The Nobel laureate in physics Richard Feynman, in his famous university course in physics, showed from the first year how it was possible, with elementary numerical computation tools already on simple computers since the early 1960s, to describe and predict movements of material N points that shape planets that move under the action of universal attraction. This is typically what is called a many-body problem that is known to be very difficult to solve analytically, whether with planets, stars in a galaxy or electron gas in a solid. .
In fact, there is a whole theory largely constituted initially by the works of Lagrange, Laplace, Gauss but also by Hamilton, Siméon Denis Poisson and Sophus Lie (all mathematicians) of the XVIIIAnd in 19And century, which allows to calculate analytically and numerically up to a certain point the movements of at least three non-punctual bodies in celestial mechanics. Modern forms of this theory, with corrections coming from Einstein’s theory of gravitation and introducing the so-called non-Newtonian terms into the equations, are used to understand in particular the formation and evolution of the Solar System but also of exoplanetary systems.
We can get an idea of all these theories developed for more than two centuries now with known works such as those of Goldstein (a great classic of mechanics that provides tools for understanding quantum and relativistic mechanics as a bonus) and Fitzpatrick.
They had already allowed not only Leverrier to discover Neptune due to its influence on the movements of Uranus, but also Milutin Milankovitch, a Serbian mathematician, geophysicist, astronomer and climatologist, to discover the origin of glacial cycles as evidenced by the geological archives. the quaternary of our Blue Planet.
What are Milankovitch cycles? This video explains it to us. © The spirit of the official sorcerer
From Milankovitch to exobiology
We know from Kepler that the orbits of the planets of the Solar System are more or less eccentric ellipses, sometimes very close to a circle or on the contrary very elongated as in the case of other celestial bodies on periodic orbits, certain comets. In fact, there are several parameters that serve to characterize the movements of the Earth, not only the values of the semi-major axis and the eccentricity of the Earth’s orbit but also the inclination of its axis with respect to its orbital plane. around the Sun.
These parameters play on the sunlight of the earth’s surface, on the energy it receives from the Sun and therefore definitely on the existence of the seasons and as we said of the glacial cycles (see video above). Milutin Milankovitch showed that these were initially due to periodic changes in the eccentricity of the Earth’s orbit and the obliquity of its axis of rotation.
He showed that they are the consequence of the gravitational attraction of the other planets of the Solar System, in particular Jupiter and Saturn, due to their large mass, but also Venus or Mars due to their proximity. Since eccentricity and obliquity govern the insolation and seasons on Earth, these modifications change the climate and affect the habitability of the Earth, that is, its ability to keep liquid water long-term on its surface.
We know that the question of habitability is in fact a complex question because we must also take into account the existence of an atmosphere capable of creating a greenhouse effect, which can also make a planet first too cold because basically too far from its sun, welcoming life, raising its average temperature or, on the contrary, transforming it into a Venusian hell.
However, both for the long-term evolution of the habitability of the Earth and of some exoplanets, it is potentially useful to study the influence of gravitational disturbances on the orbital and rotational parameters of the Earth or other exoplanets to specify the past, present or future. habitability of the latter.
The future of the solar system?
A group of American and Australian astronomers again addressed these questions by performing complex N-body calculations and taking into account general relativity in which they varied the eccentricity of Jupiter’s orbit but not the value of its semi-major axis, providing an estimate of La distance of Jupiter from the Sun.
As they explain in an article published on Astronomical Journal and available for free on arXiv, these researchers found that this in turn would induce major changes in the shape of Earth’s orbit.
” If Jupiter’s position remains the same, but the shape of its orbit changes, it could actually increase the habitability of this planet. “Summarizes in one sentence the astronomer Pam Vervoort, principal author of the study and stationed at the University of Riverside in California.
In the press release of this University it is stated that ” many are convinced that Earth is the epitome of a habitable planet and that any change in Jupiter’s orbit, being the massive planet it is, could only be harmful to Earth. We show that both hypotheses are false. “.
The researchers’ new calculations show that the eccentricity of Earth’s orbit would change so that it would be somewhat warmer on average and that the polar regions would have correspondingly less ice cover, which would therefore increase, according to them, the habitability of the our Blue Planet.
If, on the other hand, Jupiter had, in addition to a more eccentric orbit, a shorter semi-major axis, then it would be the obliquity of the Earth to change, i.e. the inclination of its rotation axis with respect to that of its orbital plane and this would lead to a greater inclination and wider regions that would be covered with ice.
All of these conclusions would potentially apply to another exoplanet system with an exo-Earth as well. Let us also remember that our Solar System is subject to a certain chaotic instability, so the researchers’ scenario could perhaps become the reality of tomorrow.