When we talk about the solar system, we are usually talking about the Sun, the planets, and a handful of asteroids that are very close to the orbits of Jupiter, Mars or just after Neptune. However, in addition to dwarf planets like Pluto, Eris, and Makemake, there appears to be a dark and icy wilderness full of objects known as the Oort Cloud. But where exactly does the solar system end? And what does the edge of the solar system look like?
4.6 billion years ago, the Solar System was born from the protoplanetary disk that revolved around our Sun, when it was still a very young star. This disk formed of dust and gas gave birth to the first protoplanets, bricks of the worlds that were to develop. Some of these blocks, however, failed to gain mass and grow, and formed objects like huge asteroids. In other parts of the same disc, millions of rocks and comets have emerged.
These objects would have formed closer to the Sun, but gravitational interactions with giant young worlds such as Jupiter kicked them out. us to the farthest orbit. Some models suggest that there was then a series of collisions that destroyed most of the comets before reaching the Oort Cloud region – a large area that surrounds the entire solar system, made up of boulders.
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The first who suggested the existence of the Oort cloud seems to have been the Estonian astronomer Ernst Öpik, in 219. The idea was to explain comets with a long period, that is, they travel in space for decades, if not centuries, before approaching the Sun again. . The proposal was put forward in 1950 by the Dutch astronomer Jan Oort to solve a paradox.
(Image: Reproduction / William Crochot / NASA)
What Oort noticed was that there was a spike in the number of long period comets that managed to move away by about 20.10 AU (astronomical units; an AU equivalent to the distance between the Earth and the Sun), which suggests the existence of a deposit of objects in this region, with an isotropic (equal in all directions) and spherical distribution. The Cloud would be made up of two parts: an inner disc-shaped part and a spherical outer part.
In this outer part, would be the gravitational limit of the solar system, that is to say the last place in the universe where the Sun exerts enough gravity to “hold” objects in its orbit. Thus, the Oort cloud is at an estimated distance of between 5,000 and 97,000 astronomical units. However, astronomers have not yet been able to get any images of the Oort Cloud, simply because these objects would be too far away to be seen, especially at such a great distance from our star.
Although this region is even considered hypothetical, it is the most accepted idea – or at least the most popular – to explain the population of long-lived comets. In fact, astronomers agree that the outer cloud marks the limit of the solar system. It is believed that the Oort cloud may be formed from a few trillions of comets over 1 km in diameter and billions of about 20 km in diameter.
Notice how interstellar space begins before the Oort Cloud. The distances marked are in astronomical units (Image: Reproduction / NASA / JPL-Caltech)
Some simulations show how the Cloud may have formed, some suggesting that the rocks were born there with the exchange of materials between the Sun and its sister stars (it has long been assumed that the Sun has at least one twin star, and both stars would have separated shortly after their formation). body type there, the total mass of the Oort cloud could be 3x²⁵, about five times that of Earth. This is the official limit of the solar system, and it is estimated that Voyager probes will take 239 years to reach this border and 30,000 years to permanently leave the solar system. Yes, there is a lot of space there.
Heliosphere and heliopause
Although the Oort Cloud is considered the frontier of the solar system, there is some confusion when talking about the limits of the influence of the Sun and interstellar space. The Voyager probes, for example, passed through the region known as the Heliopause, which marks the meeting of the sun’s rays with interstellar cosmic radiation. This shock causes a kind of “shield”, which ends up protecting us from most of the external radiation. However, the Oort cloud is well beyond the heliopause.
To differentiate these regions, we must first understand that the Solar System has a kind of “bubble” that surrounds it, and which extends well beyond the orbit of Pluto. This bubble is held by two forces: one emitted from the inside (the pressure of the solar wind, which moves at a supersonic speed) and the other from the outside (the pressure of the interstellar medium). This bubble is called the heliosphere.
The heliosphere, however, is often described as something elongated in shape, due to the movement of the Sun (and therefore the solar system) relative to the Galaxy. This is because our “cosmic backyard” orbits the center of the Milky Way at a speed of 121 km / s. Thus, the Sun completes a revolution in the galaxy in 121 million years. This high speed causes the bubble that surrounds the solar system to leave a trail behind it.