Jana Pittichová

We report observations of main-belt comet (MBC) 427P/ATLAS (previously designated P/2017 S5) using the Astrophysical Research Consortium’s Apache Point Observatory 3.5 m telescope, Palomar Observatory’s 5 m Hale Telescope, and the 4.3 m Lowell Discovery Telescope, on UT 2023 July 26, UT 2023 October 10, and UT 2023 December 8, respectively. These observations confirm for the first time that the comet exhibits recurrent near-perihelion activity, indicating that its activity is likely driven by the sublimation of volatile ice. These results validate a previous dust modeling analysis suggesting that its discovery apparition activity was likely due to sublimation. 427P is now the 15th MBC for which recurrent near-perihelion activity has been observationally confirmed.

We report results from an analysis of the volatile composition and evolution of the main-belt comet (MBC) 133P/Elst–Pizarro using JWST NIRSpec and NIRCam observations and ground-based observations during its 2024 active apparition, and also assess the body of JWST MBC observations acquired to date. Using NIRSpec, we measure water vapor outgassing rates at two points in 133P’s orbit, finding Q H 2 O = ( 1.9 ± 0.6 ) × 1 0 25 molecules s ⁻¹ on UT 2024 June 12 (at a true anomaly of ν = 8° and heliocentric distance of r _h = 2.674 au), and Q H 2 O = ( 1.4 ± 0.4 ) × 1 0 25 molecules s ⁻¹ on UT 2024 October 14 (at ν = 37 . ° 4 and r _h = 2.747 au). These measurements nominally represent a decline of ∼25% in Q H 2 O between the visits, although they are also consistent with no change within uncertainties. We do not detect CO, CO ₂ , or CH ₃ OH, placing 133P’s hypervolatile depletion ( Q CO 2 / Q H 2 O < 0.009 ) at a similar level found for previously observed MBCs. We find log ( A f ρ / Q H 2 O ) values for the three MBCs for which water vapor outgassing has been successfully detected that are consistent within uncertainties with an average value of log ( A f ρ / Q H 2 O ) = − 24.6 ± 0.2 . Lastly, we find no clear correlations of water production rates with nucleus size, semimajor axis, or heliocentric distance among MBCs observed by JWST so far, but would particularly encourage future JWST observations of additional MBCs interior to the 5A:2J mean-motion resonance with Jupiter and at high inclinations, as well as multiple observations of MBCs during single active apparitions to further investigate areas of interest identified from the current sample of JWST-observed MBCs.

We present JWST NIRSpec and NIRCam observations of 457P/Lemmon-PANSTARRS, a main-belt comet that displayed activity around its 2020 perihelion and that was observed to regain activity during its 2024 perihelion by a ground-based observing campaign. The previous successful measurements of water production from two main-belt comets by the JWST NIRSpec instrument confirmed the hypothesis that H ₂ O reservoirs are responsible for activity in dynamically stable main-belt comets. However, the main-belt comets observed with JWST thus far, 238P/Read and 358P/PANSTARRS, occupy orbits in the outer main belt, with main-belt comets with smaller semimajor axes not yet sensitively tested for H ₂ O. We find that, despite clearly displaying dust activity in both ground-based and JWST imaging over a broad period, there were no corresponding H ₂ O, CO, CO ₂ , or CH ₃ OH emissions within sensitive upper limits—notable given that 457P is the first main-belt comet with a semimajor axis within the 5:2 mean-motion resonance with Jupiter. We show that we were sensitive to production rates of gas predicted by the dust/gas ratios of 238P and 358P, and we hypothesize that 457P may be more depleted than its companions; Q _H2O must be less than 2 × 10 ²⁴ molecules s ⁻¹ , or 0.035 kg s ⁻¹ . Further surveying of main-belt comets across the parameter space of semimajor axis and eccentricity will shed light on whether 457P represents an edge member of a spectrum or a distinct subclass of main-belt comets.

We present the first results from the Cometary Object Study Investigating their Nature and Evolution (COSINE) project, based on a uniformly processed data set of 484 comets observed over the full 15 yr duration of the Wide-field Infrared Survey Explorer (WISE)/NEOWISE mission. This compilation includes 1633 coadded images spanning 966 epochs with signal-to-noise ratios greater than 4, representing the largest consistently analyzed infrared comet data set obtained from a single instrument. Dynamical classification identifies 234 long-period comets (LPCs) and 250 short-period comets (SPCs), spanning heliocentric distances of 0.996–10.804 au. LPCs are statistically brighter than SPCs in the W1 (3.4 μm) and W2 (4.6 μm) bands at comparable heliocentric distances. Cometary activity peaks near perihelion, with SPCs exhibiting a pronounced postperihelion asymmetry. Multiepoch photometry reveals that SPCs show steeper brightening and fading slopes than LPCs. The observing geometry of WISE/NEOWISE—constrained to a fixed ∼90° solar elongation from low-Earth orbit—introduces systematic biases in the sampling of orientation angles for extended features. Collectively, the results reveal a continuous evolutionary gradient across comet populations, likely driven by accumulated solar heating and surface processing. This study establishes a foundation for subsequent COSINE analyses, which will separate nucleus and coma contributions and model dust dynamics to further probe cometary activity and evolution.

We report the detection of water vapor associated with main-belt comet 358P/PANSTARRS on UT 2024 January 8–9 using the NIRSPEC instrument on board JWST. We derive a water production rate of Q H 2 O = ( 5.0 ± 0.2 ) × 10 25 molecules s⁻¹, marking only the second direct detection of sublimation products of any kind from a main-belt comet, after 238P/Read. Similar to 238P, we find a remarkable absence of hypervolatile species, finding Q CO 2 < 7.6 × 10 22 molecules s⁻¹, corresponding to Q CO 2 / Q H 2 O < 0.2 %. Upper limits on CH₃OH and CO emission are also estimated. Photometry from ground-based observations shows that the dust coma brightened and faded slowly over ∼250 days in 2023–2024, consistent with photometric behavior observed in 2012–2013, but also indicates a ∼2.5× decline in the dust production rate between these two periods. Dynamical dust modeling shows that the coma’s morphology as imaged by JWST's NIRCam instrument on 2023 November 22 can be reproduced by asymmetric dust emission from a nucleus with a midrange obliquity (ε ∼ 80°) with a steady-state mass-loss rate of ∼0.8 kg s⁻¹. Finally, we find similar Af ρ-to-gas ratios of log 10 ( Af ρ / Q H 2 O ) = − 24.8 ± 0.2 for 358P and log 10 ( Af ρ / Q H 2 O ) = − 24.4 ± 0.2 for 238P, suggesting that Af ρ could serve as an effective proxy for estimating water production rates in other active main-belt comets. The confirmation of water vapor outgassing in both main-belt comets observed by JWST to date reinforces the use of recurrent activity near perihelion as an indicator of sublimation-driven activity in active asteroids.

We report the detection of water vapor associated with main-belt comet 358P/PANSTARRS on UT 2024 January 8-9 using the NIRSPEC instrument aboard JWST. We derive a water production rate of Q(H2O)=(5.0+/-0.2)x10^25 molecules/s, marking only the second direct detection of sublimation products of any kind from a main-belt comet, after 238P/Read. Similar to 238P, we find a remarkable absence of hypervolatile species, finding Q(CO2)<7.6x10^22 molecules/s, corresponding to Q(CO2)/Q(H2O)<0.2%. Upper limits on CH3OH and CO emission are also estimated. Photometry from ground-based observations show that the dust coma brightened and faded slowly over ~250 days in 2023-2024, consistent with photometric behavior observed in 2012-2013, but also indicate a ~2.5x decline in the dust production rate between these two periods. Dynamical dust modeling shows that the coma's morphology as imaged by JWST's NIRCAM instrument on 2023 November 22 can be reproduced by asymmetric dust emission from a nucleus with a mid-range obliquity (~80 deg) with a steady-state mass loss rate of ~0.8 kg/s. Finally, we find similar Afrho-to-gas ratios of log10(Afrho/Q(H2O))=-24.8+/-0.2 for 358P and log10(Afrho/QH2O)=-24.4+/-0.2 for 238P, suggesting that Afrho could serve as an effective proxy for estimating water production rates in other active main-belt comets. The confirmation of water vapor outgassing in both main-belt comets observed by JWST to date reinforces the use of recurrent activity near perihelion as an indicator of sublimation-driven activity in active asteroids.

This study provides a pre-impact map of the albedo of the Double Asteroid Redirection Test (DART) target Dimorphos corrected for all the effects of viewing geometry, as well as an estimate of photometric roughness for the hemisphere imaged by DART. Other photometric properties are derived for the (65803) Didymos binary system based on DART and ground-based measurements obtained at JPL’s Table Mountain Observatory. The roughness, geometric albedo, phase curve and phase integral, and single particle phase function are typical of the S-family of asteroids. The major remaining uncertainty lies in the behavior of the phase curve below 7°. These results provide a baseline for comparison with Hera measurements, leading to an understanding of the quantitative effects of the kinetic impactor mitigation strategy.

Hyperactive comet activity typically becomes evident beyond the frost line (∼3–4 au) where it becomes too cold for water-ice to sublimate. If carbon monoxide (CO) and carbon dioxide (CO₂) are the species that drive activity at sufficiently large distances, then detailed studies on the production rates of these species are extremely valuable to examine the formation of the solar system because these two species (beyond water) are next culpable for driving cometary activity. The NEOWISE reactivated mission operates at two imaging bandpasses, W1 and W2 at 3.4 μm and 4.6 μm, respectively, with the W2 channel being fully capable of detecting CO and CO₂ at 4.67 μm and 4.23 μm in the same bandpass. It is extremely difficult to study CO₂ from the ground due to contamination in Earth’s atmosphere. We present our W1 and W2 photometry, dust measurements, and findings for comets C/2014 B1 (Schwartz), C/2017 K2 (Pan-STARRS), and C/2010 U3 (Boattini), hereafter, B1, K2, and U3, respectively. Our results assess CO and CO₂ gas production rates observed by NEOWISE. We have determined: (1) comets B1 and K2 have CO₂ and CO gas production rates of ∼10²⁷ and ∼10²⁹ molecules s⁻¹, respectively, if one assumes the excess emission is attributed to either all CO or all CO_2; (2) B1 and K2 are considered hyperactive in that their measured Af ρ dust production values are on the order of ≳10³ cm; and (3) the CO and CO₂ production rates do not always follow the expected convention of increasing with decreased heliocentric distance, while B1 and K2 exhibit noticeable dust activity on their inbound leg orbits.

Hyperactive comet activity typically becomes evident beyond the frost line (3 to 4 au) where it becomes too cold for water-ice to sublimate. If carbon monoxide (CO) and carbon dioxide (CO2) are the species that drive activity at sufficiently large distances, then detailed studies on the production rates of these species are extremely valuable to examine the formation of the solar system because these two species (beyond water) are next culpable for driving cometary activity. The NEOWISE reactivated mission operates at two imaging bandpasses, W1 and W2 at 3.4 and 4.6 microns, respectively, with the W2 channel being fully capable of detecting CO and CO2 at 4.67 and 4.23 microns in the same bandpass. It is extremely difficult to study CO2 from the ground due to contamination in Earth's atmosphere. We present our W1 and W2 photometry, dust measurements, and findings for comets C/2014 B1 (Schwartz), C/2017 K2 (Pan-STARRS), and C/2010 U3 (Boattini), hereafter, B1, K2, and U3, respectively. Our results assess CO and CO2 gas production rates observed by NEOWISE. We have determined: (1) comets B1 and K2 have CO2 and CO gas production rates of 1e27 and 1e29 molecules per second, respectively, if one assumes the excess emission is attributed to either all CO or all CO2; (2) B1 and K2 are considered hyperactive in that their measured AfRho dust production values are on the order of greater than or equal to 1e3 cm; and (3) the CO and CO2 production rates do not always follow the expected convention of increasing with decreased heliocentric distance, while B1 and K2 exhibit noticeable dust activity on their inbound leg orbits.

The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos’s orbit substantially, largely from the ejection of material. We present results from 12 Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ∼1.4 mag, we find consistent dimming rates of 0.11–0.12 mag day⁻¹ in the first week, and 0.08–0.09 mag day⁻¹ over the entire study period. The system returned to its pre-impact brightness 24.3–25.3 days after impact though the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role.