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Abstract We report the discovery of activity emanating from (18916) 2000 OG₄₄(alternately designated 1977 SD), a minor planet previously reported to be both an extinct comet and an asteroid on a cometary orbit. We observed 2000 OG₄₄with a thin tail oriented towards the coincident antisolar and antimotion vectors (as projected on the sky) in images we acquired on UT 2023 July 24 and 26 with the Apache Point Observatory 3.5 m Astrophysical Research Consortium telescope (New Mexico, USA). We also include observations made in Arizona with the Vatican Advanced Technology Telescope at the Mount Graham International Observatory and the Lowell Observatory Lowell Discovery Telescope near Happy Jack. We performed dynamical simulations that reveal 2000 OG₄₄most likely originated in the Oort cloud, arriving within the last 4 Myr. We find 2000 OG₄₄, which crosses the orbits of both Jupiter and Mars, is at present on an orbit consistent with a Jupiter-family comet. We carried out thermodynamical modeling that informed our broader diagnosis that the observed activity is most likely due to volatile sublimation. 

Abstract We report the discovery of recurrent activity on quasi-Hilda comet (QHC) 362P/(457175) 2008 GO₉₈. The first activity epoch was discovered during the perihelion passage of 362P in 2016, so we were motivated to observe it for recurrent cometary activity near its next perihelion passage (UT 2024 July 20). We obtained observations with the Lowell Discovery Telescope, the Astrophysical Research Consortium telescope, and the Vatican Advanced Technology Telescope and identified a second activity epoch when 362P had a true anomaly (ν) as early as 318 $\stackrel{\text{°}}{.}$1. We conducted archival searches of six repositories and identified images obtained with Canada–France–Hawaii Telescope MegaCam, Dark Energy Camera, Pan-STARRS 1, SkyMapper, Zwicky Transient Facility, and Las Cumbres Observatory Global Telescope network data. Using these data, we identified activity from a previously unreported time span, and we did not detect activity when 362P was away from perihelion, specifically 83^∘<ν< 318^∘. Detection of activity near perihelion and absence of activity away from perihelion suggest thermally driven activity and volatile sublimation. Our dynamical simulations suggest 362P is a QHC, and it will remain in a combined Jupiter-family comet (JFC) and quasi-Hilda orbit over the next 1 kyr though it will become increasingly chaotic nearing the end of this timeframe. Our reverse simulations suggest 362P may have migrated from the orbit of a long-period comet (∼53%) or Centaur (∼32%); otherwise it remained a JFC (∼15%) over the previous 100 kyr. We recommend additional telescope observations from the community as 362P continues outbound from its perihelion on UT 2024 July 20, as well as continued observations for a third activity epoch. 

Abstract The boundary of solar system object discovery lies in detecting its faintest members. However, their discovery in detection catalogs from imaging surveys is fundamentally limited by the practice of thresholding detections at signal-to-noise (SNR) ≥ 5 to maintain catalog purity. Faint moving objects can be recovered from survey images using the shift-and-stack algorithm, which coadds pixels from multi-epoch images along a candidate trajectory. Trajectories matching real objects accumulate signal coherently, enabling high-confidence detections of very faint moving objects. Applying shift-and-stack comes with high computational cost, which scales with target object velocity, typically limiting its use to searches for slow-moving objects in the outer solar system. This work introduces a modified shift-and-stack algorithm that trades sensitivity for speedup. Our algorithm stacks low-SNR detection catalogs instead of pixels, the sparsity of which enables approximations that reduce the number of stacks required. Our algorithm achieves real-world speedups of 10–10³× over image-based shift-and-stack while retaining the ability to find faint objects. We validate its performance by recovering synthetic inner and outer solar system objects injected into images from the DECam Ecliptic Exploration Project. Exploring the sensitivity–compute time trade-off of this algorithm, we find that our method achieves a speedup of ∼30× with 88% of the memory usage while sacrificing 0.25 mag in depth compared to image-based shift-and-stack. These speedups enable the broad application of shift-and-stack to large-scale imaging surveys and searches for faint inner solar system objects. We provide a reference implementation via thefind-asteroidsPython package and this URL:https://github.com/stevenstetzler/find-asteroids. 

Abstract We report the discovery of cometary activity in the form of a pronounced tail emanating from Near-Earth Object (523822) 2012 DG₆₁, identified in UT 2024 April 18 Dark Energy Camera images by our AI assistant TailNet. TailNet is an AI designed to filter out images unlikely to show activity for volunteers of our NASA Partner “Active Asteroids” Citizen Science campaign, from which our AI is trained. Subsequently, our archival investigation revealed 2012 DG61 is recurrently active after we found it displaying a pronounced tail in a UT 2018 April 16 Steward Observatory Bart Bok 2.3 m telescope image and UT 2018 May 14 observations by G. Borisov with the 0.3 m telescope at MARGO Observatory. Our dynamical integrations reveal that 2012 DG61, an Apollo dynamical class member, is likely in 2:1 mean-motion resonance with Jupiter. We encourage additional observations to help characterize the activity morphology of this near-Earth comet. 

Abstract We report the discovery of cometary activity from minor planet 2011 UG₁₀₄, which we classify as a Jupiter Family Comet (JFC). This discovery was aided by our Artificial Intelligence (AI) classification system:TailNet. JFC's, short-period comets with eccentric Jupiter-crossing orbits, originate from the Kuiper Belt and thus give us unique insight into the composition and distribution of volatiles in the outer solar system, past and present. Our AI assistantTailNetfirst classified 2011 UG₁₀₄as active, which was affirmed by Citizen Scientists on our NASA Partner ProgramActive Asteroids. Through further archival image searches our science team found evidence of activity on 2011 UG₁₀₄on three separate observations from 2021 February to 2021 April (81.°8 < f < 95.°0).  

Abstract We present the discovery of activity originating from quasi-Hilda Object 2018 CZ₁₆, a finding stemming from the Citizen Science projectActive Asteroids. For 2018 CZ₁₆we identified a broad (∼60°) but short (∼5″) tail in archival Blanco 4 m data from Cerro Tololo Inter-American Observatory, Chile, (CTIO) Dark Energy Camera images from UT 2018 May 15, 17 and 18. Activity occurred 2 months prior to perihelion, consistent with sublimation-driven activity. 

Abstract We report the discovery of an active asteroid, 2016 UU₁₂₁, for the first time via artificial intelligence-enhanced classification, informed by our NASA Partner programActive Asteroids, a Citizen Science project hosted on theZooniverseplatform. The early version of our deep neural network,TailNet, identified potential activity associated with 2016 UU₁₂₁in 40 Dark Energy Camera (DECam) images from UT 2021 September 10 to 11. The discovery was vetted and confirmed by ourActive Asteroidscore science team. In total, 66 DECam images of this object showed clear activity in the form of a tail. 2016 UU₁₂₁has a Tisserand parameter with respect to Jupiter of 3.161, thus we classify the object as an active asteroid. Moreover, the activity occurred near perihelion, so 2016 UU₁₂₁is also a candidate Main-belt comet. 

Abstract We report the discovery of cometary activity emanating from Main-belt asteroid 410590 (2008 GB₁₄₀), a finding facilitated, for the first time, by an artificial intelligence (AI) assistant. The assistant,TailNet, is a prototype we designed to enhance volunteer efforts of our Citizen Science projectActive Asteroids, a NASA Partner program hosted on theZooniverseplatform. Our follow-up investigation revealed eight Dark Energy Camera images showing 2008 GB₁₄₀with a tail spanning UT 2023 April 23–UT 2023 July 3, when the object was inbound to perihelion. We classify 2008 GB₁₄₀as an active asteroid and a candidate Main-belt comet (MBC)—a main-belt asteroid that undergoes volatile sublimation-driven activity. Notably, 2008 GB₁₄₀is presently near perihelion, thus the object is a prime target for follow-up observations to further characterize its activity. 

Abstract We announce the discovery of activity, in the form of a distinct cometary tail, emerging from main-belt asteroid 2015 VA₁₀₈. Activity was first identified by volunteers of the Citizen Science project Active Asteroids (a NASA Partner). We uncovered one additional image from the same observing run which also unambiguously shows 2015 VA₁₀₈with a tail oriented between the anti-solar and anti-motion vectors that are often correlated with activity orientation on sky. Both publicly available archival images were originally acquired UT 2015 October 11 with the Dark Energy Camera (DECam) on the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory (Chile) as part of the Dark Energy Camera Legacy Survey. Activity occurred near perihelion and, combined with its residence in the main asteroid belt, 2015 VA₁₀₈is a candidate main-belt comet, an active asteroid subset known for volatile sublimation. 

Abstract We present the discovery of activity emanating from main-belt asteroid 2015 FW₄₁₂, a finding stemming from the Citizen Science projectActive Asteroids, a NASA Partner program. We identified a pronounced tail originating from 2015 FW₄₁₂and oriented in the anti-motion direction in archival Blanco 4 m (Cerro Tololo Inter-American Observatory, Chile) Dark Energy Camera images from UT 2015 April 13, 18, 19, 21 and 22. Activity occurred near perihelion, consistent with the main-belt comets (MBCs), an active asteroid subset known for sublimation-driven activity in the main asteroid belt; thus 2015 FW₄₁₂is a candidate MBC. We did not detect activity on UT 2021 December 12 using the Inamori-Magellan Areal Camera and Spectrograph on the 6.5 m Baade telescope, when 2015 FW₄₁₂was near aphelion.