The James-Webb telescope unlocks the secrets of the ice chemistry of embryonic planets

We know that there are dense and cold molecular clouds at the heart of about 1% of the dust formed by stars at the end of their life and which are surrounded by a mantle of ice. Prebiotic chemical reactions take place there, the full complexity of which is not yet known. This dust is also the basic material for the formation of planets and the James-Webb telescope can observe it like never before. These observations should help us understand whether the appearance of life and Earth-like planets is a rarity or not in the observable cosmos.

In the interview he gave to Futura about his latest book, Jean-Pierre Bibring explained to us that the discovery of the diversity of the planets of the Solar System, and in particular the moons of Jupiter, had led to the taking of awareness that many bifurcation points between paths of evolution determined by chance and necessity existed in the formation and evolution of the planets. Similar conclusions could be reached with regard to exoplanets and the prebiotic chemistry of matter in the dense and cold dusty molecular clouds which by their gravitational collapse can give rise to stars surrounded by protoplanetary disks and ultimately planets.

We could therefore ask ourselves the question of the universal character or not of the appearance of life and also of Earth-like planets in the Universe, at least in the Milky Way. The question remains open. To progress, we need to clarify many points such as the one concerning the formation and evolution of prebiotic molecules in molecular clouds and in protoplanetary discs.

Exobiology and cosmic ice

Radio astronomy has taught us that there are indeed organic molecules in these clouds. Elementary astrochemical models have been constructed in which grains of silicates and carbonaceous materials are surrounded by a gangue of ice, mainly water, a gangue in which, under the effect of ultraviolet photons from young stars, the heating of waves of shock and bombardment of cosmic rays, chemical reactions occur leading to the molecules already observed by radio astronomers.

In models of the formation of planets in the Solar System, icy giants like Jupiter and Neptune first form with a core of rock and ice resulting from a process of snowball-like agglomeration of icy dust. Telluric planets such as Earth and Mars have undoubtedly received an initial supply of water, but we do not know in what quantity or in what form. In the case of the Earth, which is all the same in the end poor in water if we compare it to the heart of Neptune for example, it is not clear whether its oceans are due to primordial degassing with a main water reservoir at the heart of our blue Planet or whether the water of its oceans came later with the last major bombardments of asteroids and comets at the beginning of the Hadean.


The Solar System is a laboratory for studying the formation of giant planets and the origin of Life that can be used in conjunction with the rest of the observable Universe for the same purpose. Mojo: Modeling the Origin of JOvian planets, i.e. modeling the origin of the Jovian planets, is a research project that has resulted in a series of videos presenting the theory of the origin of the Solar System and in particular of the gas giants by two renowned specialists , Alessandro Morbidelli and Sean Raymond. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “subtitles” and finally on “translate automatically”. Choose “French”. © Laurence Honnorat

It is not known if the molecules of life, such as sugars, DNA and RNA, were initially brought to Earth by comets and asteroids or if they were born in the famous primitive hot soup of the famous experiment. by Miller Ulrey. In short, the formation of planets and the appearance of life are unquestionably conditioned at the beginning by simple ices coating dusts and which become more and more complex over time through a variety of chemical pathways which depend on their environmental conditions. . Much remains to be discovered and understood about it and it is only by combining new astronomical observations, cutting-edge laboratory experiments on this icy dust and comprehensive chemical modeling that we can see more clearly.

It is with all these considerations that researchers have come together within the framework of the ice age project with among them and at their head, Melissa McClure, astronomer at the Leiden Observatory. They just let know in particular via a recent publication in Nature Astronomy that they had used the penetrating infrared gaze of the James-Webb telescope to dive like never before into the icy, dark heart of a famous molecular cloud in the Milky Way to unlock some of the secrets of these protoplanetary and prebiotic ices.

A rich cocktail of organic molecules

Remember that the organic molecules of life as we know it are composed of only four elements: hydrogen (H), oxygen (O), carbon (C) and nitrogen (N). These elements represent 99.4% of the human body while the rocks of the Earth are largely dominated by refractory minerals containing mainly as elements, iron (Fe), silicon (Si), nickel (Ni) and oxygen .

In fact, organic molecules are often collectively referred to in terms of CHON, or even CHONS, as some add as a fifth important element, sulfur. They are found as important ingredients both in planetary atmospheres and in molecules such as sugars, alcohols and simple amino acids. They are also found in the icy dust at the origin of comets and carbonaceous asteroids.

What the James-Webb telescope has just made it possible to do, according to a joint press release from NASA and ESA, is an in-depth inventory of the ice located in the deepest and coldest parts studied to date in a molecular cloud. In this case, it is the Chameleon I cloud (abbreviated to Cha I for Chameleon, in English), one of the closest active star-forming regions to the Solar System and containing a few hundred stars and protostars.

Astrochemists have thus identified a wide range of molecules ranging from carbonyl sulphide, ammonia and methane, to the simplest complex organic molecule already identified by radio astronomers for decades: methanol CH3OH.

In this press release, Melissa McClure explains that the studies conducted have provided results that “ provide insight into the initial dark chemistry phase of ice formation on interstellar dust grains that will turn into centimeter-sized pebbles from which planets form into disks. These observations open a new window on the formation pathways of the simple and complex molecules that are needed to make the building blocks of life. “.

A key to determining the place of life in the cosmos

Our identification of complex organic molecules, such as methanol and potentially ethanol, also suggests that the many star and planetary systems developing in this particular cloud will inherit molecules in a fairly advanced chemical state. This could mean that the presence of prebiotic molecules in planetary systems is a common result of star formation, rather than a feature unique to our own Solar System. adds his colleague Will Rocha, also an astronomer at the Leiden Observatory and who contributed to this discovery.

This is just the first in a series of spectral snapshots we will get to see how the ices evolve from their initial synthesis to the comet-forming regions of protoplanetary disks. This will tell us what mixture of ices and therefore what elements may possibly be delivered to the surface of terrestrial exoplanets or incorporated into the atmospheres of gas or ice giant planets. McClure also adds.


STScI Webinar by Melissa McClure on IceAge: Chemical Evolution of Ices during Star Formation (program ERS 1309), recorded on March 11, 2020. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © JWST Observer

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