A few short decades ago, we could only speculate about the possibility of planets beyond our own solar system, but then we started finding them. Little by little, the universe has become a bustling place with more exoplanets being discovered every year. How many? NASA JPL says as of March 21st, there are just over 5,000 of them. To celebrate this milestone, the agency has produced a neat “data sonification” of the road to 5,000 exoplanets. Sonification is the use of non-speech audio to represent information.
The first exoplanets were discovered in the early 90s, but they’re not the kind of planets you’re probably expecting. They’re more like charred husks tethered to a millisecond pulsar, a type of dead star that blasts out radiation like a rapidly spinning lighthouse. Throughout the 90s and early 2000s, telescopes spotted a few hundred exoplanets, but it wasn’t until the launch of the Kepler Space Telescope that things got cooking.
NASA’s sonication begins in 1991 prior to the first exoplanet confirmations. Each time a new planet enters the catalog, there’s a chime and the counters at the top advance. It shows not only the approximate location of the exoplanet in the sky (using the central band of the Milky Way as a guide) but the types of detection. Early on, the detections are mostly from radial velocity, a technique that scans for minute wobbles in a star caused by the mass of orbiting planets. After Kepler, transits take over in a big way.
Most exoplanet discoveries have come by way of transit observations, which is the technique Kepler and the current Transiting Exoplanet Survey Satellite (TESS) operate. They watch large swaths of the sky for stars that drop in brightness in a predictable way. That indicates there may be a planet partially obscuring the light as it orbits. Kepler spotted a lot of these worlds, the first batch appearing in the sonication in 2014. Even after Kepler was hobbled by hardware failures, it continued to identify new exoplanets, though only in a small area of the sky — you can actually see the ‘plus’ shape of Kepler’s observational campaign in the animation.
By the end of the video, most areas of the sky have at least a few detections, but nothing is as dense as the Kepler K2 region. There aren’t more exoplanets there, we just looked for longer. As technology improves and instruments like the James Webb Space Telescope come online, the number of known exoplanets will continue to increase, and there’s no end in sight. Estimates based on current exoplanet data suggest there are at least as many planets in the galaxy as there are stars. That means potentially hundreds of billions of worlds out there. Suddenly, 5,000 doesn’t sound like that many.
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