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A brief overview about exoplanet history

by Ludwig Scheibe (TU Berlin), January 2025

The first confirmed extrasolar planets were found in 1992 by Aleksander Wolszczan and Dale Frail, who discovered two planets around the pulsar PSR B1257+12, later named Phoebetor and Poltergeist.

Then, in 1995, the first exoplanet around a Sun-like star followed, found by Didier Queloz and Michel Mayor around 51 Pegasi. This planet, about half as massive as Jupiter but on an orbit roughly one seventh that of Mercury, was later named Dimidium. It kicked off an age of exoplanet discoveries that is going to this day.

A mock-up travel poster showing travel borchures and postcards from different exoplanets, with a hand holding one priminently that says "51 Pegasi b". Subtitle says "Greetings from your first exoplanet".

Travel poster for a fictional tourism journey to 51 Pegasi b, the actual first exoplanet around a sun-like star. Credit: NASA/JPL

51 Pegasi b was discovered using the radial velocity method, and in the following years it was the only method by which exoplanets could be observed. Then, in 1999, for the first time, two groups of scientists measured the transit of an extrasolar planet, HD 209458 b. The planet had originally been detected by radial velocity (RV) measurements. This marked the first time a completely independent method could be used to verify an exoplanet’s detection.

In 2001, the first planet in the habitable zone was discovered – HD 28185 b, although it was a planet about six times the mass of Jupiter. The same year saw the first measurement of an exoplanet’s atmosphere composition (HD 209458 b).

A year later, in 2002 the first planet was found by the transit method itself – as opposed to using transits to verify and further characterize planets found with RV.

Discoveries took up pace now, as the transit method allowed to survey many stars at the same time. Dedicated telescopes for extrasolar planets went into service. A significant early one was the European CoRoT mission, launched 2006, that was the first telescope in space that was dedicated to searching for exoplanets.

Another leap came in 2009, when the Kepler space telescope went into service. This NASA space telescope surveyed a large area of the sky during its 9-year-lifetime and was able to discover over 2000 confirmed exoplanets, bringing us a never-before seen insight into the statistics and demographics of the exoplanets out there.

At present, as of early 2025, there are over 5500 confirmed exoplanets discovered in total, with several thousand candidates more to be confirmed.

For a vastly more detailed timeline of exoplanet research by NASA, click here.

Malcolm Fridlund talks about “Exoplanets from an historical perspective” in the SPP 1992 Webinar.

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