# What size asteroid is needed to move the Sun?

What kind of asteroid would it take to hit our sun out of its current position, even by just 50 meters? And how big does it need to be in order for it to do so? Would it continue to travel through space after being knocked out of our system, or is this simply not possible? If so:

What size asteroid would be able to 'shatter' the sun?

• You're crashing a fly into a cargo ship. francisuy.blogspot.com/2011/03/weight-of-world.html Jan 17 '15 at 14:43
• If we can freely interpret "even if it is ever so slightly", then a small pebble will be sufficient. You should define how much you would like to move it, for example, would moving it by a small fraction of a femtometre count?
– vsz
Jan 18 '15 at 11:16
• Surely if it's big enough to move the sun, it can't really be called an asteroid. Jan 18 '15 at 11:35
• An asteroid? To move the sun? I... Just... Can't... Jan 19 '15 at 20:17
• @SerbanTanasa I was just curious, and by at least 50 meters if anyone has any other suggestions Jan 23 '15 at 11:38

tl;dr: It can't be done.

Meteors and all the various different classifications of them (meteorites, meteoroids) are small. The sun is big. More importantly, the sun is hot. If a meteor is heading for the sun, not only would it do almost nothing when it hits, it would be vaporised long before it hits.

However, in theory:

Let's assume you have a meteor 100 tons in mass. That's 100,000kg. Let's say it's travelling pretty fast, $3 \times 10^5 \text{ms}^{-1}$We can work out how much momentum it has:

$$\text{momentum (kgms}^{-1})= \text{mass (kg)} \times \text{velocity (ms}^{-1})$$ $$= 100,000 \times (3 \times 10^5)$$ $$= 3 \times 10^{10} \text{ kgms}^{-1}$$

The Sun has a mass of $1.989 \times 10^{30} \text{kg}$. Therefore, if we divide the two we can find the resulting velocity of the Sun after impact:

$$\frac{3\times 10^{10}}{1.989\times 10^{30}}$$ $$= 1.508\times 10^{-20} \text{ ms}^{-1}$$ $$= 0.00000000000000000001508 \text{ ms}^{-1}$$

It is important to note that this same math applies to a vaporised asteroid as conservation of momentum still applies; however, if some of the vaporised material passes the Sun, it won't affect it. However, as shown in this article, this is unlikely as the acceleration of dispersion is not enough to disperse the material sufficiently before reaching the Sun.

So even a fairly "heavy" meteor only results in the Sun moving at a fraction of a metre per second, at which speed its gravity would keep all the planets in orbit with it.

Lastly, it is impossible to "shatter" the sun, as it is made of gas and would simply part and reform around an asteroid.

• It doesn't matter whether the meteor vaporises or not; it will still preserve its momentum and affect the Sun equally much with it. A non-vaporised meteor might on the other hand cause more damage to whatever it hits, but that is another aspect of the impact. Jan 16 '15 at 10:36
• @HelloGoodbye A vaporised meteor will be quickly deflected by the sun's convection currents and magnetic fields and will not affect noticeably. Yes, it will affect it but the effect is negligible and so I have excluded it. Jan 16 '15 at 10:39
• @ArtOfCode - it always will interact, unless it has gone into orbit (and even then it will interact, just not as an impactor) - in addition, deflections that move the object from impactor trajectory into orbit still count, because they have transferred momentum between the two interacting objects. Jan 16 '15 at 12:25
• @ArtOfCode: Incorrect, they will be identical. You cannot cheat the laws of physics (and in this case specifically Newton's third law, and conservation of momentum). The same momentum transfer happens regardless. The only exception here could be if the material flowed past the sun and continued on its way. This would not happen to a solid object impacting the sun. The vaporisation distance is too close Jan 16 '15 at 13:09
• @ArtOfCode: This is a great answer, but you gotta listen to HelloGoodbye and Neil Slater - you are incorrect about the vaporization affecting the transfer of momentum. You should edit your answer accordingly - the rest of your answer is awesome. Jan 16 '15 at 17:13

Something the other answers seem to have missed and I will focus on is:

would "it" (the Sun) continue to travel through space after being knocked out of our system

Let's ignore the impracticalities of moving the Sun and focus on what would happen once the Sun starts moving. The answer is also not a lot would happen.

For a start, our Sun is already moving, along with the rest our solar system, at 230 km/s around the "Galactic Central Point". This "Galactic Central Point" is the galaxy's centre of mass, just like the moons of Jupiter, or the planets of our Sun, all stars in our galaxy are orbiting this centre of mass.

So when we talk about moving the Sun, what we really mean is significantly altering its orbital speed. This would change our path around the galaxy, but the consequences of that may not be seen for millions of years and are therefore difficult to predict. But due too the vast emptiness of interstellar space, there is a high chance nothing would happen.

That is if you ignore the effects of something large enough to change the Suns course in the first place. As has already been pointed out by other answers, you need something massive to influence the Sun.

Jupiter is the second largest object in our solar system, its mass alone is 2.5 times larger than the rest of our solar system combined. It's so massive that it forces our solar system's centre of mass outside of the Sun, if only slightly (Our moon has a similar, but much smaller effect on us). But as massive as Jupiter is, slamming it into the Sun will hardly affect its orbital velocity (as already pointed out).

So we're going to need something bigger than the biggest planet in the solar system and this is where we run into tangible problems for Earth. As I already pointed out, Jupiter is so big that it moves the centre of the solar system, anything that big entering the inner solar system, on a direct collision course with the Sun, is much more likely to disrupt our orbit before it disrupts the Sun.

This new gravity source could alter our path, taking us out of the habitable zone, perhaps making the planet too hot or cold too support life for much longer. It could even elongate our orbit enough to put our highest point into the asteroid belt where the planets surface would be bombarded by asteroids. Worst case Earth could even be accelerated out of the solar system.

In short if anything big enough to affect the Sun ever comes that close to the Sun, we are probably already dead. Where the Sun goes, the rest of the solar system follows, unless another force disrupts the planets orbits.

• +1 for answering the implied questions as well as the voiced question. Jan 17 '15 at 18:01
• Exactly, the concept of moving the sun, as though you could take it out of the solar system is missing the point that the suns gravity is what predominately makes up the solar system. Side note, our galaxy, which our solar system is orbiting the center of, is also moving...
– MER
Jan 17 '15 at 22:43
• Indeed, I didn't go into that because my primary goals were to establish the idea that our sun orbits something and introduce the concept of orbiting the centre of mass rather than a specific body. Introducing galactic level motion was a needless layer Jan 18 '15 at 1:02

Technically, everything would cause the sun to move, whether we have the ability to measure or see its effects are something different.

Every object in the solar system causes an attraction due to gravity and mass. The sun would move towards the planet slightly less as it's mass is larger, but it is attracted and does move towards the planets slightly. This is called the stars wobble.

This is the principle used initially when we began really looking for planets outside of our solar system.

• Actually the sun is attracted the same as say the earth is attracted to it, but the sun's larger mass makes it less affected. Jan 16 '15 at 18:31
• @mpg You are correct in everything is attracted to each other. Even a single atom will pull the Sun. However, your statement that "the sun is attracted to the object slight less" is completely wrong. An atom and the sun are attracted to each other with exactly the same force. Equal and opposite reactions, you know... Laws of physics. That force attracts them at different rates of movement though due to mass. Jan 16 '15 at 20:57
• You are correct, I apologize. My phrasing on that was way off. I should have worded that as: The sun would move towards the planet slightly less as it's mass is larger than (in this case) the asteroid.
– mpg
Jan 16 '15 at 21:47
• And if you can hold an object in the same position relative to the Sun you have a "Gravity Tractor" and it will pull the Sun along behind it. Very, very, very slowly. Jan 19 '15 at 2:33

If we strech the definition of asteroid well past what is reasonable.

Jupiter has an orbital energy of $1.544×10^{35} J$. WolframAlpha

So if we crash Jupiter into the sun(deorbiting it by magic) in a inelastic collision we will impart 8.6 m/s of velocity. WolframAlpha

This corresponds to a 0.029% change in the earths orbital velocity. WolframAlpha

I have no idea how noticable this would be. The effects from the sudden lack of Jupiter would definitly be more noticable.

• Well, if you want to get really ridiculous, you could suppose the collision to be perfectly elastic (i.e. Jupiter and the Sun bounce off each other like billiard balls), but I think you might have difficulty with the audience's willing suspension of disbelief here. Jan 16 '15 at 17:10
• We could also crank our Jupiter up to relativistic speeds. With a Jupiter travelling at around 0.1c, we could impart about 100,000 m/s of velocity to the sun. Jan 16 '15 at 17:40
• @ckersch: I think such an impactor would actually pass through the sun (or rather a lot of its momentum would do so, in the form of ejected matter on the opposite side), rather than be fully absorbed, but may do some damage and impart some percentage of its momentum as a consequence. An impact at that speed may also cause unusual atomic fusion events due to extreme pressure as material collided. Jan 16 '15 at 18:54
• @ckersch this is starting to sound like a "what if" XKCD... Jan 16 '15 at 19:19
• Doesn't that 8.6m/s of impulse merely cancel the velocity change due to the increased gravitational pull of the approaching Jupiter? At every instant during the approach, the center of mass of the sun-Jupiter system remains on a single trajectory (its orbit around a galactic center, perhaps), and the impact doesn't move the new combined mass off this trajectory either. Jan 16 '15 at 21:49

It will not happen, no matter how big a meteorite is.

Now, some data:

A meteorite is a rock that has fallen to Earth from space, so it can not impact Sun at all. Meteors are the traces of falling stars on sky. So I'll talk about meteoroids for the remaining of the answer.

(Check Meteoroid at Wikipedia)

Sun's mass is $(1.98855±0.00025)×10^{30} \text{ kg}$, while meteoroids are, by definition, smaller than 1m size. Such a small rock will not even be noticed by Sun.

EDIT

Biggest asteroid in the Solar System is Ceres, currently classified as a dwarf planet like Pluto. Ceres' mass is $(9.43±0.07)×10^{20} \text{ kg}$ (ten orders of magnitude less that Sun's). On its own, Eris, which is the biggest dwarf planet (bigger than Pluto), has a mass of $(1.67±0.02)×10^{22} \text{ kg}$, 8 orders of magnitude less than Sun's mass (this is a hundred millions times minor).

It will simply not move the Sun at all.

• Incorrect. The Sun will move due to gravitational attraction to the projectile (believe it or not, you are exerting a gravitational pull on the Earth right now) - it's just the resulting movement is negligible. May 7 '15 at 8:36

The answer is not impact, but gravitational attraction.

The Sun is a giant ball of gas.

If you launch a meteorite of a "magical" material strong enough to survive its interior, and with speed/aerodinamics enough that it does not get slowed down by friction (another thing that is easier said than done, given its size), such meteorite would emerge at the opposite side (although with, probably, some deviation).

If you want to move the Sun, you want to pull something massive near it and have it attract the Sun. Of course, such a massive object would also affect the planet orbits by itself, so I do not think you would get the Sun to move away from the planets (most likely, the planets will end crashing in the new object).

• What if an asteroid of such a size sweeped through the milky way that it effects the positioning of every planet / gas-giant and sun, would the planets get launched out of the milky-way or would they all collide with one another Jan 16 '15 at 9:46
• @Gerwin Something of that size wouldn't be an asteroid - it would be a black hole - and a huge one at that. Jan 16 '15 at 9:55
• @TimB so you're saying that an asteroid of such a scale couldn't exist, because it would've turned into a black hole? Jan 16 '15 at 9:56
• I do not really know, but it will depend of the relative position. Out of the envelope, if the object was in the elliptical I would expect most of the inner planets to crash in it. If it was perpendicular and/or close to the Sun, maybe it would result in orbits closer to the Sun (but some could be expelled). Jan 16 '15 at 10:17
• @Gerwin If it's passing through the milky way throwing planets around then it's absolutely massive. Anything that large would almost certainly have collapsed into a black hole. I really think you don't understand the scales involved here. Space is massive. Jan 16 '15 at 16:09

This reminded me of an xkcd what-if.

https://what-if.xkcd.com/20/

lots of people here saying that it's impossible but that's not strictly true, an asteroid going close enough to the speed of light could absolutely do something bad to the sun.

It may have to be going at 99.9999999[keep adding 9's until you get enough] % of the speed of light but eventually you hit a point where the energy it hits the sun with is enough to cause something catastrophic...

unfortunately the speeds/energy involved would have to be so insanely huge that it would be almost impossible to come up with something even vaguely plausible that could get the asteroid moving fast enough.

• An asteroid would not turn into a black hole no matter what its velocity in space is. Cosmic ray nuclei are accelerated to incredibly fractions of light speed and they are still just nuclei Jan 16 '15 at 17:23
• Fair enough, I was thinking of something I'd read about photons with enough energy being able to create their own micro-black holes. en.wikipedia.org/wiki/Planck_scale Found a better explanation for how I was incorrect: physics.stackexchange.com/questions/3436/… still, I stand by the rest of my post, keep adding 9's and eventually you reach a point where an asteroid would cause problems for the sun. Jan 16 '15 at 17:53
• Quite so. Although I would imagine the problem would be that the sun would be blasted to 'fragments' rather than knocked away like a billiard ball. Jan 16 '15 at 17:56
• I like the answer as it implies the speed of the asteroid makes a large difference here. Only big issue is protons and the sort that can hit the speeds required here are generally sped up to those speeds via magnetism. Jan 16 '15 at 22:23
• "Lots of people here saying that it's impossible", I think most of us have acknowledged that anything is theoretically possible, just not plausible. Even your proposed method employees energy levels you consider "almost impossible" Jan 16 '15 at 22:33

In order to move the Sun, we have two basic requirements:

1. Deliver enough momentum to the Sun to move it. I'll start with enough to get it moving $1~\text{km}/\text{s}$. Not very fast, but let's just see what happens. The momentum is just $p=mv=2.0\times 10^{33}~\text{kg}\cdot\text{m}/\text{s}$
2. Deliver little enough energy to the Sun so it is not destroyed. As an absolute upper estimate, I'll use the gravitational binding energy, which, for the Sun, is about $T=2.3\times 10^{41}~\text{J}$ (about 20 million years of solar output).

We just have $p=mv$ and $T=\frac 12mv^2$. Just by dividing those equations we get: $$v=\frac{2T}{p}= 2.3\times 10^8~\text{m}/\text{s}=0.76~c\\ m=\frac{p^2}{2T}= 8.7\times 10^{24}~\text{kg}=1.45~\text{M}_\text{Earth}$$

Ok, I see really high speeds which means we need to take relativity into account. Fiddling with the proper equations gives us: $$v= \left(\frac{p}{2T}+\frac{T}{2pc^2}\right)^{-1} = 2.0\times 10^8~\text{m}/\text{s}=0.67~c\\ m= \frac{p^2}{2T}-\frac{T}{2c^2}= 7.4\times 10^{24}~\text{kg}=1.24~\text{M}_\text{Earth}$$

For a more reasonable Sun's speed of $100~\text{km}/\text{s}$ the minimum mass goes up to: $$v= \left(\frac{p}{2T}+\frac{T}{2pc^2}\right)^{-1} = 2.3\times 10^6~\text{m}/\text{s}=0.76\%~c\\ m= \frac{p^2}{2T}-\frac{T}{2c^2}= 8.7\times 10^{28}~\text{kg}=4.4\%~\text{M}_\text{Sun}$$

(Remember, this represents an absolute minimum mass required. You'll have to go with something heavier (and therefore slower) to avoid punching right through the Sun.)

So you're not looking at an asteroid, but more like shooting a dwarf star into the sun at a speed of $2000~\text{km}/\text{s}$. Good luck with that!

• If I follow that, you chose values for momentum and kenetic energy and found a unique mass and velocity that had those values. What would happen if the energy was too large? The question did speculate on disrupting the sun, not just moving it. Say, an asteroid (Ceres mass) not a (non-dwarf)*planet* or KBO; moving at ultrarelativistic speeds. May 7 '15 at 3:03
• @JDługosz It depends on how efficient the energy transfer is. If you're going fast enough to punch right through the Sun (especially if you don't hit head-on) the Sun will definitely notice, but will pretty much return to normal after 10k years or so. On the other hand, if most of the KE gets transferred to the Sun, then the energy release will be enough to blow all of the parts of the Sun out of the solar system. May 7 '15 at 13:02

Pea-sized.

That's what size asteroid can move the sun, but, not in the way you expect.

First though, an asteroid implies something that is currently traveling through space in a typical fashion. What would a typical object do when crashing in to the sun?

Fist, it will be moving the sun long before it 'hits'. Gravitational effects will cause both objects to accelerate toward each other. Due to it's mass, the sun's acceleration will be significantly less than the asteroid's, but it will move. The question is really whether the impacting force (in the opposite direction) is more or less than the cumulative effects of the force that was exerted in the opposite direction before the impact.

That largely depends on the velocity of the object before it entered the gravitational boundary of the sun (where the gravitational pull of the sun is more assertive than the pull of the rest of the universe).

In turn, that implies that the asteroid is on a collision course long before it enters the cosmographical boundary which is on the far side of the Oort cloud - 50,000 to 100,000 or more Astronomical units away. (Pluto is up to 50AU from the sun).

Something that is 'pulled' in to the sun through its gravity, will not ever be going fast enough for the impact forces to outweigh the forces that were exerted before the impact.

Note that this happens regularly. In fact, it is how the sun was created. Additionally, comets regularly impact the sun. They have no measurable effect on the suns position (though they can produce spectacular solar flares).

Something that is 'shot' in to the sun may. But also, something shot in to the sun would simply pass through it, unless it burned up first.

Something bigger than the sun? (or close to the same size)

Well, that's interesting, because then the logic all gets reversed, and you really should talk about our sun being shot in to it, not the other way around.

The bottom line is that there's no way for an object to have any significant impact on the sun without being so huge that it will pull all the planets out of place before it gets to the sun, or it is 'fired' in to the sun from outside the solar system (it would be impossible to fire something like that from inside the system)