Comet Origins: Blame the Solar Nebula!


As we’ve discussed before, many comets are thought to exist in the Oort Cloud.  Others exist in the Kuiper Belt (more about that later).  I thought it would be interesting to explore the origin of the comets themselves.  Where did they come from?

Scientists generally agree today that comets were formed at the same time that our solar system was formed – about 4.6 billion years ago.  At that time, the solar system was an enormous spinning disk of dust and gas called the Solar Nebula.   Over time, gravitational attraction caused the dust and gas in the center to form our Sun and other areas consolidated into clumps of matter called planetesimals.  Planetesimals were about one kilometer across.

a comet and it's tail

A comet with it's visible tail

As you can imagine, there were a lot of these objects spinning around the early Sun and many of them smashed, crashed and bumped into one another.  Sometimes, they would stick together gaining mass and attracting other planetesimals which eventually formed the planets we know today.  Others were moved around by the larger planetary objects and pushed or  tossed into orbits of their own.

As the solar system matured, cometary bodies have found their way into two orbital areas – the Kuiper Belt and the Oort Cloud.  The Kuiper Belt lies outside of Jupiter’s orbit.  The Oort Cloud lies well beyond the orbit of Pluto and is at the edge of what we define as our Solar System.

Why are comets so interesting?  Well for one thing, they occasionally get bumped from their orbits and get pulled towards the Sun – sometimes we see them as beautiful arcs of light in the night sky for a couple of weeks as they make their way by.  They are also interesting because it is thought that they contain matter from the beginning of our Solar System.    Several space probes have been sent to comets including the Deep Impact mission in 2005.  Future missions include the European Rosetta probe which is on it’s way to Comet Churyumov-Gerasimenko when in 2014 it will go into orbit around the comet and attempt to place a small lander on it’s surface!

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