Exploring Exoplanets with Kepler

This activity features real-world applications of math concepts related to transits and gives students practice calculating the movements of planets in our solar system and other star systems.

• Students can work individually or in pairs to solve the problems on the student worksheet.
• Calculators are optional but can simplify the calculations.

In the early 1600s, Johannes Kepler discovered that both Mercury and Venus would transit the sun in 1631. It was fortunate timing: The telescope had been invented just 23 years earlier and the transits wouldn’t happen in the same year again until 13425. Kepler didn’t survive to see the transits, but French astronomer Pierre Gassendi became the first person to see the transit of Mercury (the transit of Venus wasn’t visible from Europe). It was soon understood that transits could be used as an opportunity to measure the apparent diameter – how large a planet appears from Earth – with great accuracy.

In 1677, Edmond Halley observed the transit of Mercury and realized that the parallax shift of the planet – the variation in Mercury’s apparent position against the disk of the sun as seen by observers at distant points on Earth – could be used to accurately measure the distance between the sun and Earth, which wasn’t known at the time.

Today, radar is used to measure the distance between Earth and the sun with greater precision than can be found using transit observations, but the transit of Mercury still provides scientists with opportunities for scientific investigation in two important areas: exospheres and exoplanets.

Some objects, like the moon and Mercury, were originally thought to have no atmosphere. But scientists have discovered that these bodies are actually surrounded in an ultra-thin atmosphere of gases called an exosphere. Scientists want to better understand the composition and density of the gases that make up Mercury’s exosphere and transits make that possible.

“When Mercury is in front of the sun, we can study the exosphere close to the planet,” said NASA scientist Rosemary Killen. “Sodium in the exosphere absorbs and re-emits a yellow-orange color from sunlight, and by measuring that absorption, we can learn about the density of gas there.”

When Mercury transits the sun, it causes a slight dip in the sun’s brightness as it blocks a tiny portion of the sun's light. Scientists discovered they could use that phenomenon to search for planets orbiting distant stars, called exoplanets, that are otherwise obscured from view by the light of the star. When measuring the brightness of far-off stars, a slight recurring dip in the light curve (a graph of light intensity) could indicate an exoplanet orbiting and transiting its star. NASA’s Kepler mission has found more than 1,000 exoplanets by looking for this telltale drop in brightness.

Additionally, scientists have begun exploring the exospheres of exoplanets. By observing the spectra of the light that passes through an exosphere – similar to how we study Mercury’s exosphere – scientists are beginning to understand the evolution of exoplanet atmospheres as well as the influence of stellar wind and magnetic fields.

Kepler-5b, 6b, 7b and 8b with their low Kepler- numbers have relatively short orbital periods compared with Kepler-452b. Why do you think that is?

Stars observed by the Kepler mission with confirmed exoplanets are named Kepler-1, Kepler-2, Kepler-3, etc. The exoplanets around these stars are given a letter that corresponds to the order in which they were discovered, starting with b. So, Kepler-5b is the first exoplanet discovered around the fifth star found to have a planet.

Kepler-5b, 6b, 7b, and 8b were all discovered early in the mission (as indicated by their low Kepler- number). Kepler discoveries require multiple drops in the light curve to be confirmed. This can be accomplished in several weeks with orbital periods like those of Kepler-5b, 6b, 7b, and 8b. Kepler-452b, with its long orbital period, took several years to cause multiple dips in the light curve. As a result, it took much longer to be discovered, and many other exoplanets were discovered first, hence the high number.

• Individuals or pairs of students should compare work and discuss how their results agree or disagree. For disagreements, students should talk through how they arrived at their answers.
• Check students' work against the answer key below:

• Student answers may vary slightly from each other, and from the answer key. This is the result of variations in students' interpretations of drops in the light curve and from the actual measurements. Data provided was also rounded from more precise mission data. Student answers should generally agree with the answers provided, but shouldn't be marked as incorrect for not matching exactly.

Kepler Exoplanet Discoveries - Click on each planet referred to in the student worksheet to view an interactive of the exoplanet system, the light curve that led to its discovery, and a chart pinpointing its location in the sky.

Activities

• Kepler Education Activities

Multimedia

• Exoplanet Travel Bureau Posters
• Video: What’s in an Exoplanet Name?
• Video: The Search for Another Earth

Interactives

• Eyes on Exoplanets

Websites

• Kepler Mission Website
• Exoplanet Exploration Website

Explora Más en Español

• Article for Kids: ¿Qué es el Tránsito?
• Article for Kids: ¿Qué es un exoplaneta?