Comets: the Ugly Ducklings of Our Solar System
by Bruce Mattson
Late bloomers, do not despair! On a scale as grand as that of our own solar system, there is precedent for astonishing transformation well into adulthood (how does 4.5 billion years sound).
Trillions of non-descript, rock-encrusted ice boulders encircle the outer solar system even now, patiently awaiting their moment in the Sun; few will get their chance to shine. A tiny percentage will find themselves touring the inner solar system with inspirational news for us all. Their simple message: dare to dream, because late-emerging beauty is not strictly for the birds.
So with renewed hope for that neglected modeling career, and deepest apologies to Han Christian Anderson, let's explore...
Comets: the Ugly Ducklings of our Solar System.
The objects in our solar system can be roughly sorted into a handful of categories. Holding court at the center of it all is our very own star, the Sun, which presides over a cast of nine large, spherical bodies we call planets. Many of these planets have their own natural satellites, called moons. There are asteroids - huge boulders the size of a city; and meteoroids – “space rocks” as big as your house, or as small as a grain of sand. And yes, there are comets.
All of these objects have at least one thing in common: they all formed out of a single cloud of gas and dust. This cloud (all that remained after the star that used to live here blew up) was mostly composed of heavier elements, such as oxygen, silicon, iron, carbon, calcium, and aluminum. These heavier elements were manufactured by the fated star's fusion processes from lighter elements, primarily hydrogen and helium, which dominated the early universe.
Although the available building materials where the same throughout this cloud, the objects that eventually took shape were not all the same. Those differences depended largely upon where they were located in the primordial cloud, and the random collisions that regulated their growth. Fortunately we have a reliable, if not easily interrogated, eyewitness to this period of prehistory in the form of the comet.
The Nature of Comets
Far from the Sun, a comet isn’t much to look at (a bit of an ugly duckling, you might even say). Imagine an enormous black potato the size of a big city. These huge lumps of ice, rock, and dust are called comet nuclei. They have extremely low albedos, about 4 percent in fact, which means they reflect very little of the sunlight that strikes their surface. For this reason, astronomers have difficulty seeing them through telescopes. Their surface terrain is varied by peaks and impact craters.
Close to the Sun – now that’s a different story. If a comet nucleus finds its way into the inner solar system (inside of Jupiter's orbit), the ugly duckling is slowly transformed into a magnificent swan, with a softly glowing head bigger than the Sun itself, and a gossamer tail longer than the distance from the Earth to the Sun.
Now for our first Comet Quiz! question. Take your time - don'tcha dare cheat.
That’s right, your planetarium needs you. Crowds of people will gather under its glittering dome to hear you describe how energy from the Sun spreads out in waves, called solar wind. Your vivid depiction of a comet nucleus, washed and eroded by these gentle waves of energy like a rock submerged in a lazy mountain stream, will captivate visitors and lead, quite possibly, to a lucrative second career narrating science documentaries for the Discovery Channel.
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