For roughly a decade, a small family of icy bodies sharing Neptune's orbit stayed hidden, because from Earth they lay against the blazing heart of the Milky Way. Now a team led by Queen's University Belfast researchers, working with data from the Vera C. Rubin Observatory in the Chilean Andes, has pulled two asteroids and a candidate out of that glare and confirmed them as lasting members of the trailing group. It is a quiet reminder that what we can know depends as much on patience and the drift of the heavens as on the power of our instruments, and that the outer edge of our solar system is
Rubin Observatory Data Helps Locate Neptune's Long-Missing Trojan Asteroids
Faint, distant, icy bodies simply vanished against that glare.
Mark
Why did it take until now to find Neptune's trailing Trojans, when Jupiter's were spotted in 1906?
Mimi
Distance and position. Neptune's Trojans are faint and far away, and for roughly the past ten years the trailing cloud has sat in front of the Milky Way's center, where the sky is crowded and bright.
Mark
So the cloud moving out of that region mattered as much as the telescope?
Mimi
Dr. Schwamb described it as both: the cloud has begun to leave that region, and Rubin's depth and sky coverage did the rest.
Luke
Let's be clear on the scale. This is two asteroids and one candidate, not a huge catalog.
Mimi
Right. The team says it doubled the known objects on long-lived orbits in this population, which tells you how small the starting number was.
Luke
And the candidate isn't confirmed in the way the other two are, as far as the reporting says.
Mark
What did the filters add?
Mimi
Images through different filters let the team show that leading and trailing Neptune Trojans have similar surfaces.
Luke
Worth noting that comes from this early data. The article doesn't say what the surfaces are made of.
Mark
And what's next?
Mimi
Nine more years of the LSST survey, with expectations of tens to hundreds of Neptune Trojans.
Luke
Those are expectations, not results. We'll see what the survey actually delivers.
Le Pouls
- Neptune's trailing Trojans sat hidden for about a decade, lost against the dense glow of the Milky Way.
- Their slow drift out of that crowded sky finally opened a window for detection.
- Rubin Observatory's deep, wide-sweeping survey pulled two asteroids and one candidate from the background.
- The discovery doubles the known long-lived objects in this population, with nine years of survey data still ahead to reveal tens to hundreds more.
For roughly a decade, a small family of icy bodies sharing Neptune's orbit stayed hidden, because from Earth they lay against the blazing heart of the Milky Way. Now a team led by Queen's University Belfast researchers, working with data from the Vera C. Rubin Observatory in the Chilean Andes, has pulled two asteroids and a candidate out of that glare and confirmed them as lasting members of the trailing group. It is a quiet reminder that what we can know depends as much on patience and the drift of the heavens as on the power of our instruments, and that the outer edge of our solar system is only beginning to show its neighbors.
For about a decade, Neptune's trailing Trojans were the hardest objects to find in the solar system. They sat directly in front of the bright, crowded center of the Milky Way as seen from Earth, and their faint, icy bodies disappeared into that glare. Astronomers had long since found similar companions around Jupiter, Saturn and Uranus, but Neptune's trailing group stayed out of view.
Now a team led by Dr. Meg Schwamb of Queen's University Belfast has brought a few of them into the light. Using early data from the Vera C. Rubin Observatory in Chile, they identified two asteroids and a further candidate as permanent members of the population, and published their findings in The Astrophysical Journal Letters. The work drew on a wide collaboration spanning several countries and institutions.
Rubin's power lay in its depth, its sky coverage and its timing. As the trailing cloud slowly moved out of the crowded region in front of the galactic center, the observatory could finally see it clearly. Imaging through different filters also showed that the leading and trailing Trojans share similar surfaces.
This is only the beginning. Over the nine years of the survey still ahead, Rubin is expected to reveal tens to hundreds more Neptune Trojans, along with tens of thousands of icy bodies in the Kuiper Belt.
For about a decade, Neptune's trailing Trojans sat in the worst possible place for anyone trying to see them: directly in front of the dense, bright center of the Milky Way, as seen from Earth. Faint, distant, icy bodies simply vanished against that glare. Now, a team led by researchers at Queen's University Belfast has pulled a few of them out of the background using data from the Vera C. Rubin Observatory.
The finding, published in The Astrophysical Journal Letters, identifies two asteroids and one further candidate as permanent members of Neptune's trailing Trojan population. Trojans are asteroids that share a planet's orbit, gathering in groups ahead of and behind it. Astronomers first saw such populations around Jupiter beginning in 1906, and they became known as the Trojan and Greek groups. Similar families have since been found around Saturn and Uranus. Neptune's trailing group was the one that stayed missing.
The team was led by Dr. Meg Schwamb, a lecturer at the Astrophysics Research Centre at Queen's University Belfast. She worked with colleagues 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.
Their data came from Rubin, perched high in the Andes in Chile. The observatory pairs an 8.4-meter 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. Rubin began operations in June 2025 and is now carrying out the Legacy Survey of Space and Time, a vast survey of the southern sky, while also mapping the northern sky, building an ultra-wide, ultra-high-definition time-lapse of the cosmos. Among its goals are insights into dark matter and dark energy, a map of the Milky Way and its faint satellite galaxies, the detection of transient events such as supernovae, variable stars and rogue planets, and a census of objects in the Solar System. That last aim drew Schwamb's team to Rubin's early test observations from last year.
After combining that large body of data, the researchers identified the objects as primordial members of the trailing Neptune Trojan population. "Early data from Rubin Observatory is already expanding our knowledge of the solar system's 'small bodies,' including asteroids, comets, and other minor planets," Schwamb said in a Queen's press release, adding that the observations gave "our clearest view yet of Neptune's trailing Trojan cloud."
Timing mattered as much as the instrument. Schwamb explained that the trailing cloud has begun to move out of the crowded part of the sky in front of the galactic center. Combined with Rubin's depth and sky coverage, that shift allowed the team to double the number of known objects on long-lived orbits in this population.
Rubin also imaged the objects through different filters. That let Schwamb and her colleagues show that the Trojans leading Neptune and those trailing it have similar surfaces.
What follows is a much longer count. Over the nine years of the LSST survey still ahead, Rubin is expected to find tens to hundreds of Neptune Trojans in both the leading and trailing groups, along with tens of thousands of icy bodies in the Trans-Neptunian Region and the Kuiper Belt.
Citations marquantes
Early data from Rubin Observatory is already expanding our knowledge of the solar system's 'small bodies,' and gave our clearest view yet of Neptune's trailing Trojan cloud.— Dr. Meg Schwamb, Queen's University Belfast
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