The photo voltaic system is a gigantic place. Our cosmic neighborhood contains eight planets, round half a dozen dwarf planets, a number of hundred moons and hundreds of thousands of asteroids and comets, all spinning across the solar — and in lots of circumstances one another —at speeds of hundreds of miles per hour, like an enormous prime.However the place does it finish? Nicely, the reply could rely on whom you ask and the way they outline the photo voltaic system.There aren’t one, however three potential boundaries to the photo voltaic system, in response to NASA: the Kuiper Belt, the ring of rocky our bodies past the orbit of Neptune; the heliopause, the sting of the solar’s magnetic subject; and the Oort Cloud, a distant reservoir of comets which might be barely seen from Earth. The arguments for every boundary “all have benefit,” which makes selecting between them sophisticated, Dan Reisenfeld, a researcher at Los Alamos Nationwide Laboratory in New Mexico, instructed Reside Science in an e mail. However there may be one that the majority astronomers mostly agree upon.Associated: Have all 8 planets ever aligned? Kuiper BeltThe Kuiper Belt is especially made up of asteroids. (Picture credit score: Getty Photos)The Kuiper Belt stretches between 30 and 50 astronomical items (AU) away from the solar, in response to NASA. (One astronomical unit is the same as the space between Earth and the solar.) Get the world’s most fascinating discoveries delivered straight to your inbox.This area is stuffed with asteroids and dwarf planets, similar to Pluto, which have been ejected from the interior photo voltaic system by one-sided gravitational tugs-of-war with the planets.Some astronomers argue that the Kuiper Belt ought to be thought of the sting of the photo voltaic system as a result of it loosely represents the sting of the place the solar’s protoplanetary disk — the swirling ring of gasoline and mud that later turned the planets, moons and asteroids — would have been.”If one narrowly defines the photo voltaic system as simply the solar and its planetary our bodies, then the sting of the Kuiper Belt might be thought of to be the sting of the photo voltaic system,” Reisenfeld mentioned. However this definition of the photo voltaic system is taken into account to be far too easy by some astronomers, similar to Caltech’s Mike Brown. “It is not likely true,” Brown instructed Reside Science in an e mail. “Issues have moved round quite a bit — principally outward — for the reason that planets have been shaped.” This implies the Kuiper Belt doesn’t include all the photo voltaic system’s “stuff,” such because the elusive, hypothetical Planet 9, which (if it exists) seemingly lies far past the Kuiper Belt.In October 2023, the invention of a dozen new objects past the Kuiper Belt additionally hinted that there could also be a “second Kuiper Belt” lurking even additional out. The uncertainty round this area’s personal periphery subsequently makes it an unreliable boundary for the photo voltaic system as an entire, some researchers argue.HeliopauseThe heliopause is the purpose the place photo voltaic wind meets interstellar area. (Picture credit score: NASA/JPL-Caltech)The heliopause is the outer fringe of the solar’s magnetic affect, generally known as the heliosphere. At this level, the stream of charged particles emitted by the solar, generally known as the photo voltaic wind, turns into too weak to repel the oncoming stream of radiation from stars and different cosmic entities within the Milky Means. “As a result of the plasma contained in the heliopause is of photo voltaic origin, and the plasma exterior the heliopause is of interstellar origin, some folks think about the heliopause to be the boundary of the photo voltaic system,” Reisenfeld mentioned. Because of this, the area past the heliopause can also be also known as “interstellar area,” or the area between stars, he added.Two spacecraft have traveled past the heliopause: Voyager 1, which made the crossing in 2012, and Voyager 2, which crossed over in 2018. Because the Voyager probes crossed the heliopause, they shortly detected adjustments within the varieties and ranges of magnetism and radiation hitting them, signifying that that they had crossed some sort of border, Brown mentioned.Nevertheless, regardless of its title, the heliosphere isn’t an ideal sphere. As a substitute, it’s extra of an rectangular blob as a result of a lot of the interstellar plasma bombarding the photo voltaic system hits us from one course, which creates a bow shock — a rounded shock wave that deflects incoming radiation round the remainder of the photo voltaic system. The bow shock is situated round 120 AU from the solar, and creates an extended tail that stretches at the least 350 AU from the solar in the other way.Utilizing the heliopause to delineate the photo voltaic system subsequently leaves us with a lopsided neighborhood, which fits towards some researchers perceptions of planetary techniques.Oort CloudThe Oort Cloud (left) is far bigger than the interior photo voltaic system (proper) or the Kuiper Belt (heart). (Picture credit score: Getty Photos)The Oort Cloud is the furthest and most expansive potential photo voltaic system boundary, extending as much as round 100,000 AU from the solar, in response to NASA. “Individuals who outline the photo voltaic system as all the things that’s gravitationally sure to the Solar think about the sting of the Oort cloud to be the sting of the photo voltaic system,” Reisenfeld mentioned.For some researchers, that is the clear alternative for a photo voltaic system boundary as a result of in idea, a planetary system consists of all objects orbiting a star.”I do not perceive how anybody considers something apart from the Oort Cloud to be the sting of the photo voltaic system,” Sean Raymond, an astronomer on the Bordeaux Astrophysics Laboratory in France, instructed Reside Science in an e mail. “Every other definition appears ludicrous. It’s actually the sting of the place one thing can orbit the Solar.”Nevertheless, different researchers consider that as a result of the Oort Cloud is situated in interstellar area, it lies past the photo voltaic system even whether it is sure to our dwelling star. There’s additionally a considerable amount of uncertainty about the place the Oort Cloud truly ends, which some would argue makes it simply as unreliable a border because the Kuiper Belt.Which boundary is greatest? Out of the three doable boundaries, the heliopause is the one that’s most frequently utilized by researchers, and by NASA, to outline the photo voltaic system’s edge. It is because it’s the best to pin down and since the magnetic properties on both aspect of it are considerably totally different.”I might argue for the heliopause to be the boundary as a result of it truly is a boundary,” Reisenfeld mentioned. “As soon as you have handed it, you already know it.”However that does not imply that all the things past the heliopause ought to be thought of an interstellar object, similar to the big area rock ‘Oumuamua, Reisenfeld added. “The Oort Cloud was initially a part of the identical stuff that the planets have been shaped from, so it’s composed of photo voltaic system materials, not interstellar materials,” he mentioned.However whereas some researchers are completely happy to select a aspect on this argument, others see no cause why the photo voltaic system can not have a number of boundaries.”I might say that there is no such thing as a precise debate,” Brown mentioned. “There are simply alternative ways to outline it relying on what’s vital for the query you are attempting to reply.”