On January the second, 1959, with the space age barely a year old,
the Soviet Union launched Lunik, or little moon
It was sent to plant a Soviet pennant on the moon
Within hours of the launch it became clear that Lunik was going to miss its target
As the Soviet Scientists watched their tiny probe sail out
to join the planets in an endless journey around the sun,
an inspired thought occurred to them:
They renamed their spacecraft Mechta - the dream
In 1926, when this recording of Holst's Planet Suite was made,
there were thought to be eight planets
Then, in 1929 a young man arrived at an observatory in Flagstaff,
Arizona to start a search for a ninth
At that time little was known about the planets
Closest to the sun lies Mercury,
a tiny world of iron and rock barely discernible in the glare
Then Venus, perhaps a second earth hidden, beneath a blanket of cloud
Then Earth
And beyond us - Mars, the red planet
It has seasons, polar caps and the possibility of life
Far beyond these rocky worlds are the distant giants
Jupiter, over a thousand times bigger than the Earth,
and Saturn with its distinctive and dramatic rings
The two remaining planets are 15 times the size of the earth,
yet they are so distant that they appear as the faintest of stars
Uranus, an aquamarine mystery
And finally Neptune, a world that moved unevenly across the sky
This irregular movement suggested the presence of a more distant planet,
whose faint gravitational tug might be toying with Neptune's orbit - planet X
February the eighteenth 1930, Clyde Tombaugh,
sitting in an office very near to where we're sitting right now,
looking at the photographs that he had taken of the night sky,
sitting with his eye at the eye piece of that blink comparator back there,
and he had been searching on the plates
that were centred on a star in the constellation of Gemini, the twins
He had started that morning, he had moved very closely,
very slowly across and click, click, click,
and seeing one image then the other, then the other,
keeping on moving back
All of these images were negatives,
all the stars and anything else would be black on a white background
But for Clyde that afternoon, he crossed the very centre of the plate,
he passed the area right where the guard star was,
the star Delta Geminorum, big, big bright star,
and moved a little bit more,
little bit more and then he saw a very faint,
a very faint black dot,
and then he blinked to the other one and it appeared on the other plate,
and he saw it appear here and appear there
On his plates, taken several days apart,
Tombaugh noticed that a point of light had moved
Tombaugh knew instantly that this was what he was looking for
It was an historic moment
He took the walk from the comparator room
all the way down to the director's office and he stopped and he did his tie,
and combed his hair a little bit,
and he said, "I wanted to appear a little nonchalant about this"
So then he stepped into the office,
"Doctor Slipher, I have found your planet X"
Planet X was soon named Pluto. It marks the end of the solar system
A tiny world of ice, smaller than our moon,
now known to have its own satellite, Charon
But Pluto patrols the outer edge of the solar system,
in the distant realm of giants - worlds of swirling water,
like the azure Neptune, and Uranus,
which mysteriously orbits the sun spinning on its back
Pluto lies way beyond the gargantuan worlds,
the gas planets that have no landscapes
Saturn, with wind reaching thousands of kilometres per hour, and Jupiter,
that has an Earth-sized storm that has lasted for centuries
The closest worlds to the Sun are small islands of rock and iron
Mars, with its faint atmosphere of carbon dioxide,
and Venus, smothered in clouds of sulphuric acid
Then there is Mercury, boiling in sunlight and freezing at night
Nine different worlds, with seemingly little in common save
that they orbit a single Sun and are bound together by its gravity
And then there is the Earth
A small planet in the measure of the solar system
It has a thin atmosphere that clings to a rocky surface
But the Earth is different. It is special. It has life
What process could create such a variety of different worlds?
Hal Levison is at the forefront of a branch of astrophysics
that is still struggling with the mystery of how the planets form
It's amazing when you really consider, all of the planets in the solar system,
the Earth and the rest of the rocky planets.,
the cores of the giant planets, Jupiter and Saturn,
and the majority of the outer planets, Uranus and Neptune and Pluto,
form from material that is very fine pieces of dust,
much finer than the dust I'm holding in my hands
About the consistency or size of particles of dust in cigarette smoke
I was an astrophysicist, interested in a sort of an obscure type of galaxy,
when about 5 years ago I got the bug of trying to understand
how material like this can form the planets that we see today
By the eighteenth century, astronomers had discovered that galaxies are filled
with drifting clouds of gas, called nebulae
Perhaps these clouds were the raw materials of the planets
Two men, the philosopher Emanuel Kant and the mathematician Simon De LaPlace,
looked at the uniform direction of the orbits of the planets in the sky
They suggested the planets were a relic of a cloud of dust
and gas that circled the Sun during its formation
In a single process, they concluded, the Solar System was born
The idea was elegant and quite brilliant,
but the complex details of their theory lay centuries in the future,
and its proof had to wait for the arrival of the space age
September 1944 - London was under siege
Mysterious weapons were raining down from the sky
Hitler's vengeance weapon threw people into confusion
Nothing had prepared them for a supersonic missile
that took just 6 minutes to travel from mainland Europe into the heart of Britain
The technology behind these missiles was highly advanced
It had been developed by a brilliant young engineer called Werner von Braun
Von Braun's rocket was called the V2
Designed to save the war for the Nazis,
eventually it became the foundation of our journey to the planets
When Germany fell, American troops headed straight for the V2 factories
Before the dust had settled in Europe,
von Braun and his team of engineers found themselves working
for the United States army
In the deserts of New Mexico,
the captured rocket parts were reassembled by German and US engineers
The modified V2's were soon flying way beyond the range of conventional cameras
To record their progress,
the engineers fixed astronomical telescopes to anti-aircraft gun mounts
The system was designed by Clyde Tombaugh,
the discoverer of Pluto, and his films still survive
Before they left the German rocket factories,
the Americans destroyed as much as they could,
to prevent von Braun's secrets
from falling into the hands of the advancing Red Army
But when they arrived the Soviets found just enough to take back to Moscow
The man given the task of piecing together the rockets was Sergei Pavlovich Korolev,
and Boris Chertok was his right-hand man
While their brief was to develop rockets which could reach America,
Korolev's eyes were firmly fixed on the planets
Everyone who came before him was a dreamer,
but Korolev was a practical person
That's why he came to be known as the one
who made the dream of space travel a reality
But it was the Americans who made all the early running
By the end of the decade,
they were strapping film cameras to rockets
and sending them high above the atmosphere
The cameras had to endure an 18-mile plummet back to earth
Miraculously, some survived
And astronomers got their first glimpse of the only planet
they couldn't see with their telescopes
For the first time, we could see the curvature of the Earth
The arcing horizon was a humbling reminder
that we were living on a gigantic ball of rock and iron
How such a world could have grown from a cloud of dust
seemed more baffling than ever
George Wetherill has dedicated his career to the question of planet formation
When he started his work, the science was dominated by one man
No great scientist ever devoted his life to understanding this problem
It was sort of a hobby, something they did on the side
And I think the first person to really devote his life to this,
was a Russian scientist named Victor Safronov,
who started working on these problems shortly after the world war 2
And he tried to identify what all the scientific problems are that
you need to understand and need to solve
in order to understand the grand problem of the formation of the solar system
And to this day his lists of problems are essentially the same problems
that we're working on today
Victor Safronov revisited the 200-year-old idea
that the planets formed from a disc of gas and dust
He set about structuring this complex process into comparatively simple stages
The first stage is still not fully understood
Remember, we're starting off with very fine pieces of dust,
and the process of how you get from something like that
to something the size of a boulder
or even the size of a mountain is actually not very well understood
The party line of the, you know what most people think actually happened,
was that you had this disc of dust,
and the dust sort of settled into the mid plain of
the protoplanetary nebula, this disc
And you got what's called a gravitational instability,
that formed big clumps,
things the size of maybe a 100 metres in diameter
Safronov's second stage was less complex. It was called accretion
He calculated that in a remarkably quick time,
the clumps would gather together, building the embryos of planets
As they grew, a new force became significant - gravity
A really amazing thing happens, though, that Victor Safronov discovered,
and that is as these things start to grow,
the bigger something gets the more it can eat
So you end up with this runaway situation,
where the bigger guys are getting bigger still,
faster than the little guys are,
and it's sort of a race to eat up all the little guys
And so you start off with an uncountable number of objects
that are the size of mountains, and you end up with maybe a 100,
in the inner part of the solar system,
objects about the size of the moon and maybe growing up to the size of Mars
Competing worlds hoovered up the surrounding debris
until there was simply no more to be had
In the inner solar system, where there are now 4 planets,
there were once upwards of a hundred
How that army of worlds became just four was still a puzzle
But Victor Safronov had a hunch that
the process would leave those planets splattered with the scars of impact
Was this what we could see on the moon?
Unknown to the west,
Safronov had taken a giant stride towards a theory of planet formation
Perhaps, somewhere in the solar system;
there might be a planet bearing the hallmarks of his theory
In 1957 the Americans announced that they were preparing to enter the space age
They were about to launch the worlds first artificial satellite
In the Soviet Union, Korolev acted immediately
For Korolev, it was the beginning of the race with Americans
And he wanted to be first, he wanted to be ahead of Americans, like all of us
And I think he want to do this maybe a hundred time more than any others
Then he call my father, he told, I want to launch this first satellite
Lets do this before Americans, as soon as we can
It would be a huge gamble, but finally Khrushchev agreed to let him try
Now Korolev had to convince his engineers that they could do it too
On October the 4th, 1957,
while the Americans were still finalising their plans, Sputnik was launched
40 years on, and Korolev's achievement is still celebrated in Russia
That evening he was very proud -
he realised that it was a great achievement -
and the next day he understood that the reaction of the outside world
was much stronger than it was in our country,
and really the feeling was much stronger than even his feeling,
specially in the United States
Korolev's rockets had opened the door to space. The planets were beckoning
Bruce Murray is a veteran of the US space programme
When his career started, the planets seemed a very long way away
He still remembers the first time he saw Mars through a telescope
And it just blew me away
I was so taken with the fact that here was a real object,
it was three-dimensional, seemed to be three-dimensional
It was colourful, it glowed,
and it really drove home to me there's another place out there,
a real place, not just something I studied in school somewhere
As a young man, Bruce Murray was taken under the wing of physicist Bob Leighton,
who had developed a way to make time lapsed films of the planets
The images were extraordinary because they could show the planet rotating,
you could time-lapse it, take one frame, wait a minute,
take another frame, and so forth, and make this timelapse
And it brought to everybody the image of Mars
that the most dedicated astronomer's only infer,
'cos they don't see it that way either, they have to remember all these frames
It was an extraordinary achievement. And he did it for fun
Leighton's films brought the planets to life
For the first time,
astronomers could see one of the moons of Jupiter orbiting its giant parent
The outer planets, the ones that are huge masses of gas,
that in the case of Jupiter
and Saturn you could actually see some beautiful structure
The first thing that strikes one, as in the inner solar system,
is to just say, "my Lord, everything is different."
But Mars, the Earth's smaller cousin, was always the most tantalising
Leighton could see mysterious dark patches rotating with the planet
But what would a close encounter with the surface reveal?
In 1963, the American probe,
Mariner 4 set off to send back the first pictures from another planet
Bob Leighton was charged with bringing back the images
He asked Bruce Murray to join him
I was dragged along, or sucked along to look at it,
and to have this wonderful experience of becoming
the first experimenters to look at Mars through a close up camera
This is Mariner control centre at JPL
The spacecraft is 134.217 million miles from earth and 50,142 miles from Mars
After a journey of 8 months, Mariner 4 was homing in on its first target
The first picture will cover an area of approximately 176 miles square
on the sunlit bit of the planet
In about 4 minutes from now we should be able to determine the camera,
taking camera shutter is operating and that the recorder is running
The anticipation of not just the scientist
but the public and the news media was incredible,
because Mars was, thought to have life and in the popular mind
maybe it had Martians as far as we were concerned
Mariner 4 was a fly-by
It would only get one chance at the pictures
...the scan position for 5605 is decimal 323
10,000 miles from the surface, Mariner 4's cameras whirled into life
These signals came back, if you think of a, one element,
one picture element, one sample of er, of light
The rate at which these came in were from Mars, was one of these per second
And so it took 3 weeks for our 20 pictures to come back
Where the devil are the Mars picture interpreters?
Yeah, data's coming in, boy, what are you doing in bed?
The planet was not what they had expected
There was no sign of life here. No vegetation
Just picture after picture of a dull flat landscape
It wasn't until frame 12 that the first features became visible
What we could see were these huge craters
300 kilometres, 200 mile craters across on Mars
lmpact craters - and that meant that that,
that Mars was preserving a signature from its earliest times,
3, 4 billion years ago, and so we had a major conclusion,
stunned everybody, from these
very few pictures we got
When the news filtered through from the Soviet Union,
one man wasn't as surprised as his western rivals
Craters were exactly what Victor Safronov expected
Soon Safronov's ideas were being discussed in the west,
where superior technology allowed George Wetherill
to take the accretion theory further
I called it the planetesimal problem
And that simply says you've got a lot of objects,
small planets, moving around the sun and orbits
And what you'd like to understand
is how they accumulate together to form large planets
Wetherill's computers uncovered a terrifying period of planet formation
What you actually find if you do the problem with a computer is that,
as they grow, they start to perturb one another into orbits
which cross the orbits of another planet
Soon the neat orbits of Safronov's army of planets became fatally disrupted
As they started tugging each other off course,
the solar system was brimming with loose cannon
World-shattering collisions were inevitable
George realised that it was sort of like a wild frat party
All sort of hell breaks loose in the inner part of the solar system
Things are swung around,
half the stuff is - either hits the sun or gets thrown out to Jupiter,
which can then knock it out of the solar system
It's a very violent happening party
If Wetherill was right then during this period the inner solar system
must have been strewn with planetary debris
The four surviving planets would have had to endure
a final stage of intense bombardment
In 1973, George Wetherill got the chance to test his work
Mariner 10 was on its way to Mercury
78 million kilometres from earth,
and way beyond the scope of even the most powerful telescopes,
the surface of this planet was a total mystery
Just a few months before the Mercury mission,
I was in a meeting where people discussed what we might find on Mercury
and sort of get out minds active for thinking about Mercury,
and a very distinguished planetary astronomer, in answer to a question,
proclaimed that Mercury would have no craters on it, or very few craters
The curious thing is that the craters on Mars
were also a surprise to most planetary astronomers
After a journey that took in a fly-by of Venus,
by February, Mariner 10 was nearing its target
Subsequently, though, however,
I had the opportunity to be invited to JPL
and sit in a little room up above mission control
and see the pictures of Mercury as they came in
The first pictures of Mercury started coming in,
first it was just sort of a fuzzy ball,
and you could sort of imagine you saw craters,
but after a while it got closer and closer,
and pretty soon it started to look just like the moon
Mercury turned out to be the most heavily crated planet in the solar system
One impact was so great
that it left shock waves set in stone on the other side of the planet
It was proof of the final stage of the accretion theory
And I was just thrilled by this, you know, I knew they were there,
but this, but actually seeing them,
that I'd been thinking about all these years,
now here they are for me to look at, made me very excited
And it also excited all these military men around,
they said, they kept saying, isn't that beautiful,
its just like a 52 drop in Nam?
Here then are the inner planets
The survivors of a life or death struggle
Mercury, Venus and Mars
Each bearing the scars of creation
But what of the Earth? Surely our planet could not have survived unscathed?
In the field, Hal Levison gets a real sense of the violence
that rained down on the planets - including our own
This hole in the ground was made in a matter of seconds
Despite being a very awesome sight,
something that tells us that the solar system is still active
and that things are still running into each other,
it's a relatively small, insignificant hole in the ground
50,000 years ago, a 50-metre fragment of a world blown apart billions of years
earlier careered into the earth in what is now Arizona
Here is evidence of the final stages of accretion
But what of the world's that dwarf the inner planets?
How does the accretion theory account for the gassy giants
that rule the distant regions of the solar system?
We have very different planets,
types of planets as we get farther from the Sun,
and that's because as you get farther from the Sun the temperatures drop
And in particular, about four times more distant from the Sun than the Earth is,
we hit a point where water would condense out and become a solid
With water turning to ice,
the amount of material available to form the outer planets was far greater
Jupiter and Saturn grew so large
that they started sucking in the primordial gases
from the original dust cloud,
swelling them to hundreds of times the mass of the Earth
This region was populated with many more worlds than exist today
Their orbits were also disrupted
We can find no traces of impacts in their gassy atmospheres,
but evidence can be seen in their rotation
It is believed that a world the size of the Earth collided with Uranus
Today Uranus still rolls around the Sun on its back
When did these planet-building impacts come to an end?
I've found a lot of comets,
and I've been involved now in the discovery of 21 of them
There is nothing like the night we found Shoemaker-Levy 9
We had no idea how important that discovery was going to be
It made page 23 in the London Times,
that Carolyn and Jean Shoemaker and I had discovered this comet
Interest increased several months later,
when it was announced that Shoemaker-Levy 9
was on a collision course with Jupiter
This was not page 23 of the London Times
This was now page one. This is a very different story
Shoemaker Levy 9 was going to show us what its all about
In all of civilisation, since Galileo first looked through a telescope in 1609,
and since he first looked at Jupiter in 1610,
this is the first time that we will ever have seen a comet strike a planet
July the sixteenth, 1994 - impact day
And every available telescope is trained on Jupiter
This is how the solar system was built, comets hitting planets
Comets first hitting each other
Very slowly and it's kind of almost an embrace rather than a collision
and then these objects get bigger their gravity gets bigger,
the collisions get faster and the speed gets higher and it gets more violent
As the solar system reaches its teenage years
it's become a little bit dysfunctional
And finally, when does it end?
Well, what Shoemaker-Levy 9 taught us, is that it hasn't happened yet
Right then in the summer of 1994,
around Jupiter there's a big yellow police fence,
that says danger, keep out, solar system under construction
It's still happening
Jupiter grew a little big during the week of July sixteenth, 1994
Water was dumped on Jupiter
It had more carbon sulphide down there than had been
It was as if nature had said,
"okay guys I'm going to show you how it works
and all you have to do is watch it."
Here, then, are the gas giants
Jupiter and Saturn mark the current limit of the planet builder's theories
Far beyond these gargantuan worlds lie the ice giants, Uranus and Neptune
But out here, the accretion theory runs into trouble
The formation of Uranus and Neptune
are the greatest mysteries in the formation of the solar system,
because everything goes more slowly at greater distances from the Sun
so all these processes slow down
When we try to run the same computer programmes out there
that we did in the terrestrial planet zone, we don't get planets forming
No matter what we do,
we can't form Uranus and Neptune using those kind of models
No matter how hard I try, I can't make Uranus and Neptune go away,
they're there, and our models can't make
So we do indeed have a lot of,
a long way to go before we really figure all this out
How these worlds formed so quickly is a puzzle
Scientists don't know enough about early conditions this far from the Sun
What kinds of worlds went into the formation of Uranus and Neptune?
In 1992, two astronomers were surveying the space beyond Neptune
when they found a substantial chunk of ice
Since then they have found many more
Called the Kuiper Belt, it is now thought
that they are the building blocks of ice giants that never were
The Kuiper Belt is a region where the small ice mountains
that we've talked about actually started accreting
and building into larger things
That's really to me the region we need to look at,
because what happened there is planet formation started there
and it was frozen in at some intermediate state,
and trying to understand that will let us know in more detail
how the accretion process started
but what it shut it off is also going to be interesting
and tell us something about the processes as well
So to me the future really lies in the outer part of the solar system
But there is a planet that lies at the inner edge of the Kuiper Belt
70 years after its discovery,
the strange tiny world of Pluto may at last be making sense
Pluto was discovered in 1930, right
And it was the oddball of the Solar System right?
Most of the planets are in nice circular orbits. Not Pluto
Most of the planets are set in this plane that represents the accretion disc
Not Pluto
And it was just an oddball, it was small and icy,
and had no similarity to anything else that we really knew about
Could this small icy world be one of the survivors of accretion?
A world that somehow escaped being swallowed up by the growing Neptune,
or being hurled out of the solar system?
Could Pluto be the missing link in the formation of the ice giants?
Turns out Pluto was just the largest known member of this population
So it went from being this lonely remote oddball,
to being essentially the grandfather of a population
and we're talking about the Kuiper Belt had,
probably has more objects in it than any other region in the solar system,
so it's the most populous region in the solar system
and yet we didn't know about it 10 years ago
In the forty years since Mechta broke free from the Earth's gravity,
we've sent probes to all the planets
We've sampled the corrosive clouds of Venus
and recorded planet-wide thunderstorms on its surface
We've survived dust-storms on Mars and seen canyons that could swallow countries
We've mapped the icy moons of Jupiter and plunged into its atmosphere
We've skimmed the rings of Saturn
We've seen active geysers on the most distant
and freezing moon in the solar system
But just as the first stage of our reconnaissance of the planets draws
to a close - we have a new region to explore
In 1992, Clyde Tombaugh got a request from NASA:
Permission to visit his planet
Clyde was melted. He melted when he got that letter
He felt that all of his life's effort, all of his life's work with Pluto,
with his work at White Sands, was coming to a head
He felt that that letter was really a sign that NASA,
through their mission to Pluto,
was finally acknowledging him as the man that he really was
Clyde Tombaugh died in 1997. Pluto Express is planned to launch in 2003
It will take 12 years to reach its goal
After analysing Pluto's composition,
it will head out in search of a Kuiper Belt object - perhaps something
in their cratering record or their chemistry
will provide the final piece of the creation jigsaw
Whatever the craft finds Pluto's importance in the grand order
of the solar system is assured
It will be a manned mission to Pluto in a very special sense
It's not going to have a real living person,
but is, but you can bet that it's going to have Clyde's spirit on board
on its way to Pluto to see really what kind of a planet
that little guy really is