They are All the Same

It is becoming increasingly obvious that there is no big difference between comets and asteroids as far as their makeup is concerned. They are both rocky objects. The tail of comets are due to the eccentricity of their orbits in a charged environment. The tails are evidence of electric discharge rather than an indication of an abundance of water.

Comet

By Philipp Salzgeber - http://salzgeber.at/astro/pics/9703293.html, CC BY-SA 2.0 at, Link

The distinction between large planets and small stars is also starting to blur. Jupiter is very hot. A little more heat, and it would glow like a Brown Dwarf. The distinction is one of temperature only.

And for the distinction between gas planets and rocky planets, it is purely a matter of atmosphere. A thick atmosphere makes a gas planet. A thin atmosphere makes a rocky planet, and in between we have Earth and Venus, appearing to make a transition from one state to the other.

The distinction between moons and planets are also blurring. Some of Jupiter's largest moons have atmospheres, and are as large as planets. They are different from planets only in their orbits. Was Jupiter to start glowing like a star its moons would have to be reclassified as planets.

Contrary to what was originally thought, our universe is not full of vastly different types of objects. They are all the same, with pretty much identical makeup. What makes the objects appear to be vastly different is merely their temperature, their orbits, their size and their atmosphere.