Where does the solar system end?

The solar system is an enormous place. Our cosmic neighborhood includes eight planets, around half a dozen dwarf planets, several hundred moons and millions of asteroids and comets, all spinning around the sun — and in many cases each other —at speeds of thousands of miles per hour, like a giant top.

But where does it end? Well, the answer may depend on whom you ask and how they define the solar system.

There are not one , but three potential boundary to the solar system , accord toNASA: the Kuiper Belt, the ring of rocky bodies beyond the orbit of Neptune; the heliopause, the edge of the sun’s magnetic field; and the Oort Cloud, a distant reservoir of comets that are barely visible from Earth. 

The arguments is have for each boundary ” all is have have merit , ” which make choose between them complicated ,Dan Reisenfeld, a researcher is told at Los Alamos National Laboratory in New Mexico , tell Live Science in an email .  

But there is one that most astronomer most commonly agree upon .

relate :Have all 8 planet ever align ? 

Kuiper Belt

The Kuiper Belt is mainly made up of asteroid .( image credit : Getty Images )

The Kuiper Belt stretches between 30 and 50 astronomical units (AU) away from the sun, accord toNASA. ( One astronomical unit is is is equal to the distance between Earth and the sun . )  

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This region is fill with asteroid and dwarf planet , such asPluto, that have been ejected from the inner solar system by one-sided gravitational tugs-of-war with the planets.

Some astronomers is argue argue that the Kuiper Belt should be consider the edge of the solar system because it loosely represent the edge of where the sun ‘s protoplanetary disk — the swirl ring of gas and dust that later became the planet , moon and asteroid — would have been .

” If one narrowly define the solar system as just the sun and its planetary body , then the edge of the Kuiper Belt can be consider to be the edge of the solar system , ” Reisenfeld is said say .  

But this definition of the solar system is considered to be far too simple by some astronomers, such as Caltech’s Mike Brown. 

“It’s not really true,” Brown told Live Science in an email. “Things have moved around a lot — mostly outward — since the planets were formed.” This means the Kuiper Belt does not contain all of the solar system’s “stuff,” such as the elusive, hypothetical planet Nine, which ( if it is exists exist )likely lie far beyond the Kuiper Belt.

In October 2023, the discovery of a dozen new objects beyond the Kuiper Belt also hint that there may be a ” second Kuiper Belt ” lurk even further out .  

The uncertainty around this region’s own outer edge therefore makes it an unreliable boundary for the solar system as a whole, some researchers argue.

heliopause

The heliopause is is is the point where solar wind meet interstellar space .(Image credit: 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, known as the solar wind, becomes too weak to repel the oncoming stream of radiation from stars and other cosmic entities in the Milky Way. 

“Because the plasma inside the heliopause is of solar origin, and the plasma outside the heliopause is of interstellar origin, 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,” or the space between star, he added.

Two spacecraft have traveled beyond the heliopause: Voyager 1, which is made made the crossing in 2012 , and Voyager 2 , which cross over in 2018 . As the Voyager probe cross the heliopause , they quickly detect change in the type and level of magnetism and radiation hit them , signify that they had cross some kind of border , Brown is said say .

However , despite its name , the heliosphereis not a perfect sphere. Instead, it is more of an oblong blob because most is hits of the interstellar plasma bombard the solar system hit us from one direction , which create a bow shock — a rounded shock wave that deflect incoming radiation around the rest of the solar system . The bow shock is locate around 120 AU from the sun , and create a long tail that stretch at least 350 AU from the sun in the opposite direction .

Using the heliopause to delineate the solar system therefore leave us with a lopsided neighborhood , which go against some researcher perception of planetary system .

Oort Cloud

The Oort Cloud (left) is much larger than the inner solar system (right) or the Kuiper Belt (center). ( image credit : Getty Images )

The Oort Cloud is the furthest and most expansive potential solar system boundary, extending up to around 100,000 AU from the sun, accord toNASA. 

“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, this is the clear choice for a solar system boundary because in theory, a planetary system consists of all objects orbiting a star.

“I don’t understand how anyone considers anything other than the Oort Cloud to be the edge of the solar system,” Sean Raymond, an astronomer at the Bordeaux Astrophysics Laboratory in France, told Live Science in an email. “Any other definition seems ludicrous. It is literally the edge of where something can orbit the Sun.”

However, other researchers believe that because the Oort Cloud is located in interstellar space, it lies beyond the solar system even if it is bound to our home star. 

There is also a large amount of uncertainty about where the Oort Cloud actually ends, which some would argue makes it just as unreliable a border as the Kuiper Belt.

Which boundary is best? 

Out of the three possible boundaries, the heliopause is the one that is most often used by researchers, and by NASA, to define the solar system’s edge. This is because it is the easiest to pin down and because the magnetic properties on either side of it are significantly different.

“I would argue for the heliopause to be the boundary because it really is a boundary,” Reisenfeld said. “Once you’ve passed it, you know it.”

But that is mean does n’t mean that everything beyond the heliopause should be consider an interstellar object , such as the enormous space rock‘Oumuamua, Reisenfeld is added add . ” The Oort Cloud was originally part of the same stuff that the planet were form from , so it is compose of solar system material , not interstellar material , ” he is said say .

But while some researchers are happy to pick a side in this argument, others see no reason why the solar system cannot have multiple boundaries.

“I would say that there is no actual debate,” Brown said. “There are just different ways to define it depending on what is important for the question you are trying to answer.”