A 'serious' scientist in 1992 or 1993 had to admit the possibility that planets were really rare, that most stars might not have planets. We've gone from there to here - where most stars have planets.
If few worlds have microbial life, it dramatically reduces the chances that more complex organisms exist.
Science requires speculation, creativity, and wild ideas.
Naturally, we think that finding another Earth-like planet is identifying a site that's at least friendly here for the evolution of life. The primary goal of the Kepler mission is to statistically assess the occurrence of these small terrestrial worlds.
In 1999, my team discovered that the star Upsilon Andromedae was circled by three gas-giant planets - the first distant multiplanet system ever found. That same year, other researchers observed the first 'transit' of an exoplanet - a planet blocking out a small fraction of the starlight as it passes in front of the star.
Because Alpha Centauri is so close, it is our first stop outside our solar system. There's almost certain to be small, rocky planets around Alpha Centauri A and B.
It can be very hard to know the history of a particular star, but once in a while, we get lucky and find stars with chemical compositions that likely came from in-falling planets.
Generally speaking, exoplanets can be any size, and they are found in a wide range of orbits. Some have massive gas atmospheres; others are smaller with an icy or rocky composition.
One of the first thoughts I had, when doing early exoplanet research, was that Earth and its many companions seemed very different from the planetary systems we were detecting.
I hope that vigorous space exploration continues and that humankind will have a space station that resides between Earth and the moon. Outside the gravitational field of Earth, we could launch robotic spacecraft to other destinations in our solar system.
Further ahead, I'd like to see tiny spacebots - smaller than your cell phone - travel outside our solar system to the nearest star system, Alpha Centauri. By keeping the mass of those spacebots low, we could more easily accelerate them.
The building blocks of life are readily available throughout the universe.
Within the scientific community, there is healthy skepticism. And the question is, 'How do you ever get to a meaningful null result? How long and how hard do SETI scientists have to look for extraterrestrial intelligence and find nothing before they say, 'There is nothing. We are alone.'