Name: ______Date: ______
Student Activity 6—Sheet 1
The Search for Exoplanets
Science Background
An exoplanet is a planet that orbits a star in the way that Earth orbits the Sun. When scientists look for exoplanets, they set their telescopes on a small piece of sky for a very long time and look for small changes in the amount of light that is received from stars that they are tracking. When an exoplanet moves across the face of the star, the light that the telescope receives dims slightly. (When an exoplanet crosses in front of a star, we say that it has transited the star.)
In this activity, you will simulate an exoplanet transiting a star. By performing some calculations, you will be able to graph the data and see the characteristic dip in light intensity that helps scientists find exoplanets.
Label
1. Examine Figure 1. This diagram represents an exoplanet moving across the star. Label the larger circle “star.” Label each of the smaller circles with the numbers 0 through 8, in order from left to right.
Figure 1 The larger circle represents a star. The smaller circles represent the movement of an exoplanet as it transits a star.
Calculate
2. Suppose that the radius of the star is 6 cm and the radius of the exoplanet is 3 cm. Calculate the area of the star and the area of the exoplanet. Be sure to include the correct units.
Area of star: ______Area of exoplanet: ______Units: ______
3. In position 0, what percent of the star’s light is blocked by the exoplanet? ______
In position 0, what percent of the star’s light is being received by the telescope? ______
What other position(s) will result in the same amount of light being received by the telescope?
4. In position 4, what percent of the star’s light is blocked by the exoplanet? ______
In position 4, what percent of the star’s light is being received by the telescope? ______
What other position(s) will result in the same amount of light being received by the telescope?
5. In position 2, assume that exactly half of the exoplanet is blocking the star.
(a) Given this assumption, in position 2, what percent of the star’s light is blocked by the exoplanet?
(b) In position 2, what percent of the star’s light is being received by the telescope?
(c) What other position(s) will result in the same amount of light being received by the telescope?
Summarize Your Learning
1. Fill in the table of values. In the first column, write the position number for the exoplanet (0 through 8) and in the second column, write the percent of the star’s light that is received by a viewing telescope. Give the table a title and label the columns appropriately.
2. Graph the data from your table of values. Label both sets of axes and give the graph a title.
3. In this activity, the radius of the exoplanet is half the radius of the star. (The area of the exoplanet is one-quarter the area of the star.) Typically, however, an exoplanet is tiny compared to its star.
(a) If the exoplanet is much smaller than the star, how will the amount of light blocked be different than in our activity?
(b) How will the percent of light received by a viewing telescope be different?
(c) How would your graph be different if the exoplanet were tiny compared to the star?
Post-Activity Assessment
Answer the following questions to check your understanding of modelling the transit method two-dimensionally.
1. Exoplanets are very small compared with the size of the star that they orbit. If the radius of the star is known and the percent light drop is known, the radius of the exoplanet can be calculated.
To calculate the radius of the exoplanet, scientists use the formula where R is the radius of the star and r is the radius of the exoplanet. In our activity, R = 6 cm. If an exoplanet transits the star and the percent drop of light received is 1%, calculate r, the radius of the exoplanet in centimetres.
2. Recall that in our activity, the star had a radius of 6 cm.
(a) If the percent drop of light received is 0.5%, calculate the radius of the exoplanet in centimetres.
(b) If 1 cm represents 100 000 km, what is the real radius of the exoplanet?
3. The star Kepler-452 has a radius of about 386 000 km. When its exoplanet, Kepler-452b, transits the star, the percent drop in light intensity is 0.06%. Calculate the radius of exoplanet Kepler-452b in kilometres.
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