Over the centuries, scientists have
solved countless mysteries about the
cosmos through careful observation and
experimentation.
But one of the most enduring mysteries
is closest to home. We still have never
seen how a solar system like our own is
born.
Our current model of how planetary
systems form is mostly based on
extrapolation of data from meteorites
and observations of our neighboring
planets. And for the most part,
scientists think we've broadly got it
right. At least the models we've built
seem to make sense. There are, however,
stages that have remained somewhat
mysterious. Exactly how, when, and where
planets form being the big one.
But that's about to change.
Earlier this year, the James Webb Space
Telescope found a baby star hidden in a
cocoon of gas. And amongst that gas and
dust, planets are being made. For the
first time, we've been able to see the
very earliest phases of planetary
formation. So, not only are we finally
getting to the bottom of the puzzle, it
could even show us something about how
our own solar systems planets came to
be.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we unravel the
secrets of HOPS 315,
consider what its future planetary
system might look like, and dive into
how this discovery is refraraming our
understanding of planet formation across
the universe.
Given that we live on a planet, have
visited seven others in our solar
system, and found more than 6,000 beyond
that, you'd think that we should have a
pretty good idea as to how planets form.
Well, unfortunately, that's not
necessarily the case. Much of what we
know today is thanks to the analysis of
meteorites that have landed on Earth and
observations we've made of the planets
in our own solar system as they are now.
The rest of it has been left up to
models and simulations. Why? Well, it
turns out the earlier stages of star and
planetary formation are extremely
difficult to see.
It all starts with huge molecular clouds
made up of dust and gas particles. As
they move around, they create thermal
pressure pushing outward on the cloud.
But these particles also have to obey
the laws of gravity just like everything
else. So they also pull each other and
the [music] cloud inward. This push and
pull remains in perfect balance for
millions of years keeping the nebula
stable. But a nearby cosmic event, for
instance, the shock wave resulting from
a supernova explosion, can suddenly send
everything into disarray. If gravity
starts pulling this gas cloud inward
faster than the pressure of its moving
particles can push back, we get a
runaway effect, a gravitational [music]
collapse. The dust and gas from the
outer regions begin [music]
raining inward. And as everything gets
denser and hotter, it [music] begins to
spin faster and faster, speeding up like
a figure skater pulling their arms in. A
heat gradient forms with temperatures
reaching more than 1,000 Kelvin within
one astronomical unit of the center and
cooling to 400 Kelvin at a distance of
five astronomical units.
Over the next 100,000 years, most of the
mass concentrates [music] in the middle
of the cloud, eventually forming a
protoar. The rest is dispersed outward,
forming a protolanetary disc of swirling
dust. a womb for this stellar embryo.
It's all this gas and dust that make the
stellar formation process so tricky to
see. Our telescopes can't peer through
it. But as technology has improved over
the decades, we have [music] started to
catch glimpses.
In 2013, a team led by Amelia Stutz
turned the attention of the Hersel Space
Telescope to the Orion Molecular Cloud
Complex, the biggest [music] site of
star formation near our solar system.
Known as the Hershel Orion Protoar
Survey, or HOPS, it searched the Messia
78 Nebula.
Hops found 15 new protoars, each with
masses between 1/5 and two times that of
the sun. These protostars had never been
seen before because their gas envelopes
are so cold, heated to just 20° above
absolute zero. With the protoars hidden
deep inside, this indicates that the
star hadn't yet had time to warm the
gas. They are young. In fact, Stutz and
her team believe they are some of the
youngest protoars to ever have been
found, finally giving us something to
compare our models to. But the initial
star formation isn't the only process we
know very little about. How planets
[music] themselves come to be is just as
much of a mystery.
Our simulations tell us that in the main
body of this disc, the dust and gas
particles begin to accrete. They
condense into microscopic solids which
clump together into larger and larger
grains over millions of years.
Eventually, these solidifying clumps of
spinning debris become planetessimals,
the building blocks of primordial
planets spanning [music] several kilome
across. If enough come together, either
via gravity or collisions, they can form
a planet. The problem is we've never
seen most of this happen. We found young
planets. This one [music] is four times
the mass of Jupiter and less than 5
million years old. And this [music] gas
giant is even younger. Its star is only
2 million years old. But that's as early
as it gets. And they are already fully
formed objects. There's hundreds of
thousands, if not millions of years gap
to fill in. That is until now.
1,300 lighty years away in that Orion
Nebula, a baby solar system is being
born. And we're watching it with our own
eyes. Well, James Webb's lens.
This is Hops 315, a star that's less
than 150,000 years old and 0.6 solar
masses. It's still growing, feeding on
an envelope of dust and gas that hides
in a cloudy veil.
But incredibly, researchers found a gap
in the clouds and managed to snap a
photo. And they saw something
extraordinary.
Web's infrared [music] spectra showed
the presence of both warm silicon
monoxide gas and tiny silica crystals
near the young star. We were witnessing
the moment gas condenses into a solid
for the first time.
This is a big deal because as a
protolanetary disc starts [music] to
cool, compounds begin crystallizing in a
specific order based on their
condensation temperatures. This is known
[music] as a condensation sequence. We
can infer this sequence from our
understanding of chemistry and our
analyses of primordial asteroids which
are like time capsules of our early
solar system.
The oldest condensates trapped in these
asteroids are calcium aluminium
inclusions or CIS and crystalline
silicut materials.
The fact that we saw both silicon
monoxide gas and solid crystalline
silicut around hops 315 indicates that
this star and its system are at the very
beginning of their formation. In other
words, we were watching the very first
stage of planet formation as it's
[music] happening for the very first
time. This was a major breakthrough. And
as lead author of the landmark paper,
Melissa Mccclure puts it, for the first
time, we've identified the earliest
moment when planet formation is
initiated around a star other than our
sun. They wanted to explore further. So,
professors Melissa Mccclure and Merril
Vanhoff focused the Atakama Large Millm
Submillm array telescope or ALMA on this
baby star.
Whilst James Webb Space Telescope
revealed the warm inner regions of a
young star through infrared light, ALMA
specializes in observing much colder
material, the dust and [music] gas that
emit millimeter and subm wavelengths of
electromagnetic radiation. This allows
astronomers to trace the chemical
composition and structure of molecular
clouds. By combining [music] the two
observatories, Mccclure and Van Hoff
could connect the dots. [music] James
Webb found the evidence of early
planetary formation and Alma pinpointed
where in the disc that process was
taking place.
What's most interesting about this is
that it's roughly in the same region
around HOPS 315 as asteroids made of
similar materials are found around our
sun.
We don't know exactly what this means
yet, but it suggests that the same early
building steps [music] for planets may
happen in many young systems. And
there's more. It's worth mentioning that
although silicut were found, the outflow
jet they studied is actually
suspiciously low in silicon, the most
important element for making silicut and
therefore planets. There's just 2% of
what Mccclure expected relative to the
amount of carbon they found. But this
isn't a bad thing for planet formation.
Mccclure says that may be a hint that
[music] planet decimals are already
forming there in a similar way that they
must have in our solar system. An
intriguing finding given the system is
so young. We are finally able to time
stamp the beginnings of planetary
formation to less than [music]
150,000 years after a star begins to
form, which is turning our models on
their heads. Initially, we thought gases
only began condensing once the central
star formed a class 2 system or when the
stellar envelope is mostly gone. The
star has stopped growing. What remains
is a relatively calm, well- behaved
debris disc. But over the last decade,
mounting evidence from several young
protostars like these have suggested
[music] that planet formation actually
starts way earlier. Still, these discs
were not well categorized. HOPS 315 has
gone one better and [music] confirmed
our suspicion.
But there's still one mystery about the
nebula hypothesis. Scientists have long
struggled to explain how millimetersized
condrils grow into rocks kilometers in
diameter. Small particles don't
naturally stick together, and
medium-sized objects fall into the star
within about 100 years due to gas drag.
One proposal is that [music] dust
collapses in pockets of gravitational
instability, directly forming [music]
planetessimals, a rock emerging from a
sandstorm. By repeatedly observing how
the gas to solid ratio changes in HOPS
315, [music]
scientists can uncover how fast solids
grow within the inner disc, what might
limit their coalescence, and how that
affects planet development. [music]
But perhaps most impactful of all, the
HOPS 315 system is one of the best that
we know to actually probe some of the
processes that happen in our solar
system. By comparing HOPS 315's dust
chemistry with meteorites from Earth,
scientists can see whether the same
condensation sequences and elemental
distributions that shaped our planets
occur in other parts of the universe. We
can finally test our models against the
real thing. But just as with anything in
science, as soon as you make a
discovery, it leads to many questions.
So, what's next for Hops 315?
How many planets will it have?
Will they be split into small rocky
planets in the inner solar system and
icy gas giants in the outer reaches of
the stars influence? Well, the
condensation sequence in the
protolanetary disc has a direct impact
on what kinds of planets form and where.
This lets us at least make an educated
guess. Since the early disc isn't
uniform in temperature, different
compounds will condense [music] first in
different parts. One feature of this is
called the snow line. The point beyond
which conditions allow ices to form. In
our early solar system, this line was at
about 2.7 astronomical units for water
ice. Beyond this snow line, ice and dust
accumulate, slowly snowballing into
giant planetary cores. The colder
temperatures out here also mean gas
travels slower. Slow enough to be
captured by the growing gravity of these
frozen cores. Eventually, enough gas is
captured to form a planet and a gas
giant is born. This process happens very
fast. We think it's how Jupiter and
Saturn formed in as little as 10 million
years. Meanwhile, on the other side of
the snow line, ice and volatiles are
completely vaporized.
Here, only materials with very high
melting points like iron, nickel,
aluminium, and rocky silicut survive. By
now, most of the gas in the system has
been captured either by the growing star
or the gas giants, meaning there's
almost none left for these longer
gestating worlds. The result is smaller
rocky planets like the ones we see in
our inner solar system, including Earth.
We don't know how many planets will form
around Hops 315, but we'd expect to see
a similar setup to our own solar system
with inner rocky worlds and outer gas
giants, although we still can't rule out
planetary migration and hot Jupiters.
Given that the current beginnings of
planet formation are happening at the
approximate location of our asteroid
belt, one question is whether HOPS 315
will have one. Ours sits between 2.2 2
to 3.2 astronomical units from the sun.
And we've already established that
asteroid belts aren't a feature unique
to us. In 2001, researchers found the
first asteroid belt outside of our solar
system, 70 lighty years away around Zeta
Laorus, a star 1,000 times older than
Hops 315. But whether one develops
around this baby star depends on a few
factors. We have our asteroid belt
thanks to Jupiter. Initially the region
between Mars and Jupiter was full of
dust and planet decesses. There was
plenty of material to form another
planet. But once Jupiter formed it got
massive fast and that strong
gravitational pull and orbital
resonances disrupted the surrounding
region halting accretion and trapping
planetimals in stable orbits around the
sun. This left behind a population of
primordial space rubble that never
coalesed into a planet, instead becoming
the asteroid belt we know today. So, one
way for Hops 315 to end up with an
asteroid belt is for it to create a
planet with enough mass to cause a
gravitational disturbance like Jupiter
did. But if a large enough planet never
forms, Hops 315 could end up with an
intermediate world around the snow line,
something our own solar system never
developed.
So, HOPS 315 is a portal to our past.
Studying it is like looking at our own
solar system 4.6 billion years ago when
Earth was still a dispersion of gas and
dust. But its discovery also raises big
questions.
How common are solar systems like ours?
Does planet formation always start at
2.2 astronomical units? How fast does
the disc go from microscopic dust to
planet decessimals? To answer these
questions, researchers are eager to
start expanding the search to more very
young stars to see if they can spot any
others like Hops 315. If multiple
systems show the same hallmarks of
creation, we'll have found a
protolanetary gold mine, a wealth of
observations and data to pour over to
better understand our origins. Whatever
they find, one thing is for sure. We
were once a swirling cloud of dust. And
billions of years from now, we'll be
dust again. So perhaps while we're here,
we should make the most of it.