Space · Discovery archive · March 27, 2023

A thermometer for a distant world

How can a telescope measure the temperature of a planet it cannot photograph?

Original editorial illustration; not a scientific image or measured diagram.

The story

Webb detected infrared light from TRAPPIST-1 b. A 2023 study estimated its dayside temperature at about 500 kelvins. Scientists compared that measurement with models to investigate how an atmosphere might move heat around the planet.

Read the source: NASA · Webb measures TRAPPIST-1 b ↗

Explore the evidence

NASA’s comparison graphic places Earth at approximately 290 K, TRAPPIST-1 b at 500 K, and Mercury at 700 K. These are rounded reference values, not uniform temperatures across each planet.

Choose your way in

Allow 15–25 minutes. Work in your binder: show calculations, label units, and explain what your result means. Read the story first; choose a task with your teacher.

Compare temperaturesGrade 6 · Whole-number operations

Find the temperature differences between each pair of worlds. Put the three values on a number line. Why does a temperature difference alone not tell us whether a planet supports life?

A hint

List the known quantities and their units. Identify the quantity you need. Use a sketch, table, or equation to connect them.

Check your reasoning · Open after an attempt

Differences: 210 K, 200 K, and 410 K. Atmosphere, liquid water, and many other conditions matter.

Compare a modelGrade 7 · Percent and ratios

An atmosphere-distributing-heat model predicts 400 K. The measured value is about 500 K. How much higher is the measurement, as a percent of the prediction? State your comparison base.

A hint

List the known quantities and their units. Identify the quantity you need. Use a sketch, table, or equation to connect them.

Check your reasoning · Open after an attempt

(500 − 400) / 400 = 25%. The base is the predicted 400 K. This comparison alone does not prove an atmospheric explanation.

Translate the scaleGrade 8 Algebra 1 · Linear equations

Use C = K − 273.15 and F = 1.8C + 32. Write F directly in terms of K. Convert 500 K to °F. Explain the meaning of the slope; is this relationship proportional?

A hint

List the known quantities and their units. Identify the quantity you need. Use a sketch, table, or equation to connect them.

Check your reasoning · Open after an attempt

F = 1.8K − 459.67. At 500 K: 440.33°F. Each extra kelvin adds 1.8°F; the nonzero intercept makes the relationship nonproportional.

Look beyond the answer

Which number or assumption most affects your conclusion? What additional evidence would make your answer more useful?