Where is the end of the Solar System?

Depending on the definition, the border of the Solar System can be the Kuiper Belt, the corona, or the Oort Cloud.

The Solar System is very large, containing 8 planets, 5 dwarf planets, hundreds of moons, millions of asteroids and comets. They all orbit the Sun, in many cases orbiting each other, at speeds of thousands of kilometers per hour. So where is the end of the Solar System? The answer depends on how this planetary system is defined.

The Solar System includes 8 planets. (Photo: NASA/JPL)

According to NASA, the Solar System has up to 3 potential borders : the Kuiper Belt (a belt of rocky bodies outside Neptune's orbit), the heliotroposphere (the edge of the Sun's magnetic field) and the Oort Cloud (a region contains distant comets, almost invisible from Earth).

Kuiper Belt

The Kuiper Belt stretches from 30 - 50 astronomical units (AU) from the Sun (1 AU is equal to the distance between Earth and the Sun). This region is filled with asteroids and dwarf planets, such as Pluto, pushed out of the inner Solar System by gravitational battles with the planets.

Some astronomers believe that the Kuiper Belt should be considered the edge of the Solar System because it represents what would have been the edge of the Sun's protoplanetary disk. The protoplanetary disk is a belt of gas and dust that later evolved into planets, moons and asteroids.

"If the Solar System is narrowly defined as just the Sun and the planets, then the edge of the Kuiper Belt can be considered the edge of the Solar System ," said Dan Reisenfeld, a researcher at Los Alamos National Laboratory in Los Angeles. New Mexico, USA, said.

The Kuiper Belt is filled with asteroids that surround the Solar System. (Photo: BBC).

But some astronomers consider this definition too simple. "That's not really true. Things have moved a lot - mostly outward - since the planets formed ," explained expert Mike Brown at the California Institute of Technology (Caltech).

Accordingly, the Kuiper Belt does not contain everything of the Solar System. In October 2023, the discovery of a series of new objects outside the Kuiper Belt showed that a "second Kuiper Belt" may exist even further. Some researchers believe that uncertainty about the outer edge of this region prevents it from being a reliable Solar System boundary.

Nhat satisfied

The heliopause is the outer edge of the heliosphere - the area affected by the Sun's magnetic field. At solar corona, the solar wind, or stream of charged particles emitted from the Sun, becomes too weak to repel incoming radiation from stars and other cosmic entities in the Milky Way.

"Because the plasma inside the corona originates from the Sun and the plasma outside the corona originates in the interstellar region, some consider the corona to be the boundary of the Solar System ," Reisenfeld said. The region of space outside the corona is also often called "interstellar space" (the region of space between stars).

Two spacecraft have gone beyond coronal: Voyager 1 in 2012 and Voyager 2 in 2018. Once beyond coronal, the Voyager probes quickly detected changes in the type and level of magnetism and Radiation rushes towards them. This suggests they crossed some kind of boundary, Brown said.

However, the heliosphere is not spherical but resembles an oblong mass. Therefore, using the solar system to determine the Solar System will create a distorted system, going against the views of some researchers on planetary systems.

Simulate two spacecraft Voyager 1 and Voyager 2 flying in space. (Photo: NASA/JPL-Caltech).

Oort Cloud

According to NASA, the Oort Cloud is the farthest and widest potential frontier of the Solar System, stretching up to about 100,000 AU from the star. "Those who define the Solar System as everything gravitationally bound to the Sun consider the edge of the Oort Cloud to be the edge of the Solar System," Reisenfeld said.

For some researchers, this is the ideal choice for the frontier of the Solar System because, in theory, a planetary system includes all objects orbiting a star. However, other researchers believe that the Oort Cloud is located in interstellar space, so it is outside the Solar System, even when bound to the Sun. Additionally, the scientific community is uncertain about the true end point of the Oort Cloud, making it as unreliable a boundary as the Kuiper Belt.

Most common border

Of the three potential frontiers, the corona is most frequently used by researchers and NASA to define the Solar System. The reason is that this place is easiest to identify and the magnetic characteristics on the two sides are significantly different.

But this doesn't mean everything beyond the corona must be an interstellar object, such as the giant space rock 'Oumuamua, according to Reisenfeld . "The Oort Cloud is also part of the mass of material that makes up planets. So it contains Solar System material, not interstellar material ," he said.