Cosmic Sweetness: Erythrulose – The First Sugar in the Interstellar Medium ✦
The origin of monosaccharides in prebiotic conditions is a central problem in origin-of-life research. Laboratory syntheses yield insufficient concentrations, and findings of sugars in meteorites point to their extraterrestrial origin. This is the first report of a sugar (erythrulose, a chiral C4-ketose) detected in the interstellar medium. The detection was made using data from ultra-sensitive broadband spectral surveys of the molecular cloud G+0.693-0.027 in the direction of the Galactic center, performed with the Yebes 40m and IRAM 30m telescopes. Erythrulose is at least eight times more abundant than similar three-carbon sugars, which remained undetected. Quantum-chemical and astrochemical models show that erythrulose efficiently forms on interstellar dust grains from simpler two-carbon aldehydes and alcohols. Since ketoses easily isomerize to aldoses in aqueous environments, interstellar erythrulose could have replenished the pool of sugars available for early metabolic and replication processes.
Context
The question of the origin of the sugars necessary for the emergence of life remains open: laboratory simulations of the early Earth do not yield sufficient concentrations. The detection of ribose and glucose in asteroids and comets has sparked the idea of their extraterrestrial synthesis. However, until now, no sugar had been found in the interstellar medium, despite advances in spectroscopy since the time of Joseph von Fraunhofer and the development of radio astronomy methods pioneered by Charles Townes. The hypothesis of Fred Hoyle regarding the extraterrestrial origin of organics awaited direct confirmation.
Methods
Using broadband radio spectroscopy with the Yebes 40m and IRAM 30m telescopes, researchers surveyed the molecular cloud G+0.693, located in the Galactic Center at a distance of 8.2 kpc. The survey covered more than 91 GHz across several wavelength bands. To identify erythrulose, precise laboratory data on rotational transitions obtained via ultrafast laser vaporization were employed. Spectral analysis was performed using the MADCUBA-SLIM software package, which allowed for the extraction of uncontaminated lines and fitting under the assumption of local thermodynamic equilibrium.
Results
Erythrulose was detected with a column density of (8.7±0.8)×10¹³ cm⁻², corresponding to an abundance of ~6.4×10⁻¹⁰ relative to molecular hydrogen. This is at least 8 times higher than the upper limits for three-carbon sugars. The rotational temperature of the gas was only 11.3±1.8 K, typical for cold clouds. The spectral lines show good agreement with the model and have high statistical significance (probability of random coincidence ~0.2%). Chemical modeling indicates that erythrulose forms efficiently on the surface of cosmic dust grains from radicals of glycolaldehyde and ethylene glycol, especially at the high cosmic-ray ionization rate characteristic of the Galactic Center. The reaction proceeds through an intersystem crossing step and has virtually no activation barrier on cold ices.
Implications
This discovery proves for the first time that chiral carbon-containing molecules with four oxygen atoms can form in the interstellar medium and then be delivered to planets via asteroids and comets. Erythrulose can isomerize into aldoses, serving as a precursor for nucleic acids, in particular threose nucleic acid — a simpler analogue of RNA. This strengthens the hypothesis of the contribution of cosmic material to prebiotic chemistry on exoplanets and explains the observed enantiomeric excesses in meteorites. Thus, the interstellar medium emerges as a full-fledged factory of prebiotic sugars.
Future development
In the future, searches for other sugars, such as ribose and glucose, are planned using even more sensitive surveys, including submillimeter telescopes. Of particular interest is the study of sugar behavior when interacting with water ice in protoplanetary disk conditions. The development of laboratory methods for the synthesis and spectroscopy of complex organic molecules will expand the list of candidates for astronomical searches.
Impact
The results will impact astrobiology, astrochemistry, and planetary science, linking the chemistry of interstellar ices to prebiotic processes on planets.
Next steps
Next steps include laboratory refinement of isomerization reaction rates and the search for erythrulose in other clouds, including protoplanetary disks, using high-resolution interferometers.
Key open problems
Connection to unresolved problems: the mechanism of the emergence of biological homochirality and the question of how common sugars are in planet-forming zones, which directly affects the probability of abiogenesis in the Universe.
🎯 Erythrulose is widely used in cosmetics as a self-tanning agent, and now it's been found about 27,000 light-years from Earth.
🎬 In Fred Hoyle's novel 'The Black Cloud,' interstellar clouds are considered as carriers of life; the detection of sugars in such clouds provides scientific grounding for the idea of cosmic distribution of prebiotic molecules.
Key numbers
- содержание эритрулозы: 6.4×10⁻¹⁰ от H₂
- колоночная плотность: 8.7×10¹³ см⁻²
- температура газа: 11.3 K
- расстояние до облака: 8.2 кпк
- превышение над C3-сахарами: в 8–17 раз