How Big is the Solar System?
Written by Fraser Cain
How big is the Solar System? It all depends on your definition. Some scientists think that the furthest influence of the Solar System extends out to 125,000 astronomical units (1 AU is the average distance from the Earth to the Sun), or 2 light years. Since the nearest star is 4.22 light-years away, the Solar System size could extend almost half way to the nearest star.
Astronomers think that the Sun's gravitational field dominates the gravitational forces of the other stars in the Solar System out to this distance. Objects in this region will fall towards the Sun, and not the other stars.
But is there anything actually out there? It's so far away that scientists have no way of detecting any objects. Astronomers believe that the Oort Cloud – the source of long period comets – extends out to a distance of 50,000 AU, and maybe even 100,000 AU. Once again, though, the Oort Cloud has never been seen directly. We just guess that it exists because comets with extremely long orbits sometimes pass near the Sun and then head back out again. The Oort cloud could have a trillion icy objects inside it.
Another boundary that separates the Solar System from the rest of the galaxy is the heliosphere. This is the region where the solar wind collides with the interstellar medium and slows down. This region extends out to about 95 AU, or 3 times the orbit of Pluto. No spacecraft have ever reached the heliopause, but NASA's Voyager spacecraft are expected to cross the region within the next decade.
Here's an article from Universe Today about how comets are damaged out in the Oort Cloud, and a new project to map the heliosphere.
Here's a story from NASA about the outer reaches of the Solar System, and here's NASA's Solar System Exploration guide to the Oort Cloud.
We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.
Filed under: Astronomy
