Richard Edmund Cannon

Contact binaries, appearing as two objects stuck together, are prevalent throughout the Solar system, making up between 30 per cent–50 per cent of asteroids and comets. Despite this, detailed shape models of contact binaries are hard to obtain remotely, requiring rare occultation events or close approaches to Earth ($\lt 0.1$ au) to observe with ground-based radar systems. Despite only 16 contact binary models being published, there already exists a wide variety of different arrangements of the two lobes relative to one another. At the same time, simulations of contact binary object formation are increasing in scale, producing 10 to 1000 s of contact binary candidates per simulation. It is therefore necessary to begin the process of characterizing the different shapes observed, and to further investigate any emerging trends. We analyse the size, period, neck prominence, volume distribution, ratio between the sizes and volumes of the individual lobes, and the alignment between them to summarize the extent of the currently modelled asteroids.

Context . Time-domain photometric monitoring is essential for characterizing cometary evolution, particularly for rare interstellar objects with limited observing opportunities. Aims . We aimed to characterize the pre-perihelion photometric behavior and dust activity of the interstellar comet 3I/ATLAS and to test the capability of the Black Hole Target and Observation Manager (BHTOM) platform and telescope network for coordinated high-cadence non-sidereal observations. Methods . We obtained 70 days of time-series photometry of 3I/ATLAS from 2025 July 4 to September 11 using 16 telescopes and 1554 images. The data were processed and calibrated with the BHTOM pipeline. High-cadence multiband imaging was used to measure the rotation period and color evolution, while the dust activity was quantified via Afρ measurements. Results . We present a pre-perihelion light curve of 3I/ATLAS from R _h = 3.18–2.19 au, which exhibited a steady brightening by ∼3 magnitudes with no evidence of anomalous behavior. We measured a rotation period of P _rot = 15.98 ± 0.08 h. The colors were statistically non-changing, with only a weak, non-significant tendency for 3I/ATLAS to become bluer at 3.5 > R _h > 2.2 au. The relative dust production increased from A (0°) fρ ∼600 to 1100 cm, and the upper limit on the dust mass-loss rate increased from ≤217 kg s ⁻¹ to ≤328 kg s ⁻¹ . We measured an activity index of n = −1.24 ± 0.02, which is consistent with a well-developed dust coma.

We report observations of main-belt comet (MBC) 433P/(248370) 2005 QN ₁₇₃ using Las Cumbres Observatory 1 m telescopes in Australia and South Africa, Faulkes Telescope North, Faulkes Telescope South, the Astrophysical Research Consortium 3.5 m telescope, the New Technology Telescope, the Lowell Discovery Telescope, and Rubin Observatory from UT 2026 March 25 to UT 2026 July 26, where visible comet-like activity was observed from UT 2026 June 10 onwards, marking the object’s third confirmed active apparition. When active in the observations reported here, the object displays a narrow tapered tail up to 20″ long aligned with the antisolar direction. These observations mark 433P’s third confirmed active apparition, reinforcing its identification as a MBC.

We report observations of main-belt comet (MBC) 259P/Garradd (2008 R1) using Faulkes Telescope South, Las Cumbres Observatory 1 m telescopes in South Africa and Australia, and the European Southern Observatory’s New Technology Telescope from UT 2026 July 10 to UT 2026 July 17 showing visible comet-like activity, marking its third confirmed active apparition. In all observations reported here, the object displays a relatively narrow fan-shaped tail approximately 30″ long aligned with the antisolar direction. These observations mark 259P’s third confirmed active apparition, solidifying its identification as a MBC. We measure an average apparent r ′ -band magnitude of m _r ∼ 19.5 mag over the reported observing period.

There is strong evidence of rubble-pile asteroids and comets being tidally disrupted by planets in our Solar System. First and foremost, the destruction of comet Shoemaker-Levy 9 was directly observed as it flew by Jupiter at a distance of 1.33 Jovian radii and was disrupted into 21 fragments due to the overwhelming tidal forces [1]. Second, observations form of crater chains on the moons of Jupiter that likely originate from impacts with fragments from a disruption event [2]. Third, population studies further indicate that tidal disruption of near-Earth objects (NEOs) by terrestrial planets would explain discrepancies between the observed and predicted NEO populations [3]. While analytical models can approximate the tidal distance at which a given rubble pile structurally fails [4], numerical simulations using discrete elements emphasise that the nature of granular mechanics introduces complex dynamical behaviour during the disruption process [5]. For example, computational rubble-pile models consisting of non-spherical elements with randomised packing have significantly higher internal strength [5,6]. In this work, we expand on this topic, showing that the choice of particle-size frequency distribution (SFD) also strongly affects the outcome of a given disruption event. Further, we find that tidal chains serve as efficient environments for the formation of contact binaries via low-velocity mergers, providing a complementary mechanism to mergers between fragments created in sub-catastrophic impacts [7].Figure 1: Tidal chains generated from tidal disruption of four different progenitors with identical hyperbolic orbits. The progenitors have irregular or spherical particles, and polydisperse or monodisperse SFDs. Each chain has been aligned with the inertial x-axis of the equatorial plane of the planet. Note the difference in scale, showing the variance in length. Each disruption simulation was modelled using the discrete element method N-body code GRAINS [8], which can use both spherical and irregularly shaped particles. We generated four progenitors with different configurations and let them undergo close encounters with Earth on hyperbolic orbits defined by the periapse distance, q, and the encounter velocity at infinite separation, v. While the resulting mass distributions of fragments are comparable for the four different progenitors when q < 1.7 planetary radii, R, there is a distinct variance further out. In Figure 1, we show the tidal chain 6.3 h after the periapsis passage when q = 1.8R and v = 2 km/s. It is evident that using irregularly shaped particles with a polydisperse SFD leads to a more confined and less continuous tidal chain, where the largest fragment is more massive compared to the other cases. Hence, the heterogeneous internal structure makes both the progenitor and its fragments more stable against disruption. The inherent mechanical strength of the rubble piles consisting of boulders of varying size also plays a role during mergers that occur between remnants in the tidal chain. Given that the individual fragments have velocities that only deviate slightly from the group velocity, there are many cases of bodies remaining gravitationally bound and merging. The same mechanism without a collision can also produce highly eccentric binary systems [9]. We find that more than 150 mergers between fragments across 36 simulations with a mass ratio of at least 0.1 all occur in the sub-escape-velocity regime. The combination of a low impact velocity and significant internal strength allows both the target and impactor to retain their initial shape and create distinct bilobate features in many cases [10]. We show two examples of bilobate objects formed in a tidal chain that remain structurally stable by the end of the simulation in Figure 2.Figure 2: Two bilobate objects formed in a tidal chain from a disruption event. The colours of a given particle indicate if it originates from the target (blue), the impactor (orange) or from other sources (green).The number of known bilobate objects in the NEO population is steadily growing, from both radar observations [e.g. 11] and in-situ imaging [12], highlighting that contact binaries are common in the Solar System. One such object with a seemingly bilobate shape is Apophis [13], which will approach the Earth within a distance of 32,000 km in 2029. It is likely that Apophis has undergone previous close encounters with Earth [14], which means tidal disruption provides a solid explanation for its unusual shape. Upcoming missions such as RAMSES [15] that will visit Apophis during its fly-by will be an excellent opportunity to better constrain its shape and bulk density, providing further insights into its origin. J.W. and F.F. acknowledge funding from the Swiss National Science Foundation (SNSF) Ambizione grant No. 193346. M.J. acknowledges support from SNSF project No. 200021_207359. References1. Sekanina et al. (1994), Astronomy & Astrophysics, 289, 607-636.2. Schenk et al. (1996), Icarus, 121, 249-274.3. Granvik & Walsh (2024), The Astrophysical Journal Letters, 960, L9.4. Holsapple & Michel (2006), Icarus, 183, 331-348.5. Movshovitz et al. (2012), The Astrophysical Journal, 759, 93-104.6. Zhang & Michel (2020), Astronomy & Astrophysics, 640, A102.7. Jutzi & Asphaug (2015). Science, 348, 1355-1358.8. Ferrari et al. (2020), MNRAS, 492, 749-761.9. Walsh & Richardson (2006), Icarus, 180, 201-216.10. Wimarsson et al. (2025), Astronomy & Astrophysics, 704, A29.11. Cannon et al. (2026). MNRAS, 548, stag543.12. Demura et al. (2006). Science, 312, 1347-1349.13. Brozović et al. (2018). Icarus, 300, 115–128.14. Brož et al. (2026). Astronomy & Astrophysics, 708, A162.15. Lazzarin et al. (2025). EPSC-DPS 2025, 806.

We report results from an analysis of the volatile composition and evolution of the main-belt comet (MBC) 133P/Elst–Pizarro using JWST NIRSpec and NIRCam observations and ground-based observations during its 2024 active apparition, and also assess the body of JWST MBC observations acquired to date. Using NIRSpec, we measure water vapor outgassing rates at two points in 133P’s orbit, finding Q H 2 O = ( 1.9 ± 0.6 ) × 1 0 25 molecules s ⁻¹ on UT 2024 June 12 (at a true anomaly of ν = 8° and heliocentric distance of r _h = 2.674 au), and Q H 2 O = ( 1.4 ± 0.4 ) × 1 0 25 molecules s ⁻¹ on UT 2024 October 14 (at ν = 37 . ° 4 and r _h = 2.747 au). These measurements nominally represent a decline of ∼25% in Q H 2 O between the visits, although they are also consistent with no change within uncertainties. We do not detect CO, CO ₂ , or CH ₃ OH, placing 133P’s hypervolatile depletion ( Q CO 2 / Q H 2 O < 0.009 ) at a similar level found for previously observed MBCs. We find log ( A f ρ / Q H 2 O ) values for the three MBCs for which water vapor outgassing has been successfully detected that are consistent within uncertainties with an average value of log ( A f ρ / Q H 2 O ) = − 24.6 ± 0.2 . Lastly, we find no clear correlations of water production rates with nucleus size, semimajor axis, or heliocentric distance among MBCs observed by JWST so far, but would particularly encourage future JWST observations of additional MBCs interior to the 5A:2J mean-motion resonance with Jupiter and at high inclinations, as well as multiple observations of MBCs during single active apparitions to further investigate areas of interest identified from the current sample of JWST-observed MBCs.

We present JWST NIRSpec and NIRCam observations of 457P/Lemmon-PANSTARRS, a main-belt comet that displayed activity around its 2020 perihelion and that was observed to regain activity during its 2024 perihelion by a ground-based observing campaign. The previous successful measurements of water production from two main-belt comets by the JWST NIRSpec instrument confirmed the hypothesis that H ₂ O reservoirs are responsible for activity in dynamically stable main-belt comets. However, the main-belt comets observed with JWST thus far, 238P/Read and 358P/PANSTARRS, occupy orbits in the outer main belt, with main-belt comets with smaller semimajor axes not yet sensitively tested for H ₂ O. We find that, despite clearly displaying dust activity in both ground-based and JWST imaging over a broad period, there were no corresponding H ₂ O, CO, CO ₂ , or CH ₃ OH emissions within sensitive upper limits—notable given that 457P is the first main-belt comet with a semimajor axis within the 5:2 mean-motion resonance with Jupiter. We show that we were sensitive to production rates of gas predicted by the dust/gas ratios of 238P and 358P, and we hypothesize that 457P may be more depleted than its companions; Q _H2O must be less than 2 × 10 ²⁴ molecules s ⁻¹ , or 0.035 kg s ⁻¹ . Further surveying of main-belt comets across the parameter space of semimajor axis and eccentricity will shed light on whether 457P represents an edge member of a spectrum or a distinct subclass of main-belt comets.

Context . With over 6000 exoplanets discovered to date, approximately 12 % are classified as hot-Jupiters. Due to their large sizes and short orbital periods ( P < 10 day), they are easier to detect and provide crucial insights into planetary formation, atmospheric properties, and orbital dynamics. Among these, ultra-short-period exoplanets ( P ≤ 1 d) are particularly interesting, as they are expected to undergo orbital decay driven by strong tidal interactions. Despite theoretical predictions, WASP-12 b and WASP-4 b remain the confirmed hot-Jupiters experiencing measurable orbital decay. Aims . This study presents a homogeneous analysis of WASP-19 b to investigate both its orbital dynamics and atmospheric composition. Leveraging a 15-year dataset, our goal is to assess whether the system exhibits long-term deviations from a constant orbital period and to investigate whether any detected variations are consistent with tidal orbital decay, apsidal precession, or periodic signals indicative of a potential planetary perturber. Additionally, we also construct a photometric transmission spectrum to characterize its atmosphere. Methods . We analyze multi-wavelength light curves, incorporating starspot modeling with PRISM to account for stellar inhomogeneities. To assess orbital evolution, we fit linear, quadratic, and cubic ephemeris models to transit timing residuals with respect to a non-decaying orbit. Results . Our analysis, which includes 27 new transits, reveals no statistically significant periodic signal in the transit timings. Although none of the tested ephemeris models fully reproduce the observed timing scatter, the mid-transit times exhibit systematic deviations from a strictly constant orbital period and are best reproduced by the cubic ephemeris in a relative model-comparison sense, indicating a slow, non-periodic long-term trend over the ~ 15-year baseline. This behavior is more consistent with gradual orbital precession than with monotonic tidal decay, for which a dominant quadratic trend would be expected. Fitting a precession model yields a rate of ω̇ _obs = (1.00 ± 0.12) × 10 ⁻⁴ rad/orbit, corresponding to a planetary Love number k _{2 p} = 0.107 ± 0.08, in agreement with recent independent estimates. The transmission spectrum reveals signatures of Na, K, and H ₂ O, with no strong evidence of TiO/VO, likely due to the resolution limits of the photometric data. Conclusions . Our results support that apsidal precession could be the dominant process governing the long-term orbital evolution of WASP-19b, possibly sustained by weak eccentricity forcing from the wide companion WASP-19 B. These orbital dynamics can, in turn, impact the atmospheric structure by modulating the irradiation history, potentially altering molecular abundances over time. Our findings highlight the importance of combining TTV analyzes with multi-wavelength atmospheric data, while emphasizing that additional high-quality timing and spectroscopic observations are required to corroborate the fidelity of the proposed orbital model.

Near-Earth asteroid (275677) 2000 RS₁₁ was observed over 5 days in March 2014 with both the Arecibo (2380 MHz, 12.6 cm) and Goldstone (8560 MHz, 3.5 cm) planetary radar systems. The continuous-wave spectra and delay-Doppler images collected revealed a sub-km-sized object with a strongly bifurcated shape. We used these radar observations, in combination with 7 optical lightcurves collected in 2014 and one lightcurve from 2023, to create a comprehensive shape and spin-state model for RS₁₁. We find a rotation period of P = (4.445 ± 0.001) hours around a pole of λ = (225 ± 80)^○ and β = ( − 80 ± 9)^○ relative to the plane of the ecliptic. The shape of RS₁₁ is unusual in that it does not resemble many of the other near-Earth asteroids modelled with ground-based radar. Whilst RS₁₁ consists of a largely spherical, smaller lobe attached to an elongated, larger lobe via a narrow neck, the smaller lobe is not aligned with the long axis of the larger lobe, but is closer to the larger lobe’s shortest principal axis. In combination with a large concavity observed on the outer face of the larger lobe, this may point to an unusual formation or event in the object’s past. We estimate that RS₁₁ has an geometric albedo of p_v = (0.16 ± 0.06) and a radar albedo 0.08 < η_OC < 0.16. Analysis of its gravitational environment reveals that for standard S-type asteroid densities, we would not expect rotational instability and it is possible for RS₁₁ to be a low tensile strength rubble-pile asteroid.

In this work, we present a transit timing variation analysis for 20 hot Jupiter systems, which we interpret with theoretical tidal dissipation models. For the majority of the sample, we conclude that a constant orbital period model represents the timing data best. Only WASP-12 b, TrES-1 b and WASP-121 b exhibit a changing orbital period, according to the most up-to-date results. We updated the orbital decay rate of WASP-12 b to P ̇ = − 29.4 ± 4.0 ms yr − 1 and the corresponding stellar tidal quality factor to Q ∗ ′ = 1.72 ± 0.18 × 1 0 5 . For TrES-1 b, the median quadratic model suggests a period decrease at a rate of −14.9 ± 0.6 ms yr ⁻¹ , but the corresponding Q ∗ ′ = 570 ± 60 does not agree with the theoretical estimates, which suggest Q ∗ ′ ∼ 1 0 6 due to internal gravity wave dissipation. Lastly, WASP-121 b exhibits orbital growth at a rate of 15.1 ± 0.8 ms yr ⁻¹ , and theoretical results support outward migration due to strong inertial wave dissipation.