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The solar system is a vast place. Our near universe includes eight planets, about six dwarf planets, hundreds of moons, and millions of asteroids and comets, all orbiting the sun and many They are spinning around each other like giant tops at thousands of miles per hour. .
But where does it end? Well, the answer may vary depending on who you ask and how they define it. solar system.
According to , the solar system has not one, but three potential boundaries. NASA: Kuiper belt, a ring of rock beyond orbit Neptune; heliosphere, the edge of the Sun’s magnetic field. and the Oort cloud, a distant reservoir. Comet Something that is almost invisible from Earth.
The arguments for each boundary are “all-wins,” which complicates the choice between them. Dan Reisenfeldresearchers at Los Alamos National Laboratory in New Mexico told Live Science via email.
But there is one thing that most astronomers most commonly agree on.
Related: Have you ever had all eight planets?
kuiper belt
The Kuiper belt extends between 30 and 50 astronomical units (AU) from Earth. Sunaccording to NASA. (One astronomical unit is equal to the distance between the Earth and the Sun).
This region is filled with asteroids and dwarf planets. Plutowhich was ejected from the inner solar system by a unilateral gravitational tug of war with a planet.
Some astronomers believe that the Kuiper Belt roughly represents the edge of where the Sun’s protoplanetary disk (a swirling ring of gas and dust that later became planets, moons, and asteroids) would have been They argue that the belt should be considered the edge of the solar system.
“If you define the solar system narrowly as just the sun and its planets, you can think of the edge of the Kuiper belt as the edge of the solar system,” Reisenfeld said.
However, this definition of the solar system is considered too simplistic by some astronomers, including those at the California Institute of Technology. mike brown.
“That’s not true,” Brown told LiveScience in an email. “Since the planets formed, things have moved largely outward.” This means the Kuiper belt doesn’t contain all of the “matter” in our solar system. planet nine,(If there) Probably far beyond the Kuiper belt.
In October 2023, More than a dozen new objects discovered beyond the Kuiper belt He also suggested that a “second Kuiper belt” may be lurking further out.
Some researchers therefore argue that the uncertainties around the outer edges of the region itself make it an unreliable boundary for the entire solar system.
heliopose
The heliopause is the outer edge of the Sun’s magnetic influence known as the heliosphere. At this point, the stream of charged particles emitted by the Sun, known as the solar wind, becomes too weak to repel the stream of radiation from stars and other cosmic entities in the Milky Way.
“Some people think of the heliopause as the boundary of the solar system because the plasma inside the heliopause is of solar origin and the plasma outside the heliopause is of interstellar origin,” Reisenfeld said. As a result, the space beyond the solar interface is also called “interstellar space.” space between starshe added.
Two spacecraft flew beyond the heliopause. voyager 1crossed it in 2012, and Voyager 2 crossed it in 2018. As the Voyager probes crossed the heliopause, changes in the types and levels of magnetism and radiation hitting them were quickly detected, indicating they had passed through some type of Earth. The border, Brown said.
But despite its name, the heliosphere not a perfect sphere.Instead, it is more rectangular blocks That’s because most of the interstellar plasma that hits our solar system hits us from one direction, causing a bow shock (a round shock wave that deflects radiation from entering the rest of the solar system). The bowshock is approximately 120 AU from the Sun and forms a long tail that extends in the opposite direction at least 350 AU from the Sun.
Therefore, using the heliosphere to delineate the solar system leaves a biased neighborhood, which is contrary to some researchers’ perception of planetary systems.
oort cloud
The Oort cloud is the farthest and potentially most expansive boundary in the solar system, extending up to about 100,000 astronomical units from the Sun. NASA.
“People who define the solar system as gravitationally bound to the sun think of the edge of the Oort cloud as the edge of the solar system,” Reisenfeld said.
For some researchers, this is an obvious choice for the boundary of the solar system, since in theory a planetary system consists of all the celestial bodies orbiting a star.
“I don’t understand how people think that anything other than the Oort cloud is the edge of the solar system.” sean raymondastronomers at France’s Institute of Astrophysics in Bordeaux told Live Science via email. “Any other definition seems ridiculous. It’s literally the limit to which something can orbit the sun.”
However, other researchers believe that because the Oort cloud is located in interstellar space, it is outside our solar system, even though it is tied to our home star.
There is also considerable uncertainty as to where the Oort Cloud actually ends, and some would argue that it is as unreliable a border as the Kuiper Belt.
Which border is best?
Of the three possible boundaries, the heliopause is the one most often used by researchers and NASA to define the edge of the solar system. This is because it is easiest to pin together and the magnetic properties of its two sides are very different.
“I argue that the solar interface is a boundary, because it is, in fact, a boundary,” Reisenfeld said. “Once you go through it, you’ll understand.”
But that doesn’t mean that everything beyond the heliosphere, such as giant space rocks, should be considered interstellar objects. ‘Oumuamuaadded Reisenfeld. “The Oort cloud was originally part of the same material from which planets were formed, so it is composed of solar system material rather than interstellar material,” he said.
But while some researchers are happy to take sides in this debate, others don’t understand why there can’t be more than one boundary in the solar system.
“I would say there’s no real debate,” Brown said. “There are different ways to define it, depending on what’s important to the question you’re trying to answer.”
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