One of the hottest areas of study in planetary science today is the revelation that our solar
system sees a very high number of objects passing through it that are of interstellar
origin.
Most famously is the mysterious object Oumuamua, one of the first such objects we detected
happened to also be so weird that it has been floated that it might have been artificial.
But also there was the very mundane comet Borisov which would have been an unremarkable
comet if it weren’t for its interstellar origin.
And of course reports of meteorites entering earth’s atmosphere so rapidly that they
must be of interstellar origin, and the possibility of recovering one.
But our connection to interstellar objects may be much deeper than that.
On the one hand, it is possible that the first detection of an interstellar object happened
centuries or even thousands of years ago.
Comets are sometimes visible with the naked eye, sometimes spectacularly so, and it is
in principle possible that a pristine interstellar comet has at some point passed near enough
to Earth to produce a spectacular, if fast moving comet.
Or, at some point, someone seeing a falling meteorite might well have caught one of interstellar
origin.
But there may be a connection to interstellar objects even more poignant, that if it were
not for an interstellar object long ago, Earth may have never existed at all.
There are actually two mysteries here.
The first mystery is in planet formation itself.
We don’t really know how you go from a disk of dust and gas to forming planets accreting
material.
This is known as the meter-size barrier, where particles grow into pebbles and their interactions
become more energetic.
This leads to the particles reaching a size where they don’t accrete together, but rather
bounce off each other, ostensibly preventing planetary formation.
But there is now a contender for how this occurs.
And it’s interstellar objects.
Very young star systems with new suns and a protoplanetary disk have different dynamics
than a mature star system like our own.
Young stars move more slowly through the galaxy than mature stars, and there is a kind of
braking effect that happens due to the presence of the disk of dust and gas.
This in turn would allow stars to more easily capture interstellar objects early in their
history.
If you have enough of these, they could be the seeds for material to accrete around solving
the meter size barrier problem.
The question is, are there enough interstellar objects out there to do this.
It appears that the answer is yes, we’re seeing these things already even though we’ve
only just barely acquired the technology to even detect them.
And we should have a pretty good idea of how common they are overall when the Vera Rubin
observatory comes online and begins its task of rapid all sky surveys.
But we do have a hint of what we may find already.
In a paper by Amaya Moro-Martin and Colin Normal at the Space Telescope science institute,
link in the description below, they detail that they modeled the early solar system to
try to get an idea on how many interstellar objects a young star system might trap.
The number was startling, to the tune of 600 billion interstellar objects over a meter
in size in a span of ten million years.
That’s an enormous amount of interstellar material.
So to see how the birth of earth unfolded in this scenario, think of the early solar
system.
The sun was brand new, significantly dimmer than it is now, illuminating its protoplanetary
disk of dust and gas.
Embedded within this disk, is an interstellar object, perhaps a few meters wide getting
past the meter sized problem, that could have originated anywhere in the galaxy and was
ejected from its system of origin only to be captured by the infant sun.
Around that, a slow accumulation of material began, and proto-earth was born.
This process would continue for millions of years, all while other objects bombarded it
constantly, adding again to its bulk until eventually another minor world, theia, hit
proto-earth, itself having been seeded by an interstellar object, the collision flinging
off the material that would coalesce into the moon.
A cataclysmic process of the birth and growing pains of a planet that would some day host
life and a civilization.
But this process would inevitably leave a bunch of material, especially in the outer
solar system, of interstellar origin that’s probably still there sitting in a pristine
state.
It would be difficult to find these objects out in the oort cloud and Kuiper belt, but
there may be a veritable treasure trove of extremely ancient material out there available
for study, and conceivably material so primitive that it might date from the earliest time
in the universe when it first became populated with the building blocks of planets.
But finding one of these objects randomly out there is pretty unlikely, that's a vast
amount of space in which to find a small object.
But if you did, it should be isotopically very different from the rest of the solar
system.
Another idea to kick around is if these interstellar objects formed the seeds of all large objects
in the solar system, or at least some of them, and that at the heart of pristine comets that
are themselves relics of the early days of the solar system there might be an interstellar
object in their cores.
A fun sci-fi scenario here would be a piece of defunct alien technology getting captured
by the early solar system only to have a comet form around it, appearing totally natural
until some adventurous space miners find the object when mining it for raw materials.
It’s all fun and games until the von neumann probe locked in ice reactivates once it detects
space mining and either starts communicating with us realizing we’re advanced enough
to bother with after waiting in the heart of a comet for billions of years, or it prints
out a xenomorph to take down the miners.
Add this to an earlier suggestion that due to the presence of Jupiter, there are already
collection points in the solar system where interstellar objects could congregate if captured.
One of the reasons the discovery of interstellar objects has become of great interest is that
this also relates to the building blocks of life and how the chemical components of life
came to be distributed around the galaxy.
And it’s actually good news for life in the universe.
With so much interaction between star systems all over the galaxy, it’s conceivable that
this might play a role in the so-called Phosphorus problem in astrobiology.
This is not to be confused with the other phosphorus problem, the idea that our fertilizers
we use for agriculture are largely based on mined phosphorus that we are depleting the
sources of.
In this context, there is the idea that some areas of the galaxy may be too poor in phosphorus
for life to get going, given that element’s critical importance to life on earth.
Here the problem may not really exist, or is less of a problem, because, well the stars
sneeze material on each other.
Phosphorus might get distributed relatively evenly throughout the galaxy with so many
interstellar objects and interactions going on.
Another possibility is the transfer of amino acids.
This is one step closer to life in nature and we see amino acids everywhere in carbonaceous
chondrite meteorites.
While they are not biological in origin, they are the building blocks of life and it may
be that the original amino acids that were involved in abiogenesis on earth were interstellar
in origin.
The original chemistry of life may well have required an interstellar component, though
it pays to remember that early earth was part of an open star cluster of cousin stars that
formed from the same materials as the sun.
And that in itself is an interesting idea.
The sun has siblings, and several candidates for stars that formed alongside the sun in
the same open cluster have been identified through their very similar chemical make-up
to the sun.
This means that there are stars out there that have planetary systems that would be
similar compositionally to the solar system, and since this star system spawned a space
age civilization, those sibling systems might make for excellent SETI search targets as
we identify more of them.
Another odd aspect of this is that the solar system itself is generating interstellar objects
and has since its formation as various objects are ejected into the interstellar medium,
especially in the outer solar system.
This could mean that our star system seeded some other star system with interstellar objects
that served as the core seeds of the planets in that system.
This possibility unfortunately would be impossible to ever prove, but there’s no reason to
not expect that process to have happened, and for that matter is still happening.
The solar system could well be reproducing if this modeling of planetary formation is
correct.
More, when the sun was still part of its birth cluster, transferring materials between protoplanetary
disks would have likely been occurring, so some of the siblings of the sun could have
seeded our planets, and the solar system itself could likewise have seeded them.
What implications this has on the distribution and generation of terrestrial planets in the
milky way is an open question, but the further study of interstellar objects should shed
light on the answer.
But there is one other aspect of this that presents a very big, brand new mystery.
This is one of the things I love about science, new mysteries often crop up where you never
really expected them.
If indeed interstellar objects serve as the seeds of planetary formation, then what originally
kicked this process off?
Think of it like this, the galaxy originally had no planets at all.
It had to generate those materials with supernovas to populate the galaxy with all the iron,
nickel, silicon and so on that planets are made of.
Once that material is present, the meter size barrier rears its ugly head in that there
should be no planets at all.
Instead we should live in a pebble universe where planets never get going.
Somewhere along the line in the very distant past there had to be a primordial event that
kicked off interstellar object formation to get around the meter size problem.
This paper is very new and I’m unaware of anyone thinking about this yet, but one candidate
I would toss out there are supernovas.
In a 2015 paper by Soker and Tsebrenko link in the description below, they present another
model for how the galaxy gets its iron.
It’s known as a supernova bullet, and it’s kinda spooky that these things may lurk out
there.
One type of supernova, Type 1a, should generate huge amounts of iron.
Some supernova remnants, but not all, there’s something very situational here, exhibit ears
or protrusions that could indicate that the supernova ejected enormous clouds of iron
traveling at very, very high speed.
But they aren’t really bullets, more very massive clouds of iron atoms, sometimes more
massive overall than Jupiter which would then go on to seed the galaxy with iron, which
then becomes incorporated in planets.
The point is, supernovas are very energetic environments, so could it be that a shockwave
moving through dust and gas causes a collapse of material into an interstellar object suitably
large to kick off the initial process of planetary formation if indeed interstellar objects are
the answer?
We shall see, I’m just tossing it out there, but welcome indeed to one of the newest mysteries
of the universe.
Thanks for listening!
I am science fiction author and futurist John Michael Godier currently growing increasingly
alarmed at the shooting gallery that is the universe.
Interstellar objects, passing star encounters, rogue black holes … The solar system truly
is playing a game of frogger with a broken joystick.
Very disturbing 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.