Discovery of the Asteroid Belt

Mercury, Venus, Earth, Mars, Asteroid Belt, Jupiter, wait…what, asteroid belt?

Yes, our solar system has an asteroid belt, located between Mars and Jupiter. Like detritus on the ocean shore, asteroids appear to be remnants of events that went awry.

Tycho Brahe was a precise, methodological observer of the heavens in the 16th century.  Even though his geocentric ‘Tychonic System’ of planetary motion was flawed, his accurate observations placed planets at close to correct distances.  But he did not notice or did not document what appeared to be a weird anomaly. His late-life assistant, young, but future great astronomer Johannes Kepler did take notice and announced it to the world in 1596.  There needed to be a planet between Mars and Jupiter!

Why did Kepler believe this? There appeared too wide a gap between Mars and Jupiter.  The search for a planet commenced but to no avail. Eventually the topic was dropped.

Then in the early 18th century, astronomers David Gregory and Christian Wolff described how planets appeared to be in orbits of predictable distances.  Not much was made of it until 1766, when while translating a work by naturalist Charles Bonnet, Johann Daniel Titius noted the pattern in planetary orbital distances.  A few years later, Johann Elert Bode credited Titius in his own description of the phenomena.   Each planet was approximately twice as far from the Sun as the next closer planet.  They developed a mathematical solution together and named it the Titius-Bode law. Using their solution, Titius and Bode predicted a planet should occupy the space between…yep, Mars and Jupiter.  Here we go again!

While the search for a planet between Mars and Jupiter progressed, William Herschel discovered Uranus in 1781 using the Titius-Bode law.  Its orbit matched the prediction almost perfectly. Finally, in 1801 Giuseppe Piazzi found something between Mars and Jupiter.  At last, a planet! He named it Ceres after the Roman goddess.  Ceres was called a planet until the 1850s when numerous other small objects were found in the area. Astronomers then recognized the region between Mars and Jupiter was populated by asteroids. So, technically Giuseppe discovered the asteroid belt.  Ceres is the largest object in the asteroid belt and now also known as a dwarf planet, (along with Kuiper Belt objects Pluto, Eris, Makemake, and Haumea).

It appears the event that went awry was the formation of a planet between Mars and Jupiter, eh?!  Current theory suggests gravitational perturbations from Jupiter and Mars resulted in too much momentum of the primordial protoplanetary material between them.  They just could not accrete into a proper planet.


What’s in the Sky?

The Orionid Meteor Shower Peaks

October 20 late night into morning October 21.  Looking east – southeast toward Orion, rising after 10pm.

Twice per year Comet 1P/Halley’s debris trail provides us with this view of dust to pebbles burning up in Earth’s atmosphere.  The other is in May, the Eta Aquariid meteor shower.