It is difficult to imagine that the next 100 years will reveal as many fundamentally new concepts as what we have already encountered. The last 100 years uncovered the existence of galaxies, the chemistry of stars, the evolution of stars, the expansion of the universe, the existence of extra-solar planets, the nature of the surfaces of the planets in the solar system, and the universe through the various electromagnetic windows from gamma rays to radio waves. This period is absolutely unique in human history, and this pace of discovery will not repeat itself again. The next 100 years will be a period of refining what we already know, but there is still much to be done in that arena, although it is not going to rival anything like the previous 100 years of excitement.

The wild card is, of course, the nature of Dark Matter and Dark Energy. They constitute more than 96% of the contents of the universe. Even though we may understand the visible content completely, this larger invisible arena in which they operate is truly the biggest mystery of 21st century astronomy and physics!

A second wild card is the search for life beyond Earth. We have the intriguing mysteries of extra-solar planets which we are discovering at a very brisk clip. Each of these new worlds is an enigma waiting to be explored and 'solved'.