Four large worlds located in a multi-planet system called HR 8799 will someday end up playing space pinball with one another. As of right now, these planets are orbiting their host star located about 135 light-years away from us in an organized and locked rhythm, but that will eventually change when their sun dies.
According to astronomers in a new study, these massive planets (they are over five times the mass of Jupiter) will be sent “pinballing” around their system after their star dies (it is currently between 30 and 40 million years old) as they will lose their perfect orbits and starting crashing and bouncing off of each other.
Their orbits are presently perfect as one planet completes double the orbit of the previous closest world. To understand this better, when one planet completes an orbit, the next one does two orbits, followed by the next world completing four orbits, and the last one doing eight.
Researchers from the universities of Warwick and Exeter have calculated that the “pinballing” event won’t happen for another three billion years when the host star will begin its phase of becoming a red giant. When this happens, the star will lose almost half of its mass and grow several hundred times the size it is now until it becomes a white dwarf.
At that point, the planets will begin to bounce around as explained by Dr. Dimitri Veras from the department of physics at the University of Warwick, “The planets will gravitationally scatter off of one another.” “In one case, the innermost planet could be ejected from the system. Or, in another case, the third planet may be ejected.” “Or the second and fourth planets could switch positions. Any combination is possible just with little tweaks.”
He went on to say, “They are so big and so close to each other the only thing that's keeping them in this perfect rhythm right now is the location of their orbits.” “All four are connected in this chain. As soon as the star loses mass, their locations will deviate, then two of them will scatter off one another, causing a chain reaction amongst all four.”
And that’s not all as there are two debris discs located in the system – one inside the innermost planet’s orbit, and the other on the outside of the outermost world’s orbit. When the “pinballing” event happens, the debris in the discs will more than likely become scattered and fly into the star. (A picture of the HR 8799 system can be seen here.)
The study was published in the Monthly Notices of the Royal Astronomical Society where it can be read in full.