Oort Cloud

Episode Transcript

Speaker 1 (00:00):
Hello listeners, time once again for another episode the Science
Stuff to Blow Your Mind Podcast, a show dedicated to
blowing your mind with science. We've got a good episode
for you today. We're going to talk about the Ort Cloud.

(00:23):
You heard me. The Ort cloud is a vast spherical
shell of icy objects believed to surround the Sun at
a great distance, far beyond the orbit of Pluto and
the Kuiper Belt. This theoretical cloud extends roughly from two

(00:47):
thousand astronomical units to possibly one hundred thousand or more
an au, being the average distance between Earth and the
Sun about ninety three million miles. It forms the outermost
boundary of the Sun's gravitational influence, marking the edge of

(01:08):
our Solar System's realm and transitioning into the interstellar medium.
The Ort Cloud is not directly observable with current telescopes
due to its extreme distance in the small size of
its constituents, but its existence is inferred primarily from the

(01:31):
trajectories of long period comets entering the inner Solar System.
The concept of the Ort cloud was first proposed independently
in nineteen fifty by Dutch astronomer Jan Ort and also
by astronomers Ernst Opik and others to explain the source

(01:55):
of long period comets. Jan Ort observed that these comets
appeared to come from all directions in the sky, which
suggested a spherical distribution of cometary bodies rather than a
flat disk like the planets. This idea was revolutionary as
it implied a distant reservoir of cometary nuclei extending far

(02:19):
beyond known Solar System objects. The hypothesis helped explain the
origin of comets with orbits lasting thousands or even millions
of years, something that could not be accounted for by
closer sources such as the asteroid belt or Kuyper Belt.

(02:39):
The objects populating the or cloud are thought to be
composed primarily of ices, water, ice, methane, ammonia, carbon dioxide,
and other frozen volatiles mixed with rocky material. These bodies
are remnants from the early Solar System, left over debris

(03:00):
that fail to coalesce into planets. They are often referred
to as icy planetesimals because of their vast distance from
the Sun. These objects remain frozen, solid, dormant, and inactive
until gravitational perturbations send them hurtling inward, where solar heating

(03:23):
causes them to develop glowing commas and tails, the characteristic
feature of comets. Astronomers divide the ork Cloud into two regions,
the inner ort cloud sometimes called the Hills Cloud in
the outer ort cloud. The inner oort Cloud lies roughly

(03:45):
between two thousand and twenty thousand AU and is thought
to be a thick taurus or disk shaped region containing
a dense population of cometary bodies. The outer or cloud
extends from twenty thousand AU up to possibly one hundred
thousand AU and forms a spherical shell around the Solar System.

(04:09):
The outer cloud is much less densely populated, but is
the source of the long period comets that occasionally visit
the inner Solar System. This layered structure likely results from
the complex gravitational interactions with the giant planets and passing
stars during the Solar System's early history. The prevailing theory

(04:32):
of the Ork Cloud's formation posits that it originated from
the protoplanetary disc of the early Solar System about four
point six billion years ago. During the chaotic period of
planet formation, gravitational interactions with the giant planets, especially Jupiter

(04:54):
and Saturn, scattered I see planetesimals outward. Some were ejected
entirely from the Solar System, but many were slowed down
by the Sun's gravity and nudged into distant, stable orbits
over millions of years. Interactions with passing stars and the

(05:14):
gravitational pull of the Milky Way galaxy helped shape these
orbits into the roughly spherical distribution we associate with the
Orc Cloud today. The Ork Cloud is considered the primary
source of long period comets, whose orbits can last thousands
or even millions of years. When gravitational disturbances caused by

(05:39):
passing stars, galactic tides, or molecular clouds perturb objects in
the Ork Cloud, some are sent plunging toward the inner
Solar System. As they approached the Sun, the ices on
these comets sublimate, forming commas and tails visible from Earth.

(05:59):
This influx of new comets from the distant or cloud
replenishes the population of observed comets, which otherwise would have
depleted over time by disintegration and solar radiation. Though both
the Ork Cloud and Kuiper Belt are reservoirs of icy
bodies in the Solar System, they differ in location, structure,

(06:23):
and dynamics The Couper belt lies beyond Neptune's orbit, approximately
thirty to fifty Au from the Sun, and forms a
relatively flat, disc shaped region populated by dwarf planets like pluto,
asteroids and comets. It is the source of short period

(06:45):
comets in orbital periods under two hundred years. In contrast,
the Oor cloud is a distant spherical shell extending tens
of thousands of Au and is the source of long
period comets with orbital periods of thousands to millions of years.
The kuyperbelled objects orbit in a plane similar to the planets,

(07:08):
while ork cloud objects orbit in all directions. Direct detection
of or cloud objects has so far eluded astronomers because
these bodies are tiny, dark, and extremely far away. Instead,
the existence of the Orc cloud is inferred through indirect

(07:28):
evidence the observed orbits of long period comets that derive
from random directions in the sky inconsistent with known Solar
system planes. Computer simulations solar system formation also support the
presence of such a cloud. Additionally, the distribution and velocity

(07:48):
of these comets fit models of gravitational interactions with a
distant spherical reservoir. Future detection may rely on extremely sensitive
telescopes or space probes sent far beyond the Kuiper Belt.
The ORT cloud serves as a historical archive of the

(08:10):
early Solar systems of formation and evolution. The ic bodies
contained within are essentially pristine rimbants of the primordial material
from which the planets formed. Studying comets from the Ore
cloud provides clues about the composition of the early Solar
nebula and processes that shaped the planetary systems. Moreover, the

(08:36):
Oor cloud plays a dynamic role by periodically sending out
comets inward, potentially influence planetary atmospheres and surfaces through impacts
and delivery of organic compounds in water. The orbits of
objects in the Ort cloud are weakly bound to the
Sun's gravity and can be influenced by external forces such

(08:59):
as passing stars, molecular clouds, and the tidal forces exerted
by the Milky Way galaxy. Occasionally, a nearby star passing
through the Solar neighborhood can perturb parts of the cloud,
nudging comets into the inner Solar System. Galactic tides caused
by the gravitational pull of the Milky Way's disc create

(09:22):
a steady but subtle effect that alters comet orbits over
millions of years. These interactions explain the continuous supply of
new comets and the dynamism of the Ork clouds structure.
Though the ork cloud is distant, the comets it sends

(09:43):
inward can pose impact threats to Earth. Long period comets
from the ork cloud travel at high speeds, making collisions
potentially devastating. Historical mass extinction events such as the one
that wiped out the dinosaur are often hypothesized to be
caused by comet or asteroid impacts. Because or cloud comments

(10:07):
approach from all directions and with little warning, they represent
a harder to predict risk compared to nearer pasteroids. Scientists
study their orbits and develop detection methods to mitigate potential risks. Unfortunately,
that's all the time that we've got for today's episode
of the Science Stuff to Blow Your Mind podcast, and

(10:30):
I can't thank you enough. Tuning into another one until
next time.