Saturn's moon empire: 128 new worlds in a single day

Overview

On March 11, 2025, the International Astronomical Union dropped a bombshell: 128 new moons orbiting Saturn. Not over a year. Not over a decade. All at once. A team led by Edward Ashton stacked thousands of telescope images from 2019 to 2023, revealing a swarm of tiny irregular satellites—each just a few kilometers across—that had been hiding in plain sight. Saturn now has 274 confirmed moons, more than all other planets in the solar system combined.

In This Story

4 Videos

3 People

3 Orgs

Detection Limits Reached, Moon Count Plateaus

3 Context

Pluto's Demotion and the Definition Crisis (2006)

Key Indicators

274

Saturn's Total Moons

More than all other planets combined

128

Moons Found in Single Announcement

Largest batch discovery in history

192

Moons Found by Ashton's Team

70% of Saturn's known satellites

~3 miles

Detection Limit

Smallest detectable moon around Saturn

Interactive

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Debate Arena

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People Involved

Edward Ashton

Postdoctoral Fellow, Academia Sinica Institute of Astronomy and Astrophysics (Lead discoverer of 192 Saturn moons)

Brett Gladman

Professor of Astronomy, University of British Columbia; Canada Research Chair in Planetary Astronomy (Co-discoverer, has found more moons than anyone in human history)

Christiaan Huygens

Dutch Astronomer and Physicist (Deceased (1629-1695))

Organizations Involved

International Astronomical Union Minor Planet Center

Scientific Organization

Status: Official body for designating moons and minor planets

The single worldwide authority for receiving and distributing positional measurements of minor planets, comets, and irregular moons.

Canada-France-Hawaii Telescope

Observatory

Status: Operational on Mauna Kea

A 3.6-meter optical/infrared telescope on Mauna Kea equipped with MegaCam, a 340-megapixel camera covering one square degree of sky.

Academia Sinica Institute of Astronomy and Astrophysics

Research Institution

Status: Leading planetary astronomy research

Taiwan's premier astronomy research institute, home to Edward Ashton's postdoctoral work on Saturn's irregular satellites.

Timeline

IAU Announces 128 New Saturn Moons
Announcement

Largest single batch of moon discoveries in history brings Saturn's total to 274—more than all other planets combined.
March 11th, 2025
Follow-Up Campaign Confirms More Moons
Research

Team revisits same sky fields for three consecutive months, bringing total new discoveries to 128.
2023
Initial CFHT Observations
Research

Ashton and Gladman conduct observations revealing 64 new moons using shift-and-stack technique.
2019-2021
Ashton Begins PhD Moon Hunt
Research

Edward Ashton starts systematic search for Saturn's irregular satellites at University of British Columbia.
2018
Huygens Lands on Titan
Mission

First successful landing on an outer solar system moon reveals methane lakes and hydrocarbon weather.
January 14th, 2005 • 1:34 PM
Cassini Enters Saturn Orbit
Mission

Cassini-Huygens mission begins 13-year study of Saturn system, discovering numerous small moons.
July 1st, 2004
Ground-Based Irregular Moon Hunt Begins
Discovery

Brett Gladman's team discovers twelve irregular moons using large CCDs and modern telescopes.
2000
Voyager 2 Saturn Encounter
Mission

Voyager 2 discovers additional moons and provides first evidence Enceladus might still be geologically active.
August 25th, 1981
Voyager 1 Saturn Flyby
Mission

Voyager 1 reveals shepherd moons and transforms Saturn's satellites from points of light into worlds.
November 12th, 1980 • 11:46 PM
Cassini Finds Four More Moons
Discovery

Jean-Dominique Cassini discovers Iapetus, Rhea, Tethys, and Dione.
1671-1684
First Saturn Moon Discovered
Discovery

Christiaan Huygens spots Titan using his 50-power refracting telescope.
March 25th, 1655

Scenarios

Detection Limits Reached, Moon Count Plateaus

Discussed by: Edward Ashton, astronomical technology experts

Current telescopes have hit their practical limits for detecting moons around Saturn smaller than three miles across. Without significant technological advances—next-generation space telescopes or novel detection methods—Saturn's official count will remain near 274. Astronomers estimate they've surveyed most of the gravitationally-dominated region, though only 2.2 of 26 square degrees were covered. Future discoveries may add dozens more fragments, but not hundreds. The moon race between Jupiter and Saturn effectively ends here.

Future Mission Discovers Moonlets Inside Rings

Discussed by: Planetary scientists, mission planners

A dedicated Saturn orbiter equipped with high-resolution imaging could detect embedded moonlets within the ring system itself—objects that create gaps and waves but remain invisible from Earth. Cassini hinted at these "propeller moons," but a future mission with better instruments might find hundreds of kilometer-sized objects shepherding ring particles. These would technically count as moons but represent a different class of object: rubble embedded in a debris disk rather than independent satellites.

Revised Definition Shrinks Moon Count

Discussed by: International Astronomical Union working groups, planetary dynamics researchers

Growing unease about what constitutes a "moon" versus "ring debris" could trigger an IAU reclassification. If the union establishes minimum size thresholds—say, 10 kilometers in diameter—or requires moons to be dynamically independent from ring systems, Saturn's count could drop dramatically. This mirrors the 2006 Pluto controversy: as detection improves and populations explode, authorities sometimes tighten definitions rather than accept exponential growth in recognized objects.

Historical Context

Pluto's Demotion and the Definition Crisis (2006)

2006

What Happened

As astronomers discovered hundreds of Pluto-sized objects in the Kuiper Belt, the IAU faced a choice: accept dozens of new planets or redefine what "planet" means. They chose the latter, demoting Pluto to "dwarf planet" and establishing size, orbit-clearing criteria. The decision sparked public outcry but prevented the solar system from having 50+ planets.

Outcome

Short Term

Pluto lost planetary status; IAU established clear classification framework.

Long Term

Astronomy shifted toward population-based thinking rather than expanding traditional categories indefinitely.

Why It's Relevant Today

Saturn's exploding moon count raises similar questions: when does a debris fragment become a moon? The IAU may eventually impose size limits to prevent the count from reaching thousands.

Jupiter's Moon Race Lead (2023)

2023

What Happened

In February 2023, Jupiter briefly reclaimed the "moon king" title with 95 confirmed satellites, surpassing Saturn's then-count of 83. Astronomers celebrated Jupiter's return to dominance. The lead lasted mere months before Saturn's team announced 62 new moons in May 2023, then 128 more in 2025.

Outcome

Short Term

Jupiter held the title for less than three months.

Long Term

Saturn's irregular moon population proved far larger; experts now say Jupiter has no chance of catching up.

Why It's Relevant Today

The back-and-forth demonstrated how rapidly improving detection capabilities can reshape our understanding of planetary systems. Saturn's decisive victory reflects fundamental differences in how the gas giants captured debris.

Asteroid Belt Population Explosion (1990s-2000s)

1990-2010

What Happened

Automated sky surveys like LINEAR and Catalina discovered asteroids at exponential rates—from a few thousand known asteroids in 1990 to over 500,000 by 2010. The flood of data required new computational techniques to process observations and automated systems to assign provisional designations. Scientists stopped trying to name every asteroid individually.

Outcome

Short Term

Naming conventions shifted to alphanumeric codes; provisional designations became permanent for most objects.

Long Term

Astronomy embraced statistical approaches to studying populations rather than cataloging individual objects.

Why It's Relevant Today

Saturn's irregular moons follow this pattern: modern instruments reveal vast populations of small objects, forcing astronomers to think statistically about debris fields rather than treating each fragment as a unique world.