Precursors of fatty alcohols in the ISM: Discovery of n-propanol

¹ Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir km 4, 28806 Torrejón de Ardoz, Spain
e-mail: ijimenez@cab.inta-csic.es
² INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Florence, Italy
³ Dipartimento di Chimica “Giacomo Ciamician”, Universitá di Bologna, via F. Selmi 2, 40126 Bologna, Italy
⁴ Star and Planet Formation Laboratory, Cluster for Pioneering Research, RIKEN,2-1 Hirosawa, Wako, Saitama 351-0198, Japan
⁵ Department of Applied Chemistry, Faculty of Engineering, Kanagawa Institute of Technology, Atsugi, Kanagawa 240-0292, Japan
⁶ The Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan
⁷ Observatorio de Yebes (IGN), Cerro de la Palera s/n, 19141 Guadalajara, Spain
⁸ University of Maryland, College Park, ND 20742-2421, USA
⁹ Department of Physics, Astronomy and Geosciences, Towson University, MD 21252, USA
¹⁰ European Southern Observatory, Alonso de Córdova 3107, Vitacura, 763 0355 Santiago, Chile
¹¹ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, 763 0355 Santiago, Chile

Received: 19 November 2021
Accepted: 18 April 2022

Abstract

Context. Theories of the origins of life propose that early cell membranes were synthesised from amphiphilic molecules simpler than phospholipids, such as fatty alcohols. The discovery in the interstellar medium (ISM) of ethanolamine, the simplest phospholipid head group, raises the question whether simple amphiphilic molecules are also synthesised in space.

Aims. We investigate whether precursors of fatty alcohols are present in the ISM.

Methods. To do this, we have carried out a spectral survey at 7, 3, 2 and 1 mm towards the Giant Molecular Cloud G+0.693-0.027 located in the Galactic centre using the IRAM 30 m and Yebes 40 m telescopes.

Results. Here, we report the detection in the ISM of the primary alcohol n-propanol (in both conformers Ga-n-C₃H₇OH and Aa-n-C₃H₇OH), a precursor of fatty alcohols. The derived column densities of n-propanol are (5.5 ± 0.4) × 10¹³ cm⁻² for the Ga conformer and (3.4 ± 0.3) × 10¹³ cm⁻² for the Aa conformer, which imply molecular abundances of (4.1 ± 0.3) × 10⁻¹⁰ for Ga-n-C₃H₇OH and of (2.5 ± 0.2) × 10⁻¹⁰ for Aa-n-C₃H₇OH. We also searched for the AGa conformer of n-butanol [AGa-n-C₄H₉OH] without success, yielding an upper limit to its abundance of ≤4.1 × 10⁻¹¹. The inferred CH₃OH:C₂H₅OH:C₃H₇OH:C₄H₉OH abundance ratios are 1:0.04:0.006:≤0.0004 towards G+0.693-0.027, that is, they decrease roughly by one order of magnitude for increasing complexity. We also report the detection of both syn and anti conformers of vinyl alcohol, with column densities of (1.11 ± 0.08) × 10¹⁴ cm⁻² and (1.3 ± 0.4) × 10¹³ cm⁻², and abundances of (8.2 ± 0.6) × 10⁻¹⁰ and (9.6 ± 3.0) × 10⁻¹¹, respectively.

Conclusions. The detection of n-propanol, together with the recent discovery of ethanolamine in the ISM, opens the possibility that precursors of lipids according to theories of the origin of life, could have been brought to Earth from outer space.