Interpret planetary temperature and surface gravity data
Compare supplied planetary properties without inferring them from orbital distance or mass alone.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Compare numerical values with units.
- Use weight = mass × field strength.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
For identical test masses, what controls their weights in a supplied local model?
What you will learn
- Compare supplied planetary properties without inferring them from orbital distance or mass alone.
- Interpret temperature and surface-field columns without unsupported mass or distance-only claims.
Keep the comparison evidence visible
This illustrative model table supplies A: distance 1 unit, temperature 500 K, surface g 8 N/kg; B: distance 2 units, temperature 600 K, surface g 10 N/kg; C: distance 4 units, temperature 150 K, surface g 6 N/kg. B is farther than A but hotter in this model. The data do not support a strictly decreasing temperature rule.
Actual planetary surface or reference-level temperatures depend on atmospheric effects and the location being measured, as well as received sunlight. Outer giant planets do not have an Earth-like solid surface at the top of their atmosphere; quoted values need a defined reference level. Supplied model values are not claims about named real planets.
Use a local surface-field approximation
For each model, treat the supplied g as uniform over the small local region stated in the problem. That approximation supports weight calculations near that location. It does not make g constant across the whole Solar System or at every altitude around the planet.
A larger supplied surface g means greater weight for the same test mass. It does not by itself prove the planet has more total mass than every other row, because surface radius also matters. Separate what the table provides from extra quantities it omits.
Sources for this lesson
Pause and explain
Which conclusion follows from the supplied A–B–C temperatures?
Worked example
Which model is hottest and which gives a 2 kg test object the greatest weight?
Show the worked solution
- B has the largest supplied temperature, 600 K.
- B also has the largest supplied g, 10 N/kg.
- For the same 2 kg test mass, weight there is 20 N.
Answer B is hottest and gives the greatest weight, 20 N.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Rank the model temperatures 500 K, 600 K and 150 K from coolest to hottest.
Give me a hint
Use temperature values rather than the distance column.
Compare my reasoning
- C has 150 K.
- A has 500 K.
- B has 600 K.
C < A < B.
Look for these in your work
- Rank the correct quantity.
- Retain kelvin units.
Find the weight of a 3 kg test object at model C’s local g = 6 N/kg.
Give me a hint
Use the given local field, not a memorised Earth value.
Compare my reasoning
- Write W = mg.
- Calculate 3 × 6.
- The force is 18 N.
18 N.
Look for these in your work
- Use the stated field.
- Report force in newtons.
A learner extends one row’s uniform surface g to a spacecraft much farther away. Correct the inference.
Give me a hint
Identify the spatial limit of the local approximation.
Compare my reasoning
- The row gives a near-surface local field.
- The planet’s field decreases with centre distance.
- A new location needs its own supplied or calculated g.
The local surface approximation cannot be used unchanged far from the planet.
Look for these in your work
- State the limited region.
- Identify the distance dependence.
Common mistakes
- Temperature need not decrease strictly with orbital distance.
- Define the surface or reference level used.
- Local uniform g is not a global field model.
What can you explain now?
Which conclusion follows from the supplied A–B–C temperatures?
Compare with the explanation
B is hotter than A despite greater orbital distance
The supplied values directly show 600 K versus 500 K, so strict distance-only temperature ranking fails.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Interpret temperature and surface-field columns without unsupported mass or distance-only claims.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.