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1. The debiased Near-Earth object population from ATLAS telescopes

   https://doi.org/10.1016/j.icarus.2024.116316  

   Deienno, Rogerio; Denneau, Larry; Nesvorný, David; Vokrouhlický, David; Bottke, William F; Jedicke, Robert; Naidu, Shantanu; Chesley, Steven R; Farnocchia, Davide; Chodas, Paul W (January 2025, Icarus)

   NA (Ed.)

   This work is dedicated to debias the Near-Earth Object (NEO) population based on observations from the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescopes. We have applied similar methods used to develop the recently released NEO model generator (NEOMOD), once debiasing the NEO population using data from Catalina Sky Survey (CSS) G96 telescope. ATLAS is composed of four different telescopes. We first analyzed observational data from each of all four telescopes separately and later combined them. Our results highlight main differences between CSS and ATLAS, e.g., sky coverage and survey power at debiasing the NEO population. ATLAS has a much larger sky coverage than CSS, allowing it to find bright NEOs that would be constantly ‘‘hiding’’ from CSS. Consequently, ATLAS is more powerful than CSS at debiasing the NEO population for H ≲ 19. With its intrinsically greater sensitivity and emphasis on observing near opposition, CSS excels in the debiasing of smaller objects. ATLAS, as an all sky survey designed to find imminent hazardous objects, necessarily spends a significant fraction of time looking at places on the sky where objects do not appear, reducing its power for debiasing the population of small objects. We estimate a NEO population completeness of ≈ 88%+3% −2% for H < 17.75 and ≈ 36%+1% −1% for H < 22.25. Those numbers are similar to previous estimates (within error bars for H < 17.75) from CSS, yet, around 3% and 8% smaller at their face values, respectively. We also confirm previous finding that the 𝜈6 secular resonance is the main source of small and faint NEOs at H = 28, whereas the 3:1 mean motion resonance with Jupiter dominates for larger and brighter NEOs at H = 15. 

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2. Strong Nongravitational Accelerations and the Potential for Misidentification of Near-Earth Objects

   https://doi.org/10.3847/1538-4357/ad85e3  

   Taylor, Aster G; Seligman, Darryl Z; Holman, Matthew J; Vereš, Peter; Farnocchia, Davide; Lewis, Nikole; Micheli, Marco; Wright, Jason T (November 2024, The Astrophysical Journal)

   Abstract Nongravitational accelerations in the absence of observed activity have recently been identified on near-Earth objects (NEOs), opening the question of the prevalence of anisotropic mass loss in the near-Earth environment. Motivated by the necessity of nongravitational accelerations to identify 2010 VL₆₅and 2021 UA₁₂as a single object, we investigate the problem of linking separate apparitions in the presence of nongravitational perturbations. We find that nongravitational accelerations on the order of 1 × 10^–9au day⁻²can lead to a change in plane-of-sky positions of ∼1 × 10³arcsec between apparitions. Moreover, we inject synthetic tracklets of hypothetical nongravitationally accelerating NEOs into the Minor Planet Center orbit identification algorithms. We find that at large nongravitational accelerations (∣A_i∣ ≥ 1 × 10⁻⁸au day⁻²) these algorithms fail to link a significant fraction of these tracklets. We further show that if orbits can be determined for both apparitions, the tracklets will be linked regardless of nongravitational accelerations, although they may be linked to multiple objects. In order to aid in the identification and linkage of nongravitationally accelerating objects, we propose and test a new methodology to search for unlinked pairs. When applied to the current census of NEOs, we recover the previously identified case but identify no new linkages. We conclude that current linking algorithms are generally robust to nongravitational accelerations, but objects with large nongravitational accelerations may potentially be missed. While current algorithms are well-positioned for the anticipated increase in the census population from future survey missions, it may be possible to find objects with large nongravitational accelerations hidden in isolated tracklet pairs. 

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3. r-Process Radioisotopes from Near-Earth Supernovae and Kilonovae

   https://doi.org/10.3847/1538-4357/ac2d90  

   Wang; Clark, Adam M.; Ellis, John; Ertel, Adrienne F.; Fields, Brian D.; Fry, Brian J.; Liu, Zhenghai; Miller, Jesse A.; Surman, Rebecca (December 2021, The Astrophysical Journal)

   Abstract The astrophysical sites where r -process elements are synthesized remain mysterious: it is clear that neutron star mergers (kilonovae (KNe)) contribute, and some classes of core-collapse supernovae (SNe) are also possible sources of at least the lighter r -process species. The discovery of 60 Fe on the Earth and Moon implies that one or more astrophysical explosions have occurred near the Earth within the last few million years, probably SNe. Intriguingly, 244 Pu has now been detected, mostly overlapping with 60 Fe pulses. However, the 244 Pu flux may extend to before 12 Myr ago, pointing to a different origin. Motivated by these observations and difficulties for r -process nucleosynthesis in SN models, we propose that ejecta from a KN enriched the giant molecular cloud that gave rise to the Local Bubble, where the Sun resides. Accelerator mass spectrometry (AMS) measurements of 244 Pu and searches for other live isotopes could probe the origins of the r -process and the history of the solar neighborhood, including triggers for mass extinctions, e.g., that at the end of the Devonian epoch, motivating the calculations of the abundances of live r -process radioisotopes produced in SNe and KNe that we present here. Given the presence of 244 Pu, other r -process species such as 93 Zr, 107 Pd, 129 I, 135 Cs, 182 Hf, 236 U, 237 Np, and 247 Cm should be present. Their abundances and well-resolved time histories could distinguish between the SN and KN scenarios, and we discuss prospects for their detection in deep-ocean deposits and the lunar regolith. We show that AMS 129 I measurements in Fe–Mn crusts already constrain a possible nearby KN scenario. 

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4. NEOMOD 3: The debiased size distribution of Near Earth Objects

   https://doi.org/10.1016/j.icarus.2024.116110  

   Nesvorný, David; Vokrouhlický, David; Shelly, Frank; Deienno, Rogerio; Bottke, William F; Fuls, Carson; Jedicke, Robert; Naidu, Shantanu; Chesley, Steven R; Chodas, Paul W; et al (July 2024, Icarus)

   NA (Ed.)

   Our previous model (NEOMOD2) for the orbital and absolute magnitude distribution of Near Earth Objects (NEOs) was calibrated on the Catalina Sky Survey observations between 2013 and 2022. Here we extend NEOMOD2 to include visible albedo information from the Wide-Field Infrared Survey Explorer. The debiased albedo distribution of NEOs can be approximated by the sum of two Rayleigh distributions with the scale parameters 𝑝V,dark ≃ 0.03 and 𝑝V,bright ≃ 0.17. We find evidence for smaller NEOs having (on average) higher albedos than larger NEOs; this is likely a consequence of the size-dependent sampling of different main belt sources. These inferences and the absolute magnitude distribution from NEOMOD2 are used to construct the debiased size distribution of NEOs. We estimate 830±60 NEOs with diameters 𝐷 > 1 km and 20,000±2,000 NEOs with 𝐷 > 140 m. The new model, NEOMOD3, is available via the NEOMOD Simulator — an easy-to-operate code that can be used to generate user-defined samples (orbits, sizes and albedos) from the model. 

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5. Near-term tropical cyclone risk and coupled Earth system model biases

   https://doi.org/10.1073/pnas.2209631120  

   Sobel, Adam H.; Lee, Chia-Ying; Bowen, Steven G.; Camargo, Suzana J.; Cane, Mark A.; Clement, Amy; Fosu, Boniface; Hart, Megan; Reed, Kevin A.; Seager, Richard; et al (August 2023, Proceedings of the National Academy of Sciences)

   Most current climate models predict that the equatorial Pacific will evolve under greenhouse gas–induced warming to a more El Niño-like state over the next several decades, with a reduced zonal sea surface temperature gradient and weakened atmospheric Walker circulation. Yet, observations over the last 50 y show the opposite trend, toward a more La Niña-like state. Recent research provides evidence that the discrepancy cannot be dismissed as due to internal variability but rather that the models are incorrectly simulating the equatorial Pacific response to greenhouse gas warming. This implies that projections of regional tropical cyclone activity may be incorrect as well, perhaps even in the direction of change, in ways that can be understood by analogy to historical El Niño and La Niña events: North Pacific tropical cyclone projections will be too active, North Atlantic ones not active enough, for example. Other perils, including severe convective storms and droughts, will also be projected erroneously. While it can be argued that these errors are transient, such that the models’ responses to greenhouse gases may be correct in equilibrium, the transient response is relevant for climate adaptation in the next several decades. Given the urgency of understanding regional patterns of climate risk in the near term, it would be desirable to develop projections that represent a broader range of possible future tropical Pacific warming scenarios—including some in which recent historical trends continue—even if such projections cannot currently be produced using existing coupled earth system models. 

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