Exoplanets are planets that orbit stars that are not our sun. They are interesting because they help us understand our place in the universe and possible environments for other forms of life.
This scatterplot attempts to answer the question as to how exoplanet detection has changed since scientists discovered the first planets orbiting other star systems in the mid-1990s. The size of exoplanets is represented by the circle size.
Plotted on the y-axis is distance from Earth, so you can see that as time has passed and detection methods have become more sensitive we are able to detect exoplanets farther and farther, especially via the transit method (light dims as exoplanets pass in front of their star) or the microlensing method (where light from extrasolar stars and planets is bent due to gravity of objects in space). The distance from Earth is measured in units of lightyears.
This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.