Where did the Earth's water come from? Although comets with their ice-chain nuclei act as ideal candidates, analyzes so far have shown that their water differs from that in our oceans. Now, however, there is an international team bringing together researchers from the CNRS at the Radiation and Radiation Laboratory in Astrophysics and Atmospheres (Paris Observatory – PSL / CNRS / Sorbonne University / University of Cergy-Pontoise) and the Laboratory of Space Studies and Instrumentation in Astrophysics. (Paris Observatory – PSL / CNRS / Sorbonne University / University of Paris) has found that a family of comets, the hyperactive comets, contains water similar to terrestrial water. The study, published in the journal Astronomy and Astrophysics on May 20, 2019, is based in particular on measurements of the comet 46P / Wirtanen by SOFIA, NASA's Stratospheric Observatory for Infrared Astronomy.
According to the standard theory, it has been thought to have formed from the collision of small celestial bodies known as planetary decimal. Since such organs were poor in water, the water of the earth must have been delivered either at a larger planetary or by a shower of smaller objects such as asteroids or comets.
To trace the source of groundwater, the researchers are studying isotope conditions and, in particular, the ratio of deuterium water to hydrogen, known as the D / H ratio (deuterium is a heavier form of hydrogen). As a comet approaches the sun, its ice sublimates, forming an atmosphere of water vapor that can be analyzed externally. However, the D / H ratios between comets measured so far have generally been double to three times that of seawater, which means that comets only supplied about 10% of the Earth's water.
When comet 46P / Wirtanen approached Earth in December 2018, it was analyzed using the SOFIA airborne observatory aboard a Boeing aircraft. This was the third comet that proved to exhibit the same D / H ratio as terrestrial water. Like the two previous comets, the category of hyperactive comets belongs to which, as they approach the Sun, release more water than the surface of their core should allow. The surplus is produced by icy particles present in their atmosphere. Intrigued, the researchers determined the active fraction (i.e., the fraction of the core surface area required to produce the amount of water present in their atmosphere) of all comets having a known D / H ratio . They found that there was an inverse correlation between the active fraction and the D / H ratio in the water vapor. The more a comet tends to hyperactivity (ie, an active fraction of more than 1), the more its D / H ratio drops and approaches the ground. Hyperactive comets, whose water vapor is partly derived from ice grains ejected in their atmosphere, thus have a D / H ratio corresponding to the soil water, as opposed to comets, if the gas halogen is produced only by surface ice. The researchers suggest that the D / H ratios measured in the atmosphere of the latter are not necessarily indicative of the ice present in their nucleus. If this hypothesis is correct, the water in all comet nuclei can really resemble the soil water and re-open the debate on the origin of Earth's oceans.
Publication: Soil conditions between deuterium and hydrogen in water in hyperactive comets, DC Lis, D. Bockelee-Morvan, R. Guesten, N. Biver, J. Stutzki, Y. Delorme, C. Duran, H. Wiesemeyer, Y Okada. Astronomy & Astrophysics, May 20, 2019. Doi: 10.1051 / 0004-6361 / 201935554