skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Volatile Abundances, Extended Coma Sources, and Nucleus Ice Associations in Comet C/2014 Q2 (Lovejoy)
Abstract High-resolution infrared spectra of comet C/2014 Q2 Lovejoy were acquired with NIRSPEC at the W. M. Keck Observatory on two post-perihelion dates (UT 2015 February 2 and 3). H 2 O was measured simultaneously with CO, CH 3 OH, H 2 CO, CH 4 , C 2 H 6 , C 2 H 4 , C 2 H 2 , HCN, and NH 3 on both dates, and rotational temperatures, production rates, relative abundances, H 2 O ortho-to-para ratios, and spatial distributions in the coma were determined. The first detection of C 2 H 4 in a comet from ground-based observations is reported. Abundances relative to H 2 O for all species were found to be in the typical range compared with values for other comets in the overall population to date. There is evidence of variability in rotational temperatures and production rates on timescales that are small compared with the rotational period of the comet. Spatial distributions of volatiles in the coma suggest complex outgassing behavior. CH 3 OH, HCN, C 2 H 6 , and CH 4 spatial distributions in the coma are consistent with direct release from associated ices in the nucleus and are peaked in a more sunward direction compared with co-measured dust. H 2 O spatial profiles are clearly distinct from these other four species, likely due to a sizable coma contribution from icy grain sublimation. Spatial distributions for C 2 H 2 , H 2 CO, and NH 3 suggest substantial contributions from extended coma sources, providing further evidence for distinct origins and associations for these species in comets. CO shows a different spatial distribution compared with other volatiles, consistent with jet activity from discrete nucleus ice sources.  more » « less
Award ID(s):
2009910 2009398
PAR ID:
10332689
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
The Planetary Science Journal
Volume:
3
Issue:
1
ISSN:
2632-3338
Page Range / eLocation ID:
6
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, The Astronomical Journal)
    Abstract We present a comprehensive analysis of the chemical composition of the Jupiter-family comet and potential spacecraft target 46P/Wirtanen, in the near-IR wavelength range. We used iSHELL at the NASA Infrared Telescope Facility to observe the comet on 11 pre-, near-, and postperihelion dates in 2018 December and 2019 January and February during its historic apparition. We report rotational temperatures, production rates, and mixing ratios with respect to H2O and C2H6or 3σupper limits of the primary volatiles H2O, HCN, CH4, C2H6, CH3OH, H2CO, NH3, CO, C2H2, and HC3N. We also discuss the spatial outgassing of the primary volatiles, to understand their sources and the spatial associations between them. The spatial profiles of H2O in 46P/Wirtanen suggest the presence of extended H2O outgassing sources in the coma, similar to the EPOXI target comet 103P/Hartley 2. 46P/Wirtanen is among the few known hyperactive comets, and we note that its composition and outgassing behavior are similar to those of other hyperactive comets in many ways. We note that the analyzed parent volatiles showed different variations (relative mixing ratios) during the apparition. We compared the chemical composition of 46P/Wirtanen with the mean abundances in Jupiter-family comets and the comet population as measured with ground-based near-IR facilities to date. The molecular abundances in 46P/Wirtanen suggest that although they were changing, the variations were small compared to the range in the comet population, with CH3OH showing notably more variation as compared to the other molecules. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, The Astronomical Journal)
    Abstract We report production rates of H2O and nine trace molecules (C2H6, CH4, H2CO, CH3OH, HCN, NH3, C2H2, OCS, and CO) in long-period comet C/2020 S3 (Erasmus) using the high-resolution, cross-dispersed infrared spectrograph (iSHELL) at the NASA Infrared Telescope Facility, on two pre-perihelion dates at heliocentric distancesRh= 0.49 and 0.52 au. Our molecular abundances with respect to simultaneously or contemporaneously measured H2O indicate that S3 is depleted in CH3OH compared to its mean abundance relative to H2O among the overall comet population (Oort Cloud comets and Jupiter-family comets combined), whereas the eight other measured species have near-average abundances relative to H2O. In addition, compared to comets observed atRh< 0.80 au at near-infrared wavelengths, S3 showed enhancement in the abundances of volatile species H2CO, NH3, and C2H2, indicating possible additional (distributed) sources in the coma for these volatile species. The spatial profiles of volatile species in S3 in different instrumental settings are dramatically different, which might suggest temporal variability in comet outgassing behavior between the nonsimultaneous measurements. The spatial distributions of simultaneously measured volatile species C2H6and CH4are nearly symmetric and closely track each other, while those of CO and HCN co-measured with H2O (using different instrument settings) are similar to each other and are asymmetric in the antisunward direction. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, The Astronomical Journal)
    Abstract High-resolution near-infrared ground-based spectroscopic observations of comet 67P/Churyumov–Gerasimenko near its maximum activity in 2021 were conducted from the W. M. Keck Observatory, using the facility spectrograph NIRSPEC. 67P is the best-studied comet to date because of the unprecedented detail and insights provided by the Rosetta mission during 2014–2016. Because 67P is the only comet where the detailed abundances of many coma volatiles were measured in situ, determining its composition from the ground provides a unique opportunity to interpret Rosetta results within the context of the large database of ground-based compositional measurements of comets. However, previous apparitions, including in 2015, have been unfavorable for in-depth ground-based studies of parent volatiles in 67P. The 2021 apparition of 67P was thus the first-ever opportunity for such observations. We report gas spatial distributions, rotational temperatures, production rates, and relative abundances (or stringent upper limits) among seven volatile species: C2H2, C2H6, HCN, NH3, CH3OH, H2CO, and H2O. The measured abundances of trace species relative to water reveal near average or below average values compared to previous comets studied at infrared wavelengths. Both gas rotational temperatures and the spatial distributions of H2O, C2H6, and HCN measured with Keck-NIRSPEC in 2021 are consistent with the outgassing patterns revealed by Rosetta in 2015 at very similar heliocentric distance  (post-perihelion). These results can be integrated with both Rosetta mission findings and ground-based cometary studies of the overall comet population, for which we encourage a wide-scale collaboration across measurement techniques. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal)
    Abstract Gas-phase molecules in cometary atmospheres (comae) originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) coma (photo)chemical processes. However, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so their production/release mechanisms remain uncertain. Here we present observations of six molecular species toward comet 46P/Wirtanen, obtained using the Atacama Large Millimeter/submillimeter Array during the comet’s unusually close (∼0.1 au) approach to Earth in 2018 December. Interferometric maps of HCN, CH3OH, CH3CN, H2CO, CS, and HNC were obtained at an unprecedented sky-projected spatial resolution of up to 25 km, enabling the nucleus and coma sources of these molecules to be accurately quantified. The HCN, CH3OH, and CH3CN spatial distributions are consistent with production by direct outgassing from (or very close to) the nucleus, with a significant proportion of the observed CH3OH originating from sublimation of icy grains in the near-nucleus coma (at a scale lengthLp= 36 ± 7 km). On the other hand, H2CO, CS, and HNC originate primarily from distributed coma sources (withLpvalues in the range 550–16,000 km), the identities of which remain to be established. The HCN, CH3OH, and HNC abundances in 46P are consistent with the average values previously observed in comets, whereas the H2CO, CH3CN, and CS abundances are relatively low. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Astronomy & Astrophysics)
    We present the results of a molecular survey of long period comets C/2021 A1 (Leonard) and C/2022 E3 (ZTF). Comet C/2021 A1 was observed with the Institut de radioastronomie millimétrique (IRAM) 30-m radio telescope in November-December 2021 before perihelion (heliocentric distance 1.22 to 0.76 au) when it was closest to the Earth (≈0.24 au). We observed C/2022 E3 in January-February 2023 with theOdin1-m space telescope and IRAM 30-m, shortly after its perihelion at 1.11 au from the Sun, and when it was closest to the Earth (≈0.30 au). Snapshots were obtained during 12–16 November 2021 period for comet C/2021 A1. Spectral surveys were undertaken over the 8–13 December 2021 period for comet C/2021 A1 (8 GHz bandwidth at 3 mm, 16 GHz at 2 mm, and 61 GHz in the 1 mm window) and over the 3–7 February 2023 period for comet C/2022 E3 (25 GHz at 2 mm and 61 GHz at 1 mm). We report detections of 14 molecular species (HCN, HNC, CH3CN, HNCO, NH2CHO, CH3OH, H2CO, HCOOH, CH3CHO, H2S, CS, OCS, C2H5OH and aGg’-(CH2OH)2) in both comets. In addition, HC3N, and CH2OHCHO were marginally detected in C/2021 A1, and CO and H2O (withOdin) were detected in C/2022 E3. The spatial distribution of several species (HCN, HNC, CS, H2CO, HNCO, HCOOH, NH2CHO, and CH3CHO) is investigated. Significant upper limits on the abundances of other molecules and isotopic ratios are also presented. The activity of comet C/2021 A1 did not vary significantly between 13 November and 13 December 2021, when observations stopped, just before it started to exhibit major outbursts seen in the visible and from observations of the OH radical. Short-term variability in the outgassing of comet C/2022 E3 of the order of ±20% is present and possibly linked to its 8h rotation period. Both comets exhibit rather low abundances relative to water for volatile species such as CO (<2%) and H2S (0.15%). Methanol is also rather depleted in comet C/2021 A1 (0.9%). Following their revised photo-destruction rates, HNCO and HCOOH abundances in comets observed at millimetre wavelengths have been reevaluated. Both molecules are relatively enriched in these two comets (~0.2% relative to water). Since the combined abundance of these two acids (0.1–1%) is close to that of ammonia in comets, we cannot exclude that these species could be produced by the dissociation of ammonium formate and ammonium cyanate if present in comets. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email