It's a Big, Busy Solar System

Article excerpt

There should be little doubt that we live in a golden age of solar system exploration. Spacecraft have visited every planet in the solar system, numerous moons, and some asteroids and comets. Currently, there is a spacecraft on the way to Mercury, one in orbit around Venus, five operating at Mars, one that just flew by Jupiter, and another in orbit around Saturn. A small armada of missions is observing the Sun and examining its interaction with Earth. And, because Earth is a planet as well, space is being used to look back at Earth with a planetary perspective. Dwarf planet Pluto will have a visitor in 2015, pieces of a comet and particles of the solar wind were just delivered to Earth from space for analysis, and an asteroid mission recently began its voyage. The two venerable Voyager spacecraft, launched in 1977, are still functioning, returning data from the extreme edge of the solar system where the Sun's influence yields to the winds of the Milky Way galaxy. NASA's science missions list can be found at http://science. The European Space Agency's mission lists are at (see "ESA activities" navigation bar in the upper left of the page). Russia, Japan, India, and China have Earth and space science missions or aspirations.

As of this writing, we live in a solar system with an inventory of eight planets, three dwarf planets, 162 moons of major planets, four moons of dwarf planets, and countless asteroids, comets, trans-Neptunian objects, and Kuiper Belt objects. The notion of a solar system has been altered by the discovery of planets around other stars, now numbering over 200 but expected to explode in number as our ability to detect them improves.

Anyone who teaches about the solar system can't help but be impressed by the vast array of solar system objects, all of the robotic explorers, and the rapidly evolving view of each object and the systems they inhabit. Far from being a disconcerting jumble of, literally, alien places, the study of the solar system is a perfect example of how science progresses and evolves in the presence of new evidence and analysis.

In fact, the whole notion of something so seemingly straightforward as the definition of planet got tossed in 2006 when the International Astronomical Union defined the term in such a way as to change the number of planets from nine to eight, while defining the new category of dwarf planet with three charter members. But today's science isn't the last word on natural facts. It is the pursuit of the next generation of questions and mysteries. The more you know about planetary science, the more you appreciate how much more there is to know. Teachers of inquiry, rejoice!

The National Aeronautics and Space Administration (NASA) is a great place to look for the latest news, statistics, and images. Three key pages to bookmark are the NASA Science Mission Directorate's "Solar System Exploration" web page for all sorts of information (http://solarsystem.; the Directorate's descriptions of past, present, and future solar system missions ( missions/solar_system.html); and the "Planetary Photojournal" for amazing images ( Also, the "New Releases" link at the bottom of the Photojournal title page has images, with captions, released over the prior seven days (

Science education standards across the nation typically include the solar system explicitly at multiple grade levels. But, with so many wonderful topics, the modest time allocated to solar system instruction cannot possibly cover everything. For the greatest impact, educators and students should address major misconceptions on the size and scale of the solar system, and how our solar system fits within the universe (Grier et al. 2005; Schneps and Sadler 1988).

Scale models of the solar system are handicapped by the difficulty in showing size and distance correctly at the same time within the same model (see "The Dimensions of the Solar System" article on pg. …