In January of 1992, the first two planets outside the solar system, or exoplanets, were discovered. And just a few days ago, NASA declared that it had confirmed the existence of 5,000 exoplanets. This milestone was no easy feat; it was achieved through ingenious techniques and state-of-the-art technology combined.

It started when astronomers Aleksander Wolszczan and Dale Frail observed a “pulsar”. Pulsars are rapidly rotating radio sources that send radio waves in the Earth’s direction at a regular frequency. This frequency should be completely consistent, like a metronome — so when they noticed that the signals were off-beat, they knew there had to be at least one object revolving around the pulsar, blocking the signals every once in a while to create the blip. 

Thus the hunt for exoplanets started. The first exoplanet orbiting a regular star was discovered in January of 1995; it was named Pegasi 51b. But although the data seemed conclusive, it was extremely difficult to prove that there were no errors in the instruments or discrepancies, and so the paper was only published in October. They used the technique of observing radial velocity, or detecting tiny “wobbling” motions of stars in the sky as their planets exerted their small gravitational pulls on them.

After these arduous early days, progress sped up with the use of space telescopes. Various telescopes have been used to discover these planets, but the Kepler Space Telescope is by far the most successful, at over 2,700 planets discovered. The technique these telescopes used is known as “transit”. When the planets move in front of a star, they can block a small amount of light from reaching the Earth, creating a small but detectable difference in the brightness of the stars.

Along with more minor techniques, transit and radial velocity have steadily increased the amount of confirmed exoplanets over the past 30 years. In 2013, the milestone of 1,000 exoplanets was reached. And on March 21, 2022, the Jet Propulsion Laboratory confirmed that 5,000 exoplanets had been discovered.

But 5,000 is not the limit — it is not even close to what there could be out there. It is estimated that there are 100–200 billion planets in the Milky Way Galaxy alone, and the recent launch of the James Webb Space Telescope, the successor to the Hubble Space Telescope, promises to help observatories study planets in much greater detail.

References:

1. Hernandez, Joe. “More than 5,000 exoplanets beyond our solar system, NASA confirms.” NPR, 22 March 2022, https://www.npr.org/2022/03/22/1088009414/there-are-more-than-5-000-confirmed-exoplanets-beyond-our-solar-system-nasa-says. Accessed 28 March 2022.
2. Howell, Elizabeth. “5000 Exoplanets! NASA Confirms a Cosmic Milestone.” Scientific American, 25 March 2022, https://www.scientificamerican.com/article/5-000-exoplanets-nasa-confirms-a-cosmic-milestone/. Accessed 28 March 2022.
3. Major, Jason. “There Are Now Officially Over 1,000 Confirmed Exoplanets!” Universe Today, 23 October 2013, https://www.universetoday.com/105683/there-are-now-officially-over-1000-confirmed-exoplanets/. Accessed 28 March 2022.
4. NASA. “Cosmic Milestone: NASA Confirms 5,000+ Exoplanets!” Exoplanet Exploration: Planets Beyond our Solar System, https://exoplanets.nasa.gov/. Accessed 28 March 2022.
5. Wenz, John. “How the first exoplanets were discovered | Astronomy.com.” Astronomy Magazine, 8 October 2019, https://astronomy.com/news/2019/10/how-the-first-exoplanets-were-discovered. Accessed 28 March 2022.