Andrew Dunkley: Hello again and thank you for joining us on
another episode of Space Nuts. My name is
Andrew Dunkley, your host. It's great to have
your company. I hope you're well and I hope
you can stick around. We've got some really
great storeys today. These are fascinating.
Remember that asteroid impact that led to the
loss of the dinosaurs, you know, happened a
couple of weeks ago? Uh, well, uh, it
may have been much worse than we first
thought. Lost lots of, uh, crispy critters as
a consequence. We'll explain all that. Uh,
there was a near Earth asteroid discovered
around 30 years ago. 30 years ago. Well, now
new evidence suggests it may
have been a comet. And I love
this storey. This is about a Canadian amateur
astronomer who was planning a trip online
using, uh, using online maps. And
he made a massive discovery. We'll tell you
all about it on this episode of space nuts.
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Jonti Horner: Space nuts.
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nuts.
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Andrew Dunkley: And joining us, uh, this time around
with Fred Watson, gallivanting around chasing
solar eclipses is Professor Jonty
Horner, professor of Astrophysics at the
University of Southern Queensland. Welcome
back, Jonty.
Jonti Horner: Oh, uh, thanks for having me. It's good to be
the substitute Yorkshireman again.
Andrew Dunkley: Yes, we've got a whole set of them.
It's really good stuff.
Um, now we've got some amazing
storeys. I know you've been a very busy young
fellow for, um. Well, since we last
spoke to you, uh, you do your own sort of
gallivanting, but we managed to nail you down
for a couple of weeks, which is fantastic.
Uh, let's get straight into it because, um,
these storeys dovetail. Well, we've got an
asteroid that
may have been a comet. Then we've got an
asteroid that hit Earth that seems, uh, to
have done more damage than we thought. And
then we've got a hole in the ground
discovered while someone was planning a
holiday. All kind of related.
So let's get stuck into the, uh, first
storey. A near Earth asteroid that
was discovered 30 years ago they think might
have been a comet.
Jonti Horner: Yeah, this is a lovely storey and it ties
into something that we've talked about in
different lights previously when I've been on
the show, and I'm sure Fred Watson spoken
about it quite frequently as well, which is
that, uh, very human need to break things up
into manageable chunks, you know, so you
go from being a child to being a teenager to
being an adult and there's A miraculous day
when you wake up and you're suddenly legally
able to drive.
Andrew Dunkley: Yes.
Jonti Horner: And in different countries, that's a
different debt. But we all have it. But
fundamentally, you're not really any
different as a person the day before that and
the day after it. What we're doing is we're
breaking up this kind of continuum of human
experience into chunks, where we group things
that are similar together and we put things
that are more different into separate groups.
And I've talked about this in the past when
we've talked about the difference between
planets and stars and that amazing middle
ground that are brown dwarfs, where in
effect, you've actually got objects of all
sizes from the size of a grain of sand,
actually from the size of a single atom or a
single subatomic particle, all the way up to
the biggest galaxies and beyond in this kind
of continuum of sizes. But you go through
kind of rock to planet to brown dwarf to
star. And we put these arbitrary divisions in
so that we can group things that look similar
together and study them to make life easier.
And we talked about that, of course, in the
context of Pluto, with the whole thing of
when is a planet not a planet, when it's a
dwarf planet, and why all that happened.
That's exactly the same kind of thing. In my
kind of contextualization, that was the right
decision. That's a hill I'll quite happily
plant my flag on. But
Pluto's like the gangly teenager. From a
distance, it looks big and like a serious
adult, but it's still not very good at
tidying its room up. That's the kind of
analogy you there. This
whole storey is another one of those same
things. If we had been talking
300 years ago, people would have been
familiar with comets, at least the bright
ones. You know, things that get bright enough
to see with the naked eye that have a glowy
coma and a tail. They appear briefly, then
vanish forever. And we had great comets a
couple of times in the last few years, on
average one per decade. But it's a bit hit
and miss. And the idea is, with modern
scientific knowledge, what you're seeing when
you get that phenomenon is a big dirty
snowball or a snowy dirt ball that's whizzing
around the sun on this hugely elongated
orbit. When it's far from the sun and it's
nice and cold, we just don't see it. You'd
need the biggest telescopes on the world
because you've just got this little thing
reflecting a bit of sunlight. But when it
comes near to the sun, its surface gets hot.
The volatile material on it gets too hot to
still be solid, so turns into gas. And
that gas erupts from the surface, carrying
with it dust, shrouds that snowball
in what's called a coma, a big spherical
cloud of gas. And then the solar wind pushes
the gas and dust away from the sun and you
get the tails. And so a comet, as we see
it, is pretty big, can be millions or
tens of kilometres, tens of millions of
kilometres across, which is this huge amount
of gas and dust floating around in the solar
system, all given off by an icy,
rocky, rubbly object only a few kilometres
across in the head. And that's a comet. So
it's basically something that has activity
that out gases as it goes around the sun.
Andrew Dunkley: Yep.
Jonti Horner: 19. In 1801, sorry came along
and Giuseppe Piazzi found Ceres, which
was an object between the orbits of Mars and
Jupiter. And he found it because they were
looking for a planet, because people had
suggested that might just be that there's a
planet between Mars and Jupiter. So the
celestial police were looking, but Piazzi got
there first and that was the first of the
asteroids. And over the decades, and
the couple of centuries that followed, one
object became four, became tens,
became hundreds, became thousands, and
nowadays it's over a million. And if we
were talking kind of 30 or 40 years ago, we'd
have had a very clear idea of what an
asteroid is and that an asteroid is very
different to a comet. So an asteroid is a
rocky or metallic object that
even when it gets near the sun, just stays as
a rocky metallic object. No gas comes off it,
just a lump of rock or rubble going around
the sun. So
rocky, rubbly object, icy object with loads
of gas. You've got a comet, you've got an
asteroid, very distinct.
Now, water's got a bit more muddied for
a few reasons over the last few decades.
Firstly, you had objects called the
Centaurs, which I studied for my PhD, that
are big icy objects that are too far away
from the sun most of the time to outgas. So
got kind of asteroidal classifications and a
couple of them got a bit nearer in and
started out gassing, so got a dual classific.
Chiron is the most famous. Chiron has both an
asteroidal classification and, um, a cometary
classification. Cause sometimes it looks like
an asteroid, sometimes it looks like a comet.
You then have things like the Geminid meteor
shower every December, which is our best
meteor shower. I love it dearly. Almost
all of the meteor showers are produced by
comets and we get them when we go through the
dust that has been left behind by the
activity of the comet when it was out
gassing. But when they found the parent of
the Geminids, it doesn't look like a comet,
it's an asteroid. So the idea became that
maybe it's a rock comet and it's getting so
close to the sun it's shedding dust and we
get the meteor shower. Then there were
a couple of comets that were lost. And then
many, many decades later, an asteroid was
found that looked to be moving on the same
orbit as a comet. And so maybe they're the
same object and the comet has turned off. And
when the comet has turned off and stopped
making any gas, maybe it looks like an
asteroid. So there's this blurring going on.
In reality, what you've got is a
continuum from rocky and metallic and nothing
else on one end to incredibly icy on the
other, and everything in between where you
have more rock, less ice, more ice, less rock
blurring together. That's a
hell of a lengthy introduction, hell of a lot
of background to give the context for this
storey. So, in light of all that, back in
1998 there was this near Earth
asteroid discovered. It goes by the of 1998
SH2 and it looks like a lump of rock.
It goes around the sun every four or five
years, whizzing around. It's been seen at a
few apparitions since. And, um, that's all
well and good. We know a few thousand Near
Earth asteroids now and we're finding more
and more of them all the time. And people are
particularly interested because, of course,
if they come near the Earth, there's a
possibility that eventually one of them will
come too near the Earth and will hit us and
we'll have issues. And ask the dinosaurs
about that. We can come back to that a little
bit later on. So there's a lot of interest in
learning more about near Earth asteroids and
following them because the longer you observe
them, the more accurately you know how
they're moving. So the better you can predict
into the future where they'll be and
therefore rule out the chance of that object
hitting the Earth. Uh, may also, of course,
be interesting to people who want to mine
that object in the future with off Earth
mining that if you want to go mine it, you
need to know where it is. Yeah, so
that's this object. Brilliant. We found an
Earth asteroid.
Where it gets interesting for this storey
is that, uh, back in August 2025,
which is what, 27 years after this thing was
discovered it had another close approach
to Earth. Now, this wasn't like the
forthcoming approach for the asteroid
Apophis, which is going to come closer to us
than geostationary satellites. This was close
to astronomers and distant to everybody else.
You're talking about the thing coming about 3
million kilometres away at its closest
approach. Now, that's relatively close, but
it's not something to get particularly
panicked about. That's nearly 10 times as far
away as the moon is, about 8 times as far
away as the Moon is. But it's near enough
that if you want to learn more about the
asteroid, what you can do is you can get the
planetary radar, uh, that they used to beam
radar, uh, out into space and bounce it off
things and get it back. Yeah, to try and
bounce radar, uh, off this asteroid
to get an image of what its shape is, to
learn about its rotation and figure out how
big it is. Because even with the biggest
telescopes on the planet, something like this
is always just a single pixel. You can't zoom
in. So what they did was they got the
planetary radar, uh, sent radar out to this
object and missed
a little bit. Embarrassing as you do, it
wasn't quite where it was supposed to be.
So based on all those historical
observations, you can predict into the future
where the asteroid will be based purely on
the gravity of all the planets. It's getting
pulled around by the Earth, uh, and Venus,
Jupiter, everything's pulling and tugging on
it. And you can in a very prescriptive way
run its orbit forward in time and say where
it will be in the future if the only thing
acting on it is gravity.
But it wasn't where it should be. Uh, the
fact it wasn't where it should be says
something else is happening as well.
Something else is happening to push it around
now. So at this point, sometimes that we get
the, oh, well, it must be an alien spaceship
thing happening. That's exactly what's
happened in the past with people suggesting
there's maybe something more going on that
actually hasn't happened with this one, which
is really nice to see. But what
that being out of position tells you is that
there are non gravitational forces acting on
this thing. Something other than gravity is
happening to push it around a little bit.
Now, M. If we rewind to comets for a little
bit. I remember when I was a teenager back in
the early 1990s, we had Comet Swift Tuttle
came past and, um, Comet Swift Tuttle's a
parent of the Perseid shower. And, um, that
was kind of a relief because at, uh, Its
previous apparition, Comet Swift Tuttle, had
been seen widely observed and had been
predicted that it would come back in about
120 years. It would come back in the early
1980s and it didn't show up.
M which was a bit weird because this is a
bigger and more active comet than Comet
Hallie. It's probably the biggest of the
comets with a period less than 200 years.
Pretty epic object. And it came back 10
years later. Now, by the time it came back,
people had figured out kind of what was going
on, had realised that it was going to be
late. But part of the complexity there
was that, uh, because this is quite an active
comet, when it's ejecting gas and dust to
space, that process acts like a
rocket engine that pushes it around. So it's
ejecting gas in one direction and that exerts
a force pushing the nucleus in another.
And that is not a predictable thing in
that every time a comet comes around the sun,
its rotation will be a bit different. Some
active areas will turn off and some will turn
on. So while you can get a general trend and
you can make loose predictions, there's
always going to be a bit of uncertainty in
where a comet will be in the future because
it's got these forces pushing and nudging it
around. You know, it's a bit like, I don't
know if you could strap a few fireworks to a
snowball and throw it up in the air. That's
probably not very healthy to do. But you get
the same kind of thing, they go off at
different times and be pushed around all over
the place. Um, interestingly, Comet Encke,
which is a comet with the shortest non
orbital period, has been seen every three and
a half years, 3.3 years for more than 200
years. And we've actually seen its orbital
period get shorter and then get longer again
as a direct result of the jets on its
surface, uh, pushing it around and those jets
changing the rotation direction of the
comet. Loads of cool stuff there.
So with that knowledge, you can look at this
object, 1998 SH2.
It's not where it's supposed to be. So that
suggests that there's non gravitational
forces happening. But whenever people have
observed it in the past, it has looked inert.
Uh, it's looked like an asteroid.
What that suggests is that it is active.
It's got some outgassing happening, but at
such low levels that it wasn't possible to
detect them before. So that was a clue
that seems a really likely storey.
So scientists go away and they do a couple of
things. Firstly, they look for pre discovery
observations of this, you know, times when
there was a photographic plate made 50 years
ago that just happened to have the object in
the field of view so you can get a longer
period of knowledge of how it's moved.
Andrew Dunkley: Yeah.
Jonti Horner: And um, with these really accurate
observations, you can tell that it has been
misbehaving for a long time. It's getting
pushed and nudged around. What then
happened was they used some of the really
biggest telescopes in the world to take a
look at it and detect just a tiny hint of gas
being emitted, tiny little wisp.
And so you put all that together and um, this
thing is probably, of all the comets we know
in the solar system, the least active that we
currently know of. But it is exhibiting
cometary behaviour. So it's another object
really straddling the boundary. And it's
fascinating. It'll be wonderful to learn more
about it. But it's fascinating too,
because here's the thing that looks like an
asteroid, sounds like an asteroid. It does
everything you'd expect an asteroid to do,
except it's wibbling and misbehaving a bit.
Now, if you're finding hundreds and thousands
of near Earth asteroids and you want to know
whether the Earth's safe, well, if you see
something that's an asteroid, you can predict
where it is with gravity going forward, the
Earth's safe. What this is telling you is
that, uh, gravity may not be enough. So you
can't just say, well, it looks like it'll be
safe, we'll stop looking. Because if this
object's unpredictable, what about all the
other ones we're finding too?
Andrew Dunkley: I was about to bring that up. There's got to
be more than one.
Jonti Horner: Oh, absolutely. Um, we found
quite a few of these over the years now in
various circumstances. My favourite
really is the Taurid stream of debris. We get
the Taurid meteor shower every year from
about September to December. We've got the
northern and southern Taurids. We also get a
daytime meteor shower in June called the Beta
Taurids. Result is we spend about
four months of every 12 passing
through this enormous broad swath of debris
where on any given night, when the meteor
shower is active even at its peak ulcely,
four or five meteors an hour, the debris is
very spread out. But because the Earth spends
so long going through it, we get more debris
from that stream than all other meteor
showers combined over the course of a year.
At the core of that is Comet Encke, which is
that comet with a 3.3 year period, but
also a huge amount of other rubble and
debris. There's lots and lots of asteroids or
things that behave like asteroids moving
around in the storage stream. And the idea is
that this was a, uh, mega comet 20 or
30,000 years ago that fell apart,
giving us this stream of debris. Comet Encke
was probably behaving like an asteroid if
he'd found it a thousand years ago. But
something happened 250 years ago to wake it
up and it started behaving like a comet and
we see it as a comet. And the other asteroids
in that stream are currently dormant and
there's a load of them. So it's likely in the
inner solar system that even just in the
Taurid Stream, you're going to have hundreds,
if not thousands of objects just like
1998 SH2 that straddle
that boundary between the comet and the
asteroid.
Andrew Dunkley: Fair enough. And, uh, as a consequence of
that, they've had to rename it.
Jonti Horner: Yep. So it now has a cometary classification
as well. What happens with comets is you
get. When people find a comet,
um, it's C, slash, then the year,
ah, and then a catalogue number. So basically
every comet gets a unique identifier. So we
remember Chuchinshan Atlas, which,
um. I'm trying to remember the correct ID for
it, but it was, I think it was like 2023
A, ah, 1 or something like that, A3. So
the A means that it's discovered in the first
fortnight of the year. 3 is the third object
found in the first fortnight of the year.
That tells you about the comet and then
it's named after the discoverer in brackets.
If the comet is seen at more than one
apparition, the C gets changed to a P to show
that it's periodic. In this
case, because this already has
an asteroidal name by which
it's known, it's kept that, but they've added
a P in front of it. So it's gone from being
1998 SH2 to being
P. 1998 SH2,
um, will be interesting to see whether down
the line they add the name of the discovery
facility to it. Um, that wouldn't surprise
me. That's been done for previous occasions
where we've had an asteroid that became a
comet. But it'll be interesting to see. But
it's. I guess what I love about this is
you get into the nitty gritty of it, but it's
that reminder of the beautiful complexity
we've got. There's so much more to learn.
Andrew Dunkley: Absolutely, yes. Uh, it's a really good
storey and, um, one worth reading up. You can
do that@space.com or you can
read the published findings in the journal
Nature Astronomy. This is Space Nuts with
Andrew Dunkley and Professor John T Horner.
Jonti Horner: The crew of Artemis 2 now bound for the moon.
Generic: Humanity's next great voyage begins.
Jonti Horner: Space note Nuts.
Andrew Dunkley: Let's move from a comet flying through
space to a comet, uh, or an asteroid in this
case, that stopped, uh, flying through space
because a big planet called Earth got in the
way. And the one
that, um, is referred to as, uh,
or creating the Chicxulub crater
in what is now known, uh, as the Gulf of
Mexico. Uh, and we even know the
exact impact point because they've been down
there and taken samples, uh, which was a very
exciting storey when we covered that sometime
back. But now they've taken another look at
this, uh, and gone back to the very moment of
impact and the few hours afterwards and
decided by the look of it that this thing was
much more brutal than
we first envisaged.
Jonti Horner: Absolutely. And this kind of ties in with the
storeys that were told again. Back when I was
a teenager, I remember hearing about the
impact that killed the dinosaurs and storeys
about what would have happened on the other
side of the planet and the idea of firestorms
and, you know, it was a hellish experience
worldwide. But the way you'd normally hear
this storey relatively recently is you had
the impact. Things were bad in the vicinity
of the impact. Shockwaves went out, tsunamis
went out. So over a very large area, it was
immediately fairly devastating. But
there was a huge amount of dust and debris
flung into the Earth's atmosphere, which led
to this prolonged nuclear winter type event.
You know, it blocked the sun, got really
cold, the plants died, the animals died. Then
when the clouds cleared, it got really,
really nasty because you got this period of
runaway global warming and hideous acid rain
because the impact had hit rocks that were
packed with carbon and sulphur
carbonate and sulphate rocks, which led to,
uh, carbonic and sulfuric acid
rain. It led to an atmosphere super loaded
with greenhouse gases. So it basically
made the planet fairly hellish for a few tens
of thousands of years, from one stage to the
next to the next. But when I was
younger, there were these storeys about while
there were probably global firestorms. The
idea that an impact halfway around the world
could set fire to forests elsewhere.
And in recent years I've not heard
that storey told so much. It's kind of fallen
a little bit out of fashion. But the new
research that's been done here is kind of
bringing that idea back into the picture.
Now, the idea here is that you get this
impactor that was probably about 10
kilometres across, smacking into the Yukon
Peninsula, creating a crater that was
two to 300 kilometres in diameter.
In doing that, it would have flung a huge
amount of rocky material, vaporised material,
out of the atmosphere. And a lot of that
material would have travelled at speeds
slower than the Earth's escape velocity to
rain back down into the atmosphere. And when
that material falls back into the atmosphere,
it's travelling at speeds of kilometres per
second, so it ablates like a
fireball that we see in the sky, like a
meteor. But you're not seeing one or two,
you're seeing a huge deluge of material
raining down all across the planet.
Now, when these bits of material hit
the atmosphere and ablate, what they're doing
is they're taking the kinetic energy of their
Martian and emitting, turning it into heat
and light, which, you know, if you get a
single small meteor, you're not gonna get
sunburn from it. If you get something the
size of the Chelyabinsk impact, people
actually did get sunburn, um, from that, from
the brightness of the flash. Now imagine,
instead of having one Chelyabinsk impact,
having this rain of material falling into the
atmosphere all across the planet, creating
this, what's described as a thermal pulse
that has been discussed and
previous models, things that have come out,
suggested that that effect would have been
like putting a grill on. It would have been
really quite unpleasant for thin skinned
animals that were exposed to it. You'd have
got burned, you might even have got killed.
But if you were, uh, underground or you were
underwater, you'd have been able to live
through it. I mean, you'd have lived to see
all the other horrors that were coming from
the impacts. It wasn't really a good news,
Storey, but you'd have probably survived it.
But the argument had been that that thermal
pulse from that material coming into the
atmosphere would not have got things hot
enough to ignite things like grasses. You
know, the tinder that you get that can start
forest fires and things like this, which I
think is why that idea of the global
firestorms had gone away. What
the new research has done is looking at
fossil sites in North America, which must be
remembered, was quite close to the impact,
relatively speaking, on a global sense. They
found this layer of spherules of material,
which is a debris that rained back down to
Earth, uh, in the fossil record and above it
there's this very thin layer of silicate
dust which must have fallen out at about the
same time. Now the
idea is that that silicate dust
would have effectively acted like a bit of a
doona with that raining down and that in the
atmosphere. The fact that it's fallen in the
fossil record above the spherules
means the spherules got to the ground before
the dust got to the ground, effectively. So
the researchers have said, well, what would
happen if you had all this dust, all this
silicate dust in the atmosphere and you had
these ferrules running through, giving off
all this heat? And it's effectively like that
dust in the atmosphere would have acted a bit
like a reflecting, uh, blanket or something
like that. It would have trapped even more of
the heat in the atmosphere and reflected it
back down at the ground. And, um, the
calculations that they've made suggest that
that extra energy, because of the energy
being re radiated back down to the ground,
rather than escaping to space, would have
made things hot enough for grass to catch
fire, for pine cones to catch fire. Not
enough not for an entire tree to burst into
flames, but for all the tinder that was lying
on the ground to be called a flame.
And if that happens, what you do is you
trigger global firestorms. So you
turn a situation and you make it much, much
worse. Now, what should be said
here is this, uh, work is looking at North
America and it strikes me that further
away from the impact site, you probably
wouldn't have got the impact dust. So it
might well be that you actually had a
gradiated kind of level of nastiness from the
impact. So nearby it brutal. And
then you had the tsunamis and stuff washing
out on the far side of the planet. You
probably didn't get the silicate dust, so you
just got the normal level of hellishness
where you didn't set off firestorms, but
things were nasty. But there was probably
this sweet spot like the ultimately bad
porridge in the Cinderella Storey, where
things were ultimately worse, ultimately
as bad as they could be, where the impact
way over the horizon, way in the distance,
was enough to trigger forests to burst into
flame because of igniting the tinder enough
to cook animals alive as they were on the
surface. Uh, really kind of brutal and
remarkably horrific imagery.
But it's fascinating work and m it's another
insight into just how bad impacts like this
could be. It's that whole thing that we're
playing with a detective storey that is 66
million years old and we're trying to piece
together the narrative of what happened and
every bit of information we get like this
just seems to make a more and more horrific
piece picture.
Andrew Dunkley: Yeah, I mean, the original consensus was
the, um, asteroid hit
the planet and, uh, it
created, um, tsunamis that went around the
world, um, three, four times, something like
that. Um, and uh, created
the equivalent of a nuclear winter and
everything died and there was no food and,
uh, the creatures died along with it over a
period of time. But this is suggesting that a
lot of, um, the initial death,
uh, due to these firestorms happened in a few
mere hours. Um, it's a
horrifying thought.
Jonti Horner: It is. And I mean, you start getting to that
kind of philosophical side of thing is does
this make it better or does it make it worse?
You know, if you were there at the time,
would you rather be broiled and baked and
cooked quickly or left to starve slowly in
the cold that followed it? Yeah, I mean it's
all fairly bleak, but it is also that
reminder drawing just a bit like we were
talking about in the previous storey. We are
in the crosshairs. This will happen again.
It's not like the Earth has been hit for the
last time unless we do something about
it. And it's great that we have the capacity
to discover objects further and further
from the Earth with a greater and greater
lead time before they come close to us. It's
great that we're learning the capacity to
deflect them. But it's sometimes hard to
justify to people why people are doing this
kind of research. And it's one of the
arguments we have, for example, against the
satellite megalithic constellations, because
we're finally a spec that can look out at the
cosmos and detect threats. And what we're
doing is we're throwing tinsel in the way and
hiding the view.
Andrew Dunkley: And that is a bit of a worry. Well, it's a
big worry and it's not getting any better. In
fact, it's going to get worse. We'll um,
probably discuss that more in our next
episode.
But, um, I did notice
in sort of looking at this storey that, uh,
some papers or some websites refer to
it as a meteorite impact rather than an
asteroid. Why would they do that?
Jonti Horner: This is interesting with terminology and
I'm less uncomfortable with the idea of
meteorite impact, asteroid impact being
a conflation. The terminology of
objects is a weird one and
astronomers have very specific terminology
that then gets a little bit confused when you
see popular science and you see the news and
all the rest of it when something's floating
around in space nowhere near the Earth,
we refer to it as a meteoroid
or an asteroid or comet, basically.
Um, and we talked about asteroids and comets
earlier on and where the line blurs there.
The typical boundary between
calling a meteoroid and an asteroid is
often taken as being about one metre in size,
but that's just fairly arbitrary.
When something enters the atmosphere and it's
pushing the air in front of it and it's
glowing in the sky, that phenomenon we call
a meteor, if it's really bright, we call it
a fireball. And that boundary is set roughly
as bright as a planet Venus. If we see an
explosion at the end, we call it a bolide.
And that just means exploding fireball,
basically. So meteor, bolide,
fireball are uh, atmospheric phenomena.
You're not actually seeing the thing coming
through the atmosphere, you're seeing the gas
that it's heated up and excited in the
atmosphere. That's what you're seeing as a
glow. When it reaches the ground and hits the
ground, you call it a meteorite. That's the
physical object on the ground or hitting the
ground. Now, whether
you call something like this a meteorite
impact or an asteroid impact, I think it's
probably both. You know, technically the
asteroid hits the ground, um, you
could call it a meteorite. But maybe what you
should do is have that idea in your head of
if it's less than a metre across, you could
call it a meteorite. Bigger than that, you'd
call it an asteroid. I've never seen
clarification on where that
boundary comes because terms are used in
different sensors kind of thing. So for me,
I don't think it's unreasonable to say
meteorite impact here, although you're
probably pushing the size definition.
Call it an asteroid or comet impact is
probably more reasonable. And it might be
that if you dug into the physics of it and
you were to do an IAU resolution a bit like
we did with Pluto, maybe what you do is look
at it in terms of the effect of the
atmosphere on the object coming in. So
things that create fireballs and bolides in
day to day life, the atmosphere is much
bigger in size than the object coming in,
which means wind resistance will eventually
slow it down. So the meteorite that we talked
about a few months ago that landed on
someone's driveway in Canada was travelling
at about the same speed that a rock dropped
out of an aircraft would have done. It was at
terminal velocity. Its speed was
governed by the atmosphere. Whereas with
things that are kilometre scale, the
Atmosphere is essentially not there. It's not
going to slow them down. And so I wonder
whether there is an argument that you could
set up a definition that said if it's
travelling at uh, speed less than
supersonic, you'd call it a meteorite impact.
If it's travelling faster than that, maybe
you'd call it an asteroid impact. But I don't
think that there's any official delineation
like that. That's just kind of how I think
about things in my own head.
Andrew Dunkley: No, I like that that works. Well, well,
that's probably a good way to think about it.
Um, another interesting storey that uh, the
asteroid impact uh, that killed the dinosaurs
was a lot more damaging in the early stages
than we first thought by the look of. But uh,
plenty of, plenty of websites and news
platforms have picked this one up, not
surprisingly. Uh, but you can read
at uh, the Science
Advances, uh, website published in
Science Advances. Uh, this is Space Nuts
Andrew Dunkley here with Johnty Horner.
Jonti Horner: 0G and I feel fine.
Andrew Dunkley: Space Nuts, the storey. Jonty
takes us to Canadia and
this is a storey, uh, about a
Canadian amateur astronomer who
decided to plan a holiday using online maps.
It is.
Jonti Horner: This is lovely. I think we've all done this
to some degree. You planning your holiday,
planning your road trip. I just had a lovely
holiday with the in laws. And you look at uh,
the online maps of your choice that typically
have really nice satellite images of the
places you're um, and you try and figure out
what you're going to see, what you're going
to go there. And to some degree you sat
browsing around thinking, I wonder if I can
see anything unusual, what's it like around
there? And that's what happened
here. We've got this amateur astronomer going
by the name of Joel Lapointe who back in
2024 was planning his hiking and
camping trip. And I think it's in northern
Quebec. It's near a place called Lake Mars.
And he found this unusual looking
feature next to that lake. Looks a bit odd
on the maps on the satellite imaging. Now
there is a university in Canada that has a
website called Impact Earth that allows
people to, as a kind of popular
um, collaborative endeavour for
citizen science is the word I'm looking for
to log things where people think they've
found impact features. So being an
amateur astronomer being aware of this, he
logged it. I think I found a crater. About
a year later, um, the site
as a result of this report was
explored, visited by a planetary geologist
from the university called Gordon Ozinski.
Who went there, took a lot of samples,
explored around and confirmed that
this really is an impact feature. It's an
impact crater about
390 million years old,
so way older than the impact that killed the
dinosaurs. About 25 kilometres
across, which includes a load of
incredibly well preserved features in terms
of glassy hardened volcanic type rocks from
the impact that he himself has said he's
surprised at that well preserved, given how
old it is and how far north this is, how cold
the weather gets in the winter and stuff. Now
this makes it the biggest crater found on
Earth since 2018, when there was a crater
discovered under the Greenland ice sheet. But
the difference is that the one under the
Greenland ice sheet is below a kilometre's
depth of ice. So it isn't like we can get
there and learn much more about it. That's
still quite a mysterious spot.
Whereas this is open and exposed and
accessible, so people are able to go there
and explore it, learn a lot about it. There's
some really nice imagery out there on the
Internet about this. From the maps, images
where it was found to images of
features called shatter cones, which are the
kind of thing created that are very typical
of an impact crater formed under very high
pressure, very high temperature molten rock.
So it is absolutely amazing.
But it's also to me kind of breathtaking that
here is a feature 25 kilometres in diameter
in the middle of a built up, well, not that
built up country, but in the middle of a
country near a famous lake, there is an
impact crater that had never been identified
until now. You know, we're still discovering
kilometres, tens of kilometre scale features
on the Earth. I mean, that's just
astonishing.
Andrew Dunkley: Uh, yeah, it is. And um, I
think we've talked about it in the past that
one of the problems with finding these things
on Earth is the fact that the Earth's kind
of covered up with vegetation and uh,
you know, lots of, um, weather, uh,
activity which has caused erosion and then
we've got earthquakes that have caused
mountain ranges to pop up here and there. And
so a lot of these impact points get uh,
disturbed or are hidden. Not uncommon
now.
Jonti Horner: Absolutely. And I mean 70% of the Earth's
surface is water and you need to be a bigger
impacter than the depth of the ocean to leave
a scar on the ocean floor. So the
history of impacts on the Earth is very much
muddied by all of these different
processes. The Ice Ages have scoured the
surface of the Earth clean. We've got
weathering, we've got forests, the Earth's
surface is actually an incredibly dynamic
place compared to the Moon. If you look at
the Moon, there are many craters of this kind
of size. And one of the things that is
actually discussed in the articles online
about this is whether this could be a venue
for people to learn more in preparation for
visits to the Moon where we can go to craters
or vice versa. Whether we could learn more
about craters like this by going to the ones
on the Moon that are the same size but are
pristine because we're at a similar
location with similar targets in the shooting
gallery. But on the Earth everything gets
worn away fairly effectively, whereas on the
Moon it stays pretty pristine until something
else hits it and weathers it away. The only
real way you're going to weather lunar
craters, um, with a few exceptions, is
by other things hitting them and muddying the
water. There is going to be a lot more to
learn about this. It is still relatively new
news. The geologists involved
won't be going there year round because it
gets really, really cold and really
unpleasant in the winter. So there'll be
summer expeditions going there, trying to
learn more about it, getting more and more
samples of it. Because we don't know many
craters that are that old on the Earth.
Andrew Dunkley: No, this is 390 million
years. That's a long time back, isn't
it? That's over 300 million years beyond the
dinosaur impact.
Jonti Horner: Absolutely pretty impressive. It's far from
the oldest crater on the Earth, but I would
argue that we know far more younger craters
than this than. We know older craters than
this.
Andrew Dunkley: Yeah. Didn't they recently say they found
the oldest one in Western Australia? Was it?
Jonti Horner: Yeah. Then I think that was a little bit
controversial, but there was a lot of talk
about shattercons with that one as well.
Andrew Dunkley: Yes, there was, Yeah, I remember that.
Jonti Horner: You know, these are, uh, we're finding
craters more and more and they tell us about
the history of the Earth and the heritage of
it. With the really old craters, there's even
some arguments that the, ah, largest impacts
that happened very early on in the Earth's
history were actually the seeds of the
continents to some degree. There was some
amazing work. This is probably actually best
part of a decade ago now. But there was great
work by Craig o' Neill and his team that were
looking at trying to model the initiation of
plate tectonics on the Earth. So how did
plate tectonics get going? And, um, these
incredibly talented geophysicists here in
Australia were running models where
you start the Earth with no plate tectonics,
looking at the interior, looking at how hot
it was back then. And if you started the
Earth without plate tectonics, plate
tectonics didn't happen. And uh, what they
thought could be the smoking gun was that you
had impacts that caused a big impulse of
energy and motion in the mantle
that triggered a downwelling which would then
trigger an upwelling and you could get impact
induced plate tectonics which would then
cause these things to maybe even give you the
seeds of the continents of the earliest
continents. And that's an
awesome storey. The videos that they made of
their simulations were fabulous. And
um, yeah, it's amazing what more there is
still to learn, I guess.
Andrew Dunkley: Yeah, absolutely true. And this is another
storey that's been picked up by Orlin Sundry.
Uh, so, um, yeah, you shouldn't have any
trouble finding it if you do, um, a search
for the Canadian amateur astronomer who was
planning his holiday. And uh, the storey will
pop up just about everywhere. Space.com, the
Smithsonian magazine, et cetera, et cetera.
Uh, and uh, by, by now,
when you hear this episode or very close to
this point in time, uh, the team
that uh, made the discovery will be
presenting their work at the 88th Annual
Meeting of the Meteor. Uh,
meteoritis. I can't say
it, uh, Meteorocital
Society in Germany, I think. That's right. I
don't know. Anyway, yeah, look it up. It's a
great yarn.
Uh, we've had a very rocky programme today.
Um, Jonty, it's been fascinating the
way those storeys all dovetailed into each
other. Uh, and we're at the end. Thank you
very much. Nice to see you again.
Jonti Horner: Uh, it's good to be back. Thank you for
having me and hope
Andrew Dunkley: Fred Watson's enjoying his jaunt
chasing a, uh, solar eclipse.
Jonti Horner: Yes, yes, it's a hard life but somebody's got
to do it.
Andrew Dunkley: Absolutely true. I'm waiting for one to come
to me. I only have to wait two more years.
Jonti Horner: Two more years.
Andrew Dunkley: Thanks.
Jonti Horner: And it'll be cloudy. You know it's going to
be cloudy.
Andrew Dunkley: Oh yeah, it's probably going to be raining
training and I'm m giving up a game of golf
for it too. All right, thanks Jonty. We'll
see you soon. Yeah, It's a pleasure,
Professor Jonty Horner, professor of
Astrophysics at the University of Southern
Queensland. Don't forget, uh, to visit us
online while uh, you are, ah, waiting for the
next episode,
spacenutspodcast.com
and have a look around while you're there.
Visit the shop, etc etc and thanks to Huw in
the studio couldn't be with us today. Um, put
his home address in Google Maps. We haven't
seen him since. And from me, Andrew Dunkley.
Thanks for your company. We'll see you on the
next next episode of Space Nuts. Bye. Bye.
Jonti Horner: You've been listening to the Space Nuts
podcast, available at
Apple Podcasts, Spotify,
iHeartRadio or your favourite podcast
player. You can also stream on
demand@bytes.com M.
Andrew Dunkley: This has been another quality podcast
production from bytes.com.