The early history of the solar system is surprising in how radically different it used to be compared
to now.
Early in the sun’s history, it was not the lone wanderer that it is today but rather
probably part of what’s known as an open star cluster, where a star forming region
has spawned a group of related stars, and as they all began the process of fusion the
remaining gas was dispersed leaving a bunch of stars, possibly even thousands, in a loose
cluster in relatively close proximity to each other.
The sun was once one of these stars.
Other more recent models suggest that the original cluster may actually have been denser
and more violent than a typical open cluster.
This might help to explain some features of how the solar system appears to have formed.
But as a member of a cluster, what was interesting about the sun however is that it had a huge
protoplanetary disk from which the planets as we know them today including earth would
accrete.
It stands to reason that many more of the sibling stars in the original cluster would
also have had protoplanetary disks that would have formed planets, meaning that there could
be hundreds or even over a thousand cousin star systems wandering the milky way with
planets in some way related to earth, having formed from the same cloud of dust and gas.
But open star clusters are not permanent arrangements, assuming the open cluster model is the correct
one.
Once the gas is lost in the star cluster, the stars themselves don’t have the collective
gravity needed to hold the cluster together, so they themselves wander and disperse.
The sun having formed 4.6 billion years ago, long ago left the cluster and began its wandering,
as did all of its siblings, but for a time our star was in close proximity to a very
large amount of other stars.
And we’ve identified at least one sibling of the sun, and potentially a second which
is an almost identical twin of our star.
The more probable candidate is known as HD 162826.
This star is of great interest because it shows a very similar chemical composition
to the sun, uncannily so for rare elements like barium and yttrium.
When tracking its orbit around the galactic center backwards, it fits the sun’s profile
as having originated very close together, though HD 162826 does show a higher metallicity
overall than the sun.
And that’s interesting, because it raises the likelihood of terrestrial planets in orbit
of that star.
None have yet been detected however, but that’s not surprising since terrestrial planets are
the hardest to detect, and while the star isn’t too distant, only about 110 light-years,
it’s distant enough to make a search for small planets difficult.
But HD 162286 isn’t a total match to the sun, it’s somewhat hotter and a type F star,
specifically FV8, and very slightly younger than the sun at 4.5 billion years old.
As our planet shows, that’s plenty of time for life to arise and spawn a civilization
should there be a suitable habitable world in that star system.
But, it won’t last long, F type stars depending on their specific classification don’t live
as long as G type stars like the sun, or cooler stars, but they can in principle last long
enough for life.
The second candidate is less certain.
It’s a star known as HD 186302 at a distance of about 184 light years.
It’s almost a twin of the sun, being type G3, as opposed to the sun’s classification
of G2.
It’s roughly the same size as the sun, and also could in principle have planets, but
none are currently known.
While similar to the sun, it’s uncertain if it’s a true sibling from the cluster
due to its orbit around the galaxy being very different from the sun.
But the search for the other former members of the sun’s star cluster has only just
begun, there are very likely hundreds or even thousands that will be identified as astronomers
search the stars, especially their composition.
This could yield interesting results in that they may detect chemically anomalous stars,
usually termed peculiar stars, that could even yield a technosignature.
There are possible compositions of stars that could only be of artificial origin, and there
are several candidates for this already including Pryzybylski’s star with its weird traces
of transuranic elements in its composition that shouldn’t be there.
But within the early history of the sun and its siblings is an open question, leading
to a mystery that could potentially change our view of life in the cosmos.
There are a number of factors that might end up being filters that prevent the appearance
of life in a star system.
One of these is the so called phosphorus problem, where regions of the galaxy seem to be too
poor in phosphorus which is essential for life on earth for life to be on the table.
But in the case of the sun and its siblings, of which there are potentially several thousand,
they would presumably all be phosphorus rich having formed from the same mixed cloud of
materials.
This alone makes them excellent candidates to search for exoplanets, and bio and techno
signatures.
But there’s another aspect of this early arrangement in the cluster, and it’s panspermia.
In a cluster situation the member stars would have been constantly passing by each other
in relatively close proximity opening up the possibility that if microbial life had arisen
somewhere, say earth during the late heavy bombardment as it appears to have done, then
that life could have been transferred via panspermia to any number of the other stars,
seeding life throughout the original cluster.
It’s also possible that there were members of the cluster older than the sun, which could
have spawned life earlier in the cluster’s history.
This makes for a rather strange scenario where related life ends up naturally spread across
the galaxy as the cluster dispersed, creating a common microbial ancestor then leading to
radically different evolutionary outcomes depending on each different world and its
history, including earth.
In short, we could have cousins in the Milky Way that could only be determined to be distantly
related through their genetics.
And this is a problem, any time you share a common genetic origin with something, you
are related to it, and thus it can’t be classed as alien.
This was famously explored in Star Trek from multiple angles, there was the episode The
Chase for example, but also the concept of a planet spawning multiple but related forms
of intelligent life as the Xindi, and the relation between the Romulans and Vulcans.
But this actually makes the sci fi less fun, because it means that the species aren’t
truly alien to each other, but related.
This has the rather unsavory implication of never being able to prove an alien civilization
actually is one.
Say we detect a radio signal of unambiguously technological origin, but it’s from a planet
orbiting a sibling star to the sun.
The question would then have to be asked about a common origin, and it would cast a pall
on the discovery very likely permanently.
Thankfully, the galaxy is chocked full of non-siblings of the sun, so any detection
from one of those could reasonably be determined to truly be of alien origin.
This is a debate we’ve yet to have, not yet having discovered solid evidence of alien
life.
And it’s a debate we may never have if we never discover it, but it’s an important
point.
Distant alien life is hard enough to prove, but the closer that alien life is to you,
the less likely it is to be of alien origin, whether it was once close to you in the past,
or currently is sitting in your star system.
This goes for everything, no matter how weird it is.
So, here is a scenario.
A civilization shows up in the solar system some day and says hello.
We say hello back, and they land on the whitehouse lawn or crash into New Mexico.
We get some of their technology and analyze it and see the isotopes in the metal and different
form what we see on earth, and the DNA of the aliens is clearly unrelated to us.
Case closed you might say, but it’s not.
With high technology comes advanced abilities, and those abilities might be to mess with
isotope ratios in their materials, so that can’t be trusted, and it might include DNA
manipulation or even construction from the ground up, there goes that proof as well.
So at that point, you’re left with no real way to prove something is of alien origin
unless you ask it.
Worse, if it’s a von Neumann probe 3d printing out technology from materials from the solar
system, those materials will naturally indicate a solar system origin for the technology.
You could ask the alien, but would you trust what it told you of its origins and intent?
This is all compounded by an even worse problem, the Silurian Hypothesis.
It’s actually impossible to rule out that a prior technological civilization once arose
on earth, or either went extinct, or left it for space and is somewhere relatively nearby
now.
This is because Earth constantly resurfaces itself, weathers and subducts entire continental
shelves, destroying most of the fossil record.
We only have an incomplete record, and it’s very possible that if we go extinct, our own
vast civilization on earth could get geologically unlucky and nothing survives of our brief
period of technological civilization.
And here’s the kicker, while that scenario is unlikely, it’s actually more likely than
an actual alien origin for a technology you’ve found on your planet.
This is because interstellar space travel is highly energy expensive, and also takes
vast amounts of time.
Without invoking unicorn technologies like FTL, if an alien civilization were to show
up at our doorstep, it’s very likely that they’ve been traveling for thousands of
years and expending vast amounts of energy to get here.
So in short, if you detect an alien civilization light-years away, there’s a good chance
it’s actually alien and not related, but not necessarily an airtight chance.
If that civilization is in your atmosphere with you, it’s very likely from your planet
no matter how weird it is, and proving that it’s actually alien would be far harder
than most realize.
But back to the issue of the sun’s siblings.
There’s something even stranger hidden in that story and if by some chance it is the
case, then we end up being the aliens.
It’s the idea that life on earth did not originate here, but rather was deposited here
in this case from another star system entirely early in the history of earth.
This would solve somewhat of a mystery about how life got going on this planet.
It literally did it the very first moment it could, suggesting that abiogenesis is a
straightforward, rapid process.
The problem is, it appears to have been a very complicated unclear process that we can’t
so far duplicate.
So it seems unlikely that earth would have hit it so quickly, and under the conditions
of the end of the late heavy bombardment.
This was not a nice, calm planet when life arose.
So that leaves open panspermia from either a solar system planet like Mars, in which
case we’re actually originally Martians, or from another passing star system entirely,
in which case we’ll very likely never know our origins and strangely life in its earliest
microbial form managed to still conquer interstellar travel by way of a trick of nature and proximity.
Amazing possibilities indeed.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently musing that we need
to outdo our panspermic neighbors and build a dyson sphere!
A really nice one, with chrome details and a giant 8 track tape player made of Jupiter
playing ABBA on the SETI beacon and of course a luxurious faux leather interior though we’re
gonna need a lot of faux leather for that project 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.