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Planets The 6 - Atmosphere

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A billion kilometres|from the Earth,
a small probe uncoupled from|an interplanetary spacecraft
and headed for its target.
It had a date with Jupiter.
In an encounter|that would break all records
for speed and violence,
it accelerated to the largest|planet in the solar system,
plunged|into its fearsome clouds
and was swallowed|by its atmosphere.
Without its atmosphere,
the Earth would not|be a home to us.
Rain on our faces,
wind in our hair,
the very air we breathe.
Atmosphere is what turns|our planet into our world.
To understand the other planets,
we have to understand|their atmospheres.
The journey of discovery|began here on Earth.
The first man to explore|the limits of the atmosphere
was retired US Air Force|colonel Joe Kittinger.
At the age of 72,|he is still flying.
In 1960, he attempted something|no one had tried before:
to leave the atmosphere behind.
'It was the first time anyone|went to such a high altitude.'
The first time man had been|in a space environment,
so I was concerned|about what would happen.
Project Excelsior was an attempt|to send a man to 100,000 feet
in a helium balloon.
If successful, Joe would be|the first human in space.
At 63,000 feet, unprotected,|a man's blood actually boils
because of lack of pressure.
So, for man,|space is 63,000 feet.
Any place above that,|you die without a pressure suit.
'The balloon was overhead.'
At the signal, they cut|the straps and off I lifted.
'I had confidence in myself,|the equipment and the team,
'but there's always|that unknown,
'something you may not|have covered.'
At 50,000 feet,|Kittinger hit a snag.
The glove on his rudimentary|space suit sprung a leak.
Now, what that meant was that|the blood would pool in my hand,
just continuously pool and pool.
'I didn't tell|my flight surgeon,
'because I didn't want to worry|him and felt if I did,
'he would make me|abort the flight.'
I was certain I could survive,
not having a pressure suit|glove on my right hand.
So I continued on.
'Overhead, the sky|was black as it could be.
'I couldn't see any stars,|it was that black.'
An hour and a half|after lift-off,
Kittinger reached 103,000 feet.
'I was up on a porch that was|the highest step in the world,
'looking down on our planet.
'I could see the clouds below
'and the atmosphere,|the haze layer.'
It was a very profound|feeling I had,
the realisation of just how|hostile that environment is,
and it's only 20 miles|above our Earth.
'The air outside looks the same,|but there's no air there.
'It's like being in an|environment that's cyanide -
'you take one whiff|and you're dead.
'Just 20 miles down,|there was safety and comfort,
'and an environment|that man is used to.'
Kittinger spent just|11 minutes in that netherworld,
on the brink of space.
And then he prepared to return.
So I took a final look around,|said my silent prayer,
'hit the button to start|the cameras working,
'and I jumped from the gondola.
'I fell face to Earth|for a little ways.'
And I had|no sensation of falling,
because I had|no visual reference of anything,
so I thought I was|really suspended in space.
'I turned on my back|about this time and looked up,'
and the balloon|was racing into the heavens.
I mean, at a fantastic rate.
To me, it was just flying away.
'What it was, the balloon|was standing still,
'and I was the one|that was falling so rapidly.'
Kittinger fell to Earth|at the speed of sound,
but with no air around him|it was a silent fall.
'I had no ripple of the fabric|on the pressure suit.'
'It was a very weird sensation.'
After four minutes|of falling through space,
Kittinger began to re-enter|the protective blue haze,
and was hit by the familiar|world of cloud, sky and air.
Joe Kittinger had gone|beyond the edge of the sky,
and lived to tell the tale.
'15 minutes before,|I'd been at the edge of space,
'and now I was|in the Garden of Eden.
'We don't appreciate what|a beautiful planet we have.'
'The atmosphere is a tiny layer,|it's insignificant,
'in terms of mass,|compared to the planet.
'And yet it is so key|to our experience
'and our very existence|here on this planet.'
Dave Grinspoon|is an atmospheric scientist.
'When I first got excited|about the planets,
'it was pictures|of the surface of a planet,
'the most obvious,|tangible thing that grabs you.
'But as I studied planets,
'I learned about the frontiers|of knowledge,
'some of the real mysteries,'
crucial to understanding how the|solar system became how it is,
how Earth achieved|its unique status.
And I found that a lot of|the problems that interested me
had to do with|the evolution of the atmosphere.
As far as|early astronomers knew,
other planets were just like|the Moon: airless balls of rock.
But in 1761,
a Russian star-gazer|observed an unusual event.
From an observatory|in St Petersburg,
Mikhail Lomonosov|saw the planet Venus
pass across the face of the sun.
He noticed that|the edge of the planet
wasn't crisp like the Moon.
Venus seemed fuzzy.
As the planet|crept past the sun,
he was astonished to see it|surrounded by a thick halo.
It was a sure sign|of an atmosphere.
For two hundred years,
what lay below the clouds|remained a mystery.
Was Venus a world like Earth?
The Russians sent|a probe to find out.
As Venera 4 headed for|a splash-down on Venus,
the designers' main worry
was their spacecraft might sink|and radio contact would be lost.
In October 1967,
radio dishes across Russia|were trained on Venus,
eager for news from|the world beneath the clouds.
Under a pressure|15 times that on Earth,
and when it was still 15 miles|up, Venera 4 was crushed.
The probe didn't splash into an|ocean. It never even came close.
What kind of hell lay|below the clouds of Venus?
The Russians were determined|to land a probe there.
They tested their probes|to the limit.
The Soviets set about|recreating Venus on Earth.
To mimic the severe|atmospheric conditions,
they built the world's|biggest pressure cooker.
After four years,|they had a craft tough enough
to survive the crushing inferno|of Venus: Venera 7.
Just before Christmas 1971,|Perminov and his team
saw the probe's faint signal|reporting touch-down.
They had made it.
'The first glimpses we got'
of how it looks on the surface|were from the Russian pictures
of small pieces of strange|volcanic landscapes on Venus.
'Those pictures|were mostly of the ground.
'But just in the upper corner,|you could see a bit of sky,
'this glowing - but featureless|because it's cloudy - sky.'
That was really neat,|being on the surface of Venus,
catching a glimpse of what it's|like to see the sky of Venus.
But what had the probe detected|as it fell through that sky?
'If you were plummeting through|the atmosphere of Venus,'
first you'd have to make it|through the extensive clouds.
They're not like|clouds on Earth.
They cover the entire planet,|over ten-miles thick,
so would take a long time|to get through.
'When you're actually in them,|they're diffuse, more like fog.
'But what would it be like to|stand on the surface of Venus?'
First you would scream,|and nothing else would happen.
You'd be instantly consumed|by the hot, noxious atmosphere.
But if you had a good suit
and walked out onto Venus,
the first thing you'd notice|would be the murky red light.
'On Venus,|in the middle of the day,
'it's about as light as on|a deeply overcast day on Earth.'
You'd never see|the sun from Venus,
but sunlight filters|through the clouds.
Venus is a world of|unchanging and extreme weather.
In the high clouds is a constant|drizzle of sulphuric acid.
And far below,|close to the surface,
the probes detected an unending|stream of electrical discharges.
(Eerie monotone humming)
Why there is lightning|so far below the clouds,
where it's too hot|for rain, is a mystery.
This hot, high-pressure,|corrosive atmosphere
held one more surprise.
In 1990,
an American spacecraft pierced|Venus's clouds with radar.
It saw that some of the highest|mountain tops were very bright,
as if they were covered|in something reflective.
'The high mountain|peaks seemed to be coated
'with some kind of metallic|or shiny frosting,
'something reflecting|radar energy,
'and we don't know what it is.'
It may be coated|with tellurium,
a trace metal on Earth,|which may be common on Venus,
and seems to have|the right properties.
Below a certain temperature,|above a certain altitude,
it may be frosting|all the high peaks of Venus.
Mountain tops on Earth|are covered with frozen water.
On Venus, the snowcaps|are more exotic.
It seems there's metallic snow|on the highest peaks of Venus,
which is a strange thing|to think about.
Venus turned out to be|stranger than was ever imagined.
Would our other near neighbour|be more similar to Earth?
In 1971, two Russian spacecraft|were on their way to Mars.
As the probes barrelled in,
Mars was suddenly enveloped|in a giant dust storm.
After transmitting for just 15|seconds, the craft fell silent.
The flight controllers|had no doubt
that the violent|dust storm was to blame.
But this was the first picture|from the surface of Mars.
Incomplete and fuzzy -|but there was a horizon,
and beyond it,|the shadow of a dark sky.
Five years later, another|spacecraft headed for touchdown
on the surface of Mars.
This time it was American.
It was called Viking.
'OK, maybe we could|take this opportunity
'to summarise|where we are today?'
To date, we have, of course,|landed on the surface of Mars
and taken pictures immediately|after landing, and since then.
'At the present time, we are|slowly watching the build-up
'of data that's going to be|built into a colour picture.'
And the way we're going to do it|is bring up, first the red,
which you see now.
'Here comes the green,|it'll be the second,
'and then finally the blue.
'With the last one coming down,|you're now going to see
'the surface of Mars as best|we can configure it in colour
'at the present time.
'You can see a number|of different...'
'If you douse the lights...|Oh, my gosh!'
'I wasn't even seeing|all the colours. Look at that!'
'That's pretty spectacular. It|does have a reddish hue to it.'
'And look at that sky.|Light blue sky.'
But there'd been a mistake.
Because they expected the|sky to be its familiar colour,
the engineers had unwittingly|filtered in too much blue.
The next day, they showed Mars|the way it really is.
This world has a pink sky.
Its thin atmosphere|is tinged with red dust.
Mars is a desert world.
From day to night,
the temperature swings|by hundreds of degrees.
On Mars, the colours|of the heavens
are turned on their heads.
Red skies at noon|and blue skies at sunset.
So, how did Mars and Venus,
both rocky planets|like the Earth,
get such different|atmospheres from our own?
It's a puzzle|that atmospheric scientists
are just beginning to solve.
'A big part of my study|is understanding the divergence
'of Earth's atmosphere
'from our neighbouring planet|atmospheres, Mars and Venus.'
And I say divergence,
because the three probably|started out very similar,
much more than they are today.
Four and a half|billion years ago,
the planets formed from|a giant cloud of dust and ice.
Mars, Venus and Earth|were worlds of seething lava,
pummelled by meteorites and|surrounded by a veil of steam.
Mars didn't have enough gravity|to hold on to that atmosphere.
But while the Martian air|was drifting away,
Earth and Venus remained|covered in a thick layer of fog.
After that, Earth settled down|and formed oceans. It rained.
'The same may have|happened on Venus.'
Venus probably had oceans|when it was young,
but that steam|in the atmosphere,
with enhanced sunlight,|being closer to the sun,
led to what we call|a "runaway greenhouse".
Venus never lost|its steamy clouds,
and like a thermal blanket, they|trapped the heat in forever.
The hotter it got, the more|steam boiled off the oceans.
The planet became locked|in a global greenhouse effect,
and it meant disaster.
Eventually, Venus's oceans just|kept boiling, and boiled away.
On Earth, we have|a small greenhouse effect,
because of the CO2|and water in our atmosphere.
and it's a good thing.
The greenhouse effect|gets a bad rap
because of global warming.
We worry about too much effect.
But if we didn't have one, we|wouldn't be able to live here.
'We get 30 degrees of warming|from Earth's greenhouse,
'just enough to keep it|in the temperate range it's in.'
For planetary scientist|Andy Ingersoll,
the delicate balance of|Earth's climate is fascinating.
'I would say that we've learned|there's a narrow habitable zone
'around every star.
'Mars is too cold,|Venus is too hot.
'Earth is just right, and|the extremes are frightening.'
For me, I'm a meteorologist,
the fascinating thing about|Earth compared to other planets
is it has the most unpredictable|weather in the solar system.
The dominant weather|on Venus seems to be
just the circulation|of the atmosphere.
'It'd be probably pretty boring|if you could stand the heat,
'day after day of temperatures|hot enough to melt lead.'
That's predictable.
'On Mars, the dominant|weather you'd notice
'would be the day /night cycle,
'like a desert|or semi-desert area on Earth.'
It's another sunny day|and it will get cold at night.
'And that's predictable.
'The Earth is sort|of in between,'
and that's where|the weather is unpredictable.
There is another world|with weather,
and it's written|on a colossal scale.
The giant planet Jupiter.
'The whole planet is atmosphere|because it's a gas ball.'
And there we have examples of|storms that last for 300 years,
or maybe even longer than that.
I knew there were|300-year-old storms,
and I had this picture|of these storms calmly spinning.
And when Voyager started|taking close-up pictures,
we realised that at the|smaller scales, it was chaos.
'Everything was changing.
'The tiny storms were coming|and going every few days,
'yet we had these large storms|that were very stable.
'And it deepened the mystery of|why the large storms endured.'
Jupiter's Great Red Spot has|existed for three centuries,
but its future|is by no means certain.
The Great Red Spot is three|times bigger than Earth,
but it's only one of a whole|class of large storms.
The next largest class|was three white ovals
that formed about 60 years ago
'and had been keeping their|distance from each other.
'But last year|two of them merged,'
so it was a historic event|for Jupiter weather men.
What forces could be driving|the giant storms?
Voyager could only|look at Jupiter's surface.
To find out more,
a probe would have to dive right|into those swirling clouds.
NASA put one of its|most experienced engineers
to work on the design.
'For Jupiter,|the central problem was'
that the planet|is so massive, so gigantic,
that in falling into it from a|great distance, as a probe does,
as a probe approaches a planet|it falls into the gravity field,
'and falling into Jupiter|brought you up to speeds
'of sixty kilometres per second.
'If you figure that in miles|per hour, it's a big number.'
120,000, 140,000 miles per hour,|something like that.
In the 1960s, Al Seiff had|designed the heat shields
that saved pioneers like|John Glenn and Neil Armstrong
from burning up on re-entry.
Seiff had a hand in almost every|spacecraft NASA ever built.
'Spacecraft is stable.
'Galileo is on its way|to another world.'
But Jupiter|was his biggest challenge.
'We worked, as it turned out,
'for nearly 20 years|in getting that experiment'
mounted and ready to go,
and finally to fly out into the|solar system to that distance.
And it was the least certain|of success of any mission,
because of the challenging|entry conditions.
In December 1995,
Galileo began|its kamikaze dive into Jupiter.
'The heat shield itself was|made out of carbon phenolic.'
Carbon heats up|to about 4,000 Kelvin
and then it starts to vaporise,|and that's what this shield did.
'The heat shield was about 80%|vaporised, about 20% remaining.
'It was white hot, white hot.'
When the fiery entry was over,
the probe began drifting gently|into the planet's atmosphere.
It was hoped that Galileo would|detect clouds and rainfall,
and uncover the secrets|of Jupiter's weather.
But Andy Ingersoll|was frustrated.
I was surprised at how|little water they found,
because water is so important|to the weather on Earth,
and it presumably was important|to the weather on Jupiter.
Although Jupiter|is covered with clouds,
Galileo had the bad luck to fall|into a narrow gap between them.
It appears Galileo went|into a desert of Jupiter,
and that if we'd gone somewhere|else, we would have found rain.
As it sank ever deeper|into the atmosphere,
Galileo detected|the winds picking up
and the weather|becoming more turbulent.
The probe was approaching|the source of the giant storms.
But it could give no more clues.
Three hours after|it began its descent,
Galileo ventured too far|into Jupiter's boiling interior.
'There was no buoyancy|to stop it from going down,
'so the high temperatures|in the interior'
ultimately caused the probe|to melt and vaporise,
and today the Galileo probe|is part of Jupiter's atmosphere.
We have actually slightly|contaminated this giant planet.
Was there another world|to compare to the Earth?
For centuries,|astronomers had watched
For centuries,|astronomers had watched
a tiny object circling|near the rings of Saturn.
It was bright, like Venus.
It almost seemed to glow.
Could this world|have an atmosphere too?
Astronomers were captivated.
It was the moon Titan.
'I think of the astronomers|of yesteryear -
'like Christiaan Huygens|who discovered Titan
'and those after him,|who spent their lives
'looking through telescopes,|trying to eke out information
'about the solar system,|and about Titan in particular -
'and feel a tremendous|sense of sympathy for them.'
Modern-day planetary|scientists like myself,
know that we can hypothesise|and come up with theories,
but eventually we'll know|exactly what the truth is.
The first close-up pictures|of this enigmatic moon
came in 1980,|when Voyager flew by.
'It was clear it was|a satellite with an atmosphere,
'which made it unique,
'because till then we associated|atmospheres with planets.'
The composition|of Titan's atmosphere,
the fact that it's 90%|to 95% molecular nitrogen,
along with the fact that|its atmosphere is pretty dense,
surface pressure is comparable|to that of Earth - a bit more -
makes it kind of|an analogue with the Earth,
which is surprising, because|no one expected years ago
you'd find an analogue|of Earth out near Saturn.
The surface of Titan remained|hidden from Voyager's cameras.
But since then,|the Hubble Space Telescope
has managed to peer|through the thick clouds.
There are tantalising signs
of what look like|continents and oceans.
Some say this mysterious moon|has seas of liquid methane.
It is a world|planetary scientists
are more eager|than ever to explore.
In a matter of a few years,|once we get to Titan
and once we get to Saturn,|we'll find out a great deal
about what makes|this object tick.
'Now we have an entire mission|devoted to the study of Saturn,
'and Titan is a major target.'
It's the Cassini mission,|launched in October '97.
I, of course, was there.
It was the most spectacular|thing I'd ever witnessed.
'It was also very emotional|because I and my colleagues
'have spent seven years|developing instrumentation
'in the space craft itself|to go back to Saturn,
'and now we have a six-year wait|for it to get there.'
Cassini will arrive|at Titan in November 2004,
and release a probe|that will embark on a journey
down to the shrouded surface|of this distant moon.
Parachutes will deploy,|the air shell will be jettisoned
and the probe, instrumented with|six scientific investigations,
will begin a two-and-a-half-hour|descent through the atmosphere.
'On the way down it will measure|the pressure, the temperature,
'the composition|of the atmosphere,
'and will continue down|until it finally breaks through
'what we think to be|the lower cloud deck.'
The probe will slowly sink|into an alien atmosphere,
taking pictures|throughout its descent.
'We don't know what kind|of material it might land in.'
The surface of Titan is likely|to be ice, covered with debris
that has rained|out of the atmosphere.
There may also be liquid|on the surface, seas and lakes.
With pools of methane,|oily fog, maybe even rain,
Titan could bear a frigid|resemblance to the Earth.
'Here is a body with a surface|and an atmosphere.
'You could, properly equipped,|walk on the surface of Titan,
'and see the results of wind|erosion and flowing liquids,
'and seas and waves and winds.'
It has almost a feeling|of home to it, and I think
that's a tremendously|powerful feeling for us.
Titan has brought back|the spirit of the early days
of planetary exploration.
There's a new world|out there to discover.
'Our current knowledge of Titan|is comparable to our knowledge
'of Venus in the '50s and '60s.'
In those days, when we|were trying to study Venus,
we imagined|Earth-like scenarios,
and I suppose we're doing|the same for Titan.
We're imagining lakes,
although we imagine|they're made of hydro-carbons,
but still we feel comfortable|with that concept.
It may turn out Titan is|dry as a bone, just like Venus.
'You learn humility.
'You study Earth|and think you understand it,
'then say "OK,|I have these principles,
'"I'll apply them to another|planet. Let's go there."
'You're always surprised.
'It's always|not what you expect,
'and that teaches you|how little you know,