The Eight Worlds

Eight planets orbit the Sun. The International Astronomical Union formalized this count in 2006, defining a planet as a celestial body that orbits the Sun, has sufficient mass for a round shape, and has cleared the neighborhood around its orbit. Pluto, which fails the third criterion, was reclassified as a dwarf planet. This tool gives each of the eight an equal 12.5% selection probability.

Two Families

The inner four planets (Mercury, Venus, Earth, Mars) are terrestrial: small, rocky, dense, with solid surfaces. The outer four split into gas giants (Jupiter and Saturn, composed primarily of hydrogen and helium) and ice giants (Uranus and Neptune, with interiors rich in water, ammonia, and methane ices). Jupiter alone contains more mass than all other planets combined.

The Scale Problem

If Earth were a marble (1 cm diameter), Jupiter would be a grapefruit 11 cm wide, and the Sun would be a beach ball 1.1 meters across placed 117 meters away. Neptune would orbit at 3 kilometers. The solar system is overwhelmingly empty space. These proportions defy intuition, which is why every physical model you have ever seen is dramatically compressed.

In the Classroom

Have each student pick a planet and research one fact nobody else in the room knows. With eight planets and 25 students, some planets get multiple researchers, creating natural groups for comparison. The tool works on any device, requires no accounts, and stores no student data. Project it on a screen for a live reveal: the planet zooms in from the void of space, bringing the solar system to life.