Does the Kuiper Belt extend further than we thought?

New Horizons is continually using both ground-based and space-based telescopes to search for additional Kuiper Belt objects (KBOs) to observe from a distance, or to potentially conduct a close flyby of in the future. As part of this search, we have discovered objects beyond the traditional "outer edge" of the main portion of the Kuiper Belt (see figure below). This outer edge (where the density of objects starts to decline) was thought to be at about 50 astronomical units (AU), but new evidence suggests the Kuiper Belt may extend to 80 AU or farther. The New Horizons Earth-based telescope searches are finding more objects than expected beyond 50 AU. Additionally, the Venetia Burney Student Dust Counter instrument onboard the New Horizons spacecraft is measuring elevated dust fluxes as it traverses beyond 50 AU during the New Horizons extended missions. Read more about the dust results below.

With the possibility of an extended Kuiper Belt, New Horizons has intensified its search for a future close flyby target where detailed images of the surface of the object could be obtained (similar to the close flyby of Arrokoth). As part of this search, it is expected that the New Horizons team will discover hundreds of previously unknown KBOs, but only a small number of those (about 5-20) will be able to be observed from a distance by New Horizons (where the object is still a point of light), and an even smaller fraction will be potential close flyby targets.

Kuiper Belt objects (KBOs) detected by the Subaru Telescope in 2021 (blue) and 2022 (orange). The blue and orange curves represent the orbits or paths these objects follow around the Sun. The horizontal black line is the trajectory of New Horizons, and the black dot represents the spacecraft’s position on December 15, 2022. The colored dots show the predicted locations of the KBOs that New Horizons can observe at the point on their orbits when New Horizons is closest to them. None of these objects would be very close flyby targets like Arrokoth was, but New Horizons can still make valuable and unique observations of them not possible from Earth. For reference, the spacecraft travels a distance of approximately 3 AU per year and will pass 60 AU in October 2024. Each of these KBO orbits is based on two observations spaced one month apart, and additional observations are needed to refine their orbits.

Discover Distant Kuiper Belt Objects

New Horizons is gathering a range of planetary science data that only a spacecraft in the Kuiper Belt could collect. With its Long Range Reconnaissance Imager (LORRI) instrument, New Horizons continues to observe both dwarf planets and smaller KBOs from afar to study their moons; their shapes, rotation periods, and pole positions; and their surface characteristics in ways that cannot be studied from Earth or Earth orbit.

What is a hot classical Kuiper Belt object? What about a cold classical KBO? Find out here.

Adding AI Smarts to the Kuiper Belt Object Search

By early 1930, Lowell Observatory junior astronomer Clyde Tombaugh had spent months poring over hundreds of telescopic photo plates in the search for a single moving object — which would turn out to be Pluto, the ninth planet.

Nearly a century later, the team that famously explored the planet Tombaugh discovered is expanding its own search for additional targets of discovery — and doing it with technology that would have astounded Tombaugh. Read how.

Measure Kuiper Belt Dust

KBOs are sources of small dust particles resulting from collisions with each other and also continual bombardment by interstellar dust (ISD) particles. New Horizons’ Venetia Burney Student Dust Counter (SDC) is making the first measurements of this dust distribution, providing insights into the spatial distribution of KBOs. These observations allow the comparison of our own solar system’s dust disk, known as the Zodiacal dust cloud, with dust disks around other stars.

The SDC instrument has continued to measure dust along the New Horizons trajectory beyond 50 AU during the New Horizons extended missions. Surprisingly, the amount of dust measured has remained at a high value, despite model predictions that the dust flux would start to decline in these distant parts of the solar system. Below is a figure from Doner et al., 2024, comparing the SDC measurements (points) to models of dust production (white, red and yellow curves). Detecting more dust than expected could be due to a more extended Kuiper Belt with more objects at farther distances colliding and producing more dust. Alternatively, elevated dust levels could be due to radiation pressure and other factors causing more dust from inside ~50 AU to be pushed out beyond 50 AU. New Horizons could also have encountered shorter-lived ice particles that cannot reach the inner parts of the solar system; hence, they were not accounted for in our current models.

Figure 3 from Doner et al., 2024 showing distance from the Sun on the x-axis and dust flux (the number of dust particles per area per time) on the y-axis.

New Horizons is expected to operate through the 2040s, possibly until 2050, exploring heliocentric distances beyond 100 AU. The continued operation of the SDC provides an opportunity to explore the outer edges of our solar system, and possibly record the transition into a new region in space where interstellar particles dominate the dust environment. Complementary to optical observations of the Kuiper Belt, SDC measurements provide a unique opportunity to learn more about our Kuiper Belts extent, dust sources and populations beyond it, interstellar dust, and dust disks around other stars. (Excerpt from Doner et al., 2024)

Observe 'Ice Giant' Planets

From its unique perch in the Kuiper Belt, New Horizons can observe planets and other bodies at angles and distances like no other spacecraft or telescope on Earth. Using its Ralph imager, New Horizons is building on long-distance 2019 observations it made of Uranus and Neptune to provide new insight into the atmospheres of each of these planets.

Specifically, New Horizons will build on Voyager's observations of Uranus and Neptune, seeing them at unique geometries, in longer wavelengths and through new seasons that Voyager could not. New Horizons will also complement Hubble Space Telescope observations of each world, particularly on studies of the planets' atmospheres and the transfer of heat from their rocky cores through their gaseous exteriors. Aside from a science return better than either New Horizons or Hubble could provide on its own, the activity sets the stage for observations of similar ice giant planets around other stars.

New Horizons’ long-distance observations of Uranus (top left) and Neptune (bottom left) offer looks at each planet under unique lighting conditions (simulated top and bottom right). (Credit: NASA/Johns Hopkins APL/SwRI)