# Could a collision of a rogue asteroid with Pluto pull in objects from Kuiper's belt into the inner orbit without destabilizing any other Planets?

If a rogue asteroid close to the size of Pluto collides with Pluto, could this possibly cause enough disturbance to cause objects from Kuiper's Belt to be pulled into the inner orbit of the Solar System but without destabilizing any other Planets?

• Do you mean the resulting debris field or the rogue planet on its way in? (depends on its inclination) Am I just being semantic: The collision itself does nothing other than turn some of the matter into energy. – Mazura Jun 15 '18 at 16:19
• Regarding the resulting debris field. – angelofdev Jun 16 '18 at 12:12

In the Kuiper Belt there is a whole lot of nothing.

A collision between a couple larger objects could easily distribute a bunch of their debris through the belt, and since Pluto and its moons are relatively large objects they could eventually bother something out there. But it is so large and sparse it could be a long long time coming.

It could also send mass sunward, Pluto is the size of the larger moons of the official planets. Neptune's moon Triton in fact seems like a reasonable candidate for something like this happening in the past; it is about the same size as Pluto and has a very odd orbit implying it was captured rather than formed.

If it happened to get close to any planet it might disrupt its moons, but would not likely destabilize the planet. But the solar system is pretty empty too.

Most importantly though it would melt as it came into the hotter parts of the system. Pluto has a lot of nitrogen ice that would evaporate before getting close to us. If it broke into little pieces before impacting it might even hit Earth without killing everyone.

TL;DR Pluto dying could be totally ignorable from Earth or other planets and not likely to be much of an issue to other Kuiper belt objects.

• I don't believe this is correct. A collision of Pluto with a Pluto-mass object will be very energetic unless it's carefully set up not to be. A collision big enough to disrupt Pluto would scatter its fragments in every direction, resulting in much of the mass getting out of resonance with Neptune. This would then result in it being scattered in all directions by Neptune. A non-trivial chunk of Pluto's mass would eventually make it into the inner Solar System. You'd see an initial burst of debris from the collision followed by a continuing rain of bits and pieces for thousands of years. – Mark Olson Jun 15 '18 at 11:42

No.

While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water. (Source)

Rather than creating a chain reaction of elastic collisions (like the opening shot in a game of billiards), it would create a short period of very inelastic collisions (think "snowball fight"). The result would be a lot of loose ice floating around the kuiper belt, but pretty much nothing else.

• Haven't you by chance swapped elastic and inelastic? On impact billiards balls are pretty bouncy, while snowball pretty squashy. – L.Dutch Jun 15 '18 at 5:21
• @L.Dutch, I might have, those physics classes were 30+ years ago.... – JBH Jun 15 '18 at 6:01
• I can confirm that inelastic and elastic appear to have been swapped, the parentheticals clear it up quite well. – rodolphito Jun 15 '18 at 7:20
• Thanks @Rodolvertice ! I've updated the answer to reflect the correct assignment. – JBH Jun 15 '18 at 8:10
• Um. Methane freezes at about 75K at low pressue (the ammonia and water are higher), Pluto varies between about 33K to 55K. Even the methane is going to be pretty damn solid at those temperatures. The reason the collisions will be inelastic is not the material, but that the objects are too small for their gravity to properly compress them into solid objects. – Martin Bonner Jun 15 '18 at 11:24

Anything that disturbs the Belt has the potential to cause some Belt objects to fall inward. The planets are only going to be disturbed if the objects hit them.

• Would the mass of the colliding object compared to the mass of the Planet be a deciding factor? – angelofdev Jun 15 '18 at 4:00
• @angelofdev The mass an object and the characteristics of it's (new) orbit are the important factors. Most Belt objects won't fall inward. Of the few that do fall/orbit inward, most won't hit a planet. Of the very few that fall inward and hit a planet, most will be too small to notice or otherwise inconsequential. Once every few hundred million years, Earth gets a fair-sized mass-extinction hit...which has negligible effect on Earth's orbit. – user535733 Jun 15 '18 at 4:47
• The planets are only going to be disturbed if the objects hit them Disturbed in the same way a fly disturbs a large truck's windscreen. – Reactgular Jun 15 '18 at 13:57
• @cgTag it’s true their orbits wouldn’t move. I was thinking like techtonic activity or climate disturbance. Most Belt objects are small, but there are a few “large beetle” size. :-) – SRM Jun 15 '18 at 14:04

This started as a comment, but I think it deserves to be turned into an answer: Yes, a collision like that would significantly increase the debris coming in to the inner Solar System, and would significantly affect Earth, but would not destroy it or alter its orbit.

A collision of Pluto with a Pluto-mass object will be very energetic unless it's carefully set up not to be. (If it's set up to be a gentle merger, then nothing much will happen other than Pluto melts into an incandescent mess. I assume that's not the case you're asking about.) Anything like a head-on collision would be big enough to disrupt Pluto and scatter much of its mass as gas, rubble and fragments (mostly small fragments) in every direction.

Here's the catch: Pluto is in a resonance with Neptune which has the effect of stabilizing its orbit. If that resonance was disrupted (and most of the fragments would not be left in a resonant orbit) much of the bits would be scattered by Neptune on a timescale of a few to a few tens of Neptune orbital periods -- call it on the order of a thousand years

This scattering by Neptune would then result in the debris being scattered more energetically in all directions. Much would go outwards, but a non-trivial chunk of Pluto's mass would eventually make it into the inner Solar System of basically cometary orbits. (Some of it in multiple stages in the planetary billards game Jupiter likes to play.)

So you'd see an initial burst of debris from the collision followed by a continuing rain of bits and pieces for many thousands of years. It would be dramatically larger than what we see now, but it also would be dramatically less than the Late Heavy Bombardment. It would probably be survivable, but I suspect that Tunguska and Chelyabinsk-style events would become fairly common. (And no one would pay attention to the Perseids anymore.)

So the Earth would get a modest battering, but it's orbit would not be in any way disrupted. (Nor would the orbits of any other planet, nor would the orbits of smaller bodies in the Asteroid Belt or the Kuiper Belt. The collision debris simply isn't going to be big enough have significant gravitational effect.)

• "So the Earth would get a modest battering" - unless the pieces hit something else first, or get caught by Jupiter and Saturn. – molnarm Jun 15 '18 at 15:16
• Space is very big and the planets very small in comparison. Jupiter and Saturn would no more sweep up all the fragments than they sweep up all the meteors. – Mark Olson Jun 15 '18 at 17:51

No.

The impact as you described it would at worst tear Pluto apart and turn most of its ice in a cloud of gas that will disperse in space.

For Pluto to be dragged away from its orbit, you need the passage of a substantially larger object with a hefty gravitational pull. The timing should be just perfect for Pluto to perform a slingshot and then fall toward the inner solar system.

No. First off, the impact would evaporate the frozen nitrogen and water ice forming a good part of pluto ( more on Pluto internal structure ) and a the rest of the Pluto+asteroid mass would be scattered into relativly little chunks.

Those pieces probably won't impact any Kuiper body since the Kuiper belt is very big and mostly (as in >99.99%) void space.

They also won't have enough gravity to provoke disturbances to the belt since the only disturbance we know of has been triggered by Neptune (which is far, far bigger) and it still didn't pull any object near the inner system, it just made their orbit very outwardly eccentric).

Studies since the mid-1990s have shown that the belt is dynamically stable and that comets' true place of origin is the scattered disc, a dynamically active zone created by the outward motion of Neptune 4.5 billion years ago scattered disc objects such as Eris have extremely eccentric orbits that take them as far as 100 AU from the Sun

Source on the nepune event: https://en.wikipedia.org/wiki/Kuiper_belt

• 99.99% empty is a huge understatement just how empty that region of space actually is. – Philipp Jun 15 '18 at 14:14

The Kuiper belt is a huge huge huge region of space with a few small and scattered dwarf planets and asteroids. There is not much gravitational interaction between the different dwarf planets.

However, Pluto has 5 moons. If Pluto collides with an object of similar size, then that collision might result in Pluto losing some of those moons. They might get launched towards the inner solar system.

The largest one of them (Charon) has a mass which is about 1/2500th of Earth. If it would collide with Earth (a very unlikely coincidence, but it might make for a good story), then that event would not alter the orbit of Earth much. But it would extinguish all life on it.