The moon would be daughter of the Earth – BBC

A study reinforces the idea that our satellite is born of the collision between our planet and celestial body the size of Mars.

In his science fiction cycle Foundation Isaac Asimov imagined a legendary description of the Earth, the forgotten original world of humanity. It is described as a covered oceans ball accompanied by a gigantic natural satellite, the radius is one-quarter of his companion. Nobody believes in this story, seen as a fable for children, as this couple seems incongruous.

This is a great way to capture how the existence of our Moon may seem unexpected. For the Earth, the simplest training scenario assumes a collision with an impactor the size of Mars, about 100 million years after the birth of the solar system. To explain the respective orbits of the Earth and the Moon would require the impactor happens on a trajectory similar to that of our planet. Why not after all. But in this case, models show that the Moon would be made up to 80% of material from this foreign body.

This poses a troublesome problem since the composition of the Moon is almost exactly the same as of the earth. The oxygen isotope ratios, that is to say the relative amounts between different kinds of oxygen, the atomic nucleus does not carry exactly the same weight, are almost identical. Now, every body in the solar system has a particular isotopic signature of oxygen. The probability of a impactor has the same composition seemed almost zero.

Until today. An international team shows in the journal Nature this may be relatively common. “We ran models with a thousand bodies a hundred kilometers in diameter and a hundred of a thousand kilometers,” explains Sean Raymond, CNRS researcher at the Astrophysics Laboratory of Bordeaux and co-author of the study. “We then looked at the major impacts that affected the protoplanet most similar to Earth. In 20-30% of cases, the composition of the impactor was very close. “

” This raises a major obstacle to the simplest scenario Moon training “

This is a fundamental and lock that just jumped. No more need to exotic scenarios for training involving debris cloud accreting around the Earth. “It is a work of great importance,” said Marc Chaussidon, training specialist in the solar system to petrographic and geochemical Research Centre of Nancy. “It removes a major obstacle to the simplest scenario training. It remains to be seen whether the assumptions made in the model are relevant and if we can find the isotopic signatures of other elements such as silicon. “

The researchers assumed such that the distribution of isotopes oxygen was proportional to the distance from the Sun early in their simulation. “It is true that we are not certain that this is the case,” concedes Sean Raymond. “According to the most recent models, the gravitational influence of Jupiter could have concentrated a crown disk which form the terrestrial planets.” Disturbing the same time this well-linear distribution. “We were very excited about our initial results so we have not looked further. But we will now work with the finest models and watch other isotopes to see where it takes us. But I think in five or ten years we will have a realistic modeling of the formation of the Moon. “The appointment is made.