If an Earth-sized rogue planet passed through our solar system, missing the planets, how much disruption would it cause?
Alex McDowell
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London, UK
It depends on how close it came to any planets. Venus, which is roughly Earth-sized, sometimes gets to within 0.3 astronomical units (45,000,000 km) of Mercury and causes tiny but measurable perturbations in its orbit.
If it misses planets, it might hit their satellites, causing a lot of debris to be thrown off, which could end up raining down on planets. If it came close enough to any body in the solar system, it would significantly perturb its orbit; this may lead to planets colliding or heading into the sun! It might even “steal” moons.
It would also exert tidal forces on planets – perhaps strong enough to deform rocky planets’ crusts, leading to quakes and volcanic eruptions. If it came close enough to Earth, such eruptions could lead to mass extinctions.
Planets’ axes could also be tilted – if this happened to Earth, it would affect our weather.
If a rogue planet disturbed the asteroid belt, large rocks could end up hitting the planets in the solar system
An Earth-sized object would exert the same strength of gravity on Earth’s surface as the moon does by the time it was within a distance of eight times the radius of the moon’s orbit.
If it disturbed the asteroid belt, large rocks or minor planetoids could end up hitting planets.
Sam Edge
Ringwood, Hampshire, UK
The answer depends entirely upon its trajectory.
Depictions of the solar system in textbooks or online fail to show how colossally large it is, especially compared with the bodies in it, even the sun and the gas giants Jupiter and Saturn.
The result is that the solar system as defined, say, by the aphelion of Neptune (its furthest point from the sun) is essentially empty space. The episode of the UK prison sitcom Porridge where they explored this comes to mind – well worth watching.
So for almost all trajectories, the answer would be “very little”.
If it came in perpendicular to the orbital plane defining Earth’s path around the sun, say half way between the orbits of Mars and Jupiter when they are on the other side of the sun, then it wouldn’t cause much of a ripple, especially if it were moving very fast.
However, if it came in on a curved orbit on Earth’s orbital plane, it would have a much greater chance of interacting gravitationally with a planet.
Depending on how close and how similar its mass to the encountered planet, that could cause severe shifts in the orbit of the planet and disruption of any moons it has. But again, because of how large the solar system really is, the chances of such a close encounter would still be very slim.
Eric Kvaalen
Les Essarts le Roi, France
If it came near one of our planets, then it would significantly change its orbit, and that could have severe consequences later.
Last year, 91av published an article about what would happen if a star passed through the solar system. An Earth-sized planet would have a lesser effect, but that study may still give some indication.
The effect depended of course on how deep into the solar system the star came. In some cases the orbits were only slightly altered, but if the star came near the orbit of Earth, it could throw all of the planets out of the solar system completely and immediately.
Another interesting outcome was that initially the perturbation seemed small, but after a million years, Mercury’s orbit became quite eccentric and after 10 million years it fell into the sun.
In some cases, Earth’s moon is perturbed by a close approach of one of our solar system’s planets (such as Venus) and ends up hitting Earth.
Atlant Schmidt
Nashua, New Hampshire, US
That would depend a lot on the intentions of any occupants of that planet.
More seriously, if it became obvious that there was a civilisation on that planet, it would cause massive disruption to our civilisation here on Earth.
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