Our solar system might have had another planet, but Jupiter kicked it out

Canadian researchers have used computer models to show that our solar system could have had an additional gas giant planet in the mix around 4 billion years ago – until Jupiter ejected it, that is. -say.

The idea that there were originally five gas giants – in addition to Jupiter, Saturn, Uranus and Neptune – was first proposed in 2011, to help explain why the solar system currently looks the way it does. ‘It is. It turns out that the orbit of Mars and Earth doesn’t really make sense if it were just the planets we have today.

But researchers have so far been unable to explain what could have happened to this extra planet, with Jupiter and Saturn named as potential culprits for doing the kicking.

“Our evidence points to Jupiter,” said lead researcher Ryan Cloutier of the University of Toronto, who describes the whole thing as an “interplanetary chess game.”

The mysterious lost planet in question is believed to have the mass of an ice giant, meaning it was heavier than Saturn and Jupiter, and in the same class as Neptune and Uranus. So how exactly does a lighter planet suddenly kick an ice giant out of the solar system?

Planetary ejections usually occur as a result of a close planetary encounter – though not necessarily a collision – which causes one of the objects to accelerate so rapidly that it is able to free itself from the Sun’s massive gravitational pull. and launch into the galaxy, becoming what is known as a rogue planet.

In this case, the ejection could be the result of Jupiter moving closer to the Sun from further out in the solar system, affecting the orbit of other planets in its path.

Previous studies had struggled to pinpoint exactly which of the remaining planets might have done this, but in the new research, University of Toronto astronomers realized that until now no one had considered the effect this encounter would have had on the moons orbiting the giant planets.

The team therefore decided to examine the trajectories of Callisto and Iapetus – two of the regular moons orbiting Jupiter and Saturn respectively. Using computer models, they studied the likelihood that the moons would have the same orbit as they do today if they had been involved in a massive planetary ejection 4 billion years ago.

“Ultimately, we discovered that Jupiter is able to eject the fifth giant planet while still retaining a moon with Callisto’s orbit,” Cloutier said. “On the other hand, it would have been very difficult for Saturn to do so because Iapetus would have been excessively disturbed, resulting in an orbit that was difficult to reconcile with its current trajectory.”

The computer model showed that there is about a 42% chance that Callisto would have its current orbit around Jupiter had it been involved in the planetary ejection. The results were published in The Journal of Astrophysics.

But to be clear, that doesn’t mean we have any evidence that this interaction actually took place, or even that there was an extra planet in the solar system in the first place. All of this is based on computer models, and while they may explain the current state of the planets in our solar system, they are not the only possibilities out there.

“We know that rogue planets roam the galaxy, and they were almost certainly ejected that way, so the idea of ​​a lost solar system planet isn’t crazy,” astronomer Phil Plait wrote for Discover in 2011, when the missing planet hypothesis was first proposed. “But that’s just one possible scenario.”

Still, it’s pretty cool to think that somewhere out there in the galaxy, an ice giant roams, a lost remnant of our solar system’s formation.

Arline J. Mercier