Related Experiment Video
Updated: Jul 17, 2026
11:34
Scattering And Absorption of Light in Planetary Regoliths
Published on: July 1, 2019
Chemical processing in the coma as the source of cometary HNC
W M Irvine1, E A Bergin, J E Dickens
1Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA. irvine@fcrao1.phast.umass.edu
Nature
|June 20, 1998
Summary
Hydrogen isocyanide (HNC) in comets likely forms via chemical reactions in the coma, not from preserved interstellar material. This finding impacts how we interpret cometary composition and early Solar System conditions.
Area of Science:
- Astrochemistry
- Cometary Science
- Planetary Science
Background:
- Discovery of hydrogen isocyanide (HNC) in comet Hyakutake, with abundance similar to interstellar clouds, suggested it might be surviving interstellar material.
- Preserved interstellar material in comets could constrain early Solar System processes.
- Alternatively, HNC could be photochemically produced in the coma, limiting its use as a direct indicator of early Solar System conditions.
Purpose of the Study:
- To investigate the origin of HNC in comets.
- To determine if HNC represents preserved interstellar material or is produced in the cometary coma.
- To assess the implications for understanding early Solar System composition.
Main Methods:
- Analysis of the HNC/HCN ratio in comet Hale-Bopp.
- Comparison of observed HNC/HCN ratios with predictions from chemical models.
- Distinguishing between cometary nucleus origin versus in-situ coma production.
Main Results:
- The HNC/HCN ratio in comet Hale-Bopp showed a variation with heliocentric distance.
- This observed variation aligns with models of gas-phase chemical production of HNC within the coma.
- The data does not support HNC originating directly from the comet's nucleus.
Conclusions:
- HNC is primarily formed through chemical reactions occurring within the cometary coma.
- Photochemical processes in the coma are the dominant source of observed HNC.
- Cometary HNC abundance should not be directly interpreted as preserved interstellar material; cometary chemistry must be considered.
Related Concept Videos
01:04¹³C NMR: ¹H–¹³C Decoupling
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
01:16Precipitate Formation and Particle Size Control
In precipitation gravimetry, the precipitating agent should react specifically or selectively with the analyte. While a specific reagent reacts with the analyte alone, a selective reagent can react with a limited number of chemical species.
The obtained precipitate should be either a pure substance of known composition or easily converted to one by a simple process, such as ignition or drying. In addition, the precipitate should be insoluble and easily filterable. In general, filterability...
The obtained precipitate should be either a pure substance of known composition or easily converted to one by a simple process, such as ignition or drying. In addition, the precipitate should be insoluble and easily filterable. In general, filterability...
01:09Colloidal precipitates
The high insolubility of some precipitates can result in an unfavorable relative supersaturation. This can lead to colloidal particles with a large surface-to-mass ratio, where adsorption is promoted. For instance, in the precipitation of silver chloride, silver ions are adsorbed on the surface of the colloidal particles, forming a primary layer. This layer attracts ions of opposite charge (such as nitrate ions), forming a diffuse secondary layer of adsorbed ions. This electric double layer...
01:19Inductively Coupled Plasma–Mass Spectrometry (ICP–MS): Overview
In inductively coupled plasma–mass spectrometry (ICP–MS), an inductively coupled plasma (ICP) torch is used as an atomizer and ionizer. Solid samples are dissolved and volatilized before being introduced into the high-temperature argon plasma, while solution samples are nebulized and passed through the high-temperature argon plasma. Plasma dissociates the analytes and ionizes their component atoms to form a mixture of positive ions and molecular species. The positive ions are then passed on to...
00:49Gravimetry: Inorganic And Organic Precipitating Agents
In gravimetry, the precipitant is chosen carefully to obtain a pure solid that can be easily filtered. Common inorganic precipitants can be used to determine several cations and anions. In some cases, the formation of the same precipitate can be used to determine the cation and the anion. For example, the reaction of barium and chromate ions to give barium chromate is used to determine both barium and chromate. However, precipitates such as hydroxides, oxalates, and metal ammonium phosphates...
01:182D NMR: Overview of Heteronuclear Correlation Techniques
Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds' structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other axis.