For a year, the story was simple: interstellar comet 3I/ATLAS is older than the Sun. Then astronomers read its ice, and both the number and what that number actually measures changed.
This video covers active, unsettled science. The ages here are best estimates from current measurements, not settled fact.
Here's what you get: why the original "seven billion years" came from the comet's orbit and was never proof; how deuterium (heavy water) and carbon-13 work as two independent clocks that agree; why James Webb and ALMA landed on the same reading; the honest catch almost no coverage mentions, that we may be dating the radiation-beaten crust and not the core; and what an object older than the Sun says about whether the ingredients for life are common. If you have ever searched how old 3I/ATLAS really is, this is the full answer, sourced to the papers below.
Sourcing note: every figure here is pulled from the named primary papers listed below, not from secondary coverage. If a claim wasn't in a primary source, it didn't make the script.
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For a year we have told you this comet is older than the sun.
We were wrong.
Four and a half billion years was the ceiling
for every comet we had ever seen.
This one is more than twice that.
Right straight out of its ice, old enough to reach back near
the start of the universe.
And we might still be measuring the wrong part of it.
That first number was always the shaky one.
The seven billion years, the older than the sun line,
did not come from the comet. It came from its path.
You read where something falls in from,
you know how old the stars in that part
of the galaxy tend to be, and you turn it into a
probability. Somebody in the comments on one
of the early videos said the two-thirds odds had the
same energy as saying it either happens or it doesn't.
Fair. The orbit was a good first guess
about a stranger passing through. It was never proof.
Proof had to come from the ice. And over
the following year, three different telescopes read the ice,
and the number did not survive.
Last summer, the ALMA array in the Atacama caught the comet,
six days after it rounded the Sun,
and it read the water coming off it. The water was heavy.
Some water carries a heavier twin of
of hydrogen called deuterium,
and the amount of it is set by one thing, how cold the ice
was when it froze.
You only get a lot of it when the water freezes in extreme cold,
cold enough that everything
else has frozen solid too, and once it is locked in,
a little warmth undoes it.
Heat the ice up even slightly and the deuterium bleeds back out.
A high reading works like a seal,
it says this froze brutally cold and nothing has touched
it with heat since.
When ALMA did the math,
this comet had 30 times more heavy water than anything born
around our Sun.
More than 40 times what sits in Earth's oceans.
Webb caught the same thing on its own.
Two instruments, two teams,
one reading that should not exist, and the first time anyone
had ever measured heavy water in an object from another star.
Teresa Paneque Carreño on the ALMA team said it plainly.
is proof that whatever built our solar system
is not everywhere out there. It sounds obvious,
she said, but it is one of those things you actually have to prove,
and the ice just proved
it. That clock tells you cold and sealed, it does not tell you when.
The when came from the carbon,
and Webb is what read it.
When Webb split the light coming off the gas, the heavier form of
carbon, carbon-13, was almost missing.
And that absence is the whole clock. Every time a star dies,
it stains the galaxy with a little more carbon-13,
and the stain never washes out. So the longer the
galaxy has been around, the more of it there is.
Which makes the amount in a newborn object
a kind of timestamp. Almost none, and you were born early,
before many stars had lived and died.
A lot of it, and you came late.
Our sun came late, soaked in it.
This comet came back almost clean,
which drops its birth all the way to what astronomers
call Cosmic Noon,
when the universe was forging stars faster than it ever has since.
Feed that carbon into the models of how
the galaxy's chemistry has changed, and it hands
back an age, 10 to 12 billion years.
Martin Cordiner, who led the Webb work at NASA Goddard,
called it a chance to study an ancient
object from the distant galaxy.
Something that almost certainly predates our sun and everything
in it. I am going to be careful with that number,
because there is a lazy version of it and I will
not hand it to you. The universe is 13.8 billion years old.
This comet may have formed within about
a billion and a half years of the beginning of everything.
It is not older than the universe.
Anyone selling you that has stepped past the data
and you can feel the step. But it is close enough
to the start that the star which built
this comet has almost certainly already lived its whole life
and... died. Long before our sun was even a cloud
of gas beginning to collapse. The parent is long
gone. This is the leftover. I trust the bigger number.
And not because it is newer. Two clocks.
The orbit told us where it came from.
The ice told us what it is made of. Those two things share
nothing. There is no reason a path through the galaxy
and a ratio of carbon atoms should ever
agree. And they landed in the same place.
Then a separate paper from Taylor and Seligman ran
the orbital age a completely different way
and got a range that overlaps the same window from
a third direction. One clock can fool you.
A method built on one assumption can carry that
assumption straight into its answer without you noticing.
But when three of them that share
nothing, keep landing in the same place,
the answer stops being a press release and becomes
something you can stand on.
So put the two numbers next to each other. For a year we told you 7
billion, and we set it like it was settled.
The real answer was closer to 12. We were not a little
off. We were off by more than the entire age of our own solar system.
And there is a catch
sitting inside even that number,
one that almost undoes how confident I just sounded.
I will come back to it, because first you should know why
this age is worth fighting over at all.
This is what the age buys us.
We know of exactly one place where chemistry ever became life. Here.
One example, and we are standing on it.
Which means every question about whether life is common
or whether we are a fluke hits the same wall.
We only have the one sample. This comet is a
second sample, of a different kind.
It formed around another star, out of a chemistry we
did not cook, and it carried that sealed recipe all
the way to a telescope on Earth. Sarah
Milam, another of the Goddard scientists, put it simply,
Studying these objects is a real step toward learning how common,
or how rare, the conditions
that lead to life actually are.
There is nothing alive on this comet. What it offers is quieter,
it reaches further. It lets us hold the chemistry
of another star system in our own data and ask
whether the ingredients that build us are ordinary out there.
And the early answer, in its heavy
water and its missing carbon, is that our recipe is not the default.
If this is what you come here
for, the deep time object, the things that do not fit the textbook,
that is the whole reason this
channel exists, so subscribe and stay with it.
Now the catch.
When Webb first caught the comet on the way in,
it was breathing out almost eight times
more carbon dioxide than water.
The most lopsided spectrum on record,
four and a half standard deviations of every other
comet we track.
And only Webb could catch it,
because that carbon dioxide, glows at a wavelength our
own sky blocks completely.
18 minutes of telescope time,
and it came back built unlike anything from our system,
which points straight at its surface.
Billions of years of raw cosmic radiation,
slowly rebuilding the outer shell into something
ours never became.
Then this January, the Subaru telescope
in Hawaii caught it on the way back out, more
than two months past the sun,
and that record carbon dioxide reading was lower.
comet did not age in two months.
It changed which part of itself it was showing us. On the way in,
we were reading the outside, the crust,
the skin that has been marinating in radiation
for billions of years.
As it heated up near the sun, gas started venting from deeper down,
from material that had been sealed underneath
and never touched. And that is the catch,
and I think it is the piece that actually matters.
What we dated first, and most confidently,
is the ancient, radiation-beaten skin of this thing,
not necessarily the heart under it.
The oldest, most weathered layer is exactly the layer we read.
The core could be telling a slightly different story,
and we caught only the first breath
of it as the outer shell boiled away.
That does not undo the age.
Every independent line still points old, and they still agree,
but it is the difference between a headline and the truth,
and I would rather hand you the truth.
We are reading the outside of a time capsule,
while the inside is still sealed,
and we are running out of time to read any of it.
Because right now, as you watch this, Three-Eye
Atlas is already leaving. It rounded our sun once
and the math on its path is certain, it is never
coming back. Not in your lifetime, not in anyone's.
It crossed into range during the one narrow window
when a species on the third planet had finally built
the machines to read the carbon in its
breath. A few decades earlier
and we would have watched a faint dot go by and understood
nothing. A few decades later and it would already be gone.
This is the only look anyone will ever
get. The ceiling was four and a half billion years.
We built it ourselves, just by assuming
the only comets that could exist were the ones
that came with our own sun. This thing did not
break a law of physics.
It broke an assumption we never knew we were making, and it is leaving
before we can even agree on how old it is.
So how many other things out there have we
quietly filed away as young,
only because we never held one old enough to prove us wrong?
