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I'm looking into a story where the Earth is hit by an asteroid going very fast. This must be a complete surprise and I want to go a mile further than just giving the entirely valid solution of it coming from deep space.

I want the asteroid to come through the Sun and hit the Earth afterwards.

The asteroid in question can go any speed between 0.1c to 0.9c to accomplish this. Reasons for the speed are irrelevant, but ejection from a violent explosion of neutron stars or a sort of solar sail type that ablated the asteroid while pushing it can be imagined at will.

The asteroid should be large enough to impact the Earth after going through the sun. It doesn't matter if the result on Earth will just be a crater the size of a tennis ball or rip the Earth apart. It just needs to reach the surface.

I would like the Sun to be relatively unaltered afterwards.

Extra considerations can be the solar ejections that could travel along with the asteroid.

The main question is: Can an asteroid going between 0.1c and 0.9c go through the Sun and hit the Earth?

The following additions and considerations to the answer are appreciated, but not mandatory.

  • I would like the Sun to be relatively unaltered afterwards.
  • The impact the asteroid has on the surface of the Earth.
  • Star mass that can come with the asteroid.
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  • $\begingroup$ If the object were hard and dense enough, and big enough, and going fast enough, a small core might, MIGHT, come out the other side. Maybe with a little handwavium? $\endgroup$
    – Len
    Jul 1 at 18:31
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    $\begingroup$ Do you want it to go through the center of the Sun, or passing obliquely near the surface is Ok? $\endgroup$
    – Alexander
    Jul 1 at 21:00
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    $\begingroup$ To make it simple, no. The Sun gets so hot, that any kind of material (that we've heard of) will melt and then vaporize before it even reaches the surface. $\endgroup$
    – user86525
    Jul 1 at 22:48
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    $\begingroup$ the earth could be hit tomorrow as a complete surprise, without anything like this, we don't monitor enough of the sky to spot some rouges. $\endgroup$
    – John
    Jul 2 at 3:55
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    $\begingroup$ @John moreover, we have particular difficulty observing if anything is coming from the direction of our sun. $\endgroup$
    – Alexander
    Jul 2 at 16:43
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No.

I'm not knowledgeable enough to derive what would happen in this scenario, but I bet you Randall Munroe is. More specifically, he knows what happens to a baseball that travels at .9 c from the pitcher's mound to the home plate. Spoiler alert: the ball never makes it, at least not in any form recognizable as solid matter, let alone as a ball.

If we consider the tiny mass of air the baseball is trying to "punch through" on its way across half the baseball diamond, and contrast that with the mass of the plasma an asteroid must displace or accelerate as it tries to punch through the sun, it should be apparent to even noobs like us that there's no object that could pull that off while also being small enough to be considered an asteroid.

  1. First stopper: inertia. No matter how fast your asteroid is going, the inertia of the sun will stop it. You might think: "well, if I just crank up the speed, shouldn't it eventually have enough to punch through?" But don't forget: in the frame of reference of the asteroid, it's getting hit by a slice of the sun travelling at .9 c or whatever speed you choose. Unless your asteroid's mass starts to actually compete with a slice of the sun (which I highly suspect it couldn't, and still be called an asteroid), it will be absorbed without affecting the sun's inertia noticeably.

  2. Second stopper: vaporization. (Or like...plasmification...?) Whatever we call it, what happens to Randal's Relativistic Baseball (Wondrous Item, Major, Legendary) will happen to your asteroid. Maybe the explosion would actually increase the sun's luminosity very briefly? I'm not sure, but there's definitely nothing solid left to come out the other side.

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  • $\begingroup$ FWIW, I had the exact same thought; faster ≠ better. Going faster rather increases the interaction between masses. The only way I can see this being plausible is for the impactor to be made of something that can remain coherent on its trip through the Sun, and you're going to have a difficult balancing act between going too fast and heating up too much as a result, and going too slow that you take too long and... heat up too much. Some sort of ablative shielding might be an answer, except we don't want to muck up the Sun in the process... $\endgroup$
    – Matthew
    Jul 1 at 18:32
  • $\begingroup$ Good consideration! I had forgotten about the baseball question. The baseball had the problem that the air couldn't get out of the way quick enough. That, as well as the small size, made it evaporate quickly. But can we just go slower/use an asteroid big enough to have the asteroid survive the ablation? $\endgroup$
    – Trioxidane
    Jul 1 at 18:33
  • $\begingroup$ @Trioxidane, unless it is self propelling, see the inertia problem. It's not quite that simple because the Sun doesn't have a lot of coherency on its own, but there's still a lot of mass you have to shove aside. Calculating this mass would probably be helpful. $\endgroup$
    – Matthew
    Jul 1 at 18:34
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    $\begingroup$ the baseball scenario is very different from what we have here. size (square-cube law), composition, and speed matter very much. also, i don't get where the sun's inertia matters. "affecting the sun's inertia". inertia isn't affected by anything, it's a fundamental property of mass. $\endgroup$
    – ths
    Jul 1 at 19:49
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    $\begingroup$ @jamesqf - there's no requirement that it go straight through the sun's core. Just skimming the atmosphere might qualify as "through". $\endgroup$
    – jdunlop
    Jul 2 at 19:26
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For certain values of "through" I'll give a definite yes.

To be clear, the Sun is much too dense to permit a near-central passage of anything less dense than white dwarf matter at merely orbital or even solar escape velocity; such a "center punch" impact would result in such a lesser object being absorbed and, assuming a mass less than that of a planet like Earth or Venus, virtually no longer term effect on the Sun itself.

A mass with the density of a white dwarf traveling at 0.1 C or faster might potentially punch right through the star, but doing so would be disruptive enough to star to have an effect on planets around it similar to a supernova explosion -- which pretty well fails the "sun must be largely unaffected" desideratum.

However, stars aren't solid objects with a clearly defined surface like a rocky planet. Instead, they're balls of gas, with steadily (or unsteadily) decreasing density going from the core, where the fusion takes place, out to the limits of the atmosphere (by some definitions, for our Sun, near or even beyond the orbit of Mercury). By those definitions, the Parker Solar Probe has an orbit that takes it well inside our parent star.

And that's your solution. No, nothing in the size range you'd reasonably call an "asteroid" can go centrally through the Sun (or any other main sequence star) but it can pass through the Sun's atmosphere, and if its velocity is high enough, possibly even break through the chromosphere or photosphere -- visually, this would be "inside" the star even to astronomers of the 19th century -- and spend so little time there that it merely ablates somewhat from gas interaction. So long as it's coherent enough not to break up at that point like the Chelyabinsk bolide did in Earth's atmsophere, it could then continue (and given 0.1 C or higher speed, with little change of course) toward its rendezvous with Earth.

The amount of bending of the path by the Sun's gravity might well be just about enough for the object to have come from almost directly behind the Sun (from the POV of Earth's position at collision time). The first clue we'd get would be a disruption of the Sun's atmosphere that might be mistaken for a solar flare or coronal mass ejection of unusual configuration; then, no more than 80 minutes later, "Kaboom!" Marvin the Martian will be vindicated.

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    $\begingroup$ Just grazing the top of the photosphere the density would be about 0.1 gm/ cubic meter, air at STP is about 1250. Maybe you could even graze the sun and survive. $\endgroup$ Jul 1 at 20:09
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    $\begingroup$ "Merely ablates somewhat" is a serious understatement. As other answers mention, the impact upon even the least dense parts of the Sun atmosphere would shatter any kind of known material. Unless the asteroid is actually a black hole, it will come out of the Sun as a beam of ultraheated plasma which will spread out in a cone due to electromagnetic repulsion. At 0.1C just the adiabatic compression of the atmospheric hydrogen is going to provoke huge termonuclear explosions on the front side of the asteroid. $\endgroup$
    – Rekesoft
    Jul 2 at 8:42
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    $\begingroup$ @mcalex If it's big enough not to ablate away even in the Sun's lower atmosphere, no, no "tennis ball" or even "tennis court" sized craters -- maybe one as small as Wembly stadium, but probably not, it still has to impact Earth's atmosphere at 0.1C or faster. Yes, there might be up to 80 minutes warning, probably from a day-side solar telescope (the ones that monitor sunspots, prominences, etc.) -- some of those are monitored in real time for solar weather warnings. There might also be no warning at all, if it was cloudy over the only solar telescope on the day side. $\endgroup$
    – Zeiss Ikon
    Jul 2 at 11:08
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    $\begingroup$ @mcalex Solar weather satellites aren't monitored in real time, quite, so there'd be less than 80 minutes warning from them. Further, seeing an eruption (or photospheric fusion event per other comment) wouldn't necessarily serve as warning something was headed for Earth -- someone would have to a) be monitoring in real time, b) realize what causes that event, and c) determine where the object is headed, and the time to do that is subtracted from the 80 minutes... $\endgroup$
    – Zeiss Ikon
    Jul 2 at 11:10
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    $\begingroup$ @GaryWalker At a speed of 0.1c, even a density of 0.1 gm per cubic metre is like being sandblasted with nukes. At that density, a small asteroid of radius 56 cm (cross-section 1m^2) would collide with about 3 tons of matter per second of skim-time. 3 tons * (0.1c)^2 * 0.5 is a lot of kinetic energy. $\endgroup$ Jul 3 at 3:05
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TL;DR: No, because an object moving at high speeds will break apart even quicker.

I suspect it wouldn't. I don't know if there's been any work done on relativistic impacts onto the Sun, but a group modeled comet impacts more like those we'd actually observe. I think, though, that we can extrapolate a few things from their results:

  • The body would rapidly lose mass thanks to the intense shock front it would produce in the Sun's atmosphere and, if it made it that far, the interior. The mass loss it would experience scales like $\dot{M}\propto\rho v^3$, with $\rho$ the density of the medium it's traveling through and $v$ the speed. While a faster-moving body would take less time to pass through the entire Sun, that timescale only scales as $\tau\propto 1/v$, so the total mass lost would be, roughly, $\sim\dot{M}\tau\propto v^2$, so a body traveling faster wouldn't lose less total mass.
  • Because of this, at higher speeds it actually seems that the final airburst destroying the body would happen at higher altitudes above the surface, rather than further into the Sun - although I think it's a bit more complicated at relativistic speeds.
  • In this regime, most of the lost energy would go partly into the ablated material and partly into the atmosphere, rather than entirely into atmospheric heating, which is interesting, although the ablated material would eventually become part of the surrounding medium.

In short, mass loss scales strongly with the speed of the object, and the asteroid would be torn apart even quicker.

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  • $\begingroup$ At that kind of velocity I don't think it will be anything like a spacecraft taking a bath of fire. Rather than most of the energy going into a shock front the particles are going to embed into the face of the asteroid. The only hope the asteroid has to survive is if it has enough thickness to get through before it ends up like the previously mentioned baseball. $\endgroup$ Jul 2 at 3:41
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No, but it can come "out of the sun". Ask a military pilot.

The asteroid would have to be falling almost "straight down" from interstellar space or the Sun's Oort cloud, in an orbit that will take it very close to the sun. It wouldn't be noticed while it was far from the sun. It would be hidden by the sun or the sun's glare at its closest approach, and it would come "up" from somewhere inside the orbit of Mercury on a collision path with Earth.

BTW if aliens wanted to "take out" the Earth with plausible deniability, this is probably how they would do it. Just nudge an Oort cloud object of appropriate mass into the Earth-impacting orbit. If they installed a (relatively) small terminal guidance system on the object, it would get vaporized by the impact and nobody could ever prove anything.

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  • $\begingroup$ I appreciate the idea of aliens wanting plausible deniability. $\endgroup$
    – Paddy
    Jul 3 at 17:32
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Newton came up with a fairly simple way to estimate how far a projectile can travel through a medium.

Newtons approximation for impact depth

The formula is Depth=Projectile length*projectile density/medium density

So we need some information about our asteroid. Lets assume a nickle-iron asteroid with a density of 7g/cm^3, and a diameter of 10 km.

The density of the sun averages to 1.4g/cm^3, so if the sun had uniformed density the asteroid would stop after traveling 50 km. Clearly not far enough.

But, the density of the sun depends strongly on how deep into the sun you are. At the core the density is 150g/cm^3 - our asteroid would penetrate 466 meters.

Fortunately the outer layers of the sun has much smaller densities.

So the question becomes what do you mean by "going through the sun"? - As established your asteroid will not pass through the sun core, but what about the outer layers? A natural way to view passing through the sun is passing through the photosphere, the point at which the sun becomes opaque to visible light. Here the density is 0,2g/cm^3; Our asteroid can penetrate 350 km through this density. The photosphere is about 100km thick, and we would need to traverse it twice and at an angle. - So the photosphere is on it's own almost enough to stop our asteroid. While the densities outside the photosphere drops quickly, and as such contributes less to slowing our asteroid this is probably enough that our asteroid will fail to penetrate.

Since we almost penetrates the photosphere we should be able to penetrate the chromosphere. I would definitely describe this more as a gracing the sun than going through the sun though. Alternatively we could change the asteroid; An asteroid with a diameter of 100km would penetrate easily.

Considerations that the above ignores;

  • Melting and evaporation of the asteroid. While the sun is very hot, the densities we are travelling through is low enough that heating effects from contact is limited. We are also going fast enough that there is not all that much time for heating to occur.
  • Xkcd style fusion effects from asteroid impacting the gasses of the sun. I do not think this will affect much; the asteroid is imparting momentum to the gas in front of it. The mechanism of this momentum transfer is not all that interesting.
  • Re-shaping of the asteroid; the sun is going to act on the asteroid slowing it down. This force acts on the front of the asteroid. This could cause the asteroid to flatten, lessening the length of projectile term in the approximation above. How much of an effect this has is not a question I am qualified to answer; but I think it's more of a concern if the asteroid barely penetrates, than if it penetrates easily.
  • Exit speed. The asteroid will impart momentum to the gasses it is travelling through, thus leave the sun with less speed than it arrived with. I do not know how to calculate how much speed is lost.
  • Relativistic mass - traveling at relativistic speeds the asteroid has more momentum than indicated by newtonian physics. This breaks the assumption of the approximation and will mean that you can go further than you would otherwise expect.

Impact on earth. A 10 km diameter nickle-iron asteroid has a mass of 3.665×10^9 kg. Traveling at 0.1c gives a relativistic energy of 1.659×10^24 joules. WolframAlpha tells us that this is about 3.3 times the energy that was released from the Chicxulub meteor impact. The conclusion is that this would be a mass-extinction event. The gravitational binding energy of the earth is 2x10^32, so the impact is nowhere near powerful enough to destroy the planet. If instead we look at 0.9c we get an energy of 4.263×10^26, 100 times more powerful - but still not close to destroying the earth.

The 100 km diameter asteroid that could actually penetrate the photosphere would produce impacts 1000 times more powerful, so at 0.9c would be within 1% of the gravitational binding energy of the earth.

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Yes, so long as it comes through the edge of the sun.

If it goes through the core it'll be stopped. Have it head through the outer, thinner layers at an enormous speed.

The earth will probably remain intact, but with substantial damage, depending on the speed.

https://www.calculatorsoup.com/calculators/physics/kinetic.php

Using this calculator and an estimated 10% light speed, with a mass of 10^16 kilos, it would have 4.5*10^30 joules of energy. You need 20 times that to destroy the earth, and with the slowing down the sun will do you'll probably not hit it at peak speed. You'd need a larger mass or a relativistic speed to destroy the earth. The sun will be shocked and probably be unstable, but will be generally fine.

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Like others said earlier, the answer is a big, fat NO.

The inside of the Sun is super tightly packed, super hot plasma. It's so dense that photons emitted from the core are believed to be trapped for thousands of years until they finally bubble up to the photosphere and get fired (pun not intended) into space. There is no way any solid material could get through this.

Or is there?

Well, there is, if the asteroid itself isn't just a chunk of rock, but something like an inverted tokamak. An object that emits such a strong magnetic field that it's able to move plasma out of its way. However, the energy required for this would be enormous, as it must exceed the energy of the plasma itself.

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So far all the answers discuss whether the asteroid can survive the bath of fire and don't address your secondary points at all.

Sun unaltered: That's a certainty. While you could get some pretty cataclysmic results from slamming a relativistic asteroid into the sun any such scenario destroys the asteroid. The only scenario in which the asteroid making it through is even a possibility is barely grazing the sun.

Impact on Earth: Cataclysmic. While most of the mass will burn away it won't survive at all if it's burned too small and at those kinds of speeds it won't take a lot of mass to make a mighty big boom.

Star mass brought along: Infinitesimal. At those velocities "solid" ceases to be very meaningful. Star matter doesn't hit and bounce or hit and stick, but rather penetrate into it (look at the baseball mentioned elsewhere.) Any appreciable amount of matter hitting will vaporize the layer it sticks into--and that material will leave as a very energetic plasma, taking with it the stellar gasses and their fusion results. Only on the way back out once the density has fallen low enough that the surface isn't boiling off will there actually be stellar mass retained.

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