The discovery of two new planets smaller than Neptune has scientists reconsidering the established belief about the resilience of planetary systems.

The two new planets were discovered by astronomers studying the stellar data from the Kepler space telescope. The interesting thing about these planets is that have formed in heavily unfriendly environment of a star cluster, which shows that planetary systems are not only more resilient, but also more ubiquitous than previously thought.

It was an established belief among astronomers that such planetary arrangements were extremely unlikely, since star cluster are very hostile places for planets to survive.

Before the recent discovery, only four planets had ever been found spinning in a star cluster, and they were all of the size of Jupiter or larger.

However, astronomers surveying data from the open star cluster called NGC 6811, discovered two planets just two and three times the size of Earth.

"That's after sampling just 377 stars in clusters, which is pretty good odds in such an environment," William Welsh, an astronomer at San Diego State University who was not involved in the study, said.

According to Welsh, astronomers have long believed that a star living in a dense knot of others stars would have trouble holding onto its delicate protoplanetary discs. After all, the gravity from neighboring stars in the cluster would wreak havoc on the ring of matter, possibly ripping it apart; and stellar winds and ultraviolet radiation from other hot, young stars nearby would blow much of the dusty debris away. As if that wasn't enough, much of a rising star's protoplanetary entourage could get wiped out by supernovae, or the explosions of dying stars, in the cluster.

Astronomers believed that the planets' main ingredients - star's ring of dust - would surely only survive if it were out of harm's way, far enough from other stars to be affected by its siblings.

Sustaining that belief was the fact that more than 95% of such clusters tend to dissipate in about 100 million years.