An artist illustration of the InSight lander on Mars. Image credit: NASA/JPL-Caltech

This activity is related to a Teachable Moment from Nov. 15, 2018. See "NASA’s ‘Cyber Monday’ Mars Landing to Deliver Science Firsts."

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Overview

Using a microcontroller with compatible temperature sensors and output devices, students create a program that will detect temperature changes through a soil sample. They will then calculate the rate at which heat flows through the soil.

Materials

Management

  • Safety! This activity involves the use of heating elements. To avoid burns, ensure the safe use of these tools by expressing and modeling appropriate use. Keep incandescent bulbs from touching plastic tubs to avoid melting.
  • Students can work in groups of two to four to develop code.
  • If supplies permit, provide each group with a microcontroller, temperature sensor and output device. Otherwise, allow students to develop code and upload to shared microcontroller(s) for testing.
  • If supplies permit, provide each group with a soil tub and heat source.

Plastic Tub Preparation

Vertical orientation (best with heat source below or above):

  1. Partially fill one tub with soil.
  2. Place the temperature sensor on top of the soil, centered, with connecting wires outside of the tub. (Protect the sensor in a sandwich or resealable plastic bag, if necessary.)
  3. Measure the distance from the temperature sensor to the top or bottom of the soil (whichever will be nearest the heat source) and make note of the measurement for when students calculate the rate of heat flow.
  4. Cover the sensor by adding more soil to the tub until it is level with the top.

Horizontal orientation (best with heat source to the side):

  1. Partially fill one tub halfway with soil.
  2. Place the temperature sensor on the soil, near the side of the tub that will be near the heat source, with connecting wires outside of the tub. (Protect the sensor in a sandwich or resealable plastic bag, if necessary.)
  3. Measure the distance from the temperature sensor to the side of the tub that will be nearest the heat source and make note of it for when students calculate the rate of heat flow.
  4. Fill the rest of the tub with soil.

Additional Tips

  • Wrap tubs in aluminum foil or other insulating material to minimize heat entering from the sides of tub – but do not place it on side closest to the heat source.
  • Tape connecting wire to the side of the tub so that repeated connecting and disconnecting from the microcontroller boards does not move the temperature sensors in the soil.
  • The closer the sensors are to the side of the tub facing the heat source, the sooner the temperature changes will be evident. If the sensors are too far from the heat source, it might take a long time to detect temperature changes, but if the sensors are too close to the sides, there may not be enough of a difference in temperature to make meaningful distinctions.
  • If using a single temperature sensor for every group in the entire class, there may come a point when the soil will not get any warmer, or the rate at which it changes by one degree becomes impractical for classroom application. Consider preparing multiple tubs that the sensor can be moved into, or move the sensor to the opposite end of the tub and rotate that end to be near the heat source.

Background

NASA’s Mars InSight lander is equipped with three science investigations. One, the Heat Flow and Physical Properties Probe, or HP3, will use a self-hammering probe to burrow to a depth of up to 16 feet (5 meters) into the surface of Mars, deeper than any instruments have penetrated before on Mars. At this depth, measurements won’t be affected by changes in the seasons, all four of which InSight will experience during its Martian-year-long mission.

HP3 will pull a ribbon-like cable behind it. That ribbon is filled with temperature sensors that will measure heat escaping from the interior of the planet. These measurements will help scientists understand how much heat is inside the Red Planet and what’s generating that heat.

The probe will also generate its own heat pulse every 1.5 feet. The ribbon sensors will measure how these heat pulses change over time, giving scientists information about how quickly temperatures change with depth and how heat flows inside Mars.

Procedures

  1. Prepare soil sample tub(s) in advance (see Management).
  2. Introduce students to the InSight mission and the Heat Flow and Physical Properties Probe, or HP3. The Mars InSight Overview video can be shown and/or a time lapse of the HP3 ‘mole’ test video.
  3. Present the coding challenge to students: Students must develop, test and refine code that will measure data from a temperature sensor and use an output device to indicate a 1-degree rise in temperature once a heat source has been added. Students will time how long it takes for the temperature to rise by 1 degree (C or F, as decided by the teacher), then calculate the rate of change in degrees per centimeter per minute.
  4. Allow students to develop code to meet the challenge. Keep in mind that there are multiple ways to develop code that will accomplish the task.
  5. As available materials permit, allow students to test their code with extra temperature sensors and output devices prior to testing in the soil tub(s).
  6. When ready, have students load their programs to the microcontroller and connect the microcontroller with the output device(s) to the temperature sensors in the tubs. If each group has their own microcontroller, have them make sure their most current program is loaded.
  7. Apply the heat source, and have students monitor output.
    • They should time how long it takes for the sensor to detect 1 degree of change once heat is applied and make note of anything else that happens.
    • If their code works and indicates a change in temperature of 1 degree, they should use their timing and the distance from the edge of the tub to the sensor to calculate heat flow in degrees per centimeter per minute.

  8. Students should correct their code as necessary.

Discussion

  • Which elements of the challenge proved to be more or less difficult than anticipated?
  • What properties of the soil might be affecting the flow of heat?
  • Were there differences in readings from group to group? If so, why?

Assessment

Student coding should measure the data from the sensors and create a meaningful and understandable output over time.

Extensions

  • Have students develop code that will measure how long it takes for the temperature to change by 1 degree.
  • Have students develop code to output the rate of change of the temperature to a display.
  • Have students develop code to record data over time for later viewing, in addition to using the output device(s).

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