The work targets the European Space Agency’s Jupiter Icy Moons Explorer (JUICE), planned to arrive in the Jupiter system in 2031. Until now, Kallichore’s astrometric uncertainty and shape estimates were too loose to confidently assess the feasibility of a flyby. Using a carefully coordinated set of observations, the researchers aimed to refine Kallichore’s trajectory and determine key physical parameters.

The team began with Hubble Space Telescope data, combining photometry and astrometry to improve the object’s measured position and brightness. Hubble’s resolution is crucial for separating a faint, fast-moving target from the glare of Jupiter and background sources, providing a baseline for subsequent ground-based measurements.

Next came a global ground-based stellar occultation campaign. By timing when Kallichore passed in front of distant stars, the observers extracted direct constraints on its size and geometry. Stellar occultations remain one of the strongest tools for kilometre-scale bodies, because they can reveal silhouette-scale information even when imaging fails.

To further sharpen the dynamical picture, the researchers added astrometric and photometric observations from the 10.4-m Gran Telescopio de Canarias. This multi-site strategy reduces systematics related to local weather, instrument calibration, and observing conditions, thereby tightening the orbit more effectively.

The results are striking: the orbital uncertainty was reduced by as much as ~80%. With the improved trajectory, the team could also infer Kallichore’s shape from combined constraints, finding it to be an elongated object with a minimum semi-axis ratio of a/b = 1.53 ± 0.10.

From the occultation-derived effective dimensions, Kallichore’s area-equivalent diameter is reported as 3.8_-0.3^+2.3 km. The surface appears dark, with a geometric albedo of 3.7_-2.2^+0.7%, consistent with primitive, low-reflectivity material expected for captured small bodies.

Importantly for mission planning, the study found no evidence of close companions—an essential factor when evaluating encounter risk and navigation. Together, the findings outline a viable pathway toward a JUICE flyby, turning Kallichore from a poorly known dot into a quantified target that spacecraft operations can design around.

Subject of Research:

Jupiter’s irregular satellites; characterization of the moon Kallichore for a potential JUICE flyby.

Article Title:

Kilometre-scale Jovian moon characterized for a potential JUICE flyby.

Article References:

Rizos, J.L., Gómez-Limón, J.M., Kilic, Y. et al. Kilometre-scale Jovian moon characterized for a potential JUICE flyby. Nat Astron (2026). https://doi.org/10.1038/s41550-026-02929-z

Image Credits:

AI Generated

DOI:

https://doi.org/10.1038/s41550-026-02929-z

Recent groundbreaking research from Michigan State University has shed light on the processes that craft these two-lobed formations. Utilizing a state-of-the-art high-performance computing system, graduate student Jackson Barnes has developed the first computational simulation that naturally forms contact binaries through gravitational collapse, without relying on improbable or exotic events. Published in the Monthly Notices of the Royal Astronomical Society, this work opens new avenues for understanding the early evolutionary pathways of small bodies in the outer solar system.

Traditional models faced significant limitations, often approximating these small icy objects as fluid blobs that, upon collision, merged into singular spheres. Such simplifications failed to reproduce the characteristic dual-lobed structure observed in about 10% of Kuiper Belt planetesimals. Barnes’ simulations mark a breakthrough by incorporating the mechanical strength and granular nature of these bodies. His approach allows the simulated planetesimals to rest against each other, maintain their distinct shapes, and ultimately fuse gently rather than violently.

The insights from Barnes’ research are critical because they align with the observed abundance of contact binaries. If 10% of planetesimals exhibit this fused shape, the formation mechanism must be a relatively common event in the early solar system, rather than a product of rare or catastrophic phenomena. Earth and Environmental Science Professor Seth Jacobson, a senior author on the paper, emphasizes that gravitational collapse is a compelling and elegant explanation consistent with empirical data acquired through decades of observation.

NASA’s New Horizons mission provided the first close-up images of a contact binary in January 2019 when it flew past the Kuiper Belt object known as 2014 MU69, nicknamed Ultima Thule. These crisp images revealed a distinctly two-lobed shape with smooth lobes fused at a narrow neck, challenging prior assumptions about planetesimal formation. Following this discovery, astronomers revisited other Kuiper Belt objects and identified that approximately one in ten follows this binary configuration, with little evidence of disruptive collisions owing to the sparse population density in that cosmic neighborhood.

The Kuiper Belt, formed remnant from the protoplanetary disk that once encircled the Sun, is an archive of primordial matter dating back over four billion years. Planetesimals are among the first large solid bodies to arise from this disk, developing through the slow agglomeration of pebble-sized fragments pulled together by mutual gravitational attraction. This formative stage is analogous to compaction of snowflakes into a snowball, except occurring over cosmic time scales and within a rotating circumstellar environment.

Barnes’ simulations highlight a fascinating dynamical process: as a rotating cloud of pebbles collapses under gravity, irregularities often lead to the initial formation of binary systems—two planetesimals orbiting each other. Over time, their orbits decay, spiraling closer until they make contact gently. The simulated binaries retain their smooth, rounded shapes without blending into a single sphere, thus reproducing the iconic snowman-like morphology observed in actual Kuiper Belt objects.

A key question that arises is how these delicate binary structures persist over billions of years without disruption. Barnes explains that the Kuiper Belt’s low-density environment minimizes chances of catastrophic collisions that could separate or shatter these contact binaries. This tranquil setting preserves the integrity of their shapes, consistent with the lack of significant cratering seen on many observed binaries.

While the gravitational collapse hypothesis had been proposed before, quantitative and realistic modeling was lacking due to computational constraints and oversimplifications. Barnes’ work pioneers a physics-rich simulation capable of resolving the mechanical and dynamical subtleties necessary to form and sustain contact binaries. This represents a major advancement in small-body astrophysics.

Looking forward, Barnes anticipates that his model will inspire further studies examining more complex multi-lobed systems, where three or more bodies coalesce through related mechanisms. The research team also aims to refine their simulations by incorporating more detailed physics to replicate the collapse and accretion processes with even greater fidelity.

Moreover, ongoing and future space missions venturing into the outer solar system may uncover additional contact binaries, revealing whether these “cosmic snowmen” have distant, untapped cousins. Such discoveries will further deepen our understanding of the delicate balance between gravitational forces and collisional histories that shape the architecture of our solar system’s frontier.

This new insight into the origin of contact binary planetesimals marks a significant milestone in planetary science. It not only clarifies how these peculiar objects form but also enhances our comprehension of the early conditions and evolutionary processes that govern the distant Kuiper Belt. As computational capabilities continue to expand, such interdisciplinary efforts bridging observation, theory, and simulation promise to unravel even more cosmic mysteries.

Subject of Research: Formation of contact binary planetesimals in the Kuiper Belt through gravitational collapse

Article Title: Direct contact binary planetesimal formation from gravitational collapse

News Publication Date: 19-Feb-2026

Web References: http://dx.doi.org/10.1093/mnras/stag002

Image Credits: NASA

Keywords

Kuiper Belt, contact binaries, planetesimals, gravitational collapse, New Horizons, solar system formation, computational simulation, binary planetesimals, outer solar system, planetary science

Asteroids are remnants from the early solar system, offering vital clues about the formation and evolution of our planetary neighborhood. Bennu and Ryugu, both classified as near-Earth asteroids, have become focal points of study due to their intriguing characteristics and potential insights into the solar system’s history. While they traverse the same orbital region, researchers have always wondered whether these two asteroids could share a deeper connection, possibly stemming from a larger parent body.

Dr. Anicia Arredondo, the lead author of the SwRI study, emphasizes the significance of their findings: “We believe large asteroids collided early in the solar system’s history, leading to the creation of an ‘asteroid family.’ Polana is recognized as the largest remnant of that collision.” The study meticulously compared spectroscopy data from Polana and found strong correlations with material samples analyzed from Bennu and Ryugu. These similarities in spectral signatures bolster the hypothesis of a shared origin, a theory that transforms our understanding of these intriguing celestial objects.

To conduct this comprehensive analysis, the research team sought time on the JWST, a state-of-the-art observatory capable of capturing detailed spectral data across different wavelengths. By employing two distinct spectral instruments, the researchers focused their efforts on Polana’s near-infrared and mid-infrared wavelengths. They then juxtaposed this data against the physical samples of Ryugu and Bennu, which were collected during separate space missions. The Hayabusa2 mission, organized by the Japan Aerospace Exploration Agency, successfully collected samples from Ryugu in 2018, returning them to Earth in late 2020. In contrast, NASA’s OSIRIS-REx spacecraft encountered Bennu in 2020, with its samples arriving back on Earth in late 2023.

The implications of this study stretch far beyond the mere identification of spectral similarities. Bennu and Ryugu, while classified as near-Earth asteroids and sharing similar orbital paths, exhibit distinct characteristics influenced by their journeys through the solar system. Each body has experienced various environmental factors, including solar radiation and the impacts of micrometeoroids, which can fundamentally alter their surface composition and properties over time.

Interestingly, despite the observed variances in their spectral data, the differences were not sufficient to rule out the hypothesis of a common ancestry. Dr. Tracy Becker, a co-author of the study, elaborates on this, stating, “The spectral evidence suggests that while Polana, Bennu, and Ryugu have undergone individual transformations, the underlying chemistry connecting them remains. The journey of each asteroid through the solar system has shaped its current characteristics.”

As their study unfolds, the researchers recognize that the gravitational influence of Jupiter may have played a critical role in the evolutionary history of Bennu and Ryugu. It is theorized that interactions with Jupiter’s immense gravity led to the ejection of these asteroids from their original orbits, ultimately placing them closer to the Sun. Such movements allowed for important chemical reactions and transformations to occur in the materials constituting these celestial bodies.

The scientific community has long been intrigued by the dynamics of asteroid families and their potential connections to the early solar system’s chaos. Data revealing that Bennu, Ryugu, and Polana share a common origin helps elucidate the complex interplay of collisions and gravitational interactions that shaped the current asteroid belt. Moreover, understanding this interrelationship can enhance our knowledge about asteroid potentialities, including the risks posed by near-Earth bodies and their potential for resource mining in the future.

As the findings of this study are prepared for publication in the prestigious Planetary Science Journal, the research team reflects on the broader contexts of their work. With the continual advancement of observational technologies like the JWST, researchers are now equipped to uncover deeper insights into the histories of celestial bodies that were previously obscured. The intersection of advanced spectroscopy and comparative analysis serves as a powerful tool in the quest to unravel the mysteries of our solar system.

In conclusion, the insights provided by the SwRI’s study of Bennu, Ryugu, and Polana usher in a new era in asteroid research. These findings not only highlight the value of international collaboration in space missions but also underscore the importance of interdisciplinary methodologies in advancing our scientific understanding. As researchers continue to analyze these asteroids, they pave the way for future explorations that will further enhance our knowledge of the origins of our solar system and the evolutionary paths taken by its many inhabitants.

Subject of Research: Near-Earth Asteroids
Article Title: JWST spectroscopy of (142) Polana: Connection to NEAs (101955) Bennu and (162173) Ryugu
News Publication Date: August 18, 2025
Web References: SWRI Planetary Science
References: DOI: 10.3847/PSJ/ade395
Image Credits: Credit: NASA

Keywords

asteroid family, spectroscopy, near-Earth asteroids, Polana, Bennu, Ryugu, solar system formation, JWST, gravitational interactions, celestial bodies, space missions, Southwest Research Institute, planetary science