Suppose an extra-solar object the size and mass of the Earth, travelling at a speed of $26\ \mathrm{km/s}$, the same of ʻOumuamua (the first known interstellar object crossing our solar system), hit the Sun at its equator.

What would be the consequences to the Sun in terms of heating and heliosphere modifications in the minutes immediately following the impact and in the following days/weeks?

What would be the consequences on Earth from this impact?

The Sun photosphere is very thin, with a density of about $3\times10^{-4}\ \mathrm{kg/m^3}$, compared with the object density of $5.5\ \mathrm{t/m^3}$, so the impact with the external layers will be relatively light. Before suffering significant damage the extra-solar object will sink deeply into the Sun, causing damages to the more internal layers, probably smoothing and reducing the effects outside.

I am also interested in understanding the speed at which the phenomena would affect our planet.


I did some researches and found a similar event happened in relatively recent time on Jupiter when, in 1994, the Comet Shoemaker–Levy 9 hit Jupiter, fragmented due to a previous closer approach to Jupiter in July 1992.

Citing from the Wikipedia: "The largest [impact] coming on July 18 at 07:33 UTC when fragment G struck Jupiter. This impact created a giant dark spot over 12,000 km (7,500 mi) across, and was estimated to have released an energy equivalent to 6,000,000 megatons of TNT (600 times the world's nuclear arsenal)". This fragment of comet was something like 2 Km in diameter.

"Despite published predictions,] astronomers had not expected to see the fireballs from the impacts and did not have any idea in advance how visible the other atmospheric effects of the impacts would be from Earth. Observers soon saw a huge dark spot after the first impact. The spot was visible even in very small telescopes, and was about 6,000 km (3,700 mi) (one Earth radius) across. This and subsequent dark spots were thought to have been caused by debris from the impacts, and were markedly asymmetric, forming crescent shapes in front of the direction of impact."

I think that this impact is very likely to be comparable with the one that could occurr between the Sun and the Earth-like object for the following reasons:

  1. Jupiter is a gas giant planet, with density in the upper part of the atmosphere very similar to the Sun.
  2. Proportions between the objects are very similar (Jupiter has a mass one-thousandth that of the Sun) and the comet object a diameter that is roughly one-thousandth of the Earth.
  3. The impact speed was approximately $60\ \mathrm{km/s}$, that is not so distant from the supposed speed of the Earth-like object.

My very personal conclusion is that on the Sun the effects would be very evident, with a huge spot that expands for several tens of terrestrial diameters, probably followed by a huge plume of incandescent gas.

The consequences would not be so significant for Earth, apart from a terrible electromagnetic storm with probable huge repercussions on telecommunications.

It remains to understand the effects on the average temperature of the sun and the relative temperature changes that the Earth would face.

  • 13
    $\begingroup$ Anything falling extrasolar into the sun is going to hit at 615 km/s minimum. $\endgroup$
    – notovny
    Jan 15, 2020 at 21:25
  • 5
    $\begingroup$ To back up what notovny said, en.wikipedia.org/wiki/Escape_velocity#List_of_escape_velocities solar escape velocity is 617.5 km/s, so anything hitting the sun that came from outside the solar system is going to be going at least that fast. $\endgroup$
    – Rob Watts
    Jan 16, 2020 at 17:34
  • 3
    $\begingroup$ It might disrupt planetary orbits if it passes close enough to them. Anyone whoever watched Thundarr the Barbarian knows this :-) $\endgroup$ Jan 16, 2020 at 19:20
  • $\begingroup$ It would go "bloop" and not much more. $\endgroup$ Jan 16, 2020 at 21:04
  • 1
    $\begingroup$ See also "what happens to a great big fire when you drop a very very small piece of paper in it". ; ) $\endgroup$ Jan 17, 2020 at 8:18

10 Answers 10



The sun is big.

enter image description here Source

It's not the biggest thing out there by a long shot:

enter image description here

... but in our neighborhood, it's the biggest fish in the pond by far.

Heck, the Sun belches bigger than us:

enter image description here (credit: jpl.nasa.gov, ResearchGate link)

So, an Earth-size object impacting the Sun would be less visually interesting than a bug zapper. It might produce some interaction with the corona or photosphere that would provide some insight to heliophysicists, but compared to some of the things the Sun does all on its own, it would have a negligible effect.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Monty Wild
    Jan 19, 2020 at 19:13

It wouldn't be that much.

Even at that speed there just isn't enough mass in an earth-like object to transfer enough energy to the sun to make a significant change. You would probably get some really energetic solar flares and/or Coronal Mass Ejection immediately after the collision, but that would be it. The Earth would only be affected if it were directly in the path of a flare or ejection.

Keep in mind also that even at that speed an Earth-like planet isn't likely to collide with the sun as a solid object. The tidal forces of the Sun's gravity are going to turn it into a giant pile of rubble before it gets to the atmosphere, which will just make the process of vaporizing the entire thing that much quicker.

If the impact occurred on the other side of the sun, we could probably see the effects in the form of sunspot activity a couple weeks later when that side of the sun rotated back into our view, but that would be it.

There wouldn't be any effects to either the sun OR the earth that lasted more than a few weeks.

  • 5
    $\begingroup$ @Madiozoz it absolutely would not. You're talking about the rough equivalent of shooting a watermelon with a BB gun. You'd have to examine the watermelon pretty closely to even be able to tell it'd happened. You could hit the sun with JUPITER and not not have that much of an effect on other planets. $\endgroup$ Jan 15, 2020 at 15:35
  • 23
    $\begingroup$ @Madlozoz be less lazy. $\endgroup$ Jan 15, 2020 at 16:08
  • 1
    $\begingroup$ Since the Sun weigth 333,000 times the Earth, the Sun will increase its speed of 78 meters per second in the opposite direction. This is a very tiny changes... almost irrelevant. $\endgroup$ Jan 16, 2020 at 16:05
  • 4
    $\begingroup$ @NicolaLepetit It'd actually be a lot less than that, even, because the Sun isn't a 'solid' object that the Earth could just apply it's entire kinetic energy to moving. Much of that kinetic energy would be converted to heat, and what wasn't would be just as likely to add an imperceptible amount of extra angular momentum to part of the Sun's atmosphere. $\endgroup$ Jan 16, 2020 at 16:45
  • 1
    $\begingroup$ @MorrisTheCat Jupiter being gone would affect the other planets though $\endgroup$
    – Bergi
    Jan 17, 2020 at 0:35

At 26km/s you'll get nothing. A light show. A scar on the surface that might be visible to solar telescopes for days. Maybe a mass ejection that might effect earth if it's aimed in the right direction.

But, how flexible are you on speed? If the planet is going fast enought you could . . .

Maybe destroy the sun. Depending on the impact speed. Maybe.

I want you to read this post on "physicsforums.com".

In case you can't reach that post, the takeaway is if an earth-size planet is going ~30% the speed of light it will have about the same kinetic energy as the gravitational binding energy of the sun. That's the amount of energy required to blow the sun to pieces.

The trick is to deliver that energy to the sun. If the planet punches through the star, maybe only a small percentage of the kinetic energy is transferred to the sun. It might have to hit the core directly, it might have to be going much faster.

It might be that a planet going 99% the speed of light would just punch an earth diameter hole through the sun, eject a bunch of material and leave the sun basically unchanged.

It might be that moving a bunch of material around the core will disrupt the constant fusion reaction, causing it to speed up or slow down changing the brightness of the sun for a short time. Or causing the brightness to oscillate for a long time. It's hard to run that experiment.

You have to wonder who would accelerate a planet to those speeds, because it will not happen naturally.

In summary:

At orbital speeds inside our solar system (~30km/s): Definitely not

At orbital speeds for our galaxy (~200km/s): Probably not

At relativistic speeds that could never happen naturally and could only be achieved by advanced technology operating at an inconceivable scale: Maybe, but not for certain.

  • 5
    $\begingroup$ Given that I'm not a physicist, it seems more likely to me that the 'punch straight through' option seems most likely. My understanding of the interactions involved would be that the incoming planet would cease to be a solid object well before it got to the core just due to the temperatures involved. What would come out the other side would be a jet of intensely hot gas and/or plasma that might have several times the mass of the impactor, but that's not much different from the average solar flare or CME that stars do ANYWAY. $\endgroup$ Jan 15, 2020 at 18:24
  • 1
    $\begingroup$ I would imagine there are an awful lot of astrophysicists who feel the same way. =P $\endgroup$ Jan 15, 2020 at 18:54
  • 1
    $\begingroup$ @MorrisTheCat I'm not so sure. It seems entirely possible that you'd have the planet instantaneously transform into a giant explosion, instead. IIRC XKCD has a comic about something similar happening on the Earth's surface. $\endgroup$
    – nick012000
    Jan 16, 2020 at 6:03
  • 2
    $\begingroup$ @nick012000 Do you mean what-if.xkcd.com/1 with the relativistic baseball? $\endgroup$
    – MilConDoin
    Jan 16, 2020 at 10:17
  • 7
    $\begingroup$ The core of the sun is about 100 times as dense as iron. Nothing is going to "punch straight through". $\endgroup$
    – Skyler
    Jan 16, 2020 at 14:54

I'm not as sanguine as other responders are. Magnetohydrodynamics is a really tough subject. Might the impact trigger a coronal mass ejection on a scale orders of magnitude greater than the Carrington Event? If that ejection came straight towards Earth ... well, life would probably go on, but civilisation might not. Or not without a lot of serious disruption.

I'm not qualified to say that this would happen, but how many people are qualified to say that it could not? If it's just a frame for some fiction, then almost all possible readers will go along with the premise. It's good enough that suspending disbelief is not hard (unless you are a suitably qualified magnetohydrodynamicist specializing in stellar atmosphere phenomena).

  • $\begingroup$ Exactly what I was thinking. Clearly, the thing isn't going to cleave the Sun in two, which is what most respondents seem to think the OP has in mind. But if even a small fraction of its kinetic energy was released as a solar flare , which then hit the Earth, we might have a serious impact on our highly-integrated global technological society, with all the knock-on collateral damage that that would cause. $\endgroup$ Jan 17, 2020 at 12:47

An Earth-mass planet moving at solar escape velocity will (if I haven't dropped some orders of magnitude) have about 2.5 billion times the amount of energy output by the Sun in a single second, or nearly 100 years of solar output, delivered to the Sun in an extremely short time. If a significant amount of that gets coupled to the upper radiative layers, that would be very noticeable, and potentially apocalyptic, to anything with a view of that part of the Sun. But far more energy than that is contained inside the Sun, so if the energy gets captured further inside, that shouldn't be too terrible. That's about as far as BOTE calculations can get, as someone pointed out upthread the actual impact dynamics would be extremely complex.

(Math: solar output = 4 * 10^26 joules/s (numerous sources), K.E. of planet = 1/2 (6 * 10^24 kg) * (6.2 * 10^5 m/s)^2 = 1.15 * 10^36 joules).

I don't see any way you could get an extrasolar planet to impact the Sun at less than solar escape velocity, but if you can magically make it slow down to 26 km/s, then it would be delivering only 5 million seconds worth of solar output, or about 2 months of solar output.

I wouldn't want to be on that side of the Sun, to say the least.

  • $\begingroup$ This seems a little incomplete as an answer. The math checks out and is useful to see just how much energy hits the sun, but then you aren't able to say for sure what effect it will have. Also, you seem to be using "solar output" to mean the amount of energy hitting the Earth. $\endgroup$
    – Rob Watts
    Jan 16, 2020 at 17:45
  • $\begingroup$ Excellent point! Essentially the Earth is doing a re-entry at four times the speed of the Apollo craft. This is a prima facie case that the effect would be big enough to notice, but now some math is needed to refine the estimates. (E.g., the energy dumped into the Sun's outer layers (how deep?) is big compared to the Sun's radiation, but is it bag compared to the thermal energy contain in those layers?) $\endgroup$
    – Mark Olson
    Jan 16, 2020 at 20:54
  • $\begingroup$ @RobWatts 4*10^26 joules/s is the total solar energy output, not the amount reaching Earth (OK, rounded up from 3.8). See e.g. learnastronomyhq.com/articles/… . You are right that it's an incomplete answer - that's because a complete answer requires a very specialized skillset, and probably a lot of simulation time to model such an event. $\endgroup$
    – Jon
    Jan 18, 2020 at 12:42
  • $\begingroup$ @user3124312 oh, interesting. I think the reason I got it confused might be because 2.5 billion is pretty close to the ratio of total solar output to the energy that hits the Earth every second. Looking at it again I definitely agree that you're right $\endgroup$
    – Rob Watts
    Jan 19, 2020 at 4:23

Probably a lot of interesting things

At minimum impact speed of 617 km/s the energy absorbed by the Sun would be ~$10^{36}$Joules. This is roughly 3 billion times the energy radiated by the Sun itself in a second (~$3.8\cdot10^{26}$ Watts [from Wiki]) or, in other words, it would take Sun around 100 years to radiate equal amount of energy.

In terms of mass-energy the impact would be equivalent of detonating around $10^{19}$ kg of antimatter: You can think of the event as a large asteroid size antimatter bomb. Or antimatter bomb one thousandth of Moon's mass, if that's more relateble.

At modest velocity of 26 km/s, given in the original post, the energy would be ~$10^{33}$ Joules, or around 6 million times the energy output of the Sun. This, however, equates only to few months of sunshine and mere Gaspra sized antimatter bomb.

In either case, the impact would probably cause complete annihilation of life on the surface of Earth as that much energy needs to be shed somewhere. Uncertain whether aquatic life would be spared. Life that survives under few kilometers of rock could probably also survive.

How fast? Now that's a tricky question. Direct radiation could kill in case one, so that's in something like a week? Or few months if it hit the other side. In case two you'd perhaps need a decade or so for climate to turn inhabitable.

Sun itself? Well, besides spectacular flares and temporary (years, decades, centuries?) massive increase in brightness, probably nothing.


Sun will be more or less unaffected, long-term.

The comparison with solar mass ejections is not very good - the Earth is much denser than those jets of plasma and comparable to some layer of the core.

I am not sure how fast the ablation will be. The object may get well inside, before gets completely evaporated.

Then again, Sun contains a great deal of thermal energy stored in its internal layers and usually well-insulated from the outside. I would expect a serious intermixing in the Sun interiour and a temporary increase of the energy output. It may be less than 1% (we are generally used to this) or way more (say, 50% for a year or two? I wouldn't want to endure that). The oscilations of the output may endure, say, senturies.


hm .. size-wise in every room dimension about 1:110 - so a volume of ~ 1:1,331,000 , mass-wise 1:330,000 ... going by that I would assume the sun to shake a bit .. then maybe throw out some larger protuberances and coronary ejections .. but not much else


Sol itself would be largely unaffected. The planets, on the other hand, could experience slight changes in their orbits, albeit nothing dramatic. For Earth's telescopes, it could be a good show.

  • 2
    $\begingroup$ What mechanism do you think would cause changes in orbits? $\endgroup$ Jan 15, 2020 at 17:53
  • $\begingroup$ As long as the interstellar object intersects a planet and is affected by its gravity pull. Otherwise, there's no change, or so minuscule it can't be detected. $\endgroup$ Jan 15, 2020 at 18:03

You cannot consider such great structure as the Sun as a large sphere of plasma. It is the 19 Century thinking, from the time when physics thought that ass processes are scalable.

It is the same as if you told: "The bullet is only 1/10000 of the man's mass, so it cannot influence him seriously."

Another example: The Coriolis acceleration is roughly 5000 times ~g/(R/T^2) weaker than the gravity acceleration on the Earth. But Coriolis Effect creates, for example, hills at the right banks of all rivers in the northern hemisphere. (And vice versa).

Let's go further, the pure strength or mass of the solar wind particles are absolutely negligible in comparison to the mass of the Earth. About 10^-18 of the Earth's mass/sec. And their influence changes the climate greatly. Or 10^-10/year. And the Earth is merely 3*10^-5 of the Sun. What will become on the Earth, if the Solar wind will strengthen 3*10^4 times for a year? Or 3*10^12 times for a second? Ad minimum, the total extinction of everything above bacterias.

But the real effect of the Earth falling into the Sun could be even more serious. The Sun is the complex superstructure built on structures, built on structures, built on structures, built on the turbulent streams of plasma(each of them being personally unpredictable). It is much more complex than the Earth atmosphere, due not only to the sheer size but much more due to higher energies. (Notice, here is senseless to count how many times larger or higher, for the effect is not scalable at all). And we don't know the structure, let alone the laws of its reactions.

Yes, for a long time the effect could be negligible. In millions of years, it is possible that the Sun will return to the natural state. But in shorter terms, the behaviour of the turbulent structures is very volatile and nobody(of us, people) can foretell the exact reaction.

For example, the whole convection layer in the Sun is (as every turbulent structure) very unstable, and there were hypotheses that that layer can break (totally by itself, without any external reason) the normal transport of the heat for some short time ( in order of months ). And after the convection restores we'll have many times greater heat during some short period. For example, 3 months of the sleeping Sun, and 10 days of 10x heat. -> The boiled oceans on the Earth. or maybe, even the loss of the atmosphere.

Notice, that temporary break of the transport is normal and often for many stars. Our Sun is uncommonly stable. It would be better not to play with it.

The Earth coming into the Sun layer of the radiance heat transport will definitely break the local transparency of that layer. So, the break in the above lying convection layer is very probable.

And about the greater speed, the effect could be the opposite. The processes on the Sun are slow. So, the Earth slowly flying very closely or into the Sun can cause resonance and thus enlarge the purely mechanical and gravitational effects 10-1000 times. Of course, the planet coming with the speed comparable to 'c', can destroy the star in one blast. But the slow planet is not safe even a little bit.

Also, the Earth consists mostly of heavy elements and the place where it will be evaporated will consist of different nuclei. And for several thousand years until it will be spread, the pattern of convection will be asymmetrical. Again - more than enough to break the dynamic stability of our star.

The mass and even the energy of one spit is negligible in comparison to the mass of a person. Will the effect of spitting at a policeman negligible, too? As with the Sun, you are playing against a structure, and its behaviour is not purely mechanical. But the final results for you can be mechanical, too.

Guys, read some serious book on the theme, for example:
Sun physics: https://en.wikipedia.org/wiki/Solar_physics#Further_reading
Complex structures: Nicolis, G.; Prigogine, I. (1989). Exploring complexity: An introduction. New York, NY: W. H. Freeman. ISBN 0-7167-1859-6.

  • 2
    $\begingroup$ If you're going to try to make this case, you should really actually do the math. $\endgroup$ Jan 16, 2020 at 14:07
  • $\begingroup$ @MorrisTheCat Only scalable effects can be counted and could need maths. Structural changes cannot be counted. What maths do you need? $\endgroup$
    – Gangnus
    Jan 16, 2020 at 14:47
  • 3
    $\begingroup$ Why can't I consider the Sun as a large sphere of plasma? Which of the three is wrong? Isn't it large, isn't a sphere, and isn't it made out of plasma? You're right about the turbulence, but that counteracts your answer. The turbulence is turbulent exactly because there's s much local variety that there is no overarching pattern. This is caused because the forces creating the turbulence (electromagnetism) are local. The long-range force is gravity, and it keeps the sun spherical. The small object hitting the sun simply can't affect turbulence across the sun exactly because that's local. $\endgroup$
    – MSalters
    Jan 16, 2020 at 16:17
  • $\begingroup$ @MSalters 1. Because it is structured. You can do it only if you are talking to kid auditory. 2. Turbulence in the Sun is NOT caused by electromagnetism. It is caused by mass energy transport, and is much weaker where electromagnetism is in play. (Radiance transport layer) BTW, nothing in the world "is caused because..." 3. The structure in the Sun is not a one-level one and the word "local" by itself is senseless for it. ...OMG, had you read at least one serious book on the Sun or star physics? At least some bachelor level textbook? en.wikipedia.org/wiki/Solar_physics#Further_reading $\endgroup$
    – Gangnus
    Jan 17, 2020 at 12:15

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .