As the New Horizons spacecraft continues its epic journey to explore the Kuiper Belt, it has a study partner here on Earth. The Subaru Telescope on Hawaii’s Big Island is deploying its Hyper Suprime-Cam imager to view the Kuiper Belt along the spacecraft’s trajectory. His observations show that the Kuiper Belt extends further than scientists thought.
The observations support the search for Kuiper Belt Objects (KBOs) for New Horizons to explore next. So far, Subaru has found plenty of smaller bodies out there. However, none of them are along the ship’s trajectory. In a major surprise to the science teams at Subaru, at least two of these objects orbit beyond 50 AU, the current putative “limit” of the Belt.
If observers continue to find more such objects outside that 50 AU “boundary,” it means the Kuiper Belt is bigger than everyone thought. Or it could exist in two parts – a sort of inner and outer Kuiper belt. Scientists already know that the belt is much dustier than expected, thanks to observations made with the dust counter aboard New Horizons.
Implications of an extended or two-part Kuiper belt
Beyond simply expanding the boundary of the Kuiper Belt, Subaru’s observations have profound implications for our understanding of the solar nebula, according to Fumi Yoshida, who led the research for the Subaru observing team. “Looking outside the Solar System, a typical planetary disk extends about 100 AU from the host star (100 times the distance between Earth and the Sun), and the Kuiper Belt, which is estimated to extend about 50 AU, is very compact. . Based on this comparison, we think that the primordial solar nebula, from which the Solar System was born, may have extended further than today’s Kuiper belt,” Yoshida said.
Let’s say the primordial disk was quite large. Then it is possible that undiscovered planetary bodies have cut through the outer edge of the Kuiper Belt. If this has happened, then it makes sense to search the outer limits of the current Belt to find such a sheared object. It is also possible that perhaps that truncation created a second Kuiper belt beyond the currently known belt. What it’s like is anyone’s guess, though it’s probably dusty and most likely has at least a few larger objects. So even if there’s nothing along New Horizons’ trajectory, using Subaru to study the distribution of objects it finds will help scientists understand the evolution of the Solar System.
Looking for KBOs
Subaru Telescope’s has been looking for more KBOs to explore since New Horizons passed by Arrokoth in 2019. The idea is to find additional KBOs along the flyby. The search focused two Hyper Suprime-Cam fields along the spacecraft’s trajectory through the Belt. The New Horizons team spent about 30 half-nights to find more than 240 outer Solar System objects.
The next step was for a Japanese team to analyze the images from those observations. However, they used a different method than the mission team and found seven new outer Solar System objects. The scientists then analyzed the HSC data with a Moving Object Detection System developed by JAXA. It normally detects near-Earth asteroids and other space debris. These types of bodies move very quickly, compared to the more distant ones. So looking for very faint, distant, slow-moving objects was a challenge. This is because the team had to adapt to the speed of Kuiper Belt objects. Then they applied some updated image analysis to confirm their findings. Scientists now know the orbits of two of the seven new objects and have been assigned provisional designations by the Minor Planet Center (MPC.
Continuing the search for the Kuiper belt
The discovery of more KBOs in the outer Solar System (along with the ongoing dust detection activities of New Horizons) tells scientists that there is more to the Kuiper Belt than anyone expected. The proof will be in Subaru’s ongoing observations to discover and confirm more objects “out there”.
“The mission team’s search for Kuiper Belt objects using Hyper Suprime-Cam continues to this day, and a series of papers will be published in the future, mainly by the North American group,” Yoshida said. “This research, discovering resources with the potential to expand the Kuiper Belt region using a method developed in Japan and led by Japanese researchers, serves as a precursor to these publications.”
For more information
A New Horizon for the Kuiper Belt: Wide Field Observations of the Subaru Telescope
An in-depth analysis of New Horizons’ KBO search images
PI Perspective: Needles in Cosmic Haystacks
