[Spanish National Research Council (CSIC)] Sugars are key biomolecules in living organisms, as they form the backbone of DNA and RNA and play a fundamental role in metabolic processes. In theories of the origin of life, sugars are also essential for the synthesis of the first nucleic acids.
Despite their importance, one of the major questions in origin-of-life research is how the first sugars formed on Earth, since laboratory experiments show that they do not form in enough quantities under prebiotic conditions. Sugars such as ribose and glucose have previously been detected in meteorite and asteroid samples, suggesting that some of these molecules may have originated in the primordial molecular cloud from which our Solar System formed. However, until now, no sugar had ever been directly detected in the interstellar medium.
Erythrulose — astro-ph.GA
An international team led by CAB researcher Izaskun Jiménez-Serra has now identified the first sugar in interstellar space: erythrulose. This molecule is the only possible four-carbon ketose, and on Earth it is commonly found in raspberries and sunless tanning products. Erythrulose was detected toward the molecular cloud G+0.693−0.027, located near the centre of our Galaxy, the Milky Way. The discovery was made possible by ultra-sensitive, broadband spectroscopic surveys carried out with the 40-m Yebes radio telescope and the 30-m telescope of the Institute for Radio Astronomy in the Millimeter Range (IRAM).
Finding chart for the Galactic Center region. A colour composite of the 4.5 𝜇m (white) and 8 𝜇m (green) emission from the Spitzer GLIMPSE survey (Churchwell et al. 2009), 24 𝜇m (yellow) emission from the Spitzer MIPSGAL survey (Carey et al. 2009), and 20 cm (red) emission observed by MeerKAT (Heywood et al. 2019, 2022) and the Green Bank Telescope (GBT; Law et al. 2008). Overlaid are labels highlighting several features of interest across the Galactic Centre, including the central few 100 pc known as the Central Molecular Zone (CMZ). Overlaid as a white contour is the coverage of the ACES survey (see Figure 2). The inset zoom-in shows the ACES HNCO(1-0) peak intensity map. Figure 2 shows the coordinates for the inset image. The background image for this Figure is adapted from Henshaw et al. 2023. An interactive version of the figure is available on the project homepage, https://sites.google.com/view/aces-cmz/home. — astro-ph.GA
The team identified 12 spectral lines matching the laboratory spectrum of erythrulose measured at the University of the Basque Country. The study also shows that this sugar is at least eight times more abundant than similar three-carbon sugars, none of which were detected in the same region. “This finding was unexpected, as the prevailing view in astrochemistry is that interstellar molecules grow in size through the sequential addition of carbon atoms”, says Izaskun Jimenez Serra (CAB), leading author of this work.
Working in collaboration with chemists from the University of Extremadura and Radboud University (the Netherlands), the CAB team discovered that erythrulose can form within interstellar ices from simpler two-carbon alcohols and aldehydes.
a–l, Filled histograms report the observed spectra, red lines show the line profiles of the erythrulose transitions fitted with MADCUBA-SLIM, and blue lines present the total fit to the spectra considering all the molecules identified towards the cloud. The intensity of the observed spectra is shown in units of antenna temperature, TA*. The quantum numbers of each transition of erythrulose are given in the upper part of each graph. Blue labels indicate the molecular species contributing to the observed spectra in the vicinity of the erythrulose lines. The transitions are sorted from the brightest to the weakest lines according to the LTE model. — Nature
Based on the abundance of erythrulose measured in the G+0.693−0.027 molecular cloud, the researchers estimate that between 0.5 and 50 million tonnes of this sugar could have reached Earth’s surface during the Late Heavy Bombardment, which occurred approximately 4.1 to 3.8 billion years ago. The presence of erythrulose in interstellar space therefore provides an alternative source of sugars that may have contributed to the emergence of the first metabolic and replication processes on the early Earth.
“The detection of erythrulose is very exciting because it opens up the possibility of discovering in space other sugars such as ribose, which is part of RNA, and other important molecules for the origin of life,” says Carlos Briones, co-author of the study.
- Detection of a four-carbon sugar in interstellar space, arxiv.org (open access)
- Detection of a four-carbon sugar in interstellar space, Nature (open access)
Astrobiology, Astrochemistry, Biochemistry, Biosignatures,
