This video shows a single 12-day portion of data from Kepler 17. The data (in black) come from NASA's Kepler mission. The model (in red) is our best estimate of the star+planet conditions during one full rotation of the star, or about 12 days. We then repeat this analysis every 12 days over a span of 4 years (Earth years, that is!) to learn about the evolution of the starspot features we see.
When the planet crosses in front of it's host star, we sometimes observe a "bump" in the transit. This is caused by the planet crossing or occulting a dark starspot region on the stellar surface (akin to a Sunspot). The animation shows the rotating star with spots (top), the full 12-days of data (middle), and zoom-ins during the planetary transit (bottom).
The planet (Kepler 17b) has a very short "year" indeed, going around it's host star every 1.5 days. This means during the 12 days it takes Kepler 17 to rotate, the planet eclipses 8 times! With this remarkable geometry, we are able to deduce and map the locations and sizes of at least 8 starspots. Previous techniques using imaging data without a transiting exoplanet could at most infer the approximate properties for 2 or 3 starspots. With this method we believe we can robustly detect up to 10x more starspots, and even trace their evolution. While this model has 8 spots included, there is strong evidence in the 4 year dataset that times fewer and sometimes even more spots are observed! This information will unlock details about magnetic fields and the inner workings of stars beyond our Sun. For reference, only a small handful of stars currently have detailed information about their magnetic fields or starspots. Our characterization of Kepler 17 will likely be the most detailed ever analysis of spots on any star besides the Sun.