In our solar system, most of the satellites are moving away slowly from their planet because of the tidal effects resulting from the gravitational attraction. And our moon deviates to the Earth at a rate of 3.8 cm per year. Scientists can measure it with powerful lasers and reflectors deposited on the surface of our satellite by the missions of the american Apollo and soviet Lunokhod. In fact, this is the time of round trip of the laser pulse, which allows to determine very precisely the distance between Earth and moon.

But let us return to the effects of tide... Due to the moon and, to a lesser extent, the Sun (25 million times more massive and 400 times further away), they exert not only on the water of the oceans, but also on the earth's crust, stretched and distorted. Add to this that the Earth rotates on itself and you will get a complex mechanism involving friction and leading – by virtue of the laws of conservation of energy and angular momentum of a physical system – a gradual slowdown of the Earth's rotation is compensated by an acceleration of the rotation of the moon leading to its progressive distancing. Thus, for billions of years, the length of day on Earth extends to the moon, she slowly takes off.

drift much faster

of course, this phenomenon of tide is not exercised on Land and on the couple that it forms with the moon, gravity is at work everywhere in the universe. So far, the mechanics of tidal effects is the same regardless of the planetary system in question ? Contrary to what scientists have seen so far, it would seem that no ! At least that is what indicates a new study published in the journal Nature, Astronomy concerning Saturn, gas giant planet, and the largest of its 82 moons, Titan.

In fact, thanks to data collected by the u.s. probe Cassini, whose mission has completed three years ago, two teams – one led by Valéry Lainey, astronomer of the Observatory of Paris on secondment to the Jet Propulsion Laboratory of Nasa in California, the other led by Paolo Tortora, university of Bologna in Italy, found that Titan's distance from Saturn at a rate of 11 centimeters per year, which is 100 times faster than expected ! The first mapped the stars in the background images from Cassini to track the position of Titan, while the second focused on of radio data collected by the probe during close flybys of this moon. Two methods are totally different, which have led to the same conclusion.

Consequences of science major

This discovery is not without consequence scientific. Far from it. During the last fifty years, astronomers have applied the same method of calculation to estimate the speed at which a moon derives from his planet, that it is terrestrial (i.e. rocky) or gaseous. In the presence of many moons around a planet, this model based on the behavior of the satellites of the body of the earthquakes assumed that the outer moons like Titan, the most distant planet, migrated more slowly than the moons interior. Obviously, for Saturn, which was thought to be an approximation leads purely and simply to a mistake !

The good news is that the solution to this problem may well have already been found, four years ago, by the astrophysicist Jim Fuller, of Caltech in California. In fact, in 2016, the theorist has proposed a new model that incorporates aspects of fluid mechanics involved in the envelope of gas of Saturn to calculate more than just the tidal forces acting between the giant planet and its satellites. However the value of the drift of Titan obtained in the two new studies is perfectly consistent with the mode of calculation it offers, and which could therefore advantageously be applied to Jupiter, other giant planets located outside the solar system, but also to some binary star.

As to our knowledge of the saturnian system, the consequences of this new information are just as important. Because the value of the drift of the moons is used to extrapolate to their age. The value of the drift of the Titan being a hundred times greater than that calculated so far, it is the entire history not only Titan, but the saturnian system as a whole which is now totally revised.