HowDoWhy

With all this talk about stars, planets and moons in previous posts, it’s about high time I mentioned a solar system. A solar system is exactly what the name implies - the system associated with a sun (star). Our own solar system contains 8 planets. We once had nine but the planet Pluto was downgraded as discussed in some previous posts - Weren’t there 9 planets? What happened to Pluto? and What is a planet? There’s actually more to a solar system than the planets, though. The greatest influence on a solar system is that from which it begets its name - the star. The star is the center around which everything else in a solar system is built. It “binds” everything together and influences everything that surrounds it.

You can imagine a solar system starting as a mass of gas and elements. Nothing is really cohesive but since every bit of matter has a tiny bit of gravity, things are gradually attracted to one another. Eventually, enough gas and matter come together to collapse into a star. The remaining matter surrounding the new star eventually does the same, coalescing into larger and larger bits until something recognizable as a rock or chunk of ice orbits chaotically around the star. Eventually, the evolution of a solar system leads to these chunks joining together to form planets.

A young solar system is a hellish place. Newly formed planets travel in a very chaotic neighborhood and are frequently bombarded by all the coalesced “stuff” still drifting around aimlessly or plummeting inward towards the star. As more objects, dust and gas are caught up in the early planet’s gravity wells, the solar system gradually quiets down until you have an established system like our own. The large mass bodies (planets) act like vacuum cleaners, sucking up all the dirt and debris in their paths. Impacts become less frequent, orbits more stable, stray objects more rare.

Though we’ve not traveled out to see other solar systems, I’d venture a guess that each one is unique in its own right. There are plenty surprises awaiting us, I’m sure. But, using our solar system as a general model, we can expect them to include the star, planets, a Kuiper belt (a belt of material on the same general orbital plane as the planets) in which primitive, loose material still orbits in the form of comets and icy bodies, and even an Oort cloud. An Oort cloud is a very loose conglomeration of leftover “stuff” that completely envelops a world. It differs from a Kuiper belt in that the belt is on an orbital plane with the rest of the relevant matter and an Oort cloud wraps around the entire star like an eggshell around a yolk. The Oort cloud marks the edge of the solar system, a point at which the star’s gravitational and dynamic (think solar winds) influence effectively ends. We can see stars shine through Oort clouds (and can see out through our own) because the material is so loose and widely spaced as to be invisible to the naked eye.

In addition to the physical, or more accurately, visible stuff, a solar system is packed full of radiation cast off by its star. Solar winds, which are actually streams of highly charged particles streaming from the star, also influence the objects around them. Evidence of this can be seen in comet tails (which always point away from the star rather than trailing behind the comet in the opposite direction of travel) and in a phenomenon known as Aurora Borealis, a dazzling show of mysterious light in the sky caused by charged particles interacting with particles in our magnetosphere.

The few indirect observations we’ve made of other solar systems imply that ours isn’t necessarily the definitive model. Some alien planets behave in ways that are counter intuitive to the lessons we’ve learned from our own neighborhood. Future generations will make shocking and exciting discoveries for centuries to come.