Spectroscopic identification of water emission from a main-belt comet

We present observations obtained with the Near Infrared Spectrograph on JWST of the five Jupiter Trojans that will be visited by the Lucy spacecraft—the Patroclus–Menoetius binary, Eurybates, Orus, Leucus, and Polymele. The measured 1.7–5.3 μm reflectance spectra, which provide increased wavelength coverage, spatial resolution, and signal-to-noise ratio over previous ground-based spectroscopy, reveal several distinct absorption features. We detect a broad OH band centered at 3 μm that is most prominent on the less-red objects Eurybates, Patroclus–Menoetius, and Polymele. An additional absorption feature at 3.3–3.6 μm, indicative of aliphatic organics, is systematically deeper on the red objects Orus and Leucus. The collisional fragment Eurybates is unique in displaying an absorption band at 4.25 μm that we attribute to bound or trapped CO2. Comparisons with other solar system small bodies reveal broad similarities in the 2.7–3.6 μm bands with analogous features on Centaurs, Kuiper Belt objects (KBOs), and the active asteroid 238P. In the context of recent solar system evolution models, which posit that the Trojans initially formed in the outer solar system, the significant attenuation of the 2.7–3.6 μm absorption features on Trojans relative to KBOs may be the result of secondary thermal processing of the Trojans’ surfaces at the higher temperatures of the Jupiter region. The CO2 band manifested on the surface of Eurybates suggests that CO2 may be a major constituent in the bulk composition of Trojans, but resides in the subsurface or deeper interior and is largely obscured by refractory material that formed from the thermophysical processes that were activated during their inward migration.

Section: μM Oh Bandmentioning

confidence: 74%

Section: μM Oh Bandmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

JWST Near-infrared Spectroscopy of the Lucy Jupiter Trojan Flyby Targets: Evidence for OH Absorption, Aliphatic Organics, and CO₂

Wong,

Brown,

Emery

et al. 2024

“…Furthermore, a multiwavelength campaign to observe all volatiles in all bandpasses depends not only on the brightness and productivity of comets but also on the availability of instruments capable of performing these types of measurements, which is quite challenging at heliocentric distances of more than 2 au. State-of-the-art observatories such as JWST, with high sensitivity, can detect emission features at larger heliocentric distances and for fainter targets (e.g., see Kelley et al 2023).…”

Section: Discussionmentioning

confidence: 99%

Parent Volatile Outgassing Associations in Cometary Nuclei: Synthesizing Rosetta Measurements and Ground-based Observations

Saki,

Bodewits,

Bonev

et al. 2024

Self Cite

Comets, as remnants of the solar system’s formation, vary in volatile-refractory content. In situ comet studies, such as the Rosetta mission to 67P/Churyumov–Gerasimenko, provide detailed volatile composition insights, while ground-based studies offer broader comet samples but in fewer species. Comparing 67P’s volatile correlations during the 2 yr Rosetta mission with those from remote sensing gives insights into volatile distribution in the nucleus and factors influencing their release. Our goal is to identify associations between volatiles seen from the ground and those in 67P. Given 67P’s seasonal variations, we segmented the Rosetta mission around 67P into six epochs, reflecting different insolation conditions. It has been suggested that there are at least two different ice matrices, H2O and CO2 ice, in which the minor species are embedded in different relative abundances within them. We employed various methodologies to establish associations among volatiles, such as volatile production rates, spatial distributions, patterns in mixing ratio, and local outgassing source locations. We note that different techniques of grouping molecules with respect to H2O and CO2 may yield different results. Earth’s atmosphere blocks CO2; however, due to observed differences between H2O and C2H6 from the ground and between H2O and CO2 from comet missions, C2H6 is suggested to be a CO2 proxy. Our study delves into cometary coma molecular correlations, highlighting their associations with H2O and CO2 matrices and advancing our understanding of the early solar system comet formation and evolution.

“…The D/H ratio of all comets spans a broad range from similar to Earth's water to multiple times higher, whereas the meteoritic record suggests that the D/H ratio of asteroids is more similar (Altwegg et al 2015). The "wet" asteroids in the outer main asteroid belt may be another potential candidate (Kelley et al 2023).…”

Section: Introductionmentioning

confidence: 99%

Postperihelion Cometary Activity on the Outer Main-belt Asteroid 2005 XR₁₃₂

Cheng 鄭,

Bolin,

Kelley

et al. 2024

Self Cite

We report comet-like activity on the outer main-belt asteroid 2005 XR132 discovered by the Lulin One-meter Telescope in early 2021 April. A series of follow-up observations were triggered to characterize the morphology and brightness variation of 2005 XR132. Long-term photometric data of the 2020 perihelion return reveal a 2 mag fading in 120 days, starting 20 days postperihelion, attributed to decreased cometary activity. Even though no variation indicative of the rotational period can be found in our data, we infer an a/b axial ratio of 1.32, given that the lower limit of rotational amplitude is 0.3 mag. A visible spectrum and broadband color support that 2005 XR132 has a reflectance feature similar to a BR-type Centaur object. The syndyne and synchrone simulations reveal a low-speed dust ejecta consisting of millimeter-sized dust grains released shortly after the perihelion passage. We demonstrate that 2005 XR132 has a short dynamical lifetime of 0.12 Myr, with <5% of it in the near-Earth space. Due to the strong gravitational influence from Jupiter and Saturn, the asteroid has followed a random walk orbital migrating process. We also find that since 1550 CE, the perihelion distance of 2005 XR132 has gradually decreased from 2.8 to 2.0 au, likely due to the Kozai–Lidov effect, which potentially reactivated the dormant nucleus. All these dynamical properties support a cometary origin for 2005 XR132 rather than an ice-rich main-belt object kicked out from a stable orbit, although current observational evidence has yet to confirm repeating cometary activities.