The small planets are being dubbed "mini-Neptunes." Five of the six are closer to their sun than Mercury is to ours, and the sixth is farther out.
Scientists say the planets are roughly 2 to 4.5 times the size of Earth, but seem to be extremely lightweight, suggesting they are made mostly of gases.
Two planets may have atmospheres of water, hydrogen and helium.
In finding a cluster of planets like this, scientists can get a better idea of planetary transformations.
"We can do comparative science and ... we can think about how the evolution of the planets has diverged over time," Fortney said.