Learning Objectives
- Compute and compare bulk density from mass and radius for terrestrial, giant, and ice-giant planets.
- Identify architecture trends with distance, size, composition class, surface gravity, and satellite count.
- Separate robust trends from trends that depend on rounding, classification, or small-number comparisons.
Preparation
Review Lecture 1 on scale and comparative planetology and Lecture 2 on solar-system formation. Bring a spreadsheet or calculator that can evaluate powers and unit conversions.
Materials and Data
../data/lab-01-planetary-properties.csv, a classroom table of planetary semimajor axis, radius, mass, density, gravity, and known moons.- Spreadsheet software or a scientific calculator.
- NASA Planetary Fact Sheet values, rounded to classroom precision; see
../data/lab-data-provenance.md.
Apparatus and Setup
- Open the CSV and freeze the header row.
- Create columns for volume, calculated density, density residual, planet class, and architecture note.
- Use SI units: convert radius from km to m and mass from 1024 kg to kg before calculating density.
- Record the access date as 2026-09-23 and mark the table as real public reference data rounded for instruction.
Procedure
- For Mercury, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, calculate \(\rho = M/(4\pi R^3/3)\) and convert kg m-3 to g cm-3.
- Compare your calculated densities with the supplied bulk-density column. Flag any residual greater than 0.05 g cm-3 and explain whether rounding can account for it.
- Make a scatter plot of semimajor axis versus radius, using symbol color for planet class and symbol size for known moon count.
- Rank the eight planets by density and by surface gravity. Identify one pair whose ranking changes between the two lists and explain why.
- Write a two-sentence architecture claim that uses at least three measured quantities, not just the planet names.
Measurement Record
| Object | Calculated density (g cm-3) | Listed density | Residual | Architecture evidence |
|---|---|---|---|---|
| Mercury | 5.43 | |||
| Earth | 5.51 | |||
| Jupiter | 1.33 | |||
| Saturn | 0.69 |
Analysis and Uncertainty
Treat radius values as rounded to the last listed digit and mass values as rounded to the last listed decimal place. Propagate density uncertainty with \(\Delta\rho/\rho \approx \Delta M/M + 3\Delta R/R\). In the conclusion, identify which comparisons are insensitive to this uncertainty and which depend on category boundaries such as terrestrial versus ice giant.
Deliverables
- Completed spreadsheet with calculated density, residual, and uncertainty columns.
- One scatter plot of planetary architecture with a caption that names the data file.
- A 250-word evidence paragraph explaining the strongest and weakest architecture trend.
- Provenance note citing NASA Planetary Fact Sheet and
lab-01-planetary-properties.csv.
Assessment Criteria
- Correct unit conversion and density calculation: 30%.
- Plot communicates at least three measured variables clearly: 20%.
- Uncertainty treatment uses rounding limits and identifies robust comparisons: 20%.
- Interpretation connects measurements to formation architecture without overclaiming: 20%.
- Complete provenance note: 10%.
References, Software, and Data Provenance
Data file: materials/ASTR120/data/lab-01-planetary-properties.csv. Source: NASA Planetary Fact Sheet, public reference tables, rounded for classroom use; OpenStax Astronomy 2e provides supporting discussion of comparative planetology. Software: spreadsheet or calculator. Processing state: real reference values copied into a compact teaching table.