NASA Survey Suggests Earth-Sized Planets Are Common

http://www.nasa.gov/topics/universe/features/exoplanet20101028.html

In a recent NASA study, astronomers counted the number of stars in our galaxy that had planets orbiting them, looking for a potential site of life outside of our solar system. These plants are called exoplanets. They looked at 166 stars in the Milky Way Galaxy within 80 light-years of Earth. They used the wobble technique to look for these exoplanets. This technique makes use of the fact that an orbiting planet's gravity causes its sun to wobble on its axis throughout the orbit.
These exoplanets that were studied were located .25 astronomical unites from their suns, which is much closer than Earth is to its Sun. The results of the study were as follows:
23% of the stars had planets Earth sized or small
11.8% were 3-10 times Earth
6.5% 10-30 times Earth
1.6% were 100 times Earth
1.6% were 500 times Earth
1.6% were 1000 times Earth
This means that most of the exoplanets in this study were Earth sized or smaller.
This data is not what scientists expected, based on the accepted theory of planet accretion. This theory would lead us to believe that most planets would accrete and grow in a zone that is cool and more distant from the star. That fact that most of these exoplanets accreted in a hot zone near the star was not expected and not understood.
I have read other articles about exoplanets, and this study seems to have found many more of these planets that other studies have. Some other studies have found most exoplanets to be much larger than Earth, while this study seems to indicate that most exoplanets are Earth sized or smaller. This could either be due to the fact that this study used better and more recent technology that allowed scientists to find smaller planets, or there could be some problem with the data or interpretation of the data. Obviously, more studies need to be done.
I am very interested in astronomy. By gaining a deeper understanding of how our solar system and planets were initially formed, we also gain knowledge of how our Earth is today and the processes that made our planet what it is today. After all, the molten interior that gives rise to crustal movement and volcanism is "leftover" from when our planet accreted from its original spinning ball of hot gas.

~Mike Amico