# What type of celestial body could pierce an Earth like planet without loss of trajectory or minimal loss of speed?

What type of extraterrestrial body could successfully pierce through one side of an Earth-like planet, go through all strata, through the core, and then continuing through the strata and through the other side of said planet, then continuing into space, all while maintaining its trajectory and speed?

What would the size, composition, angle of penetration and velocity of said extraterrestrial body need to be for this happen? What type of damage would be seen on the planetary body that was impacted in this manner? And would said impact, penetrating the entire planetary body, have any long term effects such as gravity, quakes, or other phenomenon plague the planet, possibly causing it long term survivability, or even destabilization in the future.

*This is my first question to the site.

• Do you want anything left of the planet? If not, neutronstar? Aug 6, 2016 at 9:10
• Define "maintaining its trajectory and speed". Are slight changes prohibited? If so then nothing at all will meet your criteria, since everything that we know of has its trajectory affected by gravity (and everything that has rest mass also has its speed affected). Aug 6, 2016 at 9:16
• Neutrinos, produced by stars, pass cleanly through the earth without incident. Do they qualify? What is the minimum definition of a varietal body. Aug 7, 2016 at 2:02

That's simple - a black hole with a mass in the 1 sol range or less. Nothing else will do.

The mass of the black hole is so great that any mass it absorbs in passing through the Earth will not slow it down.

The radius (or at least the event horizon) of a 1-sol black hole is about 3 km, and for a 0.1 sol BH it's about 300 meters. In either case, a naïve interpretation of such a body passing through the Earth is that it simply makes a cookie-cutter hole which will fill in after the passage. I suspect that a 300 meter hole would provide pretty good earthquakes but not global catastrophe. For instance, Project Gnome detonated a nuke underground and produced a 50-meter diameter cavity without major seismic results. A tunnel all the way through the earth is admittedly on a rather different scale, but at least at the crust I suspect it would not cause major distortions.

In the case of a 0.1 sol BH, the mass transferred by such a transit would amount to about $5 x 10^{15}$ kg, which sounds like a lot, but it would be about $2.5 x 10^{-14}$ the mass of the black hole, and would slow the BH by a similar amount.

And you can consider even smaller black holes, since they are so massive that they won't slow down. And since the Schwarzchild radius goes as the mass of the hole, the size of the plug of mass absorbed during penetration remains at the same proportion, so the change in velocity remains the same for different sizes. For the naïve analysis.

Of course, life isn't simple, and accretion disk effects would produce a LOT of energy, even at high closing speed and brief interaction times. Furthermore, even for brief interaction times the gravitational attraction at the "surface" of the black hole is so high that extra mass is sure to be collected.

Other, more mundane objects, simply will not penetrate a body like the earth. I know you can find YouTubes of guys throwing needles through plate glass, leaving only a small hole, but it doesn't work like that at large scales of size and velocity. Small and fast will do just as much damage as big and slow, and the depth of the crater won't even change all that much. It's energy that counts.

• "Nothing less will do." Yet you suggest smaller BH's could fit the bill. A slight contradiction? In fact, I suspect, that's my naive analysis done, any BH could do it. A sol-mass BH does seem a tad extreme. There was a suggestion that the Tunguska impactor was a micro-BH, now discredited, but basically the BH would have gone straight through and out the other side. The absence of evidence of a micro-BH exit wound kiled that as a Tinguska explanation. Aug 6, 2016 at 12:49
• It has to be a micro BH with a mass considerably smaller than the Earth, otherwise its gravitational effect on the rest of the Earth will be at least as drastic as the seismic activity! Temporarily increasing the mass of the Earth's core to a solar mass would comprehensively flatten everything on the surface, and then there is the tidal effect as it moves. Aug 6, 2016 at 15:51
• A primordial black hole with a mass as small as $10^{13}$ kg would not yet have evaporated. That is so small that if its passage through the earth might not even be noticed except by instruments, if entrance and exit sites were both ocean. Aug 6, 2016 at 16:01
• @a4android - Please reread. I did not say "Nothing less will do." I said "Nothing else will do." The difference is that I wanted to emphasize that it has to be a black hole, rather than some exotic chunk of "normal" matter. And if you'll pay attention to the preceding sentence, I called for "a black hole with a mass in the 1 sol range or less" and I fully appreciated the need for the "or less". Aug 6, 2016 at 16:04
• My apologies. A transcription error. Knowing you fully appreciated the less part, makes more sense of your answer. Aug 7, 2016 at 3:30

# None

There is no known material that can penetrate 12 000 km of planet and not be destroyed in the process, even less so while maintaining its velocity (which would be a physical impossibility).

Ok, so neutrinos can, but I hardly think that was what you had in mind.

Black holes are the obvious candidates. See other answers. Micro-BH's could be mistaken of a massive impactors striking the Earth, but there always be two impactor events on opposite sides of the Earth. Which is, if you think about it, a dead giveaway.

A small piece of cosmic string would also qualify. It has to be small, because larger pieces could have the mass of a galaxy. Cosmic string being in nature of massive defect in spacetime would penetrate the Earth as if it wasn't there. The bigger the piece of (small) cosmic string was the more catastrophic its effects.

With both BH's and cosmic string penetrations there could be powerful transient gravitational effects. With micro-BH's this wouldn't be noticable, but once the BH was an appreciable fraction of Earth mass then a sudden surge in surface gravity could be felt. Although this effect might be masked by the accompanying massive surge in seismic activity. Basically there would be one heck of an earthquake -- globally. Cosmic strings have more mass per unit length than anything else in the universe, so expect sudden transient gravitational surges.

Effectively with either BH's or cosmic strings there would be double impactor events. This could range from a simple meteor fall to a Tunguska event and upwards. The Earth would ring like a bell. There would be accompanying earthquakes.

There are a number of possible explanations for dark matter. However, it does seem like dark matter could pass through the Earth as if it wasn't here. While this does depend on the precise nature of the version of the dark matter; mostly there does appear to be a complete lack of a coupling constant between dark matter and ordinary matter. This, of course, does mean that it would no effect whatsoever on our planet. And thank goodness for that!

Apart from these candidates for Earth penetrating celestial objects, there are, as Michael Karnerfors pointed out, neutrinos. They pass through the Earth without making any significant effect. There are neutrinos passing through all our bodies every moment of the day. One of those strange quirks of physical nature.

Beyond black holes a slug of neutronium travelling at a high fraction of c should pass through the earth with little disruption. This assumes there is some artificial means of keeping the neutronium at neutron star density.

Quark matter strangelets are another candidate, assuming they generally repel matter rather than catalytically convert matter into other strangelets. There is some controversial evidence that such events have taken place, based on the analysis of global seismic networks. In 1993, two separate events were recorded which could be interpreted as quark matter passing through the earth.

Quark matter star

Since it is thought that quark matter might be created in the formation of neutron stars (the stable quark matter hypothesis), the universe might be full of the stuff, and any event with enough energy to disintegrate a neutron star or peel off a substantial chunk will accelerate the piece to a high fraction of c. At that velocity, tiny particles of quark matter will not even be slowed down when striking a normal matter planet.

A black hole could probably do that. They come in all sizes from micro black holes to much bigger than my brain can cope with.

A microscopic black hole wold have no appreciable effect, but you can grow it to a size that has whatever effect you want to achieve, up to absorbing the whole solar system.