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Cosmic Journeys: Voyage to Pandora: First Interstellar Space Flight
Poziom:
Temat: Nauka i technologia
The year is 2154. Our planet has been ruined
by environmental catastrophe.
In the movie Avatar, greedy prospectors from
Earth descend on the world of an innocent
hunter-gatherer people called the Na'vi.
Their home is a lush moon far beyond our solar
system called Pandora.
Could such a place exist?
And could our technology... and our appetite
for exploration... one day send us hurtling
out to reach it?
In fact, the supposed site of this fictional
solar system is one of our most likely interstellar
targets, until a better destination turns
up.
Pandora orbits a fictional gas planet called
Polyphemus.
Its home is a real place... Alpha Centauri...
the brightest star in the southern constellation
of Centaurus.
At 4.37 light years away, it's part of the
closest star system to our sun.
Alpha Centauri is actually two stars, A and
B, one slightly larger and more luminous than
our own sun, the other slightly smaller.
The two stars orbit one other, swinging in
as close as Saturn is to our Sun... then back
out to the distance of Pluto.
This means that any outer planets in this
system... anything beyond, say, the orbit
of Mars... would likely have been pulled away
by the companion and flung out into space.
For this reason, Alpha Centauri was not high
on planet hunters' lists... until they began
studying a star 45 light years away called
"Gamma Cephei." {SEF-ee-eye}
It has a small companion star that goes around
it every 76 years. Now, it seems... it also
has at least one planet.
That world is about the size of Jupiter, and
it has planet hunters excited. Perhaps two-thirds
of all the stars in our galaxy are in so-called
binary relationships.
That means there could be many more planets
in our galaxy that astronomers once assumed.
At least three teams are now conducting long-term
studies of Alpha Centauri... searching for
slight wobbles in the light of each companion
star that could indicate the presence of planets.
If they find a planet that passes in front
of one of the stars, astronomers will begin
intensive studies to find out what it's like.
One of their most promising tools will be
the James Webb Space Telescope, scheduled
for launch in 2014 or 2015. From a position
a million miles away from Earth, it will deploy
a sun shield the size of a tennis court, and
a mirror over 21 feet wide.
The largest space telescope ever built, it
will offer an extraordinary new window into
potential solar systems like Alpha Centauri.
With its infrared light detectors, this telescope
will be able to discern the chemical composition
of a planet's atmosphere... and perhaps whether
it harbors a moon like Pandora.
One prominent planet hunter predicted that
if a habitable world is found at Alpha Centauri,
the planning for a space mission would begin
immediately.
Here's that star duo as seen by the Cassini
spacecraft just above the rings of Saturn.
To actually get to this pair of stairs, you
have to travel as far as the orbit of Saturn,
then go another 30,000 times further.
Put another way, if the distance to Alpha
Centauri is the equivalent of New York to
Chicago, then Saturn would be just... one
meter away.
So far, the immense distances of space have
not stopped us from launching missions into
deep space.
In 1977, the twin Voyager spacecraft were
each sent on their way aboard Titan 3 Centaur
rockets.
After a series of gravitational assists from
the giant outer planets, the spacecraft are
now flying out of the solar system at about
40,000 miles per hour.
They are moving so quickly that they could
whip around the Earth in just 45 minutes,
twice as fast as the International Space Station.
Voyager I has now traveled over 110 astronomical
units. That's 110 times the distance from
Earth to the Sun... or about 10 billion miles.
But don't hold your breath...
If it was headed in the right direction, it
would need another 73,000 years to travel
the 273,000 astronomical units to Alpha Centauri.
When it comes to space travel, we've yet to
realize the dream forged by rocketeers a century
ago.
A Russian school teacher, Konstantin Tsiolkovsky,
inspired generations of space visionaries
with sophisticated ideas about multi-stage
launch vehicles.
He imagined the construction of space stations
in Earth orbit, and eventually vast permanent
space colonies.
In time, he predicted, we'd evolve into a
whole new species... Homo Cosmicus.
Since then, rocketry's greatest advances have
centered on ways of containing explosive propellants...
and methods of maintaining stable flight at
high speeds.
The problem is that chemical rockets are just
not efficient for long distance space travel.
To reach the speed needed to escape Earth's
gravity, 17,000 miles per hour, the space
shuttle must carry fifteen times its weight
in fuel. And that's efficient, compared to
some other rocket systems. And you'd need
to travel more than 25,000 miles per hour
to break free of Earth's orbit and go anywhere
else.
A NASA study showed that to send a space shuttle
sized craft to Alpha Centauri in 900 years
would take an unbelievable amount of fuel:
10 to the 137th kilograms of rocket propellant.
Suffice it to say... it's more mass than is
in the entire visible universe.
While only a very tiny percentage of NASA's
budget goes to advanced propulsion, there
are some promising ideas on the drawing board.
Rockets powered by nuclear fuel...
Or plasma... a supervolatile gas.
Huge sails pushed along by the pressure of
photons from the Sun.
Ion drives.
To reach Alpha Centauri within a human time
scale, we'll have to go with most potent fuel
in nature that we current know...
It's the science fiction fuel of choice...
Anti-matter.
In James Cameron's Avatar, hybrid nuclear
fusion and antimatter engines power a mile
long interstellar spaceship. At a speed of
670 million miles per hour, this vehicle makes
the journey to Alpha Centauri in just six
years.
Anti matter really does exist... as the mirror
image of the universe we know. It consists
of electrons and protons, but with their electrical
charges reversed. Whenever it comes into contact
with normal matter, the two annihilate each
other in a ferocious blast of energy.
Large amounts of antimatter were created and
destroyed in the fiery dawn of our universe,
the Big Bang. But somehow, in one of the great
mysteries in science, we were left with a
universe whose visible substance is almost
all normal matter.
The universe still produces antimatter through
powerful collisions... such as a jet from
a black hole slamming into a cloud of gas.
When matter and antimatter obliterate one
another, they emit gamma radiation that we
can then detect with instruments such as the
Fermi Gamma Ray Space Telescope.
Fortunately, black holes aren't the only way
to generate antimatter. In giant labs like
the Large Hadron Collider, scientists accelerate
atoms to nearly the speed of light... and
blast them together to expose their fundamental
constituents.
Small amounts of antimatter can be made this
way, but it's incredibly expensive. With a
dedicated facility, the cost of producing
it might come down far enough to produce usable
amounts.
And that's the hope of one researcher...
Dr. Gerald Smith has been working for over
a decade to find a way to trap this volatile
substance... and store it in isolation from
the rest of the universe.
Smith and his colleagues have designed a trap
the size of a cigar case.
It sits within a tank filled with liquid nitrogen
and liquid helium designed to cool it down
to 270 degrees below zero.
Once injected into this trap, antimatter particles
are suspended by magnetic fields, within a
vacuum as empty as deepest space.
But the problem is that anti-electrons, called
positrons, tend to repel each other... explosively.
That makes it tough to store more than a few
at a time.
This team now believes it may have discovered
a pathway to storing large amounts over longer
periods of time.
Their solution lies in combining positrons
with electrons, forming an element called
positronium. In theory, with the right magnetic
fields, these electrically neutral atoms might
be held indefinitely.
When released under controlled conditions,
ultra high-energy antimatter beams could turn
out to be ideal cancer killers... or lead
to revolutionary industrial applications...
Or perhaps, one day... they could power long
distance space flight.
It wouldn't take much. Antimatter is so potent
that it defies common sense: A chunk the size
of a small coin could propel the space shuttle
into orbit.
Smith estimates that once in low Earth Orbit
a human mission to Mars would take as little
as 10 milligrams worth.
The basic idea of an anti-matter rocket engine
is simple. A beam of positrons is released
into the engine core... where it annihilates
the surface of a metal plate. That creates
an explosion that propels the craft forward.
Another design uses a sail. A cloud of antimatter
particles reacts explosively to its surface...
propelling it forward.
Short of traveling to another solar system,
there may be good reasons to contemplate developing
antimatter propulsion.
A preliminary mission would speed beyond the
orbit of Pluto, sending back close-up images
at dark planet-like objects that ring the
solar system out in the Kuiper Belt.
A longer distance probe could reveal new details
about the Oort Cloud, a vast realm of comets
that envelopes the solar system.
Once out there, it could sample particles
that make up the interstellar medium... or
send back unique data sets on dark matter
- the invisible stuff that makes up the overwhelming
portion of our Universe.
To make it all the way to Alpha Centauri within
50 years, an antimatter probe would have to
gradually accelerate to around ten percent
the speed of light... that's 67 million miles
per hour.
It would then gradually decelerate as it approached
its destination.
At those speeds, hitting even a grain of dust
could destroy the spacecraft. So it might
be best to slow the journey down to a century
or more.
It's safe to assume for now that we'd only
send a probe there if we discovered a habitable
world.
There may be other choices in our solar neighborhood.
They include Proxima Centauri, a red dwarf
star 4.2 light years away that may be gravitationally
bound to Alpha Centauri.
Beyond that, not quite 6 light years away,
is Bernard's Star.
Or there's Lalande 21185, a red dwarf 8.3
light years away. We already know it has two
Jupiter-sized planets.
There are at least 22 stars within 12 light
years of Earth.
And anyway you look at it, the first interstellar
voyage will be a quantum leap for humanity.
The urge to reach out to distant horizons...
to climb the highest peaks... to push ourselves
past our perceived limits... seems to be a
vital part of what makes us human.
Yet explorers of old set off not just because
"it was there." At times it was greed, hunger,
fear, and despair that propelled them from
their homelands... and allowed them to endure
their long journeys.
Whether we attempt to make a leap to the stars...
may come to depend on how we regard this planet.
To the physicist Stephen Hawking, the journey
is imperative.
"I don't think the human race," he said, "will
survive the next thousand years unless we
spread into space. There are too many accidents
that can befall life on a single planet."
Indeed, we can't foresee the impact of wars...
social upheaval... or the course of human
civilization in coming centuries.
But today we can see the often conflicting
trends today that could one-day propel us
out into the interstellar void.
On one hand, the technological advances that
might make such a mission possible could revolutionize
many other aspects of life on this planet.
The ever-increasing rate at which numbers
of transistors can be placed inexpensively
on a computer microchip has become a metaphor
for the advance of all technologies in this
century.
From a few thousand transistors on the first
printed circuits of the 1970s... computer
chips now have billions etched onto their
surfaces.
Even that number could seem amazingly small
in another few decades.
Many observers forecast a steep rise - even
an acceleration - in the pace of invention
and basic research... and for whole of new
solutions to the problems of energy, food
production, health, and more.
On the other hand, major periods of scarcity
may loom.
In the 20th century, the world saw the largest
increase in its human population, from less
than two billion up to six billion.
The world's population is now around 6.8 billion.
It's expected to reach 9 to 10 billion by
the year 2040, with the biggest gains in Asia
and Africa.
According to a recent UN report, the world
will have to produce 70% more food by the
year 2050... and at least that much more energy...
to sustain its population.
The scarcity of simple clean water in some
regions is already frightening.
Now throw in environmental impacts like rising
sea levels or the spread of deserts linked
to a gradually warming climate. The culprit,
to most scientists, is rising emissions of
greenhouse gases like carbon dioxide since
the start of the industrial revolution.
This map charts rising temperature readings
from the year 1885 through to the present.
In some places, they've gone up by as much
two and a half degrees Fahrenheit.
Computer models project the trend out to the
end of this century. Depending on population
growth, energy use, and conservation... temperatures
could rise anywhere from two to eleven degrees
more.
Will technological advancements allow us to
halt the degradation of our natural environments
and increase the carrying capacity of our
planet?
Will we find ways to mitigate the impacts
of war, natural catastrophes, or political
upheavals?
No doubt, if or when we launch our first mission
beyond this solar system, the occasion will
spur reflection on who and what we have become
as a people... as a planet... just as the
first missions to the Moon and our neighboring
planets once did.
At first, we'll send a probe designed to relay
basic information on what's there... on a
world whose light we have only studied from
afar.
As this cosmic emissary makes its way across
the void, we on Earth will continue to struggle
in our pursuits of happiness, prosperity...
and mere survival.
When it arrives, we'll scan the data for evidence
of a world like our own... one that may harbor
life.
How will our perspectives on that world -
and upon our own - have changed?
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