The rate of rotation of Mars is speeding up, and as a result, the days are getting shorter, even if this reduction is only a fraction of a millisecond per year. There is still uncertainty about the cause of this change in the speed of the red planet, but, for now, two are considered: the first is related to the nature of the core of this planet – which against what was believed, it is not solid–, and the second, with the ice on the surface.
The discovery, published in the journal Nature, has been made possible thanks to the data obtained by NASA’s InSight module, which has managed to break the most important problem faced by scientists in the study of the internal structure of the planet : the interior of Mars is not directly accessible.
For this reason, until the arrival of this mission “most of the geophysical data provided global information, in which it was not possible to separate the core from the layer and the crust”, the article alleges.
More specifically, it was one of the instruments, a radio transponder and antennas collectively known as RISE (Internal Structure and Rotation Experiment), which allowed tracking the speed of rotation of the red planet. They identified and quantified its acceleration, which is about four milliseconds of arc per year, which translates into a cut of a fraction of a millisecond for each revolution it makes around the sun.
As a whole, the InSight module represents the most precise technology that has been used, so far, for a Martian exploration. In fact, already on landing he detected, for the first time, that the core of Mars was moving, which led to the argument that it is liquid (of molten iron), and not solid, as was believed. It has also been possible to measure its size, which is estimated to be between 1,790 and 1,850 kilometers in radius.
That it is liquid and not solid would imply a loss in the internal homogeneity of the planet. Therefore, one of the causes studied in this analysis is that the acceleration of the rotation rate of Mars “could be the result of a long-term trend in the internal dynamics of the planet”.
The other cause that is proposed is a change in the mass of the planet, caused by an accumulation (extremely slow, according to the assessment of scientists) of ice in the polar caps of Mars. Because, although there is no liquid water on this planet, it is possible to find it in the form of ice in the ice caps or in the form of steam in the atmosphere.
Although the temperature of Mars is suitable for liquid water (as on Earth) its atmosphere is too tenuous (about a hundred times less dense than the atmosphere of our planet) and, consequently, it is not able to keep water liquid.
Also in relation to the polar caps, the post-glacial rebound (through which land masses rise after being buried by ice) is considered as a possible influencing factor in the change in speed of the planet. In essence, they all relate to the internal or surface mass distribution of Mars. “These changes in the mass of a planet can cause it to accelerate a little, like an ice skater spinning with his arms outstretched and then retracting them,” explains NASA.
The key is in the “angular momentum” or amount of spin, a concept that is present in all spinning movements, from the rotation of the planets to that skater. Angular momentum remains constant and therefore needs to play (roughly speaking) with two of its determining factors: mass distribution and velocity.
When the skater extends his arms (expands his mass), the speed of the spin decreases to conserve angular momentum. If the skater retracts them (contracts their mass), the speed will increase for the same reason. And since this law – the conservation of angular momentum – is universal, it also applies to the red planet, even if it is not dressed in sequins or has limbs to change position.
