The age of exoplanets began in 1992, when astronomers detected a pair of planets orbiting a pulsar. Then, in 1995, astronomers discovered the first exoplanet orbiting a main sequence star. As NASA’s Kepler and TESS missions got going, the number of confirmed exoplanets continued to rise.

By 2015, NASA announced that Kepler had discovered its 1000th exoplanet. 2016 was a banner year for exoplanet detections with nearly 1500 in that year alone. The total number reached 5000 in March of 2022. Now, NASA has announced that there are 6,000 confirmed exoplanets.

6,000 is a lot, though compared to the one hundred billion that may exist in the Milky Way, it’s a tiny amount. Still, for a fledgling space-faring civilization like ours, it’s something to celebrate.

The fact that we’ve found 6,000 is impressive, considering how challenging they are to detect. There are vast distances between us and other stars. Many exoplanets will be hidden in the glare from their stars, or they’re so far from their stars that they’re practically undetectable. With history as a guide, it’s clear that technological advances will bring more of them within reach, barring the collapse of civilization or the abandonment of science.

Exoplanet science is, obviously, about more than sheer numbers. The variety of planets we’ve discovered teaches us vital things about nature, our own Solar System, and about the precious Earth. Curiously, many of the planets we’ve discovered are unlike anything in our own Solar System. There are hot Jupiters, massive gas giants that orbit their stars in a matter of days. There are ultra-short period planets that put Mercury’s short orbital period to shame by completing orbits in mere hours. One strange type of planet are so close to their stars that they’re tidally locked to their star like the Moon is to Earth. These planets have one scorching hot side and one frigid side. Some of them may be hot enough to remain molten.

Others have such extreme temperatures, pressures, and chemical constituents that they may rain iron, or may be no denser than styrofoam. Some could be covered in oceans. Others swathed in toxic gases.

Somehow they’re all part of nature. Determining how they came to be is an enduring fascination. But at the base of all of this searching and wondering is the one big question: Are we alone? “Each of the different types of planets we discover gives us information about the conditions under which planets can form and, ultimately, how common planets like Earth might be, and where we should be looking for them,” said Dawn Gelino, head of NASA’s Exoplanet Exploration Program (ExEP) at the agency’s Jet Propulsion Laboratory in Southern California. “If we want to find out if we’re alone in the universe, all of this knowledge is essential.”