Scientists detect the first interstellar sugar in a Milky Way dust cloud.
Discovery suggests life's essential ingredients can form in deep space before reaching planets.
Researchers say cometary sugar may have helped seed early Earth's prebiotic chemistry.
A simple sugar found in red raspberries and used in fake tan lotions has been detected for the first time in interstellar space, in a discovery that strengthens the case that some of life's essential building blocks were forged long before planets such as Earth came into being.
Astronomers identified erythrulose in a vast cloud of dust and gas, known as G+0.693-0.027, near the centre of the Milky Way. The finding suggests that compounds crucial to life can form in the freezing conditions of the interstellar medium before being carried to planets by comets and cosmic dust.
“This is the very first sugar to be detected in interstellar space and it is important because it tells us that these sugars are more common than we previously thought,” said Dr Izaskun Jiménez-Serra of Spain's Centre for Astrobiology near Madrid. “It opens the possibility for life to develop on other worlds in a similar fashion to what it did on Earth.”
Scientists have long struggled to explain how simple sugars became abundant on the early Earth, with laboratory studies suggesting they would not have formed easily on the young planet. Earlier discoveries of sugars in ancient meteorites and on the Bennu asteroid hinted that such compounds may have arrived from space, but this is the first direct detection of a sugar in the interstellar medium.
Jiménez-Serra and her colleagues made the discovery using two Spanish radio telescopes to study the dust cloud near the Galactic Centre. After failing to detect simpler three-carbon sugars, the team had little expectation of finding more complex molecules before identifying the spectral signature of erythrulose, a four-carbon sugar.
“To my surprise, I saw the signals,” Jiménez-Serra said.
Writing in Nature Astronomy, the researchers say erythrulose can form when glycolaldehyde and ethylene glycol — two organic compounds already known to exist in parts of space — react on microscopic dust grains. The reactions occur even at temperatures of about minus 250 degrees Celsius.
Beyond serving as an energy source for living organisms, simple sugars such as erythrulose can react to form ribonucleotides, the building blocks of RNA, which is thought to have been the earliest genetic material. DNA later evolved as a more stable store of genetic information, while RNA became the intermediary between genes and proteins.
The researchers estimate that millions of tonnes of erythrulose may have been delivered to the Earth during the Late Heavy Bombardment, when asteroids and comets repeatedly struck the young planet.
“To have suffered this kind of rain of organics, I think that seems to have been a key step,” Jiménez-Serra said. “That material could have contributed to prebiotic soups where the first biomolecules were synthesised.”
Erythrulose occurs naturally in trace amounts in red raspberries but is also widely used in fake tan lotions. It reacts with amino acids in dead skin cells to form brown polymers known as melanoidins through the Maillard reaction — the same chemical process that gives cooked steak its dark crust.
“We have been waiting for an actual detection like this,” said Prof Yoshihiro Furukawa of Tohoku University in Japan, who previously discovered sugars in the Bennu asteroid. “Sugars formed in the interstellar medium can reach Earth and other planets via cometary dust ... This supply may have helped facilitate the emergence of life, if planetary environments were able to build life from such molecules, although that process itself remains unclear.”
(With inputs from The Guardian)
