How many exoplanets are officially known to exist? What is an exoplanet? Exoplanets are planets beyond our own solar system. They are planets orbiting other stars in space. Given there are billions and billions of stars in our own Galaxy, we expect billions and billions of planets. On top of that, there are billions and billions of galaxies, meaning there are billions and billions and billions and billions of planets in the Solar System! Wow! However, we can only officially count what we detect, whether the detection method be direct or indirect.
The first exoplanet was discovered 20 years ago in 1995. The planet was discovered by searching for gravitational tugs on the star. Although the star has nearly all of the mass in a solar system, planets exert a force on the star that causes the star to slightly wobble. This is an indirect detection method because the planet is not directly imaged. Imaging a planet is extremely tough because the light reflected off the planet to us is very tiny compared to the light given off by the star.
Numbers of exoplanets increased slowly after 1995. When I first started teaching in 2001 the number of known exoplanets was less than 100. With the launch of the Kepler spacecraft in 2009, the number of exoplanets soon began to explode. Kepler is no longer taking data, but the data taken is still being analyzed and the number of exoplanets will increase. In addition, future telescopes will observe even more planets. Kepler discovered planets by studying light from stars. If a planet passes in front of a star relative to us, the star light dips a tiny bit. Kepler was sensitive enough to detect this dip in light.
Currently, at the time of this blog post (October 28, 2015) there are 1,969 known exoplanets! Wow! Where will we be in 10 years? 10,000? 10,000 plus many Earth like planets? Who knows and that's the awesomeness of science!