The inventory of prebiotic building blocks around a young, sun-like protostar
Résumé
Small molecules such as methanimine (CH_{2}NH), methylamine (CH _{3}NH _{2}), hydroxylamine (NH _{2}OH) and methyl isocyanate (CH _{3}NCO) belong to a select group of so-called prebiotic molecules that are thought to be at the basis of amino-acid and peptide-bond formation. On Earth, amino-acids are important building blocks of life, which through peptide bonds link with each other to form proteins. Recent ALMA observations have shown for the first time that CH _{2}NH and CH _{3}NCO are present around the low-mass, sun-like, protostar IRAS 16293-2422, showing that prebiotic building blocks could already have been present at the earliest formational stages of our own Solar System. [1][2] This work is conducted as part of the protostellar interferometric line survey, a broad band ALMA survey of the protostellar binary IRAS 16293-2422. The detections of CH _{2}NH and CH _{3}NCO rotational transitions are presented and integrated emission maps show their presence at Solar System scales ( 60 AU) around the protostar. Supporting solid-state laboratory data shows that CH _{3}NCO has its origin in the ice mantles of interstellar dust grains. Non-detections of NH _{2}OH and CH _{3}NH _{2} are used to constrain chemical pathways to interstellar amino-acid formation. Specifically, the abundance comparison of CH3NH2 between this low-mass protostar and the galactic centre source Sgr B2 shows that CH _{3}NH _{2} is depleted by at least 1-2 orders of magnitude in IRAS 16293-2422. This shows that around low-mass protostars CH _{2}NH might be a more relevant precursor to amino-acid formation than CH _{3}NH _{2}. [1] N.F.W. Ligterink et al., Month. Not. Roy. Astron. Soc. 469 (2017) 2219 [2] N.F.W. Ligterink et al., Astronomy & Astrophysics, subm. (2018)