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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 29P/Schwassmann–Wachmann 1 (SW1) is both the first-discovered active Centaur and the most outburst-prone comet known. The nature of SW1’s many outbursts, which regularly brighten the comet by 5 mag or more, and what processes power them has been of particular interest since SW1’s discovery in the 1920s. In this paper, we present and model four epochs of low-resolution near-infrared spectroscopy of SW1 taken with the NASA Infrared Telescope Facility and Lowell Discovery Telescope between 2017 and 2022. This data set includes one large outburst, two periods of low activity (“quiescence” or “quiescent activity”), and one midsized outburst a few days after one of the quiescent observations. The two quiescent epochs appear similar in both spectral slope and modeled grain size distributions, but the two outbursts are significantly different. We propose that the two can be reconciled if smaller dust grains are accelerated more than larger ones, such that observations closer to the onset of an outburst are more sensitive to the finer-grained dust on the outside of the expanding cloud of material. These outbursts can thus appear very rapid, but there is still a period where the dust and gas are well coupled. We find no strong evidence of water-ice absorption features in any of our spectra, suggesting that the areal abundance of ice-dominated grains is less than 1%. We conclude with a discussion of future modeling and monitoring efforts that might be able to further advance our understanding of this object’s complicated activity patterns. 

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 The UKIRT Hemisphere Survey covers the northern sky in the infrared from 0° to 60° decl. Current data releases include bothJandKbands, withH-band data forthcoming. Here, we present a novel pipeline to recover asteroids from this survey data. We recover 26,138 reliable observations, corresponding to 23,399 unique asteroids, from these public data. We measureJ–Kcolors for 601 asteroids. Our survey extends about 2 mag deeper than the Two-Micron All-Sky Survey. We find that our small inner main belt objects are less red than larger inner belt objects, perhaps because smaller asteroids are collisionally younger, with surfaces that have been less affected by space weathering. In the middle and outer main belts, we find our small asteroids to be redder than larger objects in their same orbits, possibly due to observational bias or a disproportionate population of very red objects among these smaller asteroids. Future work on this project includes extracting moving object measurements fromH-andY-band data when it becomes available. 

Abstract We present the discovery of a short, diffuse tail on minor planet 2010 MK₄₃(alternate designation 2010 RA₇₈)—an object previously identified as an asteroid in a cometary orbit—by volunteers of our Citizen Science programActive Asteroids. Our follow-up investigation revealed eight Dark Energy Camera images showing 2010 MK₄₃with a tail spanning UT 2024 February 12–UT 2024 February 18 when the object was outbound from perihelion. We now classify 2010 MK₄₃as a Jupiter-family comet based on its Tisserand parameter with respect to JupiterT_J = 2.888, though our dynamical simulations reveal that, due to frequent close encounters with Jupiter, 2010 MK₄₃was likely a quasi-Hilda within the last 10 kyr. 

Abstract We report the discovery of cometary activity emanating from minor planet 2015 VP₅₁outbound from its recent perihelion passage. The activity, in the form of a diffuse tail, was first identified by volunteers of our Citizen Science programActive Asteroids, a NASA Partner program hosted on theZooniverseplatform. This discovery was aided by the recently implementedTailNetartificial intelligence assistant which filters out images with a low likelihood of showing cometary activity. The tail is present in nine images of 2015 VP₅₁from the Dark Energy Camera and OmegaCAM between UT 2015 August 2 and UT 2015 October 18. We classify 2015 VP₅₁as a Jupiter-family comet based on its Tisserand parameter with respect to JupiterT_J = 2.931. 

Abstract Grain sizes of Martian sand dunes are critical sedimentological data on sand provenance and transport pathways. Thermal inertia values are used to characterize the grain sizes of dune sand. Most early characterizations involved single dune fields. Recent work based on global data sets has provided more wide‐spread dune sand locations, though these data sets include the non‐sandy interdune areas. To provide a more accurate grain size characterization, we leverage a global thermal inertia data set, a global dune database and a global imaging mosaic to develop a freeware‐based methodology for deriving grain sizes. This methodology involves delineation of sand‐only areas within dune fields and collection of thermal inertia values from those areas. We consider a unimodal histogram of values with a mode <∼350 thermal inertia units (J m⁻² K⁻¹ s^−1/2) to imply an effective exclusion of non‐sand surfaces. Application of this methodology to dune fields for which thermal inertia values have been previous derived shows our results fall within the envelope of those values. We apply our methodology to tropical dune fields on Mars for which Dust Cover Index data imply dust‐free surfaces. Conversion of these thermal inertia values to sand grain sizes yields a range of sand classifications of fine sand to granules. Comparison of sand size classifications with geographic location shows grain size ranges that are distinctive by location, consistent with local sourcing. This work points toward geographically diverse sand formation mechanisms yielding diverse grain sizes, while providing a freeware‐based and thus widely accessible method for expanding the derivation of these critical data. 

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 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.