Greenhouse Effect

Overview

Being in the habitable zone is necessary but not sufficient for a planet to be life-friendly. The composition of its atmosphere matters just as much. This experiment compares how quickly a sealed air-filled container and a CO₂-filled container heat up under the same infrared light source — a direct analogy to the greenhouse effect on Venus and the atmospheric conditions of exoplanets.

Grades	7–10
Subject	Physics, Natural Sciences
Method	Student experiment
Duration	~30 minutes (two runs of 15 minutes each)
Language	German, English
Sensor	TI SensorTag (temperature)

Background

The greenhouse effect arises because some atmospheric gases — primarily CO₂, water vapour, and methane — absorb infrared radiation re-emitted by a planet's surface, trapping heat. Venus, despite lying near the inner edge of the Sun's habitable zone, has a surface temperature of ~465 °C due to its overwhelming CO₂ atmosphere. Any exoplanet candidate must be assessed for its atmospheric composition, not just its orbital distance.

Materials

• Transparent, sealable container (glass or clear plastic)
• Effervescent tablet (produces CO₂ when dissolved in water)
• Water (~2 cm depth)
• One or two TI SensorTags (temperature)
• Smartphone with phyphox
• Sensor mount (to hold the sensor at least 4 cm above the container floor)
• Red light / infrared lamp
• Mounting material

The materials listed are examples. A standard drinking glass sealed with cling film works well.

Procedure

The experiment runs in two sequential parts, both with the same lamp–container distance and the same measurement duration (15 minutes).

Part 1 — Air only (control)

1. Fix the temperature sensor inside the container so it sits at least 4 cm above the bottom.
2. Open greenhouse.phyphox in phyphox (tab "Single setup" for one SensorTag).
3. Point the red light lamp at the container and start the measurement.
4. Record the temperature curve for 15 minutes, then stop.

Part 2 — CO₂ atmosphere

1. Pour ~2 cm of water into the same container with the sensor still in place.
2. Add an effervescent tablet. Wait until it is fully dissolved — the container is now filled with CO₂.
3. Point the red light lamp at the container and start a new measurement with the same duration.
4. Compare the two temperature curves.

Discussion

Under identical illumination the CO₂-filled container tends to warm faster and end warmer. Compare the curves and final values qualitatively and discuss:

• Why does CO₂ absorb infrared radiation?
• What does Venus tell us about the runaway greenhouse effect?
• Could a planet in the habitable zone have an uninhabitable surface because of its atmosphere?
• What atmospheric signatures would James Webb detect on a planet like the one in Part 2?

Alternative

If two sensors and two containers are available, both measurements can run simultaneously under the same lamp (tab "Comparison"), making the comparison immediate and more convincing.

phyphox Files

• One or two SensorTags (tabs "Single setup" / "Comparison"): greenhouse.phyphox
• Earlier version for a single sensor: greenhouse_single.phyphox

The file contains English, German and French texts. The phyphox files are maintained in the curious-signals-phyphox repository.