The Oort Cloud: a stepladder for the Colonization of outer space
Oort Cloud...what an amazing, fantastic cosmic animal...
It's the unicorn of fairy tales, which everyone talks about but no one has ever seen...it's
a shell of debris enclosing our solar system. It is a swarm of bees buzzing around the Sun,
it is a dynamic system of large cometary nuclei lazily revolving around our star
with periods of tens of millions of years... Just try to think about it... Billions of huge
blocks of ice slowly gravitating in the darkness of sidereal space like invisible icebergs, faintly
illuminated by a Sun that at that distance comes at most to shine like Jupiter seen from Earth.
Hundreds of billions of icebergs completely invisible from Earth,
not only individually, but also as a "Cloud": any optical technique-radio, infrared,
radar-is indeed powerless to reveal them. And even sending exploratory probes from down there
to transmit information to us is beyond current possibilities; it would be an undertaking with the
same requirements as an interstellar mission. Even when, as with Voyager, the gravitational
field of Jupiter was exploited to impart escape velocity from the Sun to the probe, it would take
millions of years to reach the Oort Cloud. We would never make it, one would be
inclined to say, resign ourselves. Yet, the colonization of the Oort
Cloud represents an unprecedented opportunity for humanity in our journey to the stars. Not
only does it offer us the chance to explore new worlds and deepen our understanding of the
universe, but it also brings us closer to the ambitious goal of reaching the nearest star.
In this video, we will explore why the progressive colonization of the Oort Cloud would be beneficial
to our species and analyze the technological steps needed to make this dream a reality.
For thousands of years, astronomers have watched comets approach Earth and light
up the night sky with their haphazard appearances.
Over time, these observations naturally led to a whole series of questions.
Where did those objects come from? Certainly, their surface material vaporized as they
approached the Sun, thus forming very long tails, and this was an indication that they came from
places where the ice must have been in a solid state--but from what regions? From what distances?
Over time, continued observations led to the belief that far beyond the Sun and planets,
there must exist a large Cloud of icy material and rock from which most of these comets came,
known as the Oort Cloud after the astronomer who first theorized its existence.
And if we said "theorized," and not "discovered" or "demonstrated," there is a good reason...
Although thousands of papers have been written about it, in fact, its existence is still only
a hypothesis, a scientific speculation. But by analyzing the orbits of the numerous
long-period comets believed to have come from those remote distances, astronomers claim to
have even been able to determine the structure and size of this immense deposit of icy cores.
Sort of like when in the Middle Ages people began to speculate about the existence of
lands beyond the Atlantic by examining branches and remnants of unknown vegetation that reached
from the west to European shores. Cloud comets are in fact so weakly
linked to the Sun that even the motions of nearby stars can easily change their orbits.
Approximately every million years a dozen stars pass within three light-years of the Sun,
and these close encounters are enough to disrupt the orbits of the bodies belonging to the Cloud,
which are thus sent toward the inner Solar System on highly elongated elliptical orbits. When they
first enter the area of the major planets, such bodies, which are cometary nuclei, suffer strong
gravitational perturbations that can either "shoot" them into interstellar space, or make
them periodic thus joining the group of comets with a long period and uniform distribution.
Numerical simulations in recent years have shown that stellar perturbations are sometimes anything
but mild. From time to time, a star comes so close to the Sun that it crosses the Oort Cloud,
and then the perturbations are most violent. Statistically, a star is expected to pass within
10 thousand Astronomical Units (One astronomical unit is the Earth-Sun distance, which is about 150
million kilometers) of the Sun every 40 million years, and within 3000 AU every 400 million years.
Comets close to the star's trajectory are hurled into interstellar space, while the orbits of
others are heavily modified. The next expected close passage will occur in 1.4 million years,
and the star will be the red dwarf Gliese 710, which will cross the outer part of the Oort Cloud
at a distance of 70 thousand AU from the Sun! This passage could increase the frequency
of comet occurrence in the inner Solar System by about 50 percent.
As far as we can speculate today, the Oort Cloud is a roughly spherical-shaped
ensemble that is believed to surround the sun at a maximum distance of about 100,000
AU, or 1.5 light-years. This places its outer Cloud boundary in interstellar space,
almost halfway between the Sun and the Alpha Centauri system.
The ensemble is also believed to consist of two distinct regions:
a spherical Outer Oort Cloud, a kind of 80,000 AU-thick shell whose first offshoots meet at
20,000 AU from the Sun, and a so-called inner Hills Cloud in the shape of a toroidal disk,
which would extend from 2,000 to 20,000 AU. The outer Oort Cloud could have trillions of
objects larger than 1 km and billions measuring about 20 km in diameter.
The vast majority of which consists of frozen volatiles, such as water, methane, ethane,
carbon monoxide, hydrogen cyanide, and ammonia. The total mass of the system is estimated very
roughly. Calculations a few years ago predicted up to 380 Earth masses, but a better understanding
of the size distribution of long-period comets has led to much lower estimates…
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As for origin, the Oort Cloud is thought to be a remnant of the original protoplanetary disk formed
around the sun about 4.6 billion years ago. The most widely accepted hypothesis is that
objects in the Oort Cloud initially coalesced much closer to the sun as part of the same
process that formed the planets and minor planets, but that gravitational interaction with young gas
giants such as Jupiter then relegated them to the distances at which they are now...
But perhaps the Sun did not form as a solitary star...
According to the most widely accepted theories of the day, the Sun may have captured a large
number of small icy bodies from the stars to which they belonged when it was still part of
a fledgling cluster of stars, thus creating its own huge envelope of cometary nuclei.
In fact, our star is believed to have formed at the same time as hundreds of
other stars closely packed within a gas Cloud. This new model shows that subsequently, the Sun
would have gravitationally captured a vast Cloud of comets as the young star cluster dissipated.
If true, the Oort Cloud would contain a hodgepodge of material samples from a large number of the
Sun's close relative stars--and it could be concluded that more than 90 percent of comets
from the Cloud could have an extrasolar origin! This hypothesis could open up truly suggestive
scenarios for what concerns the human exploration of the region, which could turn from an almost
impossible target into the high road to the stars. Or at least ... to the nearest star!
It is true that the Oort Cloud is thousands of times as far away as the Kuiper Belt...
Just as it is also true that Voyager 1 - the fastest and farthest of the interplanetary
space probes currently out of the solar system - will reach the nearest edge of
the Cloud only in about 300 years, and that it will take at least 30,000 years to cross it...
However, the idea is gaining ground among space travel experts that the Oort Cloud could become
for humankind much more than a destination worth exploring. Indeed, in that gigantic agglomeration
of icy worlds, the most visionary minds are glimpsing the possibility of using the Cloud as a
kind of stepladder on which to climb one step at a time, to get to the stars and extrasolar planets!
It has already happened with the Moon... If our species had not had at its disposal
that convenient platform with a view of the cosmos represented by our natural satellite,
we could hardly have dreamed of arriving on Mars today. Without that convenient stepping stone,
we certainly would never have even remotely thought we could make a single leap from
Earth to the red planet. The chasm would have been psychologically too great!
And the same thing is now happening with the Oort Cloud, stretching out into outer space
until its peripheral comets are almost confused with those of Alpha Centauri...
Back in the late 1990s, following this insight, astronomer Carl Sagan imagined that over time
there would be human settlements on the asteroids of the Kuiper Belt,
and then among the comets of the Oort Cloud. And that one day humans would be able to settle on
these small worlds and redirect and maneuver them to use them as "spaceships" to eventually
leave the solar system and set sail for the stars. British physicist Freeman Dyson also suggested in
his writings that within a few centuries, human civilization would move into the Kuiper belt and
then make the great leap to the Oort Cloud. First to reach the innermost comets ... and
then as happened in the past for the colonization of a large archipelago of islands,
from comet to comet they would reach the outer edge of the Cloud. And from there,
where the cometary hives of the Sun and Alpha Centauri almost merge, make the final leap.
The colonists, according to Dyson, would have been able to settle in small groups
inside large caves dug inside the icy cores, exploiting nuclear fusion...
But now we don't want to venture on the basis of what technologies we will be able to do this...
These are, of course, projects to be carried out on the scale of centuries, so any fantasy we have
about them would undoubtedly be outweighed by the reality of a still very distant future.
Many people believe that interstellar travel is impossible. But perhaps not... it is just
incredibly difficult to achieve... exactly as a flight to Mars would have appeared to Christopher
Columbus and other navigators 500 years ago. In fact, amazingly, the ratio of Earth-Mars
and Spain-Caribbean distances is 80,000 to 1: roughly identical to the ratio of
Earth-Alpha Centauri to Earth-Mars distance! Therefore, if it has taken 500 years (since
the time of Columbus) for the development of the technology that is enabling us to get to Mars,
then why not think that in another 500 years, we will have already colonized the
entire solar system and are about to bring our colonies to the Oort Cloud as well?
In the Cloud, the average separation between comets is about 20 AU. The Voyager probes took
nine years to travel a comparable distance, so obviously our colonists in the outer solar
system will want something much faster. Solar sail-based methods obviously won't
work well that far out, which leaves nuclear power as the only viable option.
The nuclear thermal rockets we could build now could cut travel times in half,
down to a few years. More advanced models could achieve further reductions,
Nuclear pulse propulsion, on the other hand, can easily reach one percent of the speed of
light or so even with early versions of the technology, which might not be enough
for a viable interstellar mission but is more than enough to move through the Oort Cloud.
A displacement of 20 AU using a constant acceleration of 1 g would take only 12
days at a maximum speed of 1.8 percent of the speed of light. This would make inter-colony
travel fairly easy and would become the dominant spaceflight technology in the outer solar system.
The same nuclear pulse propulsion that can propel a ship at 1 percent of the speed
of light could propel an entire colony, including the comet, at the same speed.
At that speed, Alpha Centauri could be reached in 430 years. At 5% of the speed of light,
which would require more advanced technology, Alpha Centauri could be reached in 86 years.
Generational time scales would be required to undertake such a "slow boat" journey, but even at
more normal speeds and normal colonization rates, eventually, the Oort Cloud civilization would
expand so much that the front line of colonization would be closer to another star than to the Sun.
From there, perhaps over many centuries, their descendants will
slowly migrate inward into a new solar system. In this way, human civilization could expand (very
gradually) to the stars even if no dedicated manned interstellar mission is ever launched.
This opens the next phase of the final frontier, that of other solar systems beyond our own.
The last frontier of the solar system, the Oort Cloud,
will eventually prove to be a mere stepping stone to a wider universe of possibilities.