ESA’s Rosetta mission, which ended in Septempber 2016, has found that organic matter constitutes almost 40% of the nucleus of comet « Tchouri » (67P Churyumov-Gerasimenko). Made up of molecules containing hydrogen, nitrogen and oxygen, this material is one of the basic building bricks of life as we know it on Earth. However, this widespread material was presumably not created at the same time as the solar system but much earlier, in the interstellar medium. That is the notion proposed today by Jean-Loup Bertaux, at the Laboratoire atmosphères, milieux, observations spatiales (CNRS/UPMC/Univ. Versailles–Saint-Quentin-en-Yvelines), and Rosine Lallement, at the Galaxies, étoiles, physique et instrumentation laboratory (Observatoire de Paris/CNRS/Université Paris Diderot). And according to these two French scientists, a large part of this organic material was presumably already well known to astronomers.
Already 70 years ago, the spectroscopy of stellar light in all directions showed up the presence of absorption lines at quite specific wavelengths : the « Diffuse interstellar bands » (DIB), attributed to complex organic molecules which presumably constituted the « the largest reservoir of organic matter in the Universe » according to the American astrophysicist Theodore Snow. This inter-stella organic material is generally in the same overall proportion as interstellar matter, , except for very dense nebulae such as a proto-solar nebula : in the core of the nebula, where the density of matter is higher, the DIB saturate, or even decrease. This shows that the organic molecules which are the source of the DIB disappear as they combine. When they are stuck together, they can no longer absorb light in the same way as when they were floating freely in space.
This kind of proto-nebula ends up by contracting to make a planetary system like ours, with planets ... and comets. Thanks to the Rosetta mission, we know that the nuclei of comets are created by hierarchical accretion of matter in the nebular : small grains stuck together to make larger ones, which in their turn agglomerated to make still larger ones, and so on, reaching finally kilometer size cometary nuclei. A non-violent process.
It is therefore quite likely that the organic molecules, source of the DIBs and which were already in the original nebulae, were not destroyed, but were incorporated into the dust grains making up the cometary nuclei, and are still there 4,6 billion years later Consequently, a sample return mission would allow us to analyze in the laboratory the organic material of a comet, and so would finally reveal the real nature of the mysterious interstellar material responsible for the absorption lines found in stellar spectra.
Which raises a new question : if the organic material in comets was really made in interstellar space, and if it played a role in the emergence of life on Earth, as scientists now believe, perhaps it could also have been incorporated in many other planets in our galaxy ... giving birth to life there also ?
Bibliography
- Diffuse Interstellar Bands carriers and cometary organic materia, Jean-Loup Bertaux Rosine Lallement, Monthly Notices of the Royal Astronomical Society, 31