Universe Today
Exploration of the outer Solar System may be getting a boost from the Vera Rubin Observatory (VRO). When this gigantic telescope opens its eye later in 2025, it begins a decade-long survey of the ever-changing sky. As part of this time-lapse vision of the cosmos, distant objects in the Kuiper Belt will be among its most challenging targets.
A team of planetary scientists led by JJ Kavelaars of Canada's Herzberg Astronomy and Astrophysics Research Centre proposes using VRO for a deep survey of objects along the trajectory of the New Horizons spacecraft. It's currently about 61 astronomical units away from Earth and is the only spacecraft transiting the Kuiper Belt. This "Deep Drilling" micro-survey will use about 30 hours of Rubin time across six 5-hour visits in about a year's time. It will begin in 2026 and should determine orbits for around 700 Kuiper Belt Objects (KBOs).
According to Kavelaars, the team needs at least five hours per night on two nights for their survey to succeed. "Getting more nights on the same field (to construct orbital arcs of the detected sources) is likely more valuable than getting deeper," he said.
Chances for New Horizons Targets
The team's proposal cites previous discoveries of objects in the Kuiper Belt by Kavelaar's colleague Wesley Fraser. In 2024, Fraser and his team reported the detection of 239 trans-Neptunian objects. Their work was part of a New Horizons survey for distant minor bodies. Those detections came via the Hyper Suprime-Cam mosaic imager on the Subaru Telescope. The Fraser team identified an overabundance of very faint objects at distances greater than 70 AU from the Sun. As they are confirmed, this expanded number of objects explains some stellar occultations and other readings made by the Student Dust Counter onboard the New Horizons spacecraft.
This shows the location of various spacecraft through the solar system. Note the position of New Horizons at about 61 AU and in the inner region of the Kuiper Belt. Courtesy NASA.
The Deep Survey using Rubin should uncover objects for New Horizons to study at a distance. Near-flyby objects will likely be much rarer, according to Kavelaar. "We will be very lucky if one of those turns out to be close enough that we can direct the spacecraft to it," he said, "but we will, at the very least, get a solid sample of objects to observe from New Horizons at longer ranges."
It would be cool if the survey finds another contact binary such as Arrokoth. New Horizons flew past that in 2019. Kavelaar pointed out that of the ~700 sources the Deep Survey uncovers, many will be binaries and contact binaries. Most will likely not be close enough for a flyby or even distant observations by the spacecraft. However, their detection is enough to tell planetary scientists that the Kuiper Belt is more richly populated than current outer solar system population models suggest.
Digging up Targets in the Kuiper Belt
The Vera Rubin Observatory's Legacy of Space and Time (LSST) Survey - which is the primary mission of the observatory - will take a series of 30-second 9.6-square-degree field images using the LSSTCam mounted on the 8.36-m Simonyi Survey Telescope. Those observations will alternate between various filter bands to get full details and a "deep look" at the sky. It will repeat this pace of deep sky imaging for ten years, all from a mountaintop in Chile. Its builders suggest that the results of that survey will provide the largest astronomical movie of all time. 
The Vera Rubin Observatory under construction. It set for first light in 2025. Courtesy NOIRLab/NSF/AURA
In the team's proposal paper to "piggyback" on the primary observations, it states that, "The currently planned cadence for LSST (see PSTN-056) will enable the discovery of an unprecedented number of small solar system bodies, including Trans Neptunian Objects (TNOs), determining precise orbits and physical properties for factors of many more such bodies than are currently known. Rubin will genuinely transform our knowledge of the Solar System."
The 30 hours wants for the micro-survey of the Kuiper Belt should be just enough to determine KBO positions and orbits. That will allow possible observations by New Horizons (if not a flyby) and also with future spacecraft.
"A very exciting possibility is that we will do this very deep search with Rubin and that will confirm the population Fraser reported and characterize its orbital distribution," he said. "Then, using that more detailed information (if no flyby was found in the Rubin search) we could design a success-oriented search to be conducted with the ROMAN observatory when it launches."
For More Information
Candidate Distant Trans-Neptunian Objects Detected by the New Horizons Subaru TNO Survey
