Saturday, January 25, 2014

How Many Planets In The Universe?

Given all the stars, galaxies and what we know about the laws governing reality, how many planets are there in our observable Universe?
Stuff your eyes with wonder, live as if you’d drop dead in ten seconds. See the world. It’s more fantastic than any dream made or paid for in factories.” -Ray Bradbury
It wasn’t all that long ago — back when I was a boy — that the only planets we knew of were the ones in our own Solar System. The rocky planets, our four gas giants, and the moons, asteroids, comets, and kuiper belt objects (which only included then-planet Pluto and its largest moon, Charon, at the time) were all that we knew of.

Image credit: NASA’s Solar System Exploration, http://solarsystem.nasa.gov/planets/index.cfm.
But all of these were just the worlds around our Sun, which houses (according to current definition) eight planets. Our Sun is just one of an estimated two-to-four hundred billion stars in our Milky Way galaxy, and looking up towards the night sky, one can’t help but wonder how many of those stars have planets of their own, and what those worlds are like.

Image credit: Free Roaming Photography, by Mike Cavaroc.
A few decades ago, discussions about planets would have been mostly speculative, and we would’ve focused on theorizing based on the one thing that was well-known at the time: the stars in our galaxy. There are a vast variety of them, in terms of size, mass, radius and color, out there in our galaxy. Our Sun is just one example — a G-class star — of the seven different main types.

For the rest of the story: https://medium.com/starts-with-a-bang/9153a05bd0d5

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