Diameter of the Solar System
Written by Fraser Cain
The diameter of the Solar System depends on your definition. So let's go through a few milestones, and you can pick the one that works best for you.
If you define the Solar System as the orbit of the most distant planet, that would be Neptune (sorry, Pluto's not a planet any more). Neptune's furthest point in its orbit is 4.5 billion km, or 30 astronomical units (1 AU is the average distance from the Earth to the Sun).
The heliosphere is the point at which the Sun's solar wind is stopped by the interstellar wind within the Milky Way. This point happens at about 90 AU from the Sun.
If you define the Solar System as the orbit of the furthest object ever detected, that would be Sedna, which can orbit out to a distance of 975 astronomical units.
Astronomers theorize that a cloud of comets called the Oort Cloud surrounds the Sun out to a distance of 50,000-100,000 astronomical units. This is about 1/3rd the distance to the closest star. So perhaps this is the diameter of the Solar System.
Finally, astronomers think that the gravitational influence of the Sun extends out to a distance of roughly 2 light years, which is about halfway from here to Alpha Centauri. So this would be the largest possible diameter of the Solar System.
Here's an article on Universe Today about the closest star to Earth, and another about how long it would take to travel to the closest star.
Here's an article from the Physics Factbook about the diameter of the Solar System, and a cool way to visualize it using the Earth as a peppercorn.
We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.
Filed under: Astronomy
