Planet Preschool

Introduction to the Planets
April 28, 2007, 11:34 pm
Filed under: Our Solar System

Today we’ll be taking a brief look at the planets in our solar system and getting comfortable with just what’s out there.  There are many ways to approach science learning with little ones; one appoach is to introduce basic concepts at an early age and follow their interest.  Memorization of key facts is not the most critical skill at this age; rather, I would encourage you to focus on two other aspects:

1. There are many worlds out there, both in our solar system and around other stars.

2. Each planet is different. 

The second point is actually key.  In our solar system, some are rocky, some are icy, and some are composed of swirling gases.  In other planetary systems, there may be rocky, icy, gaseous, earth-like planets, and/or others that we can’t even imagine.  We’re just beginning to discover planets around other stars, and we don’t even have the technology to really probe what the newly discovered planets are like at this point.  Some may be very similar to Earth (many astronomers think this must be so), but we are only starting to discover their true natures.  This is going to be a very exciting area of discovery over the next couple decades, as our kids grow up, so it’s nice to introduce them to it now.

But back to basics.  There are eight planets in our solar system (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune).  Three additional large bodies (Pluto, Ceres, and Sedna) have been recently reclassified as dwarf planets.  There are thousands of smaller rocky or icy protoplanets called asteroids (the rocky ones) and comets (the icy ones).   They all formed at about the same time, in what is called the primordial solar nebula. 

All planets orbit the sun.  Each orbit is an ellipse, and both orbital time and path are predictable using a simple mathematical relationship.  Both the size and nature of the planets change with distance from the sun, among other factors.  Here’s a brief introduction, just the facts that might fit on a name tag for each major planet:

Mercury – very small and very close to the sun.  Mercury is a planet of extremes; the “daytime” side (facing the sun) is very hot, while the “nighttime” side (away from the sun) is very cold. 

Venus – HOT!  Venus is very hot and has active volcanos, quakes, and the accompanying scars covering its crust.

Earth – the perfect distance from the sun to support life; this planet is the only one that is known to have liquid water on the surface.

Mars – the red planet.  Mars is very similar to Earth, but without an atmosphere, it can’t hold on to its water very long.

Jupiter – the largest planet, a gas giant.  It is easily identified by the great red spot, visible in the picture below and through many observatory telescopes.

Saturn – also a gas giant.  Although it is often pictured with two or three rings around it, there are actually hundreds of these dust rings, along with regular gaps where no dust or moons can be seen.

Uranus – another gas giant.  Uranus gas is composed of water, ammonia, and methane.  The methane above the atmosphere makes it look bluish-green.

Neptune – the farthest gas giant, mostly hydrogen and helium, with enough methane to make it look blue to us.

How to remember the names and order of the planets?  Here’s a simple mnemonic to try:  My Very Educated Mother Just Showed Us Neptune.

Tune in tomorrow for pictures, videos, and talk about the latest imagery of our closest star — the Sun! 


Jupiter and Saturn, the gas giants, dwarf the smaller rocky and icy bodies of the solar system.  The smaller planets in the front row are, from left to right, Earth, Venus, Mars, Mercury, and the dwarf planet Pluto. 

Resource of the day:  the planetary fact sheets at the Jet Propulsion Laboratory’s web site,