comets-book

You can now buy the recently released book, Fall of a Thousand Suns: How Near Misses and Comet Impacts affected the Religious Beliefs of our Ancestors. It is available through iBooks and Amazon.

 

This website only lists information on modern-day comets and meteor showers. The book, however, thoroughly investigates how specific ancient impacts and near misses changed religious beliefs around the world.

Where Do Comets Come From?

Definition of Perihelion

 

Early Theories regarding the Origin of Comets

Several millennia ago, comets were interpreted as gods or monsters by various cultures around the world.

 

In time science prevailed, at least in some cultures, and the true nature of everything including comets was questioned.  The Greek philosopher Aristotle  (384-322 BCE) claimed predecessors, like Anaxagoras (500-428 BCE) and the Pythagoreans, believed a comet was either a rarely seen planet that didn’t rise far above the horizon and was often too close to the Sun to be seen from Earth, or was created when two planets conjoined.

 

Comet Panstarrs 2013

Tycho Brahe sporting one of the finest mustaches known to man

Aristotle rejected these theories in favor of his own.  He believed the night sky moved with predictable, clocklike precision.  The unpredictable appearance and movement of comets meant they had to come from Earth.  The Sun heated the land causing a hot, flammable air to rise high above Earth where it ignited and became a fiery comet.

 

In the western world, Aristotle’s theory was fairly popular until 16th century German Peter Apian noticed that a comet tail always pointed away from the Sun.  A few years after Peter Apian’s observation, astronomer Tycho Brahe charted a comet against the stars night after night and claimed it was, at least, four times further than our Moon.  Aristotle was wrong.  Comets weren’t emissions from Earth, but where did they come from? Astronomers, in the wake of Brahe, spotted comets coming from the direction of the Sun.  Others witnessed comets coming from Jupiter.  Some were first observed in constellations, even constellations outside the relatively flat path traveled by all planets in our solar system known as the ecliptic.

 

 

 

 

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Comets from the Edgeworth-Kuiper Belt

The question, "where do comets come from?" continued to haunt astronomers well into the 20th century. During the 1940s, Irishman Kenneth Edgeworth theorized that thousands of small objects beyond Neptune couldn't join together to form planets when the solar system began to take shape billions of year ago. These icy objects occasionally entered the inner solar system, neared the Sun and began to grow a tail(s) as the ice melted. This area of space, home to many of our comets, became known as the Edgeworth-Kuiper Belt or simply as the Kuiper Belt.

 

Today, the Edgeworth-Kuiper Belt is considered a doughnut-shaped region in space spanning 35 to 50 AU from our Sun. It is no longer theory. Since 1992, over 1,000 objects have been detected in this area of space. The Edgeworth-Kuiper Belt consists of a stable inner ring and an unstable outer ring, known as the scattered disk. The comets, which enter the inner solar system, from this Belt orbit the Sun in less than 200 years.

 

A good example of a comet from the Edgeworth-Kuiper Belt would be Halley’s Comet (1P/Halley), which orbits our Sun once every 74 to 79 years. 

 

 

Comets from the Oort Cloud

Oort Cloud

Exploded view of thousands of objects in the Kuiper Belt surrounded by hundreds of billions of comet nuclei in the Oort Cloud.

Credit: Don Yeomans/NASA/JPL illustration adapted by Kevin Curran

What if I told you there were hundreds of thousands of asteroids in the inner solar system and that a sphere of hundreds of billions of comets existed beyond the Kuiper Belt?  Would you live off the land, watch Doomsday Preppers in your underwear and eventually move to the highest mountain?  If you answered, "yes", then you should set your DVR now.

 

The Oort Cloud is a hypothetical sphere of 400,000,000,000 comets.  It is traditionally believed to cover the space between 1,000 and 100,000 AU from our Sun.  In order to give you some idea of how big that is, Voyager 1, a spacecraft launched by the United States in 1977, is now 11,000,000,000 (118 AU) miles from our Sun.  It’s the furthest man-made object from Earth with no remaining objective except to travel into deep space with a “message in a bottle”.  Aboard Voyager is a golden record with 116 images and sounds from Earth including the wind, the surf, the song of a whale and the following message from then U.S. President Jimmy Carter.  “…This is a present from a small distant world, a token of our sounds, our science, our images, our music, our thoughts, and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.”  The problem is that despite traveling 38,000 miles (61,000 km) per hour, Voyager 1 won’t reach the near edge of our Oort cloud for another 246 years.  It won’t reach the far edge, and exit our solar system, for another 28,000 years.