Maybe not so Simple

Ken Tapping, November 13th 2013

In the sky this week…

  • Venus shines brightly, low in the southwest after sunset.
  • Jupiter rises around 8pm and Mars rises over the eastern horizon at 1am.
  • Look for Mercury low in the southeast before dawn.
  • The Moon will be Full on the 17th.

In the 17th Century Emmanual Swedborg came up with an idea as to how the Solar System formed. In the 18th Century the philosopher Immanuel Kant elaborated on it. Then in the early 19th Century, Pierre Laplace, who has been described as the French answer to Isaac Newton took this idea, gave it some additional polish and published it. These days it is customary in writing scientific papers to reference the contributions by others to the work. When Laplace wrote his ideas down he did not do that, so the credit usually wrongly given to him. However, his numerous contributions to mathematics and astronomy firmly establish him as one of history’s most important scientists.

This idea was that our Solar System came about through the collapse of a cloud of cosmic gas and dust. The cloud collapses into a disc with the inner part becoming the Sun and the rest forming the planets and all the other bodies we see in the Solar System. This seems to be right, because thanks to modern instruments such as the Hubble Space Telescope, Gemini and the Atacama Large Millimetre Array, which is now coming into action, we can now observe this happening elsewhere in our galaxy. We see clouds collapsing into discs, and stars igniting inside them. The additional part of the picture is that the radiation and strong wind blowing from the newly-ignited Sun blasted away the volatile materials from the nearer planets, leaving them as rock balls: Mercury, Venus, Earth and Mars, whereas the planets further out managed to hang onto the volatile materials, leaving them as the gas giant planets: Jupiter, Saturn, Uranus and Neptune. It all makes sense, the basic idea has stood the test of time, and we would expect planetary systems orbiting other stars to be like ours. However, they’re not.

So far we have found a thousand or so planets orbiting other stars. It now looks as though on average every star has several planets, of which one will be about the size of the Earth and the right distance from its star for liquid water to exist on its surface. However, we also see gas giant planets orbiting extremely close to their parent stars and rock balls orbiting further out. So it looks as though the idea put together by Swedborg, Kant and Laplace still seems to apply at least to the point where the planets have largely formed and the parent star has started to shine, but after that the situation remains very puzzling. The arrangements of planets we see do not make sense. Why is our Solar System different? Is it different?

One of the ways we investigate problems like this is through computer simulations. We can construct virtual clouds of material in a computer, and see them collapse, forming stars and planets. However what happens then is odd, because the simulations show a planets drastically changing orbit, rather like a game of cosmic pool. These simulations seem to fit quite well with what we see in other planetary systems, but not ours.

Our Solar System formed about 4.5 billion years ago. Life appeared on Earth pretty well as soon as our world had cooled enough for liquid water to accumulate on its surface, around 3.5 billion years ago. Fossil evidence suggests life then evolved continuously from that time to the present day. There have been extinctions, due to volcanism, asteroid impacts, ice ages and other disasters, which in once case wiped out over 90% of species. However, if the distance between the Earth and Sun had changed by just 10%, which is small compared with the standards of the cosmic pool game that seems to take place in young planetary systems, life on Earth would have been totally annihilated. This did not happen. Why?

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

Telephone: 250-497-2300
Fax: 250-497-2355
E-mailken.tapping@nrc-cnrc.gc.ca

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