The Comet's Tale: Origin of Comets

Part 1

The Oort Cloud

A Dutch astronomer named Jan Van Oort studied the orbits of 46 comets and proposed in 1950 that the comets which we see from Earth come from a huge comet 'cloud' of perhaps a trillion objects. That's 1,000,000,000,000, or 1 and 12 zeroes!


Jan Van Oort 's Oort Cloud is roughly spherical, but most dense near the center

From the comets' orbits, Oort estimated the size of this cloud to be about 50,000 to 100,000 astronomical units (AU) across. One AU is the distance from the Sun to the earth: ninety-three million (93,000,000) miles, or one hundred fifty-five million (155,000,000)kilometers (km). By comparison, the orbit of Pluto is only 40 AU across. And 100,000 AU is almost half the distance to the next nearest star, Proxima Centauri!

Scale of the Oort Cloud--sun and planets in a "tiny" (40 AU) area at the center.

Today, astronomers agree that there is a giant cloud of comets far outside the orbits of the planets, but how were the comets and the Oort Cloud originally formed?  Most scientists think it all started when the Sun and the solar system were created 4.6 billion (4,6000,000,000)years ago from a huge spinning cloud of gas and dust called the solar nebula.


Next:  Click Continue to find out how comets were born and where they hang out.

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