BYU Physics and Astronomy

With the great success of stellar occultations in probing trans-Neptunian objects (TNOs), these observations have become ubiquitous, leading to significant advances in our knowledge of TNOs. As stellar occultation predictions have improved, it has become feasible to predict and observe stellar occultations by satellites of TNOs. In this work, we develop a robust methodology for predicting occultations by large TNO satellites based on the most up-to-date and accurate ephemerides available. We validated our methodology by reproducing several previously recorded occultations by Hi‘iaka, and then used it to predict—and successfully observe—stellar occultations of two other satellites, Namaka and Tinia. As a demonstration of the scientific return of such occultations, we provide the detailed prediction, observation, and analysis of the Tinia occultation. For the satellite of Uni (2002 UX25), we recorded two positive occultation chords that yielded projected circular and elliptical profiles with equivalent diameters of 180.8 ± 0.6 and 193.0 ± 1.0 km, respectively. Using the published absolute magnitude for the system and Tinia’s relative brightness with respect to the primary, we derived an absolute magnitude of HV = 6.476 ± 0.183 mag for Tinia. This corresponds to geometric albedo values of ρV = 0.139 ± 0.023 and ρV = 0.122 ± 0.02 for circular and elliptical solutions, respectively. Under the assumption of equal albedos, we obtained a diameter of D = 571 ± 53 km and D = 610 ± 53 km for the primary. Our methods provide a precise, simple, open-source technique for predicting TNO satellite occultations, enabling diverse investigations into the properties of TNOs and their satellites as demonstrated for Tinia.

The shapes and densities of midsized and large trans-Neptunian objects (TNOs) are pivotal for understanding a variety of important aspects of planet formation. In this work, we present a Bayesian shape modeling method that combines constraints from rotational light curves and satellite orbits to construct three-dimensional shape models of TNOs. We use it to reanalyze three stellar occultations of the TNOs (229762) G!kún∣∣’hòmdímà (2007 UK126), (136108) Haumea, and (174567) Varda. By assuming that their satellites (or rings) orbit in their respective equatorial planes, we are able to derive unique shape models for both G!kún∣∣’hòmdímà and Haumea. Our derived shape for G!kún∣∣’hòmdímà is spheroidal with  km and  km, with a system density  kg m−3. For Haumea, we find  km,  km, and  km, providing  kg m−3. For Varda, after updating its mutual orbit with its satellite Ilmarë, we find that currently published data are unable to fully constrain its three-dimensional shape. Intriguingly, Varda’s elongated limb appears to point toward its satellite at the time of the occultation. With a ∼2% chance of such an alignment happening randomly, this may be suggestive of a frozen-in tidal and/or rotational bulge. Our work emphasizes the importance of how external constraints can improve occultation analyses. With continued observations of rotational light curves, stellar occultations, and satellite orbits, these—and other—TNOs can have their shapes and densities further refined.

We present You Only Stack Once (YOSO), an automated pipeline designed to detect faint, slow-moving solar system objects in wide-field astronomical surveys. The pipeline integrates a novel Gaussian motion filter (GMoF) that operates at the pixel level to enhance the signal-to-noise ratio for objects exhibiting a range of apparent rates of motion. Unlike conventional shift-and-stack methods, which rely on discrete velocity trials, GMoF amplifies trails while suppressing random noise and static background features. Applied to a subset of DEEP observations from the Dark Energy Camera, YOSO discovered 45 out of 73 previously detected objects, as well as 11 new trans-Neptunian objects. It also discovered 216 objects in the near solar system. Although alternative shift-and-stack methods are sensitive to objects about 0.88 mag fainter, YOSO’s false-positive rate is extremely low, since it detects only sources that exhibit a trail and are consistent with a point source when shifted at the right rate. We show how this method can be deployed on large surveys like LSST, and be adapted for other domains that require motion-based signal enhancement, including exoplanet imaging through angular differential imaging and near-Earth object (NEO) detection for missions like the NEO Surveyor. YOSO thus provides a versatile, scalable approach for extracting faint, motion-dependent signals in the era of data-intensive astronomy.

The Small Body Dynamics Tool (SBDynT) is software written for the community of solar system small body researchers to perform dynamical classification, characterization, and investigation. SBDynT provides advanced simulation analysis capabilities that make it straightforward to determine mean-motion resonance occupation, proper orbital elements, and a variety of stability indicators. These calculations can be performed for small bodies that are known, newly discovered, or simulated; observational uncertainties can be incorporated through the use of dynamical clones. In this paper, we describe the methods for producing proper orbital elements and stability indicators, which serve as essential tools for characterizing dynamical stability and long-term evolution. Through extensive validation, we demonstrate that this code offers a robust open-source framework for investigating the dynamics of solar system small bodies with high accuracy. We also aim for computational efficiency allowing SBDynT to provide dynamical information for the several-fold increases in small bodies expected in the Legacy Survey of Space and Time era.

We report on the observation and measurement of astrometry, photometry, morphology, and activity of the interstellar object 3I/ATLAS, also designated C/2025 N1 (ATLAS) with the NSF-DOE Vera C. Rubin Observatory. Comet 3I/ATLAS, the third known interstellar object, was discovered on UT 2025 July 1. Rubin Observatory had coincidentally collected images of the object’s region of the sky during routine commissioning. Facilitated by Rubin’s high resolution and large aperture, we successfully recovered object detections from Rubin observations spanning UT 2025 June 21 (10 days before discovery, when 3I/ATLAS was 4.5 au from the Sun) through the date of discovery, and we acquired additional images through UT 2025 July 20 as part of commissioning. We measure on-sky locations of 3I/ATLAS in Rubin ugrizy bands, with a typical precision of ∼70 mas, and briefly describe the reason this is coarser than our measured static source astrometric precision of ∼3 mas in Rubin images. We measure grizy magnitudes of 3I/ATLAS photometry at ∼0.01 mag precision, detecting no short-term photometric variability above 0.01 mag. We derive an estimated near-nucleus dust-to-nucleus scattering cross-sectional ratio of η ≳ 13 on UT 2025 July 2 based on Rubin photometry and an upper limit nucleus size computed from Hubble Space Telescope observations. We find Rubin colors of g − r =  (0.657 ± 0.013) mag, r − i =  (0.235 ± 0.018) mag, i − z = (0.147 ±  0.042) mag, and z − y =  (0.047 ± 0.052) mag. These data represent the earliest observations of this object by a large (≳8 m class) telescope and illustrate the type of measurements (and discoveries) Rubin’s Legacy Survey of Space and Time will provide after it begins in early 2026.

Mutual events of trans-Neptunian binaries (TNBs) provide rare opportunities to measure the physical and orbital properties of small bodies in the outer solar system. However, successful observations of these events have been limited by uncertain predictions. Here, we present probabilistic predictions of TNB mutual events occurring through the 2030s, using high-precision non-Keplerian orbit solutions from the Beyond Point Masses project combined with a Bayesian framework that propagates orbital and size uncertainties. Our methods generate distributions of event timing, duration, depth, and probability of occurrence, enabling direct assessment of observability. We provide predictions for five systems with ongoing or imminent mutual event seasons, including (38628) Huya, (58534) Logos–Zoe, (148780) Altjira, (469705) ǂKá̧gára-!Hãunu, and (524366) 2001 XR254. Preparing for upcoming events with long-baseline light-curve monitoring is vital, as events may be difficult to distinguish from a regular rotational light curve. Rapid dissemination of event detections will benefit the entire community, allowing predictions to be updated, ensuring that these rare mutual event opportunities can be fully exploited.