An international study has revealed that super-Earth exoplanets, planets larger than Earth but smaller than gas giants like Neptune, are significantly more common across the universe than scientists once believed
The discovery, made using the Korea Microlensing Telescope Network (KMTNet), suggests these massive rocky planets could be a staple feature of planetary systems far beyond our own.
Discovery through a rare cosmic alignment
Researchers discovered by observing a phenomenon known as gravitational microlensing, which allows astronomers to detect distant objects through the way their gravity bends and magnifies the light of background stars.
The rare alignment of a star with a planet crossing in front of a distant light source creates a temporary brightening, which researchers can analyse to infer the presence of a planet and its characteristics.
The team focused on one event, labelled OGLE-2016-BLG-0007, where a super-Earth with a mass roughly twice that of our planet was discovered.
This super-Earth orbits its star at a distance greater than Saturn’s orbit around the Sun, showing that rocky planets can exist far from their host stars, something once thought to be relatively rare.
Scientists combined the observation with a larger dataset from the KMTNet microlensing survey. Their findings revealed that for every three stars in the galaxy, at least one likely hosts a super-Earth in a wide orbit. This challenges previous assumptions that rocky planets are predominantly found closer to their stars and strengthens the case that these exoplanets are more abundant and widespread than expected.
Two distinct planet types were identified
The study also allowed researchers to classify exoplanets into two broad categories: super-Earths and Neptune-like planets on one side, and gas giants like Jupiter and Saturn on the other. These groupings help categorise planets by size and mass and provide clues into how different types of planets may form and evolve.
Although theoretical models suggest giant planets form through a process known as runaway gas accretion, some scientists argue that gravitational instability could also play a role. The current study could not confirm which process dominates, highlighting the need for further data and analysis.
KMTNet, the instrument behind the discovery, is a system of three powerful telescopes in South Africa, Chile, and Australia. These strategically placed observatories allow for continuous sky monitoring, increasing the chances of capturing the rare microlensing events required to discover such distant planets. The Imaging Sciences Laboratory at The Ohio State University designed and built the specialised cameras that enable this work.
While the microlensing technique is potent, it remains one of the most challenging methods for detecting exoplanets.
Of the 5,000 known exoplanets, only 237 have been discovered through microlensing. However, thanks to global collaborations like KMTNet and improvements in observational technology, astronomers are now better equipped than ever to uncover the hidden architecture of planetary systems across the cosmos.
This study adds to our understanding of how common super-Earths are and offers deeper insights into how planets form and where they might be found, advancing the broader quest to understand our place in the universe.
