SPACE — The solar system is a very big place. Our cosmic neighborhood includes eight planets, six dwarf planets, hundreds of moons, and millions of asteroids and comets. They all spin around the sun at thousands of miles per hour, like giant tops. In many cases, they also orbit each other.
Big and vast, where is the edge of the Solar System? The answer depends on how we define the solar system.
According to NASA, not just one, the solar system has three possible potential boundaries, viz Kuiper belt in the form of a ring of rocky objects beyond the orbit of Neptune, Heliopause which is the edge of the sun’s magnetic field, and Awan Oort in the form of a collection of distant comets that are almost invisible from Earth.
“All the arguments for each limit are equally important, making choosing between them complicated,” Dan Reisenfeld, a researcher at New Mexico’s Los Alamos National Laboratory, told Live Science. But there is one thing that most astronomers agree on.
Also read: What are the farthest objects that we can see directly in the night sky?
Kuiper belt
The Kuiper Belt consists mostly of asteroids. Image: Getty Images via Live Science
According to NASA, the Kuiper Belt stretches between 30 and 50 astronomical units (AU) from the sun. One astronomical unit is equal to the distance between the Earth and the sun or about 150 million kilometers.
The region is filled with asteroids and dwarf planets like Pluto. They were thrown from the inner solar system due to one-sided gravitational attraction with various planets.
Some astronomers argue that the Kuiper Belt should be considered the edge of the solar system because it represents the edge where the sun’s protoplanetary disk is located. Protoplanetary disks are rings of gas and dust that rotate, then become planets, moons and asteroids.
“If one defines the solar system narrowly as just the sun and its planetary bodies, then the edge of the Kuiper Belt can be considered the edge of the solar system,” Reisenfeld said.
However, some astronomers consider the definition of the solar system above to be too simple, one of the opponents is Mike Brown from Caltech. “That’s not true. Things have moved a lot, mostly outward, since the planets formed,” Brown said.
This means, he said, that the Kuiper Belt does not contain the entire solar system. For example, the elusive Planet Nine hypothesis, which if it exists is likely to lie far beyond the Kuiper Belt.
In October 2023, the discovery of dozens of new objects outside the Kuiper Belt also hinted at the possibility of a second Kuiper Belt lurking even further away. Therefore, uncertainties around the outer edge of the region make it an unreliable boundary for the solar system as a whole.
Also read: Facts about the search for a ninth planet similar to Earth at the edge of the solar system
Heliopause
The heliopause is the point where the solar wind meets interstellar space. Image: NASA/JPL-Caltech
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, or solar wind, becomes too weak to repel the stream of radiation from the stars and other cosmic entities in the Milky Way.
“Because the plasma inside the heliopause comes from the sun, and the plasma outside the heliopause comes from the interstellar, some people consider the heliopause to be the boundary of the solar system,” Reisenfeld said. As a result, the space beyond the heliopause is also often referred to as interstellar space.
Two spacecraft have traveled beyond the heliopause, namely Voyager 1 in 2012 and Voyager 2 in 2018. As the Voyager probes crossed the heliopause, they quickly detected changes in the type and level of magnetism and radiation hitting them. “That indicates they have crossed some kind of border,” Brown said.
However, despite its name, the heliosphere is not a perfect sphere. Instead, it is more of an oblong blob because most of the interstellar plasma bombarding the solar system hits us from one direction, creating a bow shock (bow shock). The shock wave had a spherical shape that deflected incoming radiation throughout the solar system. The bow shock is located about 120 AU from the sun, and creates a long tail that stretches at least 350 AU from the sun in the opposite direction.
Because of this, the use of the heliopause to describe the boundaries of the solar system is complicated and lame. It also conflicts with some researchers’ perceptions of planetary systems.
Also Read: Discovery of the Boundaries of Space and Earth, Apparently Many Astronauts Failed to Go to Space
Awan Oort
The Oort Cloud (left) is much larger than the inner solar system (right) or the Kuiper Belt (center). Image Getty Images via Live Science
According to NASA, the Oort Cloud is the farthest and widest potential boundary of the solar system, extending to about 100,000 AU from the sun. “People who define the solar system as everything that is 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, it is an obvious choice for the boundaries of the solar system because in theory, a planetary system consists of all the objects orbiting a star. An astronomer at France’s Bordeaux Astrophysics Laboratory, Sean Raymond, admits he doesn’t understand how people think of the edge of the solar system as anything other than the Oort Cloud. Because, literally, the edge of the solar system means the edge where something can orbit the Sun.
However, other researchers believe that, because the Oort Cloud is located in interstellar space, it is outside the solar system even though it is bound to our home star. There is also a large amount of uncertainty about where the Oort Cloud actually ends up, making it as unreliable as the Kuiper Belt.
Which limit is best?
Of the three possible boundaries, the heliopause is the boundary most often used by researchers and NASA to determine the edge of the solar system. Because, it is the easiest to describe and because the magnetic properties on the two sides are significantly different.
“I would argue that the heliopause is the limit because it really is a limit. “Once you get through it, you’ll know (it’s out of the solar system),” Reisenfeld said.
2024-03-30 14:00:13
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