Kuiper Belt objects (KBOs) are thought to be the dominant source of interplanetary dust particles in the outer Solar System due to both collisions between KBOs and their continual bombardment by interstellar dust particles. New measurements by NASA’s New Horizons spacecraft show higher than model-predicted levels of interstellar dust as the spacecraft approaches the putative outer edge of the Kuiper Belt.
Beyond Neptune, there is a large disk of small objects, called the Kuiper Belt and beyond that is the Oort Cloud, home of the comets. This artwork shows a section of Kuiper Belt, crowded with the icy cores of potential comets. Image credit: M. Kornmesser / ESO.
Interplanetary dust particles carry information about the birth and evolution of planetary bodies within our Solar System.
The orbital distribution of these dust particles is driven by the forces of gravity from the Sun and planets, radiation pressure etc. Additionally, the size and mass of individual particles are constantly evolving due to sputtering and mutual collisions.
While Jupiter-family comets and asteroids dominate the production of interplanetary dust particles in the inner Solar System, the Kuiper Belt is the dominant source of the particles in the outer Solar System from either mutual KBO collisions or interstellar dust bombardment.
Speeding through the outer edges of the Kuiper Belt, the New Horizons Venetia Burney Student Dust Counter (SDC) instrument is now detecting higher than expected levels of interplanetary dust.
The readings contribute to a growing body of evidence that suggests the outer edge of the main Kuiper Belt could extend billions of km farther than current estimates — or that there could even be a second belt beyond the one we already know.
“New Horizons is making the first direct measurements of interplanetary dust far beyond Neptune and Pluto, so every observation could lead to a discovery,” said lead author Alex Doner, a graduate student at the University of Colorado Boulder who serves as SDC lead.
“The idea that we might have detected an extended Kuiper Belt — with a whole new population of objects colliding and producing more dust — offers another clue in solving the mysteries of the Solar System’s most distant regions.”
The SDC instrument has detected microscopic dust grains produced by collisions among asteroids, comets and Kuiper Belt objects all along New Horizons’ 18-year journey across our Solar System — which after launch in 2006 included historic flybys of Pluto in 2015 and Arrokoth in 2019.
The first science instrument on a NASA planetary mission to be designed, built and ‘flown’ by students, the SDC counts and measures the sizes of dust particles, producing information on the collision rates of such bodies in the outer Solar System.
The latest, surprising results were compiled over three years as New Horizons traveled from 45 to 55 AU from the Sun.
These readings come as New Horizons scientists, using observatories like the Japanese Subaru Telescope in Hawaii, have also discovered a number KBOs far beyond the traditional outer edge of the Kuiper Belt.
This outer edge — where the density of objects starts to decline — was thought to be at about 50 AU, but new evidence suggests the belt may extend to 80 AU, or farther.
“As telescope observations continue, scientists are looking at other possible reasons for the high SDC dust readings,” Doner said.
“One possibility, perhaps less likely, is radiation pressure and other factors pushing dust created in the inner Kuiper Belt out past 50 AU.”
“New Horizons could also have encountered shorter-lived ice particles that cannot reach the inner parts of the Solar System and were not yet accounted for in the current models of the Kuiper Belt.”
“These new scientific results from New Horizons may be the first time that any spacecraft has discovered a new population of bodies in our Solar System,” said New Horizons principal investigator Dr. Alan Stern, a researcher at the Southwest Research Institute.
“I can’t wait to see how much farther out these elevated Kuiper Belt dust levels go.”
Now into its second extended mission, New Horizons is expected to have sufficient propellant and power to operate through the 2040s, at distances beyond 100 AU from the Sun.
That far out, the SDC could potentially even record the spacecraft’s transition into a region where interstellar particles dominate the dust environment.
With complementary telescopic observations of the Kuiper Belt from Earth, New Horizons, as the only spacecraft operating in and collecting new information about the Kuiper Belt, has a unique opportunity to learn more about KBOs, dust sources and expanse of the belt, and interstellar dust and the dust disks around other stars.
“Ongoing SDC measurements at even larger heliocentric distances will continue to constrain the contributions of dust production in the Kuiper Belt,” the authors said.
“Continued SDC measurements remain crucial for understanding the Kuiper Belt and the interpretation of dust disks around other stars.”
Their paper appears in the Astrophysical Journal Letters.
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Alex Doner et al. 2024. New Horizons Venetia Burney Student Dust Counter Observes Higher than Expected Fluxes Approaching 60 AU. ApJL 961, L38; doi: 10.3847/2041-8213/ad18b0
