Theodore Kareta

Near-Earth asteroid (469219) Kamo‘oalewa is a uniquely stable quasi-satellite of the Earth and a target of the Tianwen-2 spacecraft mission. Here we report observations taken with JWST’s NIRSpec instrument in integral field unit (IFU) mode in 2026 February. The JWST reflectance spectrum is notably less red (more neutral) from 1.0 to 2.5 μ m than previous ground-based spectrophotometric observations. New observations made with the Large Binocular Telescope (LBT) in 2026 April, observed and processed similarly to the 2021 observations, find zJ colors in agreement with JWST. Kamo‘oalewa’s infrared colors appear more similar to typical silicate-rich asteroids and unlike the reddened, space-weathered lunar-like silicates suggested by previous observations. In agreement with the ground-based spectrum, we detect a faint silicate absorption feature at 0.93 ± 0.01 μ m. We do not detect a 2.0 μ m silicate absorption. Models of Kamo‘oalewa’s faint thermal emission (beginning near 4.5 μ m) find a mean diameter of D = 18 ± 2 m and best-fit visible albedo p V = 0.5 9 − 0.17 + 0.25 , with models as low as p _V = 0.36 providing adequate model fits. This combination of color, albedo, and absorption bands is similar to oldhamite-bearing enstatite-rich compositions. Kamo‘oalewa’s brightness variations over the course of the JWST program provide independent confirmation of its rotation period of 27.9 minutes, with an axis ratio ∼1.4 ( D ∼ 15−21 m).

We report on imaging, spectroscopy, and narrowband photometry of interstellar comet 2I/Borisov obtained at Lowell Observatory from 2019 September 13 to December 16. We measured chemical composition on 4 nights before perihelion, from October 4 to November 25 (2.466–2.028 au), with CN detections on all nights. Our measurements from October 27 represent the earliest reported detections of C ₂ and C ₃ , where C ₂ -to-CN and C ₃ -to-CN log production rate ratios were −0.7 and −1.3, respectively. Both ratios increased by nearly 4× to −0.3 and −0.9 by November 25, an extremely large increase with heliocentric distance that is unprecedented in the Lowell Observatory comet database. We additionally observed OH and NH on November 25, with a derived H ₂ O production rate of 4.5 × 10 ²⁶ mol s ⁻¹ and very high log production rate ratios for CN-to-OH (−2.0) and NH-to-OH (−1.7). Monitoring from broadband R images from September 13 to December 16 suggests dust ( A (0°) fρ ) production peaked around October 19, 50 days before its December 8 perihelion passage. Narrowband images from October 4 and 27 reveal a nearly symmetric CN distribution in Borisov’s coma, suggesting activity over its entire sunward hemisphere and possibly its entire nucleus. Our results, combined with those from others, reveal a chemical composition and behavior with heliocentric distance unlike any other comet we have observed.

Between 2019 and 2024, we used the Gemini-N and JWST observatories to conduct a detailed case study of the active Centaur 450P/LONEOS, whose orbit was significantly altered by a close Saturn encounter in 1992. Gemini-N Gemini Multi-Object Spectrograph optical images likely captured the first views of 450P’s inactive nucleus, indicating a relatively small radius of R _N = 1.8 ± 0.5 km and a surface color of g ′ − i ′ = 1.15 ± 0.09. This places 450P on the red end of the neutral/gray Centaur population and may indicate comparatively limited solar-driven surface processing relative to other known active Centaurs. A coma developed as 450P changed its heliocentric distance, R _H , from 7.83 to 7.24 au, with an estimated low dust production rate of ∼4–8 kg s ⁻¹ . JWST NIRSpec integral field unit prism-mode spectra revealed an elongated dust morphology and a symmetric CO ₂ gas distribution in the coma but no H ₂ O or CO emission features, with production rates of Q CO 2 = (6.99 ± 0.07) × 10 ²⁴ molecules s ⁻¹ , Q H 2O ≤ 1.2 × 10 ²⁴ molecules s ⁻¹ , and Q _CO ≤ 5.2 × 10 ²⁴ molecules s ⁻¹ . Absorption features at 2.0 and 3.0 μ m indicate the presence of water ice and a subtle 3.1 μ m feature, which is consistent with crystalline water ice in larger grains. A Hapke-style model dominated by large ( D _eff = 5.9 μ m) dust grains with a volumetric ice fraction of f _ice = 33% fits the spectrum. A thermal model incorporating 450P’s orbital history since ∼1500 CE aligns with the observed onset of activity driven by CO ₂ outgassing from amorphous water ice crystallization between 140 and 160 K.

As the Centaurs of the outer solar system have become better studied, their relationship with the Jupiter-family comets (JFCs) and their connection to the primordial protoplanetary disk have come under deeper scrutiny: which properties of the comets observed closer to the Sun are original, and which were modified significantly en route during their Centaur phase? The active Jupiter co-orbital comet P/2019 LD2 (ATLAS) attracted significant attention after its discovery when it was realized that the object would transition from a Centaur orbit to a JFC orbit in 2063, the first time this change will be able to be observed and monitored in real time. In this study, we present new ground-based and Hubble Space Telescope (HST) imaging of the single other Jupiter co-orbital comet, P/2023 V6 (PANSTARRS), throughout late 2024 and early 2025. V6 was not detected in ground-based imaging after early October, and deep imaging with HST taken in early December is consistent with an m _V = 28.06 ± 0.03 point source at its expected location. This implies both that the object ceased activity sometime in late 2024 and is thus in a different thermal state than LD2, despite both having large active fractions, and that V6’s diameter is D ∼ 340 m. This is likely the smallest object directly observed by HST beyond the main belt, and certainly the smallest Centaur yet discovered, highlighting the ability to detect active subkilometer objects beyond Jupiter with current surveys and potentially probing smaller sizes with the Legacy Survey of Space and Time.

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 spectro-photometric griz colors for 189 near-Earth objects (NEOs) collected by the Mission Accessible Near-Earth Object Survey (MANOS). Data acquisition involved nonsimultaneous multiband exposures; thus, particular attention was given to the influence of rotational lightcurves on the derived colors. We show that colors measured without accounting for lightcurve variations can significantly influence results for individual objects and potentially introduce systematic offsets for ensemble studies. Color-based taxonomic classifications were used to investigate the distribution of spectral types. Our results were combined with other visible wavelength surveys to highlight a previously reported change in the observed taxonomic distribution of NEOs as a function of size, namely a decrease in S complex and an increase in X complex objects with increasing absolute magnitude. Plausibility arguments are given to suggest that Main Belt source region, thermal modification, discovery bias, tidal resurfacing, regolith grain size, and impact shock darkening are unlikely explanations for this size-dependent trend. Consistent with recent NEO population models and work on the connection between meteorites and young asteroid families in the Main Belt, this trend is best explained by a compositional gradient in the NEO population. In particular, the observed abundance of S complex or ordinary chondrite-like NEOs decreases by a factor of 2, from ∼65% of the population at kilometer scales down to a third at sizes ≲50 m. This result has implications for understanding the initial pre-impact population of meteorite parent bodies prior to atmospheric filtering. Furthermore, this will have implications for probabilistic impact risk assessment models.

On 26th September 2022, NASA’s Double Asteroid Redirection Test (DART) mission actively impacted the small moon Dimorphos of the Didymos-Dimorphos binary asteroid system. The impact caused a variation of about 33 minutes in its orbital period around Didymos and demonstrated the feasibility of moving an asteroid in space. As part of an international observing campaign devoted to its physical characterization, in this work we investigate the visible spectral properties of the Didymos-Dimorphos system soon after the impact. Rotationally-resolved spectra have been obtained 25 days after the impact and two months later. Geometric investigations have been performed to look for the source region corresponding to each spectrum. Here we show an overall agreement with pre-impact spectra and S-type classification despite subtle variations emerging, possibly correlated with mutual events. Furthermore a small long term color evolution from October to December spectra tentatively interpreted as related to dust cloud grain size effects or alternatively attributed to an uneven deposition of freshly exposed material from the impact on Didymos.

Interstellar objects are comets and asteroids that formed around other stars but were ejected before they could accrete into exoplanets. They therefore represent a rare opportunity to compare the the building blocks of planets in the solar system to those in other stellar systems. The third interstellar object, 3I/ATLAS, is the newest, brightest, potentially largest, and fastest member of this population. We report observations of 3I/ATLAS taken on 2025 July 3 and 4 with the NASA Infrared Telescope Facility just days after its discovery. In r ′ -band imaging with ’Opihi, we see no obvious lightcurve variability and derive a g ′ − i ′ color of 0.98 ± 0.03, which is consistent in spectral slope to other near-discovery observations. We obtained the first near-infrared (NIR) reflectance spectrum of 3I/ATLAS with SpeX. The visible color and NIR spectrum show a linear, red visible slope, a somewhat less red slope between 0.7 and 1.1 μm, and a neutral or slightly blue slope at longer wavelengths. Challenges in modeling the reflectivity of 3I may indicate that this comet has a complex grain size distribution, grain compositions unlike solar system comets, or both. Like 2I/Borisov, there are no obvious signatures of water ice in the coma of 3I/ATLAS. Observations closer to perihelion will help elucidate whether 3I has less water than anticipated or whether the interstellar objects might retain and release their ices somewhat differently from solar system comets.