdery dust so
there are these rays that go out and from
the Rays of dusty ejected material extends some 900 miles from the Tycho
impact site a mountain of debris also rises from the center of the crater this
is a result of recoil from the asteroid strike some of the highly compressed
material at the center of the impact site Springs outward once the impacting
body either ricochets or disintegrates
but long before any of the moon's specific features could be discerned
through sophisticated telescopes and space travel careful observation of
lunar behavior in appearance was still vitally important to earth dwellers
for fifteen thousand years at least man revered the moon as a source of light as
a navigational guide as a reference in agricultural pursuits
and most of all as a convenient timekeeper in the days before our modern
systems timekeeping was no simple task
early timekeepers had two choices they could monitor the Sun or the moon if you
think about trying to keep track of dates if you use a solar calendar like
we do nowadays there are 365 days a year and that's an awful lot of days to keep
track of and it's not something that the ordinary person can do very well
compare that with a lunar calendar everybody can tell when the full moon is
when the new moon is you don't see the moon at new moon you see it that's big
and round at full moon so it's easy to tell there are only 28 to 29 days in a
lunar cycle so it's easy to count them and so most societies actually start out
with a lunar calendar
early observers of the moon also recognized that our planetary neighbor
has a very real physical effect on the earth itself the moon is responsible for
the rise and fall of our ocean tides
if we think of the moon as being this tennis ball and the earth as being this
football okay the the tides are caused by the moon's attract gravitational
attraction so it's obvious okay so the moon kind of pulls the Earth's water
towards it
and so this creates a slight bulge in the direction of the moon it's less
obvious is there's also a bulge in the direction away from the moon so there's
in fact two high tides every day
the other high tide you can think of is being caused by the Earth's centripetal
force the earth and the moon are both rotating around and that causes the
water on the far side to also move out an extreme illustration of the
difference between high and low tides can be found along the shore of Canada's
Bay of Fundy the water level from high tide to low
tide drops an astounding 55 feet for some forms of life on Earth
the advance and retreat of the tides creates useful habitats
but another of the moon's gravitational effects on our planet is directly
responsible for nothing less than the continued survival of terrestrial life
itself the moon stabilizes earth's climate the gravitational effect of the
moon keeps the degree of tilt in the Earth's rotational axis constant this
tilt is what maintains the repeatable cycle of seasons as the Earth orbits the
Sun over the millennia with the moon's prominent and constant presence in our
night sky men ultimately began to speculate on its origin how did it form
how did the moon come to be in 455 BCE the Greek scholar anaxagoras
theorized that the moon was simply a rock it was flawed by the earth most of
his contemporaries on the other hand were convinced that the moon was a god
or maybe a huge ball of fire so annex Agora says notion did not get
much traction quiet speculation no doubt continued but no hard information about
the moon came until 1609 when Italian astronomer Galileo Galilei pointed one
of the first telescopes at the moon recognized that he was looking at a
landscape the terrain of another world
when you look at the moon through telescopes it looks completely different
from the way looks to the naked eye instead of looking flat the way it does
to make it eye it really looks round and you can see the shadows you can see all
these craters as the naked eye does not see and it just immediately looks like a
world it jumps out at you into three dimensions Galileo made detailed
drawings of the small planet surface and established once and for all that the
moon is a solid world not a god or a fireball but the groundbreaking
astronomer never publicly speculated on the moon's origin primarily because his
interest soon moved to other planets
not until 1873 did the first science-based theory regarding the
origin of the Moon publicly emerge it sprang from the mind of a talented
french astronomer named Edouard Roche Roche advocated what's called the
coaccretion theory which says that basically Earth and the moon grew up at
the same time other the same materials
in Roches day many scientists began to believe that the planets might have
formed from hot condensing clouds of gas
it gradually contracted and cooled and hasn't contracted it would separate out
rings of gas so you'd have a ring of gas here a ring here and so forth and these
rings of gas would then eventually coalesce and form the planets Roche saw
the earth and the moon as a solar system administrator his idea was that the
earth starts out as a ball of gas and then cools and contracts and sheds a
ring of gas that then itself coalescence and forms the moon
but there are problems with this theory for one our moon has a much lower iron
content than the earth if the two bodies form from the same materials their basic
composition should be the same but they are not this and other inconsistencies
soon led fellow astronomers to quest for new ideas to explain the existence of
the moon in the last third of the 19th century advanced theories about the
origin of the moon started to emerge in 1873 French scientist Edward Roche
proposed that the moon's simply formed alongside the earth out of essentially
the same nebular cloud of particles and gases but this idea had a fundamental
weakness the moon has a much lower iron content than the earth it's much less
dense
the big thing to remember about the moon and its composition is that it doesn't
have any iron core like the earth does you look at the earth and there's a very
large central area something like half the inside of the earth is layer
nickel-iron and that's metal that drain down to the
center of the resume birth was hot when it performed at the beginning the moon
is more like this plain Rock scientists initially deduced the mass of the moon
through observation and mathematical calculations
if the moon had formed from the same stuff that made the earth the iron
content should be similar it was a hole in the theory Edouard Roche couldn't
explain but another idea soon followed on the heels of the coaccretion
hypothesis in 1878 George Darwin announced his fission theory of lunar
origin
this idea received some attention in part because Darwin had a celebrated
father Charles Darwin an author of Origin of Species in time though George
Darwin stepped out of his father's shadow and became known as England's
leading expert on tithes and through extensive analysis of the
tide moon relationship George Darwin came to the realization that the moon is
gradually moving farther and farther away from the earth
it wasn't proved until 95 years later when astronauts landed on the moon they
put little mirrors on the moon and you can shine laser at the moon and the
laser will bounce off the mirror and come back and you can actually measure
the exact distance between the Earth and the moon and the rate at which the
distance is increasing 3.8 centimeters per year
3.8 centimeters is about an inch and a half if you made a movie extreme
time-lapse you would see the moon moving away from Earth gradually that's what we
see nowadays
Darwin began to consider what would happen if you reverse the process if you
ran the movie backwards as we move backwards in time and the moon moves
closer both the moon's orbit and the rotation of the earth get faster and
faster and so what happens is that eventually the moon must coalesce with
you must hit the earth the logical conclusion for Darwin was that a portion
of the molten rapidly spinning earth must have separated from the main mass
and spun off to become our moon
he immediately began work on mathematical calculations to reverse the
trajectory of the moon all the way back to the earth frustratingly he reaches a
point where it gets almost to earth and then he couldn't work it out any farther
the mathematics doesn't let you go any farther but you get to is a point where
the moon is whipping around the earth at a rate of five revolutions a day or six
revolutions a day so it's just zooming around the earth okay and it's it's
about five thousand miles away from the earth still the mathematics did not
allow Darwin to bring the two cosmic bodies into contact
the vision theory was debated for decades but scientists eventually
concluded that the relative movements of the Earth and Moon could not have
resulted from it the earth would have been spinning too fast to account for
its present rotation rate the quest for an explanation of lunar creation
continued and a new theory would soon originate with an American in 1909
Thomas Jefferson Jackson C was a u.s. naval captain based at Mayer island near
San Francisco his official job was to keep the standard time for the u.s. west
coast but C was also a gifted scientist as a young man he had trained as an
astronomer he was one of the first Americans to actually get a doctorate in
astronomy he went to Germany and got a PhD in astronomy which was you know
almost unheard of back then the US was still scientifically total backwater in
the 1800s cease duty station Mayer Island had an observatory
and the captain's job allowed him plenty of time to theorize he had spent time
analyzing both the coaccretion and the fission hypotheses regarding the origin
of the moon and he wasn't convinced gradually Thomas II developed a
completely different idea it came to be called the capture theory essentially
see theorized that the moon had actually formed in a different part of the solar
system from the earth that it orbited the Sun just like the other planets but
that at some point it had moved too close to Earth and was captured by
Earth's gravity
his idea was that there's something that he called the resisting medium in outer
space which we know is not there now see never adequately explained what this
resisting medium was supposed to be possibly tiny particles of matter
regardless he was sure and no longer existed his idea is that for the earth
to capture the moon the moon would have to come in from far away and then it
would hit this resisting medium and slow down and then gradually get captured
into an orbit maybe not at once might take a little while but gradually it'd
be captured into Earth's orbit it's a little bit like a bungee jumper jumping
off the bridge they go down come back up not quite as far go down come back
you know eventually they'd settle down at the bottom Thomas sees capture theory
would certainly explain the difference in iron content between the Earth and
the moon if the moon formed elsewhere its composition could be very different
on the other hand the notion that Earth's gravity could capture and retain
such a large object was unlikely since there is no obvious resisting medium to
slow down an object as big as the moon all three theories had significant
weaknesses the origin of the moon remained a mystery on July 20th 1969
u.s. astronauts set foot on the lunar surface for the first time they have
landed their lunar module on the hardened lava plain known as the Sea of
Tranquility
and Nisshin pilot Buzz Aldrin described the view as magnificent desolation the
astronauts brought back 48 pounds of moon rocks and dusty soil or regolith
geologists at Johnson Space Center in Houston eagerly awaited their arrival
the excitement when samples first came back was just electric I mean it was
just incredible nobody really knew quite what to expect
and we realized right away that we had basaltic rocks like one might see in
Hawaii in fact very similar to rocks one would see in Hawaii the NASA geologists
were intrigued to find not only basaltic rocks of another sort
rocks called breccias breccie is formed during asteroid impacts so if you can
imagine that large impact body hitting the moon is gonna be very chaotic it's
gonna throw up debris debris is gonna come flying out of this what winds up to
be a crater after it's over and you can see the many craters on the moon this
debris gets all jumbled up and lands on the ground around the crater and then he
gets compacted with the heat generated by the crater has turned into rocks that
look very chaotic you see all sorts of pieces in the rock of different sizes
different shapes all pieces of the rock that were in the area that the impacting
body impacted we have just not seen anything like this on earth the moon
rocks soon began to tell a fascinating tale
first the rocks and soil samples contain particles indicating that the moon must
have been covered by a deep ocean of lava after it formed this notion was
reinforced by the discovery that the rocks were lacking significantly in what
scientists call volatile elements
volatile elements are those that can evaporate easily and therefore be lost
when you heat up a rock and some examples of volatile elements include
water or potassium for example and if you compare the bulk earth rocks to
lunar rocks you find that the lunar rocks are extremely parched it's as if
they've been heated and they've lost a lot of their volatile elements along
with these stark contrasts the lunar samples also revealed at least one
astonishing similarity between the lunar surface and rocks and soil from Earth's
the isotopes of individual elements like oxygen in particular yeah different
forms of oxygen the moon had exactly the same ratios of different forms as the
earth did but all the other rocks we knew from elsewhere in the solar system
which are meteorites that fall out of space all have different oxygen isotope
ratios which tells you that the moon material in the Earth's material are
very very similar in the end the lunar samples had supplied a wealth of hard
evidence regarding the geological makeup of the moon but astronomers trying to
understand the moon's origin were still left with a puzzle
for William Hartmann of the Planetary Science Institute in Tucson Arizona the
information gleaned from the moon rocks supported some ideas he'd been working
on for nearly a decade now a distinguished astronomer and painter of
space images in the early 60s Hartmann was a graduate student at the University
of Arizona taking part in a project to map impact craters on the moon from the
enormous basins or seas to the smallest visible dimples we realized during this
mapping in the sixties that the big basins are actually impact features very
large asteroids hit the moon and made this huge explosion some of those are
six hundred miles across how big an object does it take to do
that something like 100 miles across so we had large objects running around in
the inner solar system as the earth was forming and they were crashing into
planets for Hartman the notion that 100 mile
wide asteroids once impacted planets begged a couple of questions could
planet-sized objects have ever collided and could that have something to do with
the formation of the moon
by 1972 Hartman and fellow Tucson astronomer Don Davis had created a
computer program to help them explore these ideas
the program made a rough attempt to simulate the accretion process in the
early solar system the astronomers wanted to see if any other planetary
bodies formed near the earth that could have crashed into it the idea was if
there was some other body there and it finally crashes into the earth blows off
all this crustal material from the earth as well as from the impactor itself
maybe the moon could form at that sure enough the simulation showed that a
second planet could have formed in the Earth's accretion zone what about the
size of Mars it wasn't the moon because it had formed from the same elements as
the earth and should therefore have had the same iron core and heavy density as
the earth the une of course does not that was evidence
enough for Hartman to formulate a new fourth hypothesis it came to be called
the giant impact theory in 1974 a new hypothesis explaining the origin of
Earth's moon debuted on the world scientific stage its proponents dubbed
it the giant impact theory the basic idea is that about 4 and 1/2 billion
years ago earth collided with an object roughly the size of the current planet
Mars
it's a very large collision and it started the earth spinning it's what
gave us our current 24-hour day we believe and this collision was so
massive that it launched material into orbit around the earth and it's from
that material that we believe the moon layer coalesced
dr. Robin Kenneth and others of the Southwest Research Institute in Boulder
have constructed a computer model to study the details of the giant impact
scenario it divides up the earth and this colliding rogue protoplanet into
many different particles and then the evolution of each particle is tracked
through the course of the impact the simulation depicts the impact from a
bird's-eye view from the top down the earth was probably partly molten even
before this impact so initially the impactor came in from this direction it
hit the earth with an off-center collision and you can see the impactor
has been stretched out into this long arm of material right here scientists
believe the upper layers of the earth became completely molten following the
impact the collision starts the earth rotating
and you can also see that the collision has substantially distorted the shape of
the earth itself
after a couple hours we see that this arm of impactor material has coalesced
gravitationally into two large clumps the inner clump of the impactor material
is actually composed overwhelmingly of the impactors core so that when this
inner clump recal ides with the earth which happens right there
the vast majority of the iron that came in with the impactor is actually
accumulated by the earth
while this outer clock comes in and makes a close pass by the earth and is
stripped by the Earth's gravity into a long arm of material which then breaks
up to form this disc the material is thought to have coalesced to form the
moon in less than a year following the massive impact
there is no sign of this impact on the earth today because at the time our
planet had only developed to about 90% of its current size the remaining 10%
would accumulate from later much smaller impacts also the Earth's own gravity had
a reshaping effect within a day after the impact the earth had reassumed a
basically spherical shape and any depression that the impact caused would
have been smoothed over giant impact theory originator bill Hartmann
presented his hypothesis at a scientific conference in 1974 but it received
little attention for nearly a decade interest in the moon dropped off sharply
at the end of the Apollo missions
finally at a lunar conference in Hawaii in 1984 twelve years after the last moon
shot the world's foremost astronomers reached a consensus
the giant impact theory was the most acceptable explanation to date for the
origin of the moon I think there's still some people who
say okay it's not really proven yet but it's what I would call the default
theory if you look at any textbook of planetary science or geology it's just
the theory that's accepted and there are certain small discrepancies which have
yet to be explained but by and large it works
even with an agreed upon theory of how our moon came to be scientists have not
finished studying our closest cosmic neighbor by any means
in fact talk of returning to the lunar surface with a permanent manned outpost
as recently emanated from the White House and NASA hit Wars
gorgeous tear down the window and click with her there and I know such
a base could provide a place to train astronauts to live in space long-term as
well as provide a more efficient launch point for eventual missions to Mars but
such lofty scientific goals are far from the minds of average residents of Earth
who occasionally peer up at the glowing mesmerizing lunar disk in the night sky
for us talk of lava oceans regolith forming micro meteorites and giant
impacts will never diminish the fascination and romance of our
mysterious neighbor world the moon
you
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