For a decade, the trailing companions of Neptune have hidden in plain sight, lying across the glowing heart of the Milky Way as seen from Earth, where their faint icy bodies were nearly impossible to separate from the crowded sky. Now a team led from Queen's University Belfast, drawing on early test images from the Vera C. Rubin Observatory in Chile, has confirmed two of these wanderers and a third candidate as lasting members of this distant population. It is a small step in a century-long human effort to map the families of bodies that share the orbits of the planets, and it completes a pict
Rubin Observatory Data Resolves Neptune's Missing Trojans, Identifying Two Asteroids and a Candidate
Neptune's Trojans sat in front of the Milky Way's center, lost in its glare
Mark
Why did it take until now to find Neptune's Trojans when Jupiter's were spotted in 1906?
Mimi
Distance and faintness, mostly. And for the last ten years the trailing group has been sitting in front of the Milky Way's center, which is a crowded, bright backdrop.
Mark
So the sky itself was hiding them.
Mimi
In effect, yes. Now the cloud is moving out of that region, and Rubin's depth lets it see the faint objects.
Luke
Let me pin down what was actually found. It's two asteroids and a candidate, not a large population.
Mimi
Right. Two are identified as permanent members of the trailing group, and one is a candidate.
Luke
And the claim about doubling the known objects. Who is making it?
Mimi
Schwamb, the lead researcher, and it refers to objects on long-lived orbits. I'd treat it as the team's own count.
Mark
What do the filters tell us?
Mimi
The leading and trailing Trojans appear to have similar surfaces.
Luke
The projections of tens to hundreds more Neptune Trojans are expectations, not results. That's worth keeping apart from what's been found.
Mark
And what comes next?
Mimi
Nine more years of the LSST survey, which is where those projections come from.
Le Pouls
- Neptune's trailing Trojans have stayed nearly invisible because they sit against the blazing density of the Milky Way.
- Astronomers who found Trojan families around Jupiter, Saturn and Uranus were left with Neptune as the stubborn exception.
- Researchers led by Dr. Meg Schwamb turned early Rubin Observatory test data into a hunt for these faint icy bodies.
- Two asteroids and one candidate now confirmed on long-lived orbits have roughly doubled the known population.
- Rubin's ten-year LSST survey is poised to uncover tens to hundreds more Neptune Trojans and tens of thousands of Kuiper Belt objects.
For a decade, the trailing companions of Neptune have hidden in plain sight, lying across the glowing heart of the Milky Way as seen from Earth, where their faint icy bodies were nearly impossible to separate from the crowded sky. Now a team led from Queen's University Belfast, drawing on early test images from the Vera C. Rubin Observatory in Chile, has confirmed two of these wanderers and a third candidate as lasting members of this distant population. It is a small step in a century-long human effort to map the families of bodies that share the orbits of the planets, and it completes a picture that had been missing one piece for generations.
For the past decade, the trailing Trojans of Neptune have sat directly in front of the center of the Milky Way, as seen from Earth. Tiny, faint, icy bodies in that foreground have been swallowed by one of the densest and brightest regions of the night sky, and they have stayed hidden from astronomers.
The search goes back to 1906, when telescopes first revealed asteroid groups leading and trailing Jupiter. Similar families were later found around Saturn and Uranus. Neptune remained the holdout, and its missing Trojans puzzled researchers for decades.
An international team led by Dr. Meg Schwamb of Queen's University Belfast has now found some of them. Using early test observations from the Vera C. Rubin Observatory in the Chilean Andes, they identified two asteroids and one further candidate as permanent members of the trailing population, with findings published in The Astrophysical Journal Letters.
Rubin's 8.4-meter Simonyi Survey Telescope and its LSST Camera, the largest digital camera ever built, survey the sky faster than any other ground-based telescope. Schwamb explained that the trailing cloud has begun drifting out of the crowded Milky Way region, and Rubin offers unmatched depth and coverage. Together these let the team double the known objects in this population. Imaging through different filters also showed that the leading and trailing Trojans have similar surfaces.
Over the coming nine years of the LSST survey, Rubin is expected to find tens to hundreds more Neptune Trojans, along with tens of thousands of icy bodies in the Kuiper Belt. Schwamb described this result as only a glimpse of what the data will reveal.
For the past decade, the trailing Trojans of Neptune have sat directly in front of the center of the Milky Way, as seen from Earth. That placement has made them close to impossible to pick out. Tiny, faint, icy bodies in the foreground get lost against one of the densest and brightest parts of the night sky.
An international team led by researchers at Queen's University Belfast has now found some of them. Using data from the Vera C. Rubin Observatory in the Chilean Andes, the group identified two asteroids and one further candidate as permanent members of Neptune's trailing Trojan population. Their findings are published in The Astrophysical Journal Letters.
The search has a long history. Starting in 1906, telescope observations revealed groups of asteroids leading and trailing Jupiter, which became known as the Trojans and the Greeks. Astronomers later found similar families orbiting Saturn and Uranus. Neptune was the holdout, and its missing Trojans remained a puzzle for decades.
The team was led by Dr. Meg Schwamb, an astronomer and lecturer at the Astrophysics Research Center at Queen's University Belfast. Colleagues came from the Instituto de Astronomia, Geofísica e Ciências Atmosféricas, the Planetary Science Institute, the DiRAC Institute, the Michigan Institute for Data and AI in Society, JHUAPL, NSF's NOIRLab and several universities around the world.
The data came from Rubin's early test observations last year. Rubin pairs its 8.4-meter (27.6-foot) Simonyi Survey Telescope with the LSST Camera, the largest digital camera ever built, and it surveys the sky faster than any other ground-based telescope. It began operations in June 2025 and is now running the Legacy Survey of Space and Time, a survey of the southern sky, while also mapping the northern sky, to build a time-lapse record of the cosmos. Cataloguing objects in the solar system is one of its stated goals, and that is what drew Schwamb's team to the early data.
After combining the large body of observations, the team classified the objects as primordial members of the trailing Neptune Trojan population. Schwamb said in a Queen's press release that early Rubin data is already expanding knowledge of the solar system's small bodies, including asteroids, comets and other minor planets, and that the observations gave the clearest view yet of Neptune's trailing Trojan cloud.
Two things came together, she explained. The trailing cloud has begun to move out of the crowded Milky Way region of sky, and Rubin brings unmatched depth and sky coverage. Together they let the team double the number of known objects in this population on long-lived orbits.
Rubin also imaged the objects through different filters. That allowed the researchers to show that the Trojans leading Neptune and those trailing it have similar surfaces.
More is expected. Over the next nine years of the LSST survey, Rubin is projected to find tens to hundreds of Neptune Trojans, in both the leading and trailing groups. It should also turn up tens of thousands of icy bodies in the trans-Neptunian region and the Kuiper Belt. Schwamb described the current result as a glimpse of how transformative the data will be.
Citations marquantes
Early Rubin observations have provided the clearest view yet of Neptune's trailing Trojan cloud.— Dr. Meg Schwamb, Queen's University Belfast
Rubin's data will be transformative, with even more exciting findings expected in the years ahead.— Dr. Meg Schwamb, Queen's University Belfast
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