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Starts With A Bang

Mini-Movie Monday: Genesis Episode 2, Our Solar System

It’s home to everything we’ve ever directly explored, but where did our Solar System come from?

“When you look at the stars and the galaxy, you feel that you are not just from any particular piece of land, but from the solar system.” -Kalpana Chawla

Our second episode of the Genesis series is live on YouTube, as we tell another part of the story of where all this comes from. In this case, that’s the story of our Solar System.

A full transcript of Episode 2: Our Solar System is attached below. Enjoy!


When it comes to the question of where our Solar System comes from, it helps to remember exactly what it is we’re dealing with. Not only do we have our own world, spinning on its axis and orbiting our central star, the Sun, but we have three other, inner rocky planets doing the same thing, a ring of asteroids, low in mass but large in number, beyond that, four giant planets a little farther out, each one with their own unique system of rings and moons, the Kuiper belt, full of icy worlds, many of which will become comets in our distant future, and the Oort cloud even farther beyond that, extending out into interstellar space.

Every star is expected to have its own unique system around it, some with gas giants in the inner solar system, some with planets far hotter than Mercury is in our own, and some with a rocky planet at the right temperatures to have liquid water on its surface; not so different from our own world!

But where do these Solar Systems come from? To find out, we have to go back more than four-and-a-half billion years, to a molecular cloud that collapsed under its own gravity.

Stars don’t form all by themselves, but rather in large clusters of hundreds, thousands or even greater numbers, with the locations starting off with the greatest amounts of mass preferentially stealing more and more matter from their surroundings.

Deep within the gas-rich nebulae, matter preferentially attracts more and more matter, with the largest individual masses within growing into not only Sun-like stars, but into stars hotter, more massive and shorter lived than our own. But it’s the less massive stars — the ones that will live for not mere millions but billions of years — that are the most interesting.

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Every new star that forms from the gas of a nebula forms from an ellipsoidal clump. The fact that it’s not a perfect sphere is important, since it leads to collapse along the shorter dimension and eventually “pancaking” into a disk, which itself begins to grow instabilities in it.

The largest of these instabilities grow into planets, accreting the matter from both closer in and farther out in the disk. Recently the Atacama Large Millimeter Array of telescopes snapped the first image of a protoplanetary disk showing exactly these features; the “holes” in the disk are where young planets are forming. If this looks familiar to you, it should; the “gaps” in Saturn’s rings are exactly where its most massive Moons are located!

The big difference is that in a solar system, the star that you’re orbiting is hot enough to eventually blow off all the icy material in the inner solar system, and the large, massive planets will kick out all the material between them beyond that. What you’re left with, pretty universally, is warm, inner planets, an asteroid belt right at the “frost line” of a solar system, gas giants beyond that, and then frozen, icy worlds at the outskirts.

In every solar system, it’s the largest initial fluctuations in a protoplanetary disk that give rise to planets, with smaller worlds either getting absorbed into larger ones or getting kicked out of the solar system entirely by gravitational interactions! After a few tens of millions of years, all you’re left with are rocky and giant planets, asteroids, moons, and frozen comet-like objects.

And on worlds around stars with just the right conditions, not only can we have liquid water, but at least once, life that’s complicated enough to ask and answer questions like where our Solar System comes from.


Missed Episode 1? Check it out here.

And leave your comments at the Starts With A Bang forum on Scienceblogs!


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