The amazing thing is that he was more optimistic than most astronomers at the time with regards to extrasolar planets. It's a funny thing, prior to the mid-1990

The amazing thing is that he was more optimistic than most astronomers at the time with regards to extrasolar planets. It's a funny thing, prior to the mid-1990s there had only been extremely incomplete searches for exoplanets, and they all came up negative. But if you looked at the search space of those studies you see right away that they were really quite pitiful. I suppose this is one of those "effort trumps reason" situations, as a lot of effort were put into searches though they had almost no hope of finding planets. And yet those efforts led to a bias against the idea that planet formation could be common, and a bias against the scientific value of looking for planets. At the onset of the great exoplanet discovery breakthrough in the mid '90s only a few very meagerly funded teams working were actually searching. Once they started to find planets then the astronomical community started paying attention, and funding as well as access to the best observatories in the world started pouring in. Also, an interesting point of fact is that Sagan was actually hugely excessively optimistic. The two techniques for exoplanet discovery he describes are direct observation through occultation or deep nulling of stellar light and astrometry. As it turns out, these techniques are very, very difficult to use and we have not actually built any special-purpose spacecraft that use either method. To date only one planet has been detected through astrometry, for example. But there are methods which work rather well (doppler radial velocity and transit detection) though they were not familiar to Sagan.