How Jupiter could make Earth even more habitable

In his famous undergraduate physics course, the Nobel Prize in Physics Richard Feynman showed from the first year how it was possible with elementary numerical calculation tools already on simple computers from the very beginning of the 1960s to describe and predict the movements of N-material points that model planets that moves under the influence of universal attraction. This is typically what is called a many-body problem, which 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 originally largely composed of works by Lagrange, Laplace, Gauss, but also by Hamilton, Siméon Denis Poisson and Sophus Lie (all mathematicians) from the XVIII.e in the 19the century, making it possible to calculate analytically and numerically up to a certain point the motions of at least three bodies, not punctual, in celestial mechanics. Modern forms of this theory, with corrections that come from Einstein’s theory of gravitation and which introduce so-called non-Newtonian terms into the equations, are used to understand especially the formation and evolution of the Solar System, but also exoplanetary systems.

We can get an idea of ​​all these theories developed for more than two centuries now with well-known works like those of Goldstein (a great classic of mechanics, providing tools for understanding quantum mechanics and relativistic mechanics as a bonus) and Fitzpatrick.

They had already enabled not only Leverrier to discover Neptune due to its influence on the movements of Uranus, but also Milutin Milankovitch, Serbian mathematician, geophysicist, astronomer and climatologist, to discover the origin of the Ice Age cycles, as appears of the geological archives. our blue planet’s quaternary.

What are Milankovitch cycles? This video explains it for us. © The Official Wizarding Spirit

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. There are actually several parameters which are used to characterize the Earth’s motions, not only the values ​​of the semimajor axis and the eccentricity of the Earth’s orbit, but also the inclination of its axis relative to its orbital plane. around the Sun.

These parameters play on the sunshine on the Earth’s surface, the energy it receives from the Sun and therefore ultimately about the existence of the seasons and as we said about the glacial cycles (see the video above). Milutin Milankovitch showed that these were originally due to periodic changes in the eccentricity of the Earth’s orbit and the tilt of its axis of rotation.

He demonstrated that they are the consequence of the gravitational attraction of the other planets in the solar system, especially Jupiter and Saturn, due to their great mass, but also Venus or Mars due to their proximity. Since eccentricity and tilt control solar radiation and the seasons on Earth, these changes alter the climate and affect the Earth’s habitability, that is, its ability to sustain liquid water over the long term, its surface.

We know that the question of habitability is actually a complex question because it is also necessary to take into account the existence of an atmosphere capable of creating a greenhouse effect, which can also make a planet a priori too cold, because it is ultimately too far from its sun, it welcomes life, raising its average temperature or, on the contrary, turning it into a Venusian hell.

Nevertheless, both for the long-term evolution of the habitability of the Earth or certain exoplanets, it is potentially useful to study the influence of gravitational perturbations on the orbital and rotation parameters of the Earth or other exoplanets in order to specify the past, present or future habitability of the latter.

The future of the solar system?

A group of American and Australian astronomers have again addressed these questions by doing complex N-body calculations and taking into account general relativity, where they have varied the eccentricity of Jupiter’s orbit, but not the value of its semi-major axis, giving an estimate of Jupiter’s distance from the Sun.

As they explain in an article published in Astronomical Journal and freely available on arXiv, these researchers discovered that this would in turn induce major changes in the shape of Earth’s orbit.

If Jupiter’s position remained the same but the shape of its orbit changed, it could actually increase the habitability of this planet. “Summarizes in one sentence the astronomer Pam Vervoort, lead author of the study and stationed at the University of Riverside in California.

The press release from this university states 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 that it is, can only be bad for Earth. We show that both hypotheses are false. “.

The researchers’ new calculations show that the eccentricity of the Earth’s orbit would change, so that it would be slightly warmer on average, and that the polar regions would consequently have less ice cover, which would therefore increase habitability, according to them. our blue planet.

On the other hand, if, in addition to a more eccentric orbit, Jupiter had a shorter semi-major axis, then it would be the Earth’s obliquity that would be changed, that is, the tilt of its axis of rotation relative to its orbital plane, and this would result in a steeper slope and larger areas that would be covered by ice.

All of these conclusions would potentially also apply to another exoplanet system with an exo-Earth. Let’s also remember that our solar system is subject to a certain chaotic instability, so the researchers’ scenario might become tomorrow’s reality.

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