Astronomers discover 18 new alien planets—and they're huge

Astronomers have found 18 new alien planets, all of them Jupiter-size gas giants that circle stars bigger than our sun, a new study reports.The discoveries increase the number of known planets orbiting massive stars by 50 percent. The exoplanet bounty should also help astronomers better understand how giant planets form and grow in nascent alien solar systems, researchers said.The haul comes just a few months after a different team of researchers announced the discovery of 50 newfound alien worlds, including one rocky planet that could be a good candidate for life. The list of known alien planets is now well over 700 and climbing fast. The researchers surveyed about 300 stars using the Keck Observatory in Hawaii and instruments in Texas and Arizona. They focused on so-called "retired" type-A stars that are at least 1.5 times more massive than our own sun.These stars are just beyond the main stage of life — hence the name "retired" — and are now ballooning out to become what's known as subgiant stars. The team scrutinized these stars, looking for slight wobbles caused by the gravitational tug of orbiting planets. This process revealed 18 new alien worlds, all of them with masses similar to Jupiter's. All 18 planets also orbit relatively far from their stars, at a distance of at least 0.7 times the span from Earth to the sun (about 93 million miles, or 150 million kilometers).