The Oort Cloud. The limits of the Solar System

solar system and astronomical distances

Scale 1 on Earth means 1 Astronomical Unit (AU), which is the distance from the Earth to the Sun. Example of Saturn, 10 AU = 10 times the distance between Earth and Sun

The Oort Cloud, also known as the «Öpik-Oort cloud», is a hypothetical spherical cloud of trans-Neptunian objects. It could not be observed directly. It is located at the limits of our solar system. And with a size of 1 light year, it is a quarter of the distance from our closest star to our solar system, Proxima Centauri. To get an idea of ​​its size with respect to the Sun, we are going to detail some data.

We have Mercury, Venus, Earth and Mars, in this order, relative to the Sun. It takes 8 minutes and 19 seconds for a ray of the Sun to reach the Earth's surface. Beyond, between Mars and Jupiter, we find the asteroid belt. After this belt, come the 4 gas giants, Jupiter, Saturn, Uranus and Neptune. Neptune is approximately 30 times as far from the Sun as Earth is concerned. Sunlight takes about 4 hours and 15 minutes to arrive. If we take into account our planet furthest from the Sun, the confines of the Oort Cloud would be 2.060 times the distance from the Sun to Neptune.

Where is its existence deduced from?

oort cloud meteor shower

In 1932, the astronomer Erns Öpik, he postulated that comets orbiting for long periods originated within a large cloud beyond the confines of the solar system. In 1950 the astronomer Jan Oort, he postulated the theory independently resulting in a paradox. Jan Oort assured that the meteorites could not have formed in their current orbit, due to the astronomical phenomena that govern them, so he assured that their orbits and all of them must be stored in a large cloud. For these two great astronomers, this colossal cloud receives its name.

Oort investigated between two types of comets. Those with an orbit of less than 10AU and those with long-period orbits (almost isotropic), which are greater than 1.000AU, even reaching 20.000. He also saw, how they all came from all directions. This allowed him to deduce that, if they were coming from all directions, the hypothetical cloud would have to be spherical in shape.

What exists and does the Oort Cloud encompass?

According to the hypotheses of origin of the Oort Cloud, is in the formation of our solar system, and the great collisions that existed and materials that were fired. The objects that form it were formed very closely to the Sun in its beginnings. However, the gravitational action of the giant planets also distorted their orbits, sending them to the distant points where they are.

oort cloud orbits comets

Comet orbits, simulations by NASA

Within the Oort cloud, we can differentiate two parts:

  1. Internal / Indoor Oort Cloud: It is more gravitationally related to the Sun. Also called the Hills Cloud, it is shaped like a disk. It measures between 2.000 and 20.000 AU.
  2. Oort Cloud Outer: Spherical in shape, more related to the other stars and the galactic tide, which modifies the orbits of the planets making them more circular. Measures between 20.000 and 50.000 AU. It should be added that it is really the gravitational limit of the Sun.

The Oort Cloud as a whole, encompasses all the planets in our solar system, dwarf planets, meteorites, comets, and up to billions of celestial bodies more than 1,3 km in diameter. Despite having such a significant number of celestial bodies, the distance between them is estimated to be tens of millions of kilometers. The total mass it would have is unknown, but making an approximation, having as a prototype Halley's Comet, It has been estimated at about 3 × 10 ^ 25kg, that is, about 5 times that of planet Earth.

The Tidal effect in the Oort Cloud and on Earth

In the same way that the Moon exerts a force on the seas, raising the tide, it has been deduced that Galactically this phenomenon occurs. The distance between one body and another reduces the gravity that one influences the other. To understand the phenomenon to be described, we can look at the force that the gravity of the Moon and the Sun exert on the Earth. Depending on the position where the Moon is with respect to the Sun and our planet, the tides may vary in magnitude. An alignment with the Sun influences such gravity on our planet that explains why the tide rises so much.

tide by the effect of the moon and the sun

In the case of the Oort Cloud, let's say that it represents the seas of our planet. AND the Milky Way would come to represent the Moon. That is the tidal effect. What it produces, like the graphic description, is a deformation towards the center of our galaxy. Taking into account that the gravitational force of the Sun is becoming weaker the further we move away from it, this small force is also sufficient to disturb the movement of some celestial bodies, causing them to be sent back towards the Sun.

Cycles of extinction of species on our planet

Something that scientists have been able to verify is that every 26 million years approximately, there is a repeating pattern. It is about the extinction of a considerable number of species in these periods. Although the reason for this phenomenon cannot certainly be stated. The tidal effect of the Milky Way on the Oort cloud it could be a hypothesis to consider.

If we take into account that the Sun revolves around the galaxy, and in its orbit it tends to pass through the "galactic plane" with some regularity, these extinction cycles could be described.

It has been calculated that every 20 to 25 million years, the Sun passes through the galactic plane. When that happens, the gravitational force exerted by the galactic plane would be enough to disturb the entire Oort Cloud. Considering that it would shake and disturb the member bodies within the Cloud. Many of them would be pushed back towards the Sun.

meteorites towards planet Earth

Alternative Theory

Other astronomers consider that the Sun is already close enough to this galactic plane. And the considerations they bring is that the disturbance could come from the spiral arms of the galaxy. It is true that there are many molecular clouds, but also they are riddled with blue giants. They are very large stars and they also have a very short life span, as they quickly consume their nuclear fuel. Every few million years some blue giants explode, causing supernovae. That would explain the strong shaking that would affect the Oort Cloud.

Be that as it may, we may not be able to perceive it with the naked eye. But our planet is still a grain of sand in infinity. From the Moon to our galaxy, they have affected from their origin, the life and existence that our planet has endured. A huge amount of things are happening right now, beyond what we can see.


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