Looking at where we are now. With our back to the sun, and the Planets, Asteroids and
comets behind us, we face Deep Space. There’s nothing between us and the stars that are
very far away. Or is there? The Empty space beyond Neptune is not empty. What if we tell
you that the Solar system is in the centre of a Giant ice-cloud! This cloud might be
filled with billions and trillions of comets and other objects. What is the Oort Cloud?
Before talking about this cloud, let’s talk about what are comets? Comets are cosmic snowballs
of frozen gases, rocks and dust, orbiting the sun. They are typically the size of a
town.These comets while orbiting the sun, get close to it and in the process are heated.
Upon heating, they emit dust and gases into a giant glowing head. The dust and gases form
a tail that stretches away from these for millions of miles. There are two main classes
of comets : Short-period comets (also called elliptical comets) and long period comets.
Short period comets are generally accepted to have emerged from either the Kuiper belt
or the Scattered Disc which are two linked flat discs of icy debris beyond Neptune’s
orbit at 30 au and jointly extending out beyond 100 au from the Sun. Short period
comets have an orbital period of less than 200 years and orbit the Sun in the same plane
as the planets. Long period comets have tilted and wildly elliptical orbits and appear from
every direction in the sky. Their orbits last for thousands of years. The orbits of comets
within the Kuiper belt are relatively stable, and so very few comets are thought to originate
there. The scattered disc, however, is dynamically active, and is far more likely to be the place
of origin for comets. Comets pass from the scattered disc into the realm of the outer
planets, becoming what are known as centaurs. These centaurs are then sent farther inward
to become the short-period comets. There are 3,364 comets discovered so far.
But there is a problem here. Comets loose material and burn up when they fly by the
sun and melt in the spectacular process which creates those gorgeous tails. After an interval
of time comets disappear, and yet new comets keep coming. It's been nearly 4.5 Billion
years to our solar systems birth and yet these comets are still appearing from nowhere. So
where are they coming from? And what makes them come toward us? This was a very puzzling
question back in the mid- 20th century. It was first theorised and solved by Dutch Astronomer,
Jan Oort in 1950. He was also the first person to find the evidence for dark matter. He also
found the distance of our Solar System from the Centre of our Milky Way. To understand
what he proposed, lets go a bit back in time, about 4.5 Billion years back. Lets Observe
our solar system, coalescing out of a flat disk of material around the sun, the inner
planets were warmer, smaller and rocky while the outer planets were in a region that was
freezing and grew huge. As this part of the solar system was chillier, water came in the
form of ice mixed with dust and other stuffs. These pieces would then collide and stick
together, and in the process they grew bigger. So, after the planets formed, the region in
which they were formed still contained lots of these leftover chunks of ice and stuff
called Planetesimals. Planetesimals formed the same material as the planets did. But
those outer Jovian planets, they had a lot of gravity and any piece of chunk that got
too close to them, were either assimilated in them or got thrown into highly eccentric
orbits. They were either thrown towards the sun or flung out into Deep Space. Trillions
upon trillions of such ice balls got tossed around by the planets. These small chunks
with a very little gravity pulled on the heavy planets and the planets did the same. Though,
the gravitational pull of these small chunks of ice was not much, but after trillions of
these encounters, it accounted. So, the overall effect of all these encounters was that the
Saturn, Uranus and Neptune moved outwards and Jupiter moved Inwards. As Neptune was
moving outwards, it had a lot of encounters with these ice chunks and flung them into
wild elliptical and tilted orbits. This shuffling and moving of the outer planets is what caused
the Late Heavy Bombardment in our solar system.Today, there are three distinct populations of these
objects. One is a region called the Kuiper belt, named after the Dutch Astronomer Gerard
Kuiper. Comets in this belt have a stable orbit aligned with the planets. The Kuiper
belt starts from beyond Neptune’s orbit, extending for about 4.5 to 7.5 Billion kilometres
from the sun. The second region is called the Scattered disc, containing of those icy
chunks that were flung into wild elliptical orbits by Neptune. It overlaps the Kuiper
belt and extends for a distance of about 150 Billion Kilometres from the Sun. Finally,
outside these two regions, there’s a spherical cloud of these icy objects starting at roughly
300 Billion kilometres and 65 times farther out than Neptune and extends out to a distance
of almost a light year! We call this the Oort Cloud, named after Jan Oort. Oort Cloud is
the origin of Long-period comets. In short, gravity from the planets shoved many icy planetesimals
away from the Sun, and gravity from the galaxy likely caused them to settle in the borderlands
of the solar system, where the planets couldn’t perturb them anymore. And they became what
we now call the Oort Cloud. The outer Oort cloud may have trillions of objects larger
than 1 km (0.62 mi), and billions with absolute magnitudes brighter than 11 (corresponding
to approximately 20-kilometre (12 mi) diameter), with neighbouring objects tens of millions
of kilometres apart. Its total mass is not known, but, assuming that Halley’s Comet is
a suitable prototype for comets within the outer Oort cloud, roughly the combined mass
is 3×1025 kilograms (6.6×1025 lb), or five times that of Earth. Earlier it was
thought to be more massive (up to 380 Earth masses), but improved knowledge of the size
distribution of long-period comets led to lower estimates. No known estimates of the
mass of the inner Oort cloud have been published. Pluto was the first Kuiper belt object to
be discovered. After six years, in 1992 QB1 was discovered, and we have discovered after
that a lot of Kuiper belt objects. We can designate Pluto as a king of these Kuiper
belt objects. While we know a lot of Kuiper belt objects, we don’t know for sure about
an Oort Cloud object. Two very interesting objects, Sedna and VP113 have been founds.
They have a highly elliptical orbits but neither of them are very close to Neptune. So, how
did they get here? They may be Oort Cloud objects that were disturbed by passing stars
a long time ago, pushing them close to the sun. But no one knows that.
Another interesting point is that, when astronomers calculated how many Oort Cloud objects should
be leftover since the formation of our Solar System, they found it to be about Six Billions.
However, when calculated using the observations of long period comets, the number they found
was about 400 Billion!. That was a big miscalculation they did! One idea about this was that there
might be aliens comets in our solar system from other solar systems stolen by our sun
when it passed near other stars. There is another highly hypothetical explanation about
this. There might be another planet in our solar system, far from Neptune. Many long
period comets coming towards us are not random, instead they have their orbits aligned in
such a way that looks like a distant planet disturbed them. Some of the Kuiper belt objects
are also aligned in a similar way.This potential planet could be ten times the size of our
Earth. But we can’t say for sure that there is a planet out there or not! We haven’t
been able to explore this region of our solar system. It every far from us and also very
huge. So huge, that you could hide an entire planet out there and it would be difficult
to find. We have to discover these realms and verify
our facts with help of every mission we could. Space probes have yet to reach the area of
the Oort cloud. Voyager 1, the fastest and farthest of the interplanetary space probes
currently leaving the Solar System, will reach the Oort cloud in about 300 years and
would take about 30,000 years to pass through it.However, around 2025, the radioisotope
thermoelectric generators on Voyager 1 will no longer supply enough power to operate any
of its scientific instruments, preventing any further exploration by Voyager 1. The
other four probes currently escaping the Solar System either are already or are predicted
to be non-functional when they reach the Oort cloud; however, it may be possible to find
an object from the cloud that has been knocked into the inner Solar System. In the 1980s
there was a concept for a probe to reach 1,000 au in 50 years called TAU; among its missions
would be to look for the Oort cloud. In the 2014 Announcement of Opportunity for the Discovery
program, an observatory to detect the objects in the Oort cloud (and Kuiper belt) called
the “Whipple Mission” was proposed. It would monitor distant stars with a photometer,
looking for transits up to 10,000 au away. The observatory was proposed for halo orbiting
around L2 with a suggested 5-year mission. It was also suggested that the Kepler observatory
could have been capable of detecting objects in the Oort cloud.
Thanks for watching everyone! What do you think about these interesting theories and
existence of a secret planet out there? We know this would take some time for you to
digest and we will answer any of your doubts related to this topic as best as we can in
our comment section. Let us know about your doubts the comments below, be sure to subscribe,
and we’ll see you next time on the channel!