Scientists at the Institut de Chimie de Nice (CNRS/Nice Sophia Antipolis University) arrived at this result from a highly detailed analysis of an artificial comet created by their colleagues at the IAS space astrophysics institute (CNRS/Paris-Sud University). Along with other teams, including one at the SOLEIL synchrotron, they propose the first realistic scenario for the formation of this key compound that had never been detected in meteorites or cometary ices until now.
Their findings, which mark a major step forward in understanding how life emerged on Earth, are published in the journal Science of 8 April 2016 and confirm the value of such work funded by CNES, as form
A molecular cloud: the “Pillars of Creation”. Credits: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).
Making ribose in the laboratory
The genetic make-up of all living organisms on Earth, as well as of viruses, consists of nucleic acids—DNA and RNA. The latter, considered more primitive, is thought to have been one of the first molecules characteristic of life to appear on Earth. Scientists have long wondered about the origin of these biological molecules.
Some believe that Earth was “seeded” by comets or asteroids containing the basic building blocks needed to form such molecules. And indeed several amino acids (the components of proteins) and nitrogenous bases (one of the components of nucleic acids) have already been found in meteorites, as well as in artificial comets produced in the laboratory.
However, ribose, the other key component of RNA, had never yet been detected in extraterrestrial material or created in the laboratory under “astrophysical” conditions. By simulating the evolution of the interstellar ice making up comets, French research teams have now successfully obtained ribose, a key step in understanding the origin of RNA and therefore of life.
As a first step, an “artificial comet” was produced at the IAS space astrophysics institute. By placing a representative mixture of water (H2O), methanol (CH3OH) and ammonia (NH3) in a high vacuum chamber at –200°C, the astrophysicists simulated the formation of dust grains coated with ice, the raw material of comets. This material was irradiated with UV, as in the molecular clouds where these grains form. The sample was then warmed to room temperature, as in comets when they approach the Sun.
Its composition was then analysed at the Institut de Chimie de Nice, optimizing an extremely sensitive and accurate method (multidimensional gas chromatography coupled with time-of-flight mass spectrometry). Several sugars were detected, including ribose. Their diversity and relative abundances suggest they were formed from formaldehyde, a molecule found in space and on comets that forms in large quantities from methanol and water.
Although the existence of ribose in real comets is yet to be confirmed, this discovery completes the list of the “molecular building blocks” of life that can be formed in interstellar ice. It also lends further support to the theory that comets are the source of the organic molecules that made life possible on Earth, and perhaps elsewhere in the Universe.
Ultraviolet processing of pre-cometary ices reproduces the natural evolution of interstellar ices observed in molecular clouds, leading to the formation of sugar molecules.
Credits: Louis Le Sergeant d’Hendecourt (CNRS).
Ribose (and related molecules such as arabinose, lyxose and xylose) have been detected in pre-cometary ice analogues using multidimensional gas chromatography. Ribose makes up the “backbone” of ribonucleic acid (RNA), thought to be the genetic material of the first living organisms. Credits: Cornelia Meinert (CNRS).
Ribose forms in the icy mantles of dust grains from simple precursor molecules (water, methanol and ammonia) under high-energy radiation. Credits: Cornelia Meinert (CNRS) and Andy Christie (Slimfilms.com).
Cornelia Meinert, Iuliia Myrgorodska, Pierre de Marcellus Thomas Buhse, Laurent Nahon, Soeren V. Hoffmann, Louis Le Sergeant d’Hendecourt, Uwe J. Meierhenrich, Ribose and related sugars from ultraviolet irradiation of interstellar ice analogs, Science, 8 avril 2016. DOI : 10.1126/science.aad8137
- Science contact at Institut de Chimie de Nice: Cornelia Meinert meinert at unice.fr
- CNES Exobiology programme leader: Michel Viso michel.viso at cnes.fr