Today, Jupiter, Saturn, Uranus and Neptune orbit the Sun on relatively stable paths. They perturb one another through their gravity, but astronomers thought this balance could last for an extremely long time, even after our star transformed into a white dwarf. A new study calls this into question.
In about five billion years, the Sun will begin to leave its current stage of life. It will swell into a red giant, then lose a large part of its matter before ending as a small, very dense star: a white dwarf. In the process, the gravitational force it exerts on its planets will decrease.
The 4 giant planets of the Solar System
SCIENCE: NASA, ESA, Amy Simon (NASA-GSFC), Michael H. Wong (UC Berkeley) IMAGE PROCESSING: Joseph DePasquale (STScI) · Public domain
It was already known that the orbits of the remaining planets should then expand. But most calculations assumed that the Sun would lose its matter fairly steadily. The researchers wanted to examine another possibility: that this loss would occur through numerous irregular gas expulsions, in different directions.
With each expulsion, the Sun would experience a tiny push in the opposite direction. Taken individually, these movements would be almost imperceptible. But their accumulation could alter the planets' paths and, above all, the relationships between their orbits. After a certain amount of time, two planets could pass close enough to each other to destabilize one another.
Orbits of the giant planets at the end of the simulation
The researchers used computers to track many possible future versions of the Solar System. In some simulations, interactions between the planets become intense. Jupiter, Saturn, Uranus or Neptune can undergo major changes in their paths, and some may be ejected into interstellar space.
With the parameters studied, about 40% of the simulations already experience major disruptions before the Sun even becomes a white dwarf. In nearly 90% of cases, the giant-planet system eventually becomes disorganized within the following three billion years.
The evolution depends strongly on how the Sun will lose its matter. Irregular expulsions are a plausible hypothesis, particularly to explain small movements observed in some white dwarfs, but their precise progression remains unknown at this stage.
The study shows that a detail of the Sun's death, long neglected in calculations, could determine the future of the giant planets. Their fate may depend less on the passage of time than on how our star dies.