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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.

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.

We present the Citizen Science program Active Asteroids and describe discoveries stemming from our ongoing project. Our NASA Partner program is hosted on the Zooniverse online platform and launched on 2021 August 31, with the goal of engaging the community in the search for active asteroids—asteroids with comet-like tails or comae. We also set out to identify other unusual active solar system objects, such as active Centaurs, active quasi-Hilda asteroids (QHAs), and Jupiter-family comets (JFCs). Active objects are rare in large part because they are difficult to identify, so we ask volunteers to assist us in searching for active bodies in our collection of millions of images of known minor planets. We produced these cutout images with our project pipeline that makes use of publicly available Dark Energy Camera data. Since the project launch, roughly 8300 volunteers have scrutinized some 430,000 images to great effect, which we describe in this work. In total, we have identified previously unknown activity on 15 asteroids, plus one Centaur, that were thought to be asteroidal (i.e., inactive). Of the asteroids, we classify four as active QHAs, seven as JFCs, and four as active asteroids, consisting of one main-belt comet (MBC) and three MBC candidates. We also include our findings concerning known active objects that our program facilitated, an unanticipated avenue of scientific discovery. These include discovering activity occurring during an orbital epoch for which objects were not known to be active, and the reclassification of objects based on our dynamical analyses.

We announce the discovery of cometary activity emitting from minor planet 2018 VL₁₀in Dark Energy Camera images spanning from UT 2018 December 31 to UT 2019 March 3. The activity was identified by volunteers of our NASA Partner programActive Asteroids, aZooniverse-hosted Citizen Science project designed to find previously unknown activity in known minor planets. Notably, 2018 VL₁₀crosses the orbits of Mars and Jupiter, and experiences close approaches of less than 0.5 au with both Earth and Jupiter. We classify 2018 VL₁₀as a member of the Jupiter-family comets, a group of objects especially important to understand because they hold important clues about the solar system volatile distribution, past and present.

We report our discovery of cometary activity in the form of a diffuse tail associated with minor planet 2008 QZ₄₄during two previous orbits: 2008 and 2017. This finding was prompted in part byActive Asteroids, ourZooniverse-hosted NASA Partner Citizen Science program. Participants flagged two UT 2017 July 12 Dark Energy Camera images of 2008 QZ₄₄as active. Independently, our team identified activity in nine Canada-France-Hawaii Telescope MegaPrime images from UT 2008 November 20. During both apparitions 2008 QZ₄₄was near its perihelion passage. 2008 QZ₄₄has a Tisserand parameter with respect to Jupiter of 2.821, placing it in the Jupiter-family comet (JFC) class, and our dynamical integrations confirm this classification. JFCs contain primordial material that informs us about solar system evolution, and help us map the present-day volatile distribution. We note that 2008 QZ₄₄has previously been classified as a quasi-Hilda comet candidate.

We have discovered evidence of cometary activity originating from (551023) 2012 UQ₁₉₂(alternately designated 2019 SN₄₀), which we dynamically classify as a Jupiter Family Comet (JFC). JFCs have eccentric Jupiter-crossing orbits and originate in the Kuiper Belt. Analysis of these objects can provide vital information about minor planets in the outer solar system, such as the distribution of volatiles within the solar system. Activity on 2012 UQ₁₉₂was first recognized by volunteers on our NASA Partner Citizen Science projectActive Asteroids. Through our own examination of archival image data, we found a total of ∼30 images presenting strong evidence of activity near perihelion during two separate orbits. 2012 UQ₁₉₂is notable as we found it to be recurrently active. When 2012 UQ₁₉₂approaches its perihelion passage in 2027 September, we predict it will reactivate and will be a prime subject for follow-up observations.

We report that minor planet 2004 CV₅₀displayed cometary activity in the form of a short, diffuse tail, first identified by volunteers of the Citizen Science programActive Asteroids, a NASA Partner program hosted on theZooniverseonline platform. The activity is present in three images, from UT 2020 February 15 and UT 2020 March 14, that were acquired with the Dark Energy Camera on the Blanco 4 m telescope at the Cerro-Tololo Inter-American Observatory in Chile. We find that 2004 CV₅₀is most likely an active quasi-Hilda object rather than an active asteroid, despite 2004 CV₅₀having a Tisserand parameter with respect to Jupiter of 3.06.

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.

We have discovered two epochs of activity on quasi-Hilda 2009 DQ₁₁₈. Small bodies that display comet-like activity, such as active asteroids and active quasi-Hildas, are important for understanding the distribution of water and other volatiles throughout the solar system. Through our NASA Partner Citizen Science project, Active Asteroids, volunteers classified archival images of 2009 DQ₁₁₈as displaying comet-like activity. By performing an in-depth archival image search, we found over 20 images from UT 2016 March 8–9 with clear signs of a comet-like tail. We then carried out follow-up observations of 2009 DQ₁₁₈using the 3.5 m Astrophysical Research Consortium Telescope at Apache Point Observatory, Sunspot, New Mexico, USA and the 6.5 m Magellan Baade Telescope at Las Campanas Observatory, Chile. These images revealed a second epoch of activity associated with the UT 2023 April 22 perihelion passage of 2009 DQ₁₁₈. We performed photometric analysis of the tail and find that it had a similar apparent length and surface brightness during both epochs. We also explored the orbital history and future of 2009 DQ₁₁₈through dynamical simulations. These simulations show that 2009 DQ₁₁₈is currently a quasi-Hilda and that it frequently experiences close encounters with Jupiter. We find that 2009 DQ₁₁₈is currently on the boundary between asteroidal and cometary orbits. Additionally, it has likely been a Jupiter family comet or Centaur for much of the past 10 kyr and will be in these same regions for the majority of the next 10 kyr. Since both detected epochs of activity occurred near perihelion, the observed activity is consistent with sublimation of volatile ices. 2009 DQ₁₁₈is currently observable until ∼mid-October 2023. Further observations would help to characterize the observed activity.

We present the discovery of cometary activity on 2018 OR as part of ourActive Asteroidsproject, a NASA Partner Program fueled byZooniverseCitizen Scientists. Volunteers found 2018 OR with a long, diffuse tail in archival images from the Dark Energy Camera on the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory in Chile. Our team identified additional Canada–France–Hawaii–Telescope MegaCam and Zwicky Transient Facility archival data after classification by Citizen Scientists. Activity originating from 2018 OR and directed in the anti-solar and anti-velocity directions was visible in archival images between UT 2018 September 5–18. Our dynamical simulations indicate 2018 OR experiences close encounters with Jupiter over hundred-year timescales. The orbital period and dynamics suggest 2018 OR is a Jupiter Family Comet, and we recommend further observations from the community to reduce observational uncertainties and investigate activity patterns.