Western Slope Skies - Fun with Asteroids

Mar 5, 2021

Credit By Mdf at English Wikipedia - Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1951518

Do you watch space movies? How many have you seen with the hero’s spaceship travelling a dangerous route through the asteroid belt, bobbing and weaving to miss catastrophic collisions with numerous asteroids in order to escape and save the Solar System! Today, we are going to find out what travelling through the asteroid belt would really look like.


First some background. The present formation theory of the Solar System involved a massive cloud of gas and dust that collapsed, due to gravity, into a rotating disk. Most of the mass was gas, primarily hydrogen, that concentrated at the center. Gravity continued to collapse this central cloud of hydrogen, resulting in increasing pressure and temperature. Eventually, the conditions initiated nuclear fusion of hydrogen to helium and a star, our Sun, was born.

At the same time the outer mass of the cloud continued to rotate, producing a flat disk, just like making a pizza crust from a blob of dough. The dust grains collided and combined over millions of years in a process called accretion, to become small objects called planetesimals, which continued to grow into planets. Physics and the distribution of gas versus dust determined whether a planet became a rocky planet like Earth or Mars or a gas giant like Jupiter and Saturn.

However, between Mars and Jupiter, the influence of Jupiter’s enormous gravitational field caused the planetesimals to accelerate and collide at such high velocities that they broke up into many, many small objects, rather than combining into a planet.

Today, the total number of objects in the asteroid belt cannot be determined, but is likely in the millions, yet the total mass of the asteroid belt is only 3-4% of the mass of the Moon. 25% of the total mass of the asteroid belt is in one object, the dwarf planet, Ceres. Ceres is about 600 miles in diameter.

The main belt is donut shaped and about 100 million miles wide from the inner edge to the outer edge. Even with millions of asteroids in the main belt, it is estimated that the average distance between any two asteroids is 600,000 miles or more than twice the distance between the Earth and the moon. This is a far cry from the dense crowds of asteroids often depicted in space movies.

Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written and recorded by Bryan Cashion.