When we think of an asteroid, we typically think of a classical space rock, typically
from the asteroid belt or some other remnant from the formation of the solar system falling
to earth. Sometimes this is in the form of a run of the mill small meteorite one sees
streaking across the sky as a fireball that someone finds fragments of, but also sometimes
larger pieces that do damage such as Tunguska, the Chelyabinsk meteorite or the iron meteorite
Sikhote-Alin that went off like a grenade over a mountain range in Russia spewing iron
everywhere in 1947. And then there are huge asteroids such as that which at least contributed
to the extinction of the dinosaurs 66 million years ago during the end cretaceous event.
While the vast majority of meteorites can be classed and connected to asteroidal material,
comets also but less so, there are some that can actually be linked to Mars, having been
blasted off its surface preserving both evidence of its volcanic geology, but even tiny pockets
the Martian atmosphere hidden within the meteorites to the point that with what we see with them,
there can be only one origin. Mars. This also works for the moon, there are meteorites on
earth that have the moon’s chemistry and match no place else.
But hidden within the overarching question of the asteroid population of the solar system
are some very obscure anomalies that have arrived as meteorites in the past that don’t
quite fit any of the classifications or models. The most extreme is what appears to be an
interstellar object, a subject of great interest of late as the results from the Galileo Project’s
expedition to recover pieces of an interstellar meteor are awaited. An interstellar origin
is not yet established for the samples, but we may already have one in our meteorite collections,
and it’s extremely weird.
It’s known as the Hypatia stone, and was found in Egypt in 1996. It was originally
about 30 grams, which is small, and is now down to four grams after distribution of samples
to various institutions. This stone was found in an unusual area of the Sahara desert. This
area is known for an impact glass, formed when a meteorite impact melts sand, known
as Libyan desert glass. This material has been here for a long time, one piece of it
was found carved and mounted in a pectoral in Tutankamun’s tomb.
The stone was found in this area, and in fact near a piece of the glass, though even that
piece of glass was an outlier for its type. The two may be linked, or not linked, it’s
uncertain. If they are, the stone fell about 28 million years ago as part of the impact.
If not, it’s much more recent as far as a fall goes. But its actual age before falling
to earth is enigmatic. The material is extremely primitive, to the point that it’s generally
agreed that it’s the first sample we have of the nucleus of a comet.
But we have other meteorites that are likely of cometary origin and it’s very different
from even those. It has very high levels of carbon, which can be expected for a comet,
but very low levels of silicon for a solar system object. It’s loaded with Polyaromatic
hydrocarbons, which are more associated with interstellar dust than something commonly
found in the solar system at those levels, but not exclusively so. But here’s where
it gets really strange, it contains inclusions of metallic aluminum. On its own. Aluminum.
This is an unbelievably rare occurrence, and almost never happens in the solar system though
there are very rare native aluminum occurrences on earth in association with moissanite. And
it doesn’t stop there, silver iodine phosphide and indeed moissanite were also found in really
unusual forms. There are also grains composed of nickel and phosphorus in the meteorite
with no iron, which again is unheard of for the solar system and honestly unexpected for
any star system.
The best explanation for the Hypatia stone is that it’s a solar system rock, perhaps
far outer solar system, that came into contact and incorporated pre-solar materials, or interstellar
materials into its matrix of unknown origin, formed through unknown processes. This is
not unlike the controversial metallic spherules of weird make up found by the Galileo Project’s
expedition.
And, it has to be said, other researchers in the past have advanced certain somewhat
unlikely minerals in other meteorites as potential technosignatures for lack of a known way they
could form in nature, in the form of Heideite and bresinaite, that might be iron based superconductors,
see a paper by B. P. Embaid in the description below, but that would require a lot of experiments
and proving. But this is an unlikely scenario beyond that since it would require materials
from an alien civilization to have been ubiquitous enough in the Milky Way at least 4.6 billion
years ago to find its way into random geology, but it does show that there are chemical processes
going on in the galaxy that simply aren’t happening here.
On the other hand, given that Earth exists, it may be that there are organic chemical
processes going on here, in other words biology, that isn’t occurring in most other star
systems. We could be weird in our own right, so why not other star systems? Life’s chemistry
is either rare or it isn’t afterall. One last development regarding the Hypatia stone
is that in 2022 further work showed evidence in the rock that may be the first direct material
evidence on earth of a Type 1a supernova, but that’s not settled because while we
know supernovae salt solar systems with materials as happened here, actually pinning that down
to a class is a different matter. I wish we had more than 30 grams of this stuff for analysis.
But to show just how weird meteorites can get, we can turn the tables. Another meteorite,
this one from North West Africa, known as NWA 5400, bears chemical similarities, specifically
oxygen isotope ratios, that look more like Earth and the moon than the asteroid belt.
But not exactly. There are a few possibilities to explain this, and the first is that it
formed nearby in the solar nebula. The others are even odder. It’s possible that it was
a rock blasted off of proto-earth, perhaps during the impact that formed the moon or
before, that wandered around for a long time before falling back to the modern earth-moon
system. The other possibility is that it’s a rock from Theia, the object that hit earth
and in a glancing blow tossed off the material that would coalesce into the moon.
This essentially means that out in the solar system, and probably littering the surface
of the moon, are at least a partial record of Earth’s early history. If you can have
ancient moon and Mars rocks landing on earth, you can have ancient earth rocks landing on
the moon from impacts that could be in an extremely pristine state, far better than
anything that can be preserved down here on earth. You can even play with ideas that it’s
better to study the history of earth looking in space, than it is down here where all the
weathering, water, and so on destroy most of the geologic record.
Indeed, even evidence of abiogenesis may be preserved in earth rocks blasted into space,
or even fossils. But the one thing that was lacking in this scenario was a meteorite that
was originally from earth and was blasted into space, only to return so we could study
it. We seem to have exactly that now.
Known as NWA 13188, a 600 gram rock was found in Morocco that is identical to volcanic rock
formed here on earth. It’s an earth rock, no question, and even bears evidence of plate
tectonics which only earth does in the solar system. But it bears the telltale fusion crust
of a meteorite, the burnt skin that results from entry into the atmosphere. Moreover it
bears isotopes that can only form when an object has been in space and under cosmic
ray bombardment for a significant amount of time. This is not seen with earth rocks.
The best fit for this situation is an earth volcanic rock that was blasted into space,
where it spent several thousand to a hundred thousand years floating around in space only
to fall back to earth. The blowback on this discovery is sort of indicative of how things
in science can sometimes get silly. There is ample evidence that this was an earth rock
blasted into space and fell back down, the laws of physics doesn’t prohibit this and
it was something that was expected to eventually be found. But it got treated as an extraordinary
claim that required extraordinary evidence, so came the extraordinary criticisms.
The oddest one is that it can’t be considered a meteorite at all. This is purely semantics
because had it fallen on Mars, it would be one. Only because it fell back to its parent
body suggests that it’s not, but for all intents and purposes is because it’s a spack
rock with a fusion crust. Another criticism is that there is no corresponding relatively
fresh impact that could have thrown it into space, which means it is a meteorite from
somewhere else, but an entire 31 kilometer impact structure was found under a glacier
in Greenland that no one had any idea was there before 2018. It’s likely not the culprit,
that crater was initially suggested to be young, but appears according to recent work
to be millions of years old, but it does show that earth can still hide a large crater.
What this meteorite fall does seem to indicate is that we now have some proof of concept
of earth rocks getting blasted off the surface of the earth and deposited elsewhere, or back
here for that matter. This could mean any type of earth rock, in this case it was volcanic,
but it’s also possible for sedimentary rock to get blasted into space, a good example
being the end cretaceous impact which would have blown all manner of material into space
including sedimentary deposits, but also the granite that underlies that part of the ocean
floor. How much of that made it into space without becoming molten and dramatically changed
is a bigger question. You’d imagine most of it would be impact melt and heavily altered,
but some portion of it, maybe not.
We are already familiar with the idea of panspermia, where biology can catch a ride inside a meteorite
and potentially proliferate to other worlds, effectively planets sneezing bacteria on each
other with their rocks, though this is unproven. We also have had claims in the past of apparent
fossils in Martian meteorites of such bacteria, though this too has never been proven. But
the idea of deceased earth life proliferating as fossils is not that far of a stretch, but
there are further ideas here that have not been well considered as of yet.
One of these could be called retropanspermia, where earth life that gets blasted into space
in a rock and then lands back on earth and reproliferates perhaps in an environment it
was not originally native to, sort of like an invasive plant species might do so if carried
from one continent to another to become a weed. Such a retropanspermic organism would,
after all, be returning to its home environment, just in a different area of the world. Who
knows, could bacteria or even tardigrades expand their domain in this way?
There’s no solid evidence of this ever having happened, but there’s also never been any
real search for it. And then there is what could be called necropanspermia, where fossils
transfer. This could even include such oddities as a dinosaur bone inside a rock landing on
the moon, there to preserve indefinitely buried in the lunar soil. Alternatively, such a rock
could wander the solar system indefinitely, land on earth as a quasi-meteorite, and one
might see a sedimentary rock bearing fossils but also bearing a meteoritic fusion crust.
Perhaps most interesting would be early earth material blown off during the late heavy bombardment,
a period that is not at all well represented in the geologic record here on earth. Little
of that period remains down here, but all sorts of odd rocks from this period might
still exist in space that could be recovered and studied giving a clearer picture of Earth’s
formational history. Space could form a sort of extraterrestrial strata of sorts of blasted
off earth rocks. Our own technology certainly does, the stuff we’ve been blasting off
this world for decades now is still there, from a Tesla roadster to all sorts of probes.
And they, or at least parts of them, will last out there for a very long time.
The same could be true for Venus and Mars as well, their histories could be preserved
in space as well, along with evidence of past interaction with water on the surfaces of
those worlds and even fossils in their own right, though this is unlikely above the bacterial
level. We’ve seen sedimentary rock on Mars, recently from orbit, but the rover Opportunity
literally landed ten feet from a sedimentary outcrop at Meridiani Planum on Mars. It found
no fossil clams, and wasn’t equipped to find evidence of bacteria, but did find enigmatic
hematite spheres that could only indicate heavy, long term interaction in the area with
liquid water across at least two periods. A climate perhaps just right for life.
The discovery of NWA 13188 may be the tip of the iceberg of finding rare meteorites
preserved from a period of history earlier than today that might be found on the surface
of the earth, moon and Mars. Maybe even further, it might be that in the far future someone
finds an earth rock locked in the ice of Europa, or sunk to the bottom of its ocean. A long
shot, not just for the possibility, but the odds of finding it, but as they say stranger
things have happened, and we might even find that life on Europa, should it exist, is rather
a cousin of life on earth having originally stemmed from it, proven by genetics or vice
versa, suggesting that some unknown rock once transferred life across the solar system.
But I leave with an even more alien thought. If rocks can get blasted off earth, can they
be large? Yes. There could be asteroid sized chunks of earth floating out there. Can they
land on other worlds? Yes, with luck and gravity it is in principle possible that a few of
the craters we see on the other planets of the solar system might be due to earth born
asteroids from some point in the history of our world. Can an earth rock get blasted off
earth and then subsequently be expelled from the solar system? That’s a bit more of a
physical challenge, and may or may not be possible. But if it is, and odds of trillions
or more to one are overcome, could a piece of earth have caused the extinction of a passing
star system’s analogue of the dinosaurs? Almost certainly not statistically speaking,
but I think it’s non-zero. It does however make me think that somewhere out there Douglas
Adams is smiling at the thought.
Thanks for listening! I am futurist and science fiction author John Michael Godier currently
sorry to bring it up again, but that video I made last month about getting hit by a meteorite
is perhaps driven home by the idea that not only can you in principle be hit by a meteorite,
but also a returning earth rock acting like a meteorite. Or a fossilized dinosaur bone
that … fell from space … the irony is too much but I like it and be sure to check
out my books at your favorite online book retailer and subscribe to my channels for
regular, in-depth explorations into the interesting, weird and unknown aspects of this amazing
universe in which we live.