How many solar systems are there in the universe?

Many current projects, including the European CoRoT and NASA's Kepler mission, as well as other ground-based endeavors, aim to try and provide some answers; thus far, they indicate that a reasonable fraction of stars (roughly 10 percent or even more) have planets, but we have not really been able to find systems quite like our own.

There are approximately 300 billion stars in the Milky Way, which means that if 10% of them have planets, there would be about 30 billion planets in our galaxy alone. Additionally, there are over 100 billion galaxies in the observable Universe, meaning that there is a total of something in the order of 10^21 (that is, one plus twenty zeros) planets in the observable Universe. This figure is still quite uncertain, and we don't yet know how many of them would resemble our solar system.

I hope it's helpful! :)

Although the precise number of solar systems in the universe is unknown, estimates range from billions to trillions, given the size of the universe.