Life’s Building Blocks Created on Lab-Grown Comet

Mix water, methanol and ammonia at low temperatures and low pressure, irradiate with ultraviolet light and what do you get? A residue of organics, which when warmed to room temperature, contains ribose and other sugars that are believed to be building blocks for RNA and DNA, molecules essential for all known forms of life.

The experiment suggests that ribose and similarly structured sugars such as arabinose, xylose and lyxose could assemble under the chemical and temperature conditions of cosmic ices during the solar system’s formation.

“The identification of ribose and related sugar molecules in the simulated cometary ice is new and entirely unexpected,” astrochemist Cornelia Meinert, with the University of Nice Sophia Antipolis in Nice, France, wrote in an email to Discovery News.

The discovery, she added, “is relevant for many theories on the origin of life.”

The experiment, reported in this week’s Science, stems from work to develop an organics detector for the Philae comet lander, which was dispatched by Europe’s Rosetta spacecraft to the surface of Comet 67P/Churyumov-Gerasimenko in November 2014.

Philae didn’t find ribose on the comet, but it did detect three organic compounds that also turned up in the lab samples.

“The detection of ribose is really exciting and provides insight into the prebiotic origin of a critical compound needed for life,” said University of Washington astronomer Donald Brownlee, who was not involved in the research.

“In the first few million years the outer regions of the solar system contained massive quantities of ice-coated dust grains and the proposed UV irradiation of these grains is surely an important source of organic materials. It seems like a wonderful gift from nature, that this process can produce ribose. We might not be here without it,” Brownlee wrote in an email to Discovery News.

Scientists do not know how life began on Earth, but many theorize that key ingredients came from comets and asteroids crashing into the developing planet.

“I am sure that (ribose) can survive atmospheric entry,” Brownlee added.

“Meteorites get hot on their surfaces but not in their interiors. If they are rocky materials, they are like Baked Alaskas. It is likely some cosmic dust particles from comets could also carry ribose through the atmosphere. A very interesting question is if Earth could make ribose or other critical molecules or whether it has to come from somewhere else. Irradiation of frozen volatiles is a natural process in space, but it does not easily occur on Earth,” Brownlee said.

Meinert and colleagues do not yet know the exact mechanism that led to the formation of ribose and other sugar molecules in the simulated ices.

Previous attempts to find sugar molecules in simulated ices or meteorites failed due to analytical limitations, she added.

Follow-on studies are planned to look at the sugar molecules’ structural asymmetry, or chirality, in hopes of learning more about the evolution of DNA.

Minert also would like to look for ribose in meteorites and in asteroid samples scheduled to be brought back to Earth by NASA’s upcoming OSIRIS-REx and Japan’s Hayabusa-2 missions.

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