US scientists have for the first time found proof that planets can form and survive around sun-like stars within dense star clusters, NASA said Friday.

Astronomers have spotted two Jupiter-like orbs in the Beehive Cluster, a collection of around 1,000 stars that appear to be swarming around a common center.

"This has been a big puzzle for planet hunters," said Sam Quinn, a graduate student in astronomy at Georgia State University in Atlanta and the lead author of the paper describing the results.

"We know that most stars form in clustered environments like the Orion Nebula, so unless this dense environment inhibits planet formation, at least some sun-like stars in open clusters should have planets.

"Now, we finally know they are indeed there," he added in a statement.

Unlike Jupiter, these gas giants are boiling hot, because they are orbiting close to their parent stars.

The finding left astronomers puzzled as they theorize that gaseous planets can't form too close to a star because they would evaporate away.

The leading explanation so far is that the planets form further out and then migrate inwards toward the star.

Given the relatively young age of Beehive stars, the newly discovered planets could help scientists flesh out the theory.

If the stars are young, that means the planets must be as well, which "sets a constraint on how quickly giant planets migrate inward," said Russel White, the principal investigator on the NASA Origins of Solar Systems grant that funded the study.

"Knowing how quickly they migrate is the first step to figuring out how they migrate."

The team discovered the planets, Pr0201b and Pr0211b, by using the 1.5-meter (five-foot) Tillinghast telescope at an Arizona observatory to measure the slight gravitational wobble the orbiting planets induce upon their host stars.

Scientists had previously spotted two planets around massive stars, but had not yet found any around stars like the sun at the center of our solar system.