Exoplanets known as super-Earths have been found in large numbers close to their host stars, but their presence on wider, colder orbits has been much harder to measure. A new study published in Science now suggests these planets may also be common much farther out, in regions of planetary systems more comparable to Jupiter’s orbit in our own solar system.
The research is based on gravitational microlensing, a planet-hunting method that can detect worlds that are difficult to find with techniques such as the transit or radial velocity methods. Because microlensing is especially sensitive to planets on wide orbits, it gives astronomers a way to probe a part of planetary systems that is still poorly mapped.
What the study found
The team reported observations of the microlensing event OGLE-2016-BLG-0007, which pointed to an exoplanet with a planet-to-star mass ratio roughly twice the Earth-Sun mass ratio. According to the study, that planet lies on an orbit longer than Saturn’s. The researchers then combined this event with a broader microlensing sample to estimate how common such planets are across the galaxy.
The result was striking: the team inferred that there are about 0.35 super-Earth planets per star on Jupiter-like orbits. In other words, planets in this mass class may not be rare outer-system objects, but a substantial component of planetary systems.
Why microlensing matters here
Most well-known exoplanets have been discovered because they either pass in front of their stars or tug on them gravitationally in ways that are easiest to measure when the planets orbit close in. That has naturally biased the exoplanet census toward hot and warm planets with relatively short orbital periods.
Microlensing works differently. It detects the temporary brightening of a background star when a foreground star, and sometimes its planets, pass in front of it from our point of view. This technique is particularly valuable because it is sensitive to planets on wider orbits, including those beyond the region where many other planet-search methods are strongest.
A possible two-population picture
Beyond estimating the frequency of these worlds, the researchers argue that the observations are most consistent with a bimodal distribution of wide-orbit planets. In simple terms, the data appear to show two distinct groupings rather than one smooth continuum: one population centered on super-Earths and another on gas giants.
If that interpretation holds up, it could point to different formation pathways for these two planetary classes. Super-Earths and gas giants may not simply represent points along one uninterrupted planetary spectrum. Instead, they may arise through partially different physical processes in protoplanetary disks.
Why this matters for planet formation
The finding is important because it fills in a missing region of the exoplanet map. Astronomers have already known that close-in super-Earths are common, but the abundance of similar-mass planets on much wider orbits has remained uncertain. This study suggests that super-Earths may also be a major population in the colder outer parts of planetary systems.
That has direct implications for models of planet formation and migration. If super-Earths frequently exist on Jupiter-like orbits, theorists will need to explain how they form there, how often they stay there, and how their histories differ from those of gas giants.
What comes next
As with many population-level exoplanet results, this study is powerful but not necessarily the final word. The estimate depends on interpreting a microlensing sample and comparing it with theoretical distributions. Future microlensing surveys and next-generation observations should help test whether this bimodal pattern is robust and whether the inferred abundance remains consistent with larger datasets.
Even so, the result stands as a significant advance. It suggests that planetary systems may commonly host super-Earths not only close to their stars, but also in distant, Jupiter-like orbits that have until now remained difficult to study.
For exoplanet science, that means the galaxy may contain even more diverse planetary architectures than previously thought.