The solar system could lose its stability much sooner than previous models suggested. The reason is not just the gradual fading of the Sun, but the way it will lose mass at the end of its life - in separate, asymmetric pulses that can change its motion and the orbits of the planets.
The Sun is expected to become a white dwarf in about 6 billion years. In the process, it will lose about half its mass, and the outer planets will move away as its gravitational pull weakens. Older calculations assumed that this loss would be gradual, and that Jupiter, Saturn, Uranus, and Neptune would remain in relatively stable orbits for tens of billions of years.
The mass won't be lost evenly
Konstantin Batygin and Jim Fuller of the California Institute of Technology and Fred Adams of the University of Michigan have explored another scenario. In it, matter would be ejected in discrete bursts. Each such pulse would give the Sun a small boost, and the accumulation of thousands of such changes would act as a random walk on the planets' orbits.
The researchers ran computer simulations of different mass loss scenarios. In the most realistic set of 48 simulations, the orbits of the outer planets begin to intersect in 37 cases. In some of these scenarios, instability appears even before the Sun has shed a significant part of its outer layers.
Saturn could leave the system
The models allow for different outcomes. Uranus and Neptune could swap places or approach Jupiter's orbit. Saturn could be thrown out of the solar system. When the orbits converge, gravitational interactions are possible that could send a planet into interstellar space.
In 90 percent of the simulations, the solar system breaks up within 3 billion years after the Sun turns into a white dwarf. This is significantly shorter than previous estimates, according to which the outer system could survive for tens of billions of years. The new study suggests that instability may begin as early as the transition to a white dwarf.
The results are not an exact calendar for the future of any planet, but rather a statistical inference from multiple simulations. However, they challenge the notion that planetary systems around stars like the Sun end their lives peacefully. According to the authors, a similar process could affect other star systems, since most stars end their evolution as white dwarfs.
Sources: sciencealert.com