Question

activity a:
classifying
planets
get the gizmo ready:

• click reset ( ).

question: how are planets classified?

1. think about it: how do you think astronomers group planets? _______________

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1. gather data: select mercury from the solar system menu at left. turn on additional data.

in the table below, record mercury’s mass, mean radius, and density. then repeat for
each of the other planets as well as the dwarf planet pluto. include units.

planet	mass (×10²³ kg)	mean radius (km)	density (g/cm³)
venus
earth
mars
jupiter
saturn
uranus
neptune
pluto (dwarf planet)

1. analyze: what patterns do you notice in your data table? _______________

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1. analyze: based on the data you have collected, how would you divide the planets into two

groups? explain your reasoning. (note: do not include pluto in these groups.)
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Explanation:

1. Think about it

Astronomers likely group planets by shared characteristics like size, composition (rocky/gaseous), distance from the Sun, or orbital properties. For example, inner planets (Mercury, Venus, Earth, Mars) are rocky, small, and close to the Sun, while outer planets (Jupiter, Saturn, Uranus, Neptune) are gaseous, large, and far.

Step1: Recall/Research planet data

Use astronomical data sources to find each planet’s mass, radius, and density. For example, Mercury’s mass is $3.30\times10^{23}$ kg, radius 2440 km, density 5.43 g/cm³. Repeat for all planets.

Step2: Fill table

Input each planet’s data into the corresponding row.

Patterns: Inner planets (Mercury, Venus, Earth, Mars) have high density (≈3.9–5.5 g/cm³), smaller mass (≤5.97×10²³ kg), and smaller radius (≤6371 km). Outer planets (Jupiter, Saturn, Uranus, Neptune) have low density (≤1.64 g/cm³), larger mass (≥86.8×10²³ kg), and larger radius (≥24622 km). Pluto (dwarf) has low mass, radius, and moderate density.

Answer:

Astronomers probably group planets by characteristics like size, composition, or orbital region (e.g., inner rocky planets, outer gaseous planets).

2. Gather data (completed table with known values):

Planet	Mass ($\times10^{23}$ kg)	Mean radius (km)	Density (g/cm³)
Venus	4.87	6052	5.24
Earth	5.97	6371	5.51
Mars	0.642	3390	3.93
Jupiter	1898	69911	1.33
Saturn	568	58232	0.69
Uranus	86.8	25362	1.27
Neptune	102	24622	1.64
Pluto (dwarf planet)	0.0130	1188	1.86