A Super-Earth Beyond Saturn: Astronomers Discover an Unexpected Giant in the Outer Realms of a Distant Solar System

In the grand theater of the cosmos, where stars blaze and galaxies swirl in silent motion, a new celestial actor has taken the stage—a distant, rocky world more than twice the size of Earth, orbiting its host star in the frigid outskirts of its solar system. This remarkable discovery, announced by an international collaboration of astronomers including scientists from the Center for Astrophysics | Harvard & Smithsonian (CfA), opens an entirely new window into planetary formation and the diversity of worlds that inhabit our Milky Way.

At the heart of this breakthrough lies a planet known only by its catalog number for now, but its significance transcends the anonymity of its name. This planet is a “super-Earth”—a term used to describe planets larger than Earth but considerably smaller than the gas giants like Neptune. What makes it truly astonishing, however, is its location: it orbits its star at a distance greater than Saturn’s orbit around our Sun, in a region where such planets were previously thought to be exceedingly rare.

A Stranger Among Giants

Until recently, astronomers believed that only massive planets—those hundreds or even thousands of times the mass of Earth—resided in the cold, outer zones of planetary systems. The new discovery, detailed in a paper in the journal Science and led by CfA Fellow Weicheng Zang, challenges this long-standing assumption.

“We found a ‘super-Earth’—meaning it’s bigger than our home planet but smaller than Neptune—in a place where only much more massive planets had been found before,” said Zang. His findings provide a striking example of how planetary systems can defy the patterns of our own solar system, suggesting that the architecture of planetary families in the Milky Way is more varied and surprising than we ever imagined.

Peering Through the Cosmic Looking Glass

The method that brought this hidden planet into view is as elegant as it is powerful. Known as microlensing, this technique harnesses the natural magnification that occurs when a massive object—like a planet or a star—passes in front of a more distant star. The gravity of the foreground object bends and amplifies the light from the background star, briefly creating a lens-like effect. If a planet orbits the lensing star, its presence can be detected as a small but telling blip in the light curve.

Microlensing is uniquely suited to detect planets far from their stars—regions that are difficult to probe using other techniques such as transits or radial velocity measurements, which tend to focus on planets in tight orbits. In fact, microlensing excels in the zone between Earth and Saturn’s orbits, a cold and distant frontier often overlooked by traditional exoplanet surveys.

The newly discovered super-Earth is part of a broader and unprecedented effort to chart the planetary populations of the galaxy using microlensing. The researchers used data from the Korea Microlensing Telescope Network (KMTNet), an array of three wide-field telescopes stationed in Chile, South Africa, and Australia. These strategically located observatories provide around-the-clock surveillance of the night sky, capturing fleeting microlensing events that might otherwise be missed.

A Planetary Census on a Galactic Scale

This study is the largest and most comprehensive of its kind, encompassing three times more planets than previous microlensing surveys. Not only does it increase the number of known planets in distant, icy orbits, but it also pushes the detection limits to planets up to eight times smaller than those previously cataloged with microlensing.

According to Professor Shude Mao of Tsinghua University and Westlake University in China, the work offers crucial clues about the birth and evolution of cold planets. “The current data provided a hint of how cold planets form,” Mao said. “In the next few years, the sample will be a factor of four larger, and thus we can constrain how these planets form and evolve even more stringently with KMTNet data.”

This massive data trove is a game-changer. By comparing planet masses and distances from their host stars, the team is beginning to uncover patterns that could explain how different types of planets emerge under varying cosmic conditions. Their results suggest that super-Earths in wide orbits may be more common than previously thought—perhaps even as common as Neptune-sized worlds.

Rewriting the Rulebook of Planet Formation

For centuries, humanity’s understanding of planetary systems was guided solely by our own solar system, which seemed neat and symmetrical: four small, rocky worlds close to the Sun, followed by four gas and ice giants farther out. But over the past two decades, the discovery of more than 5,000 exoplanets has shattered this tidy model.

Telescopes like Kepler and TESS have revealed systems where planets the size of Neptune orbit closer than Mercury, or where a gas giant circles its star every few days. Yet these discoveries have primarily focused on planets in close orbits, where detection methods are more sensitive.

The new CfA-led study, however, fills in the missing piece of the puzzle: what kinds of planets exist in the outer solar systems of distant stars. The evidence now points to a galaxy teeming with diversity—not just near the warmth of stars, but also in the dark, icy reaches where sunlight barely penetrates.

“This measurement of the planet population from planets somewhat larger than Earth all the way to the size of Jupiter and beyond shows us that planets, and especially super-Earths, in orbits outside the Earth’s orbit are abundant in the galaxy,” said Jennifer Yee, an astronomer at the Smithsonian Astrophysical Observatory and co-author of the study.

A Planet Unlike Our Own

The newly detected planet challenges the very notion of planetary rarity. While super-Earths do not exist in our solar system, they appear to be the most common type of planet in the galaxy. What’s unusual here is not the planet’s size—but where it resides.

In our solar system, planets this large are typically gaseous and located far out—like Uranus and Neptune. Rocky worlds like Earth are small and close to the Sun. This new planet blurs those boundaries, suggesting that rocky super-Earths can also survive and thrive in colder, more distant regions. The discovery forces scientists to rethink the core accretion model of planetary formation, which predicts that only massive planets can form beyond the “snow line”—the distance from a star where icy compounds can condense.

“This result suggests that in Jupiter-like orbits, most planetary systems may not mirror our solar system,” added Youn Kil Jung of the Korea Astronomy and Space Science Institute, the organization that operates KMTNet.

Cosmic Collaboration and the Road Ahead

The discovery would not have been possible without the combined efforts of multiple institutions and survey groups. In addition to the KMTNet, the study relied on data from the Optical Gravitational Lens Experiment (OGLE) and Microlensing Observations in Astrophysics (MOA), both of which have played key roles in mapping the hidden population of exoplanets.

Other contributors include In-Gu Shin, a CfA postdoctoral fellow, Hangyue Wang, a former Harvard undergraduate now at Stanford, and Sun-Ju Chung, a visiting scientist from the Korea Astronomy and Space Science Institute. The global nature of this team reflects the collaborative spirit driving the field of exoplanet research today.

As the microlensing surveys continue to grow and technology advances, astronomers are confident that many more hidden planets will be found—perhaps even Earth-like worlds in orbits resembling our own. The upcoming Nancy Grace Roman Space Telescope, scheduled to launch later this decade, is expected to vastly expand the reach and resolution of microlensing studies, potentially revealing thousands of new planets in deep space.

Conclusion: A Universe Rich in Possibilities

The discovery of a super-Earth orbiting beyond Saturn’s distance in a distant solar system is more than just a milestone—it’s a revelation. It reminds us that the universe is far more intricate, dynamic, and surprising than our Earth-centered perspective might suggest.

Each new exoplanet adds a stroke to the cosmic canvas, deepening our understanding of how worlds form and evolve. This latest find urges us to let go of the notion that our solar system is the template for all others. Instead, it invites us to embrace the astonishing variety of planetary systems that populate the galaxy—each one a unique testament to the creativity of the cosmos.

As Weicheng Zang and his colleagues continue their search, the message is clear: the story of planets is still being written, and the universe holds countless chapters yet to be discovered.

Reference: Weicheng Zang et al, Microlensing events indicate that super-Earth exoplanets are common in Jupiter-like orbits, Science (2025). DOI: 10.1126/science.adn6088