Extraterrestrial hexamethylenetetramine in meteorites—a precursor of prebiotic chemistry in the inner solar system

Abstract

Despite extensive studies on the formation of organic molecules in various extraterrestrial environments, it still remains under debate when, where, and how such molecules were abiotically formed. A key molecule to solve the problem, hexamethylenetetramine (HMT) has not been confirmed in extraterrestrial materials despite extensive laboratory experimental evidence that it can be produced in interstellar or cometary environments. Here we report the first detection of HMT and functionalized HMT species in the carbonaceous chondrites Murchison, Murray, and Tagish Lake. While the part-per-billion level concentration of HMT in Murchison and Tagish Lake is comparable to other related soluble organic molecules like amino acids, these compounds may have eluded detection in previous studies due to the loss of HMT during the extraction processes. HMT, which can yield important molecules for prebiotic chemistry such as formaldehyde and ammonia upon degradation, is a likely precursor of meteoritic organic compounds of astrochemical and astrophysical interest.

Synthesis of the first nitrogen-heterocycles in interstellar ice analogs containing methylamine (CH$_3$NH$_2$) exposed to UV radiation: Formation of trimethylentriamine (TMT, c-(-CH$_2$-NH)$_3$) and hexamethylentetramine (HMT, (CH$_2$)$_6$N$_4$)

“…Third, its acid hydrolysis leads to the formation of several aminoacids (Fox & Windsor 1970). HMT has been recently detected in Murchison (846±37 ppb), Murray (29±9 ppb) and Tagish Lake (671±9 ppb) carbonaceous chondrites, as well as the methyl, amino, hidroxy and hidroxymethyl derivatives of HMT (see Oba et al 2020). The synthesis of HMT derivatives in ice irradiation experiments was previously reported (Muñoz Caro et al 2004;Sandford et al 2020;Materese et al 2020;Urso et al 2020).…”

Analytical protocols for Phobos regolith samples returned by the Martian Moons eXploration (MMX) mission

“…For non-target analysis, water extracts of the samples will further be analyzed using a Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) for high mass-resolution analysis of organic compounds (Hertzog et al 2019 ). The other inspection using high mass resolution Orbitrap mass spectrometry would support further organic profiles and new findings (e.g., Smith et al 2014 ; Oba et al 2019 , 2020 ; Orthous-Daunay et al 2020 ). Extraction residues of these organic compounds will be demineralized and analyzed with ultra-small-scale elemental analysis/isotope ratio mass spectrometry (nano-EA/IRMS; Ogawa et al 2010 , 2020 ) for elemental compositions and isotope ratios of, e.g., C, N, and S. In addition, these residues will be analyzed by FT-IR, Raman spectroscopy, XANES, EA/IRMS, and NanoSIMS to obtain information about spatial distribution of chemical species and their isotopic compositions (Kebukawa et al 2020 ).…”

Exploring the link between molecular cloud ices and chondritic organic matter in laboratory

“…The extraction of SOM from milligrams of Murchison sample results on average composition that mixes the OM from all these tiny micro-environments. Interestingly, hexamethylenetetramine, a well-known chemical marker observed in pre-accretional organic residue 18 , 39 , 40 , has been identified in Murchison SOM 41 . This compound has been observed reactive under aqueous alteration, especially at 150 °C 25 .…”