The planets, moons, and other objects in our solar system vary widely in mass, from Pluto (1.09 x 1022 kg) to the sun itself (2.03 x 1030 kg). Because these mass measurements are so large, it may be difficult to grasp how these objects compare with one another. The Planet Mass Comparison interactive helps visualize the differences between any two of these objects by putting them side by side on an old-fashioned balance scale. The scale tips toward the object with greater mass. Try to restore the balance by adding copies of the less massive planet to that side of the scale.
Note: This website has not been updated to reflect the change in Pluto's classification as a dwarf planet, rather than a planet.
Students choose an object for each pan of the scale from the dropdown menu above the pan, then click the COMPARE button between them. The chosen planets appear and the scale tips toward the one with the greater mass. Each planet's mass appears in a text field below the planet.
The animation also shows how the two planets compare in size. This can mean that the same object will appear much smaller when it is compared with a much larger object.
When two objects are compared, a "slider" control appears above the less massive planet. Students can use this control to add more copies of the smaller planet. To add copies, students can slide the pointer to the right and then click the ADD button. More copies of the object will appear, and the balance will adjust accordingly. The field to the right of the slider will show how many copies have been added. To add the same number of copies again, click ADD again. (Click MAX to control how many copies you can add at one time.)
You can introduce this interactive as an entertaining way to reinforce facts about the solar system. Students can work with it to compile a table that shows how the masses of these solar system bodies compare. Challenge students to find out which objects in the solar system are closest in mass, which are most different, etc.