Issue |
A&A
Volume 689, September 2024
|
|
---|---|---|
Article Number | A77 | |
Number of page(s) | 7 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361/202450634 | |
Published online | 04 September 2024 |
The chemical composition of CO-rich comet C/2023 H2 (Lemmon)
1
INAF – Osservatorio astrofisico di Arcetri,
Largo Enrico Fermi 5,
50125
Firenze,
Italy
e-mail: manuela.lippi@inaf.it
2
Institute for Astronomy, University of Edinburgh,
Royal Observatory,
Edinburgh
EH9 3HJ,
UK
3
NASA – Goddard Space Flight Center,
8800 Greenbelt Rd,
Greenbelt,
MD
20771,
USA
Received:
7
May
2024
Accepted:
25
June
2024
Aims. We report on the composition of comet C/2023 H2 (Lemmon) (hereafter C/2023 H2) as measured with CRIRES+ at VLT/ESO, under the Director Discretionary Time program: 2112.C-5015.
Methods. We observed C/2023 H2 between November 24 and 27, 2023, after perihelion and during its close approach to Earth. We used three settings sampling the spectral region from ≈2.5 to 5 µm, to search for fluorescence emission lines of H2O, HCN, C2H2, NH3, C2H6, H2CO, CH3OH, CH4, and CO.
Results. C/2023 H2 spectra are dominated by signatures from hyper-volatile species, namely CO, C2H6, and CH4, while it is particularly difficult to identify lines from less volatile species such as water or methanol. When compared to other comets, C/2023 H2 has an overall typical-to-enriched composition, with CO showing one of the highest infrared values reported so far in Solar System comets within 2 au from the Sun. In this respect, C/2023 H2 shares many similarities with C/2013 R1 (Lovejoy), C/2009 P1 (Garrad), and C/1999 T1 (McNaught-Hartley), although still being rather unique. Results from the analysis of optical spectra (≈300–650 nm) obtained on November 16, 2023, using the Intermediate Dispersion Spectrograph at the Isaac Newton Telescopes are consistent with the infrared ones.
Conclusions. Assuming that the composition of C/2023 H2 is original, this comet most likely formed in a region of the disc where CO was particularly enriched, or it could have been captured from other planetary systems forming in the Sun’s birth cluster. Similarities with a few other comets suggest the existence of a sub-class of CO-enriched comets, which may be currently under-sampled. Alternatively, water sublimation may have been ineffective due to the presence of a thick dust mantle covering the nucleus surface.
Key words: comets: general / Oort Cloud / comets: individual: C/2023 H2 (Lemmon)
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.