Beyond Neptune: 8,291 objects and new discoveries

The solar system’s distant census now contains more than 8,000 objects beyond Neptune, and a newly announced world could rank among its largest. On October 27, astronomers unveiled 2026 ED138, a dwarf-planet candidate found in Vera C. Rubin Observatory data. Its discovery comes six years after a University of Pennsylvania-led search reported 139 previously unpublished objects in the same broad region.

As of October 28, NASA’s Jet Propulsion Laboratory Small-Body Database listed 8,291 trans-Neptunian objects, or TNOs. Its broader asteroid catalog contained 1,577,822 bodies, including those TNOs. These are overlapping inventories, not totals to add together. Both include objects with provisional designations, and neither represents everything that exists.

Astronomers generally call these bodies minor planets, rather than “micro planets.” TNO describes an orbital category: JPL places objects there when their orbital semimajor axis, a measure of orbit size, exceeds Neptune’s. Some follow relatively circular paths through the Kuiper Belt, while others travel along stretched or tilted orbits. Centaurs, whose orbital sizes lie between Jupiter’s and Neptune’s, occupy a separate JPL category.

Minor planet also does not mean dwarf planet. The International Astronomical Union recognizes five dwarf planets: Ceres, Pluto, Eris, Haumea and Makemake. A new discovery can enter an orbital catalog long before its size, shape or physical nature becomes clear. That distinction matters when comparing thousands of cataloged bodies with a handful of formally recognized worlds.

ED138 currently lies about 46 astronomical units from the Sun; one astronomical unit equals the average Earth-Sun distance. Its brightness suggests a diameter between roughly 600 and 1,500 kilometers, depending on its surface reflectivity. That range makes it a dwarf-planet candidate, rather than a confirmed addition to the official list. Follow-up observations will help establish its properties.

Matthew Holman, a senior astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, identified it while processing Rubin observations. University of Washington astronomer Mario Jurić located additional detections, and archival images extended its observed history back to 2016. Rubin itself recorded the object 30 times between March and July 2026. Combining those measurements allowed the team to trace more than a decade of its orbit.

September brought a different kind of discovery: 27 tiny, dim TNOs studied jointly with Hubble and the James Webb Space Telescope. Two papers in The Astronomical Journal examined their colors and size distribution, with the smallest measuring about 5 kilometers across. The teams found fewer small objects than some formation models predicted. Their results also showed surface-color relationships resembling those of larger TNOs, raising questions about how collisions alter these ancient bodies.

Rubin had already announced a much larger discovery batch in April: more than 11,000 new minor bodies. Roughly 380 were TNOs, found in about six weeks of early observations. Two, 2025 LS2 and 2025 MX348, follow elongated orbits reaching roughly 1,000 astronomical units at their farthest points. Those are maximum orbital distances, not their present locations.

One of 2025’s notable additions was 2023 KQ14, nicknamed Ammonite. An international team using Japan’s Subaru Telescope identified it in 2023 observations and announced the discovery in July 2025. Published in Nature Astronomy, the research described the fourth known sednoid, a rare type of distant object with an unusually remote closest approach to the Sun. Ammonite never comes closer than about 66 astronomical units.

Its orbit differs in orientation from the other known sednoids, complicating simple explanations for their distribution. Computer simulations found that its orbit could remain stable over 4.5 billion years. That result concerns modeled orbital evolution, not direct observations across that timespan. Such objects help test competing explanations involving planetary migration, stellar encounters and a possible unseen planet.

Another discovery, 2017 OF201, was announced in May 2025 by a team led by Sihao Cheng. Its discovery paper, subsequently published in The Astrophysical Journal Letters in 2026, estimates a diameter near 700 kilometers. That estimate assumes a particular surface reflectivity. The object follows an exceptionally wide orbit with an orbital period of roughly 25,000 years, illustrating how discoveries can extend well beyond the main Kuiper Belt.

Before Rubin, the Dark Energy Survey showed how images collected for cosmology could reveal distant solar system bodies. Its published six-year search, released in 2022, cataloged 812 TNOs, one Centaur and one Oort Cloud comet. The paper reported 458 objects for the first time. Those figures describe the final published catalog, which revised the earlier preprint’s slightly larger totals.

The team analyzed roughly 80,000 exposures covering 5,000 square degrees of southern sky between 2013 and 2019. Improved processing recovered fainter sources and connected scattered detections into orbits. Researchers checked candidates visually and combined images where an object should appear but had escaped individual detection. These checks helped separate real bodies from false matches.

The six-year catalog expanded the earlier sample rather than adding 812 entirely new discoveries to it. That overlap also prevents simply summing survey totals into a global census. Some objects were already known, and later studies reobserved earlier discoveries. Reliable comparisons require distinguishing detections, first announcements and genuinely new objects.

The original Penn-led study, published in The Astrophysical Journal Supplement Series in 2020, reported 316 TNOs. Of those, 245 were DES discoveries, including 139 not previously published.

Penn’s announcement estimated that about 3,000 TNOs were known worldwide then. The present JPL inventory shows how much the cataloged population has grown, although catalog definitions and completeness must be considered when comparing totals.

Pedro Bernardinelli, Gary Bernstein, Masao Sako and collaborators developed their search around observations not designed specifically for moving objects. They reduced billions of initial detections to candidates whose positions could fit a single orbit. Stacking additional images helped verify weak signals. The approach turned a survey of galaxies and supernovas into a productive search for nearby, slowly moving worlds.

Rubin combines an 8.4-meter primary mirror with a 3.2-gigapixel camera and repeated observations of the southern sky. Its Solar System Science Collaboration expects the ten-year survey to catalog more than 40,000 Kuiper Belt objects. That is a forecast, not an achieved discovery total. Orbit-linking software must turn enormous numbers of individual detections into trackable objects.

Subaru demonstrates another route to improvement without building a new telescope. A study announced in 2024 applied JAXA software to 32-image sequences, shifting and stacking them to follow possible moving objects. The analysis uncovered seven additional outer solar system candidates; two received provisional designations. Such methods strengthen faint signals that individual exposures can miss.

NASA’s Roman Space Telescope, launched August 30, offers another opportunity through wide-field infrared observations. A white paper proposed a targeted search that could identify and determine orbits for as many as 900 Kuiper Belt objects. That is a proposal-based estimate, separate from discoveries already made. The next challenge is to turn expanding catalogs into reliable measurements of how far the outer population extends and how its orbits formed.

The growing census offers more than a longer list of distant worlds. Their orbits, sizes and surfaces preserve clues to how the giant planets moved and scattered smaller bodies. A larger, carefully measured sample could help distinguish those ancient events from the influence of an unseen planet. The question is whether the next discoveries will fit the patterns already identified or expose gaps in current explanations.

These resources trace the newest candidate worlds and the methods expanding the outer solar system census.

Rubin Observatory reveals its first dwarf planet candidate in our solar system
The discovery announcement explains how new observations and archival images established the orbit of 2026 ED138. (University of Washington, October 2026)

NASA’s Hubble, Webb Find Far-out Solar System Objects ‘Remember’ Past
Coordinated observations reveal 27 very small TNOs and examine what their colors and sizes suggest about planetary building blocks. (NASA, September 2026)

Discovery and dynamics of a Sedna-like object with a perihelion of 66 au
Ammonite’s unusual orbit provides a test of explanations for the solar system’s distant populations. (Nature Astronomy, July 2025)

The original story "Giant dark matter 'sheet' may shape galactic motion in the Milky Way" is published in The Brighter Side of News.

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