physical science
Time and THYME: The Search for Exoplanets By Abigail Dunnigan
Image by Felix Mittermeier. [CC0]
T
he unknown planet zips around its host star, undisturbed for millions of years. It continues to remain undisturbed, but for the first time we can see it. Dr. Andrew Mann and his team study these previously unknown planets, more specifically exoplanets found in telescope data from NASA’s Kepler, K2, and Transiting Exoplanet Survey Satellite (TESS) missions. Exoplanets are all planets outside of our solar system. Their goal is to look for planets in young star clusters, moving groups of stars (which move similarly through space), and star-formation regions. They hope that studying the statistical properties of stars at different ages will provide insight into planet evolution. Dr. Mann is an Associate Professor within the Department of Physics and Astronomy at UNC-Chapel Hill. He is part of the group that leads the Zodiacal Exoplanets in Time (ZEIT) Survey, as well as the TESS Hunt for Young and Maturing Exoplanets (THYME). The ZEIT Survey identifies faint or low-mass stars from K2 observations, while THYME uses data collected from bright or high-mass stars from TESS observations. “Zeit” is the German term for “time”, a clever wordplay for these projects.1 While they use different data, both the ZEIT Survey and THYME have the same overall goals: to study how statistical properties of planets evolve, thus shedding light on planet evolution. The primary tool for identifying exoplanets is through the transit method. Take a solar eclipse as an example. When
Figure 1. Image courtesy of the European Southern Observatory.
the moon passes in front of the sun, it undergoes what is called a transit. While the moon is in transit, the areas on Earth in the path of the eclipse are darkened. This darknening occurs because the moon is blocking sunlight from reaching the Earth. The same principle applies as exoplanets far away from Earth pass in front of their host star. As the planet is in transit, it causes a small dip in the brightness of Dr. Andrew Mann the star. The amount of light detected at a given point in time is referred to as flux.
“The saying you go by is that you only know planets as well as their stars” Other characteristics of the transiting planet can be calculated based off of the change in flux, but only if you know the properties of the host star. “The saying you go by is that you only know planets as well as their stars,”1 says Dr. Mann. To be able to measure the radius of the planet, “the drop [in light] is proportional to the ratio of the planet size to the star size. So you actually only measure the planet size as well as you measure the star size.”1 Dr. Mann and his team are currently focusing on THYME, which uses data from NASA’s TESS mission.1 The satellite collects
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