In A Nutshell
The Sun is a star, so it is much bigger even than Jupiter, our solar system’s biggest planet. The outer atmosphere of this big ball of gas and plasma streams away as a big magnetic bubble made out of the solar wind and the Sun’s magnetic field. This is the heliosphere, and it’s the biggest continuous structure in the solar system.
The Whole Bushel
Space experts love to show us images comparing the sizes of our Sun and its planets. There’s no competition. Jupiter is large enough to hold 1,000 Earths. However, 1,000 Jupiters will fit inside the Sun.
It’s really comparing apples to oranges. The Earth and Jupiter are planets. They don’t have nuclear explosions going on inside them. The Sun is a star and does have some serious heartburn. This ball of gas and plasma is big enough to have the kind of internal pressure that forces hydrogen to turn into helium through nuclear fusion.
Our local star is so big that astronomers jokingly refer to the solar system as the Sun, Jupiter, and assorted rubble. Yet the Sun isn’t the biggest continuous structure here. Obviously, nothing orbiting the Sun is, either. No, there is something else here with us. It’s made by the Sun but is mostly invisible to our eyes.
This structure gets its start deep inside the Sun, where millions of tons of hydrogen fuse into helium every second. The resulting heat and other kinds of energy then move up toward the surface, bringing along a bunch of charged particles. A nuclear inferno like this also makes a doozy of a solar magnetic field.
Eventually everything reaches the Sun’s surface, where things get pretty violent. There is nothing here to stop sunlight, charged particles, and the magnetic field from streaming out into space. Holes in the upper layers of the Sun’s atmosphere leak out a continuous wind of charged particles. Arching solar prominences toss out gobs of heated gas. The Sun sometimes has violent episodes where bursts of magnetic fields and up to 1 billion tons of charged matter shoot off the surface at millions of kilometers per hour. Sunspots spit out flares of magnetic energy—the solar system’s most powerful explosions.
Scientists call this outgoing blast the heliosphere. Earth’s magnetic field and its thick atmosphere protect us from its worst effects. This stream of charged particles and magnetic fields mostly flows around us and keeps on going past Jupiter and even far beyond Pluto.
The heliosphere starts losing energy after it leaves the Sun, so it has to stop somewhere. Nobody is sure just how far away this solar magnetic bubble can get before it is too weak to push back the interstellar wind any more. One thing we do know: The heliosphere surrounds the whole solar system, including the Sun. It’s definitely the biggest continuous structure we’ve got.