In 2014, the journal Nature reported that there are more planets than stars in our galaxy. It was an easy concept for the public to grasp, since everyone knows what a planet is, thanks to the fact that we live on one. And everyone also knows what stars are. It was news that people could relate to.
But astronomers yawned, because ever since Peter Van de Camp’s 1960s announcements of planets orbiting nearby stars, we realized that planets must be common rather than rare. Prior to that, in the 1950s, there were two competing ideas about how planets are born. Some thought that a star has to pass very close to another and gravitationally pull off a string of material like pizza cheese. This star stuff would then condense into a row of balls and, voila, you get a system of planets. If this was the case, planets would be very rare occurrences since close stellar encounters are unusual.
The competing view was that as any star forms from a condensing nebula, the leftover dusty gas contracts here and there, like lumps in pudding, into a series of planets. If this is the case, then planets must be common.
Actual planets started to be uncovered in 1992 by radio telescopes and in 1995 by regular telescopes using special techniques. Only massive planets orbiting lightweight stars could be detected by the star’s periodic wobbles, and yet hundreds of these were soon revealed. Since smaller planets must greatly outnumber the larger ones we were capable of finding, planets, we realized, must lurk everywhere. Even the official figure of 1.6 planets per average star is probably a great underestimate.
But when we think about it, its importance fades. Does it really matter if the Milky Way is home to 200 billion planets or if, instead, there are 800 billion? Who deeply cares whether there are half as many planets as stars or twice as many planets as stars? The point is, it’s a done deal.
There are planets everywhere.
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