Search

To prepare for the upcoming Legacy Survey of Space and Time, we develop methods for quantifying the selection function of a wide-field survey as a function of all six orbital parameters and absolute magnitude. We perform a HelioLinC3D search for Centaurs in the Pan-STARRS1 detection catalog and use a synthetic debiasing population to characterize our survey's selection function. We find nine new objects, including Centaur 2010 RJ _226 , among 320 real objects, along with ∼70,000 debiasing objects. We use the debiasing population to fit a selection function and apply the selection function to a model Centaur population with orbital and size distributions from the literature. We confirm the model's marginal distributions but reject its joint distribution, and estimate an intrinsic population of 21,400 ${}_{-2800}^{+3400}$ Centaurs with H _r

We present a dynamical study of 39 active Centaurs and 17 high-perihelion ( q > 4.5 au) Jupiter-family comets (JFCs) with a focus on investigating recent orbital changes as potential triggers for comet-like activity. We have identified a common feature in the recent dynamical histories of all active Centaurs and JFCs in our sample that is not present in the history of the majority of inactive population members: a sharp decrease in semimajor axis and eccentricity occurring within the past several hundred years prior to observed activity. We define these rapid orbital changes as “ a -jumps.” Our results indicate that these orbital reshaping events lead to shorter orbital periods and subsequently greater average per-orbit heating of Centaur nuclei. We suggest that the a -jumps could therefore be a major trigger of cometary activity on Centaurs and JFCs. Our results further imply that analyses of the recent dynamical histories could be used to identify objects that are currently active or may become active soon, where we have identified three such Centaurs with recent a -jumps that should be considered high-priority targets for observational monitoring to search for activity.

The discovery of the transient Jupiter co-orbital comet P/2019 LD2 (ATLAS) drew significant interest. Not only will LD2 transition between being a Centaur and a Jupiter-family comet (JFC) in 2063, the first time this process can be observed as it happens, it is also very active for its large heliocentric distance. We present observations and orbital integrations of the newly discovered transient Jupiter co-orbital comet P/2023 V6 (PANSTARRS), the second such object known. Despite similar modern orbits, V6 is significantly (15×) less active than LD2 and most JFCs as determined via Af ρ measurements at the same R _H . We find that V6 is co-orbital between 2020 and 2044, twice the duration of LD2, but it will not become a JFC soon. We interpret these differences in activity as evolutionary, with V6 having lost a significant fraction of its near-surface ice compared to LD2 by previously being warmer. While V6's pre-encounter orbit was somewhat warmer than LD2's, future thermal modeling will be needed to understand if this can explain their differences or if a more significant difference further into the past is required. This is more evidence that LD2 is a pristine and ice-rich object, and thus it may display very strong activity when it becomes a JFC. We use the differences between V6 and LD2 to discuss the interpretation of cometary activity at large heliocentric distances as well as the small end of the cratering record of the Galilean satellites. Continuing observations of both objects are highly encouraged.

Saturn has long been the only giant planet in our solar system without any known Trojan members. In this Letter, with serendipitous archival observations and refined orbit determination, we report that 2019 UO _14 is a Trojan of the gas giant. However, the object is only a transient Trojan currently librating around the leading Lagrange point L _4 of the Sun–Saturn system in a period of ∼0.7 kyr. Our N -body numerical simulation shows that 2019 UO _14 was likely captured as a Centaur and became trapped around L _4 ∼ 2 kyr ago from a horseshoe co-orbital. The current Trojan state will be maintained for another millennium or thereabouts before transitioning back to a horseshoe state. Additionally, we characterize the physical properties of 2019 UO _14 . Assuming a linear phase slope of 0.06 ± 0.01 mag deg ^−1 , the mean r -band absolute magnitude of the object was determined to be H _r = 13.11 ± 0.07, with its color measured to be consistent with that of Jupiter and Neptune Trojans and not statistically different from Centaurs. Although the short-lived Saturn Trojan exhibited no compelling evidence of activity in the observations, we favor the possibility that it could be an active Trojan. If confirmed, 2019 UO _14 would be marked as the first active Trojan in our solar system. We conservatively determine the optical depth of dust within our photometric aperture to be ≲10 ^−7 , corresponding to a dust mass-loss rate to be ≲1 kg s ^−1 , provided that the physical properties of dust grains resemble Centaur 29P/Schwassmann–Wachmann 1.

We utilize serendipitous observations from the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the Zwicky Transient Facility in addition to targeted follow-up observations from the Las Cumbres Observatory (LCO) and Liverpool Telescope to analyze the first observed instance of cometary activity by the newly discovered Jupiter-family comet C/2023 RN _3 (ATLAS), whose orbital dynamics place it close to residing on a Centaur-like orbit. Across our 7 month baseline, we observe an epoch of cometary activity commencing in 2023 August with an increase in brightness of >5.4 mag. The lightcurve of 2023 RN _3 indicates the presence of continuous cometary activity across our observations, suggesting the onset of a new period of sustained activity. We find no evidence of any outbursts on top of the observed brightening nor do we find any significant color evolution across our observations. 2023 RN _3 is visibly extended in LCO and Liverpool Telescope observations, indicating the presence of a spatially extended coma. Numerical integration of 2023 RN _3 's orbit reveals the comet to have recently undergone a slight increase in semimajor axis due to a planetary encounter with Jupiter; however, whether this orbital change could trigger 2023 RN _3 's cometary activity is unclear. Our estimate for the maximum dust production metric of Af ρ ∼ 400 cm is consistent with previous measurements for the Jupiter-family comet and Centaur populations.

The discovery of two thin rings around the ∼ 250 km sized Centaur Chariklo was the first of its kind, and their formation and evolutionary mechanisms are not well understood. Here, we explore a single shepherd satellite as a mechanism to confine Chariklo’s rings. We also investigate the impact of such a perturber on reaccretion, which is a likely process for material located outside the Roche limit. We have modified N -body code that was developed for Saturn’s rings to model the Chariklo system. Exploration of a reasonable parameter space indicates that rings like those observed could be stable as the result of a single satellite with a mass of a few ×10 ^13 kg that is in orbital resonance with the rings. There is a roughly linear relationship between the model optical depth and the mass of the satellite required to confine a ring. Ring particles do not accrete into moonlets during hard-sphere simulations. However, a reasonable fraction of the ring material forms into moonlets after a few tens of orbits for soft-sphere collisions. The ring-particle properties are thus key parameters in terms of moonlet accretion or destruction in this system.

Centaurs are small solar system objects on chaotic orbits in the giant planet region, forming an evolutionary continuum with the Kuiper Belt objects and Jupiter-family comets. Some Centaurs are known to exhibit cometary activity, though unlike comets, this activity tends not to correlate with heliocentric distance, and the mechanism behind it is currently poorly understood. We utilize serendipitous observations from the Asteroid Terrestrial-impact Last Alert System, Zwicky Transient Facility, Panoramic Survey Telescope and Rapid Response System, Dark Energy Survey, and Gaia in addition to targeted follow-up observations from the Las Cumbres Observatory, TRAnsiting Planets and PlanetesImals Small Telescope South (TRAPPIST-South), and Gemini North telescope to analyze an unexpected brightening exhibited by the known active Centaur (2060) Chiron in 2021. This is highly indicative of a cometary outburst. As of 2023 February, Chiron had still not returned to its prebrightening magnitude. We find Chiron's rotational lightcurve, phase curve effects, and possible high-albedo surface features to be unlikely causes of this observed brightening. We consider the most likely cause to be an epoch of either new or increased cometary activity, though we cannot rule out a possible contribution from Chiron's reported ring system, such as a collision of as-yet-unseen satellites shepherding the rings. We find no evidence for a coma in our Gemini or TRAPPIST-South observations, though this does not preclude the possibility that Chiron is exhibiting a coma that is too faint for observation or constrained to the immediate vicinity of the nucleus.

An important testable prediction of dynamical instability models for the early evolution of the solar system is that Jupiter Trojans share a source population with the Kuiper Belt. Concrete evidence of this prediction remains elusive, as Kuiper Belt objects (KBOs) and Jupiter Trojans appear to have different surface compositions. We address the long-standing question of Trojan origin by finding a dynamical subpopulation in the Kuiper Belt with Trojan-like colors. Combining existing photometric data with our own surveys on Keck I and Palomar P200, we find that the low-perihelion ( q < 30 au, a > 30 au) component of the Kuiper Belt has colors that bifurcate similarly to the Jupiter Trojans, unlike Centaurs ( a < 30 au), which have redder, Kuiper Belt-like colors. To connect the Jupiter Trojans to the Kuiper Belt, we test whether the distinct Trojan-like colors of low-perihelion KBOs result from surface processing or are sourced from a specific population in the Kuiper Belt. By simulating the evolution of the Canada–France Ecliptic Plane Survey synthetic population of KBOs for four billion years, we find that differences in heating timescales cannot result in a significant depletion of very red low-perihelion KBOs as compared to the Centaurs. We find that the neutrally colored scattered disk objects ( e > 0.6 KBOs) contribute more to the low-perihelion KBO population than to Centaurs, resulting in their different colors.

The Kuiper Belt objects (KBOs), the Centaurs, and the Jupiter-family comets (JFCs) form an evolutionary continuum of small outer solar system objects, and their study allows us to gain insight into the history and evolution of the solar system. Broadband photometry can be used to measure their phase curves, allowing a first-order probe into the surface properties of these objects, though limited telescope time makes measuring accurate phase curves difficult. We make use of serendipitous broadband photometry from the long-baseline, high-cadence Asteroid Terrestrial-impact Last Alert System survey to measure the phase curves for a sample of 18 KBOs, Centaurs, and JFCs with unprecedentedly large data sets. We find phase curves with previously reported negative slopes become positive with increased data and are thus due to insufficient sampling of the phase-curve profile, and not a real physical effect. We search for correlations between phase-curve parameters, finding no strong correlations between any parameter pair, consistent with the findings of previous studies. We search for instances of cometary activity in our sample, finding a previously reported outburst by Echeclus and a new epoch of increased activity by Chiron. Applying the main belt asteroid HG _1 G _2 phase-curve model to three JFCs in our sample with large phase angle spans, we find their slope parameters imply surfaces more consistent with those of carbonaceous main belt asteroids than silicaceous ones.

We collect near-infrared spectra (∼0.75–2.55 μ m) of four Jovian irregular satellites and visible spectra (∼0.32–1.00 μ m) of two Jovian irregular satellites, two Uranian irregular satellites, and four Neptune Trojans. We find close similarities between the observed Jovian irregular satellites and previously characterized Jovian Trojans. However, irregular satellites’ unique collisional histories complicate comparisons to other groups. Laboratory study of CM and CI chondrites shows that grain size and regolith packing conditions strongly affect spectra of dark, carbonaceous materials. We hypothesize that different activity histories of these objects, which may have originally contained volatile ices that subsequently sublimated, could cause differences in regolith grain size or packing properties and therefore drive spectral variation. The Uranian satellites Sycorax and Caliban appear similar to TNOs. However, we detect a feature near 0.7 μ m on Sycorax, suggesting the presence of hydrated materials. While the sample of Neptune Trojans have more neutral spectra than the Uranian satellites we observe, they remain consistent with the broad color distribution of the Kuiper Belt. We detect a possible feature near 0.65–0.70 μ m on Neptune Trojan 2006 RJ103, suggesting that hydrated material may also be present in this population. Characterizing hydrated materials in the outer solar system may provide critical context regarding the origins of hydrated CI and CM chondrite meteorites. We discuss how the hydration state(s) of the irregular satellites constrains the thermal histories of the interiors of their parent bodies, which may have formed among the primordial Kuiper Belt.

We calculate the upper bounds of the population of theoretically stable Centaur orbits between Uranus and Neptune. These small bodies are on low-eccentricity, low-inclination orbits in two specific bands of semimajor axis, centered at ∼24.6 and ∼25.6 au. They exhibit unusually long Gyr-stable lifetimes in previously published numerical integrations, orders of magnitude longer than that of a typical Centaur. Despite the increased breadth and depth of recent Solar System surveys, no such objects have been found. Using the Outer Solar System Origins Survey simulator to calculate the detection efficiency for these objects in an ensemble of fully characterized surveys, we determine that a population of 72 stable Centaurs with absolute magnitude H _r ≤ 10 (95% confidence upper limit) could remain undetected. The upcoming Legacy Survey of Space and Time will be able to detect this entire intrinsic population, due to its complete coverage of the ecliptic plane. If detected, these objects will be interesting dynamically accessible mission targets—especially as comparison of the stable Centaur orbital phase space to the outcomes of several modern planetary migration simulations suggests that these objects could be close to primordial in nature.

A stellar occultation of Gaia DR3 2646598228351156352 by the Centaur (2060) Chiron was observed from the South African Astronomical Observatory on 2018 November 28 UT. Here we present a positive detection of material surrounding Chiron from the 74-inch telescope for this event. Additionally, a global atmosphere is ruled out at the tens of microbars level for several possible atmospheric compositions. There are multiple 3 σ drops in the 74-inch light curve: three during immersion and two during emersion. Occulting material is located between 242 and 270 km from the center of the nucleus in the sky plane. Assuming the ring-plane orientation proposed for Chiron from the 2011 occultation, the flux drops are located at 352, 344, and 316 km (immersion) and 357 and 364 km (emersion) from the center, with normal optical depths of 0.26, 0.36, and 0.22 (immersion) and 0.26 and 0.18 (emersion) and equivalent widths between 0.7 and 1.3 km. This detection is similar to the previously proposed two-ring system and is located within the error bars of that ring-pole plane; however, the normal optical depths are less than half of the previous values, and three features are detected on immersion. These results suggest that the properties of the surrounding material have evolved between the 2011, 2018, and 2022 observations.

Centaurs are minor solar system bodies with orbits transitioning between those of trans-Neptunian scattered disk objects and Jupiter-family comets (JFCs). 39P/Oterma (39P) is a frequently active centaur that has recently held both centaur and JFC classifications and was observed with the JWST NIRSpec instrument on 2022 July 27 UTC while it was 5.82 au from the Sun. For the first time, CO _2 gas emission was detected in a centaur, with a production rate of ${Q}_{{\mathrm{CO}}_{2}}$ = (5.96 ± 0.80) × 10 ^23 molecules s ^−1 . This is the lowest detection of CO _2 of any centaur or comet. CO and H _2 O were not detected down to constraining upper limits. Derived mixing ratios of Q _CO / Q ${}_{{\mathrm{CO}}_{2}}$ ≤ 2.03 and ${Q}_{{\mathrm{CO}}_{2}}$ / Q ${}_{{{\rm{H}}}_{2}{\rm{O}}}$ ≥ 0.60 are consistent with CO _2 and/or CO outgassing playing large roles in driving the activity, but not water, and show a significant difference between the coma abundances of 29P/Schwassmann–Wachmann 1, another centaur at a similar heliocentric distance, which may be explained by thermal processing of 39P’s surface during its previous JFC orbit. To help contextualize the JWST data we also acquired visible CCD imaging data on two dates in 2022 July (Gemini-North) and September (Lowell Discovery Telescope). Image analysis and photometry based on these data are consistent with a point-source detection and an estimated effective nucleus radius of 39P in the range of R _nuc = 2.21–2.49 km.

Considering the possibility that the outbursts of (2060) Chiron observed in 1972 and 2021 may be due to collisions from its interaction with a particle swarm, a search for the progenitor object of those particles allows to find that the centaur 2015 RD277 approaches within 0.25 AU of Chiron's orbit in the vicinity of the orbital region where the outbursts occur. No other objects approach the orbit of Chiron in the vicinity of its aphelion. Two hypotheses were proposed for the generation of the particle swarm, where the one produced by a previous collision on 2015 RD277 is suggested as the best solution. • (2060) Chiron activation by collisions. • Identification of the projectile swarm parent body. • Dynamical evolution of a swarm of particles. [ABSTRACT FROM AUTHOR]

In 2019, the Research and Education Collaborative Occultation Network (RECON) obtained multiple-chord occultation measurements of two Centaur objects: 2014 YY _49 on 2019 January 28 and 2013 NL _24 on 2019 September 4. RECON is a citizen-science telescope network designed to observe high-uncertainty occultations by outer solar system objects. Adopting circular models for the object profiles, we derive a radius $r={16}_{-1}^{+2}$ km and a geometric albedo ${p}_{V}={0.13}_{-0.024}^{+0.015}$ for 2014 YY _49 and a radius $r={66}_{-5}^{+5}$ km and a geometric albedo ${p}_{V}={0.045}_{-0.008}^{+0.006}$ for 2013 NL _24 . To the precision of these measurements, no atmosphere or rings are detected for either object. The two objects measured here are among the smallest distant objects measured with the stellar occultation technique. In addition to these geometric constraints, the occultation measurements provide astrometric constraints for these two Centaurs at a higher precision than has been feasible by direct imaging. To supplement the occultation results, we also present an analysis of color photometry from the Pan-STARRS surveys to constrain the rotational light curve amplitudes and spectral colors of these two Centaurs. We recommend that future work focus on photometry to more deliberately constrain the objects’ colors and light curve amplitudes and on follow-on occultation efforts informed by this astrometry.