A Historic Discovery


The idea that planets could exist around other planets is of course not new. Speculations have always been around and within the realms of science fiction literature it has for a long time been taken for granted. But to really discover them is difficult and calls for high-tech equipment. Or maybe not? The discovery of exoplanets could have been made earlier, at least in principle. That a gas giant planet like Jupiter can obscure about 1 % of the Sun's light is simple to deduce, it is pure geometry. To measure that kind of precision has been within reach since the 1950s when light sensitive detectors, so called photomultipliers, were introduced to measure the light of the stars.  Then in the 1980s the first CCD cameras appeared. But one percent accuracy is difficult with ground based observations and in those days there was not much of powerful computers and intelligent algorithms that could automate the search.

Peter van de Kamp claimed already in the 1960s that he had found deviations in the motions of Barnard's star, using precise positional measurements. It turned out to be wrong. The astrometric precision was not high enough, even by todays standards of technology it is a challenge to find an exoplanet in this way.  When the historic discovery at last was made in 1995 other techniques were used. Since the gravitational pull of an exoplanet moves the parent star somewhat it became feasible to measure the doppler effect caused by the small extra motion of the star. With ingenious methods, by simultaneously measure thousands of spectral lines, it is possible to get enough velocity information to reach the necessary accuracy.