Andrew Dunkley: Hi there, thanks for joining us. This is Space Nuts. Andrew Dunkley
here. Good to have your company. And on this episode
we have a lot to talk
about.
The uh, first thing will be a megastructure of
epic proportions discovered in the universe. Now this is
not a uh, uh, something that was
manufactured by some incredible race
because uh, we have talked about megastructures in the past.
Now this is natural and it's called Quipu.
What's that mean? We'll tell you soon. Um, this
is uh, one of um, the biggest bugbears that
Jonti has to deal with the overselling of the
potential for life on exoplanets. Yes, there is
one in the news at the moment. We'll do an update on
M20, 24 yr, uh 4. The
odds of it hitting us have halved and
SpaceX satellites raining down on our
atmosphere. Uh, what does that mean? We'll tell
you on this episode of space. Space
nuts.
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Andrew Dunkley: And he's back again, surprisingly.
It's Jonti Horner, professor of Astrophysics at the University of
Southern Queensland. Jonti. Hello.
Jonti Horner: G'day. How are you going?
Andrew Dunkley: I am well. How are you?
Jonti Horner: I'm getting there. I've never got the hang of mornings. I think I'm a bit
like the um, characters from the Hitchhiker's Guide. Except
for me it's mornings. It's not Mondays, it's mornings.
Andrew Dunkley: Yes, I, I used to be like that and then
I started in breakfast radio and did it for 30 years.
So I, I eventually got used to being up at
Sparrows.
Jonti Horner: The breakfast shift does not sound fun.
Andrew Dunkley: Uh, I enjoyed it but that was just me. I don't
know if anyone else did, especially the audience. Boom, boom.
Jonti Horner: Uh.
Andrew Dunkley: All right, uh, let us get into it and we're going
to start off with this discovery, um, of a
megastructure which has uh, been uh,
in the news over the last week or so
and it's, it's called Quipu. We'll
explain why it's called that soon. But this is a
megastructure, uh, of natural formation in the
universe. The enormity of this is
mind splittingly amazing.
Jonti Horner: Yes, yes it is. It's one of those things that just makes
your head hurt like a lot of things in cosmology. Now
I'll happily hold my hands up right at the start and say
my expertise is on the parts of the universe that are a lot closer
than this. So I'm not a cosmologist, and if there are
cosmologists listening in or people who are cosmology
enthusiasts and I get something wrong, please don't be too
critical. Um, because, you know,
the size of the things that I don't know in cosmology is enormous.
M just like the subject itself. But
this is a really interesting one. When we think
about the universe, you see all these wonderful
simulations that come out of our models of
how the universe works that people produce all the time.
And, um, you can almost see videos on
fabulous documentary series where they start at the scale of an atom
and keep zooming out, and you eventually get to the person and
keep zooming out. And the scale of
cosmology is roughly the
same scale compared to a human being, that a human being is
compared to an atom. So that's the kind of size scale we're talking
about here, which is the study of the
ridiculously big. But as you zoom out from that human
being on the earth, you get the solar system, then you get the local
stars, then you get our galaxy. And then as you move
out, you get structures of galaxies together.
So you get small clusters of galaxies, and those
small clusters hang together in bigger clusters that
gather together in superclusters. And they,
for a long time, were kind of the biggest structures we saw in the
universe. But then as you zoom out further, you
start seeing these structures like walls
and filaments, where those clusters and super
clusters of galaxies are themselves forming structures with
huge voids in between. So on this kind of scale, when you
see those simulations, it looks almost like
a view of a sponge. So if you've
had a sponge in your bath, the
sponge is a lot of open air spaces
surrounded by lots of solid material. And all the solid material
is in contact with all the solid material, but all the
air is in contact with all the air. So you could put a bit of string and go
all the way through the sponge, through the air holes, and come out the other
side and m that's kind of what this view
of the universe looks like. It sees long filaments
and walls all connected to one another
with these enormous voids of empty space between
them. That's the context we're talking about here.
So the team of researchers who studied this have
been carrying out observations using an X
ray survey looking at very high energy electromagnetic
radiation that's produced from incredibly hot gas
in the most massive clusters of galaxies. Enormous
structures themselves, and they've looked
at a region about 250 million
parsecs across in all directions, maybe a bit
more, looking for the biggest
structures they can find in that region. And they've
identified four of these, what they're calling
superstructures. And their superstructures are
megastructures because they are bigger than normal structures.
They're structures made of structures made of superclusters made of
clusters made of local clusters made of
galaxies. On we go all the way down
again. Now, these four structures that
they found between them contain
45% of all the galaxy clusters. They could
see 30% of all the galaxies and 25%
of all the matter, but they only occupy about
13% of the volume. So that gives you the idea
of lots of empty space with these filaments
around it. The biggest of these, this is
someone quipu that's getting all the attention
is ridiculous. They talk about it being
2000-000000-00000 times the mass of the
sun. So if you remember. So for
listeners in countries that do things differently, we're using the
kind of British scale million billion system here. So a
million is 10 to the six one with six zeros after
it. A billion is a thousand million. So that's 10
to the 9. A trillion is a thousand
billion or a million million. That's 10 to the
12. A quadrillion is a thousand
trillion or a million billion or a billion million.
So it's 10 to the 15, 200 of
those means this is 2 times 10 to the 17
or 2 with 17 zeros after
it times the mass of the Sun. Now that's
a number that is bound to make your head hurt. So I converted
that down by looking at how many Milky
Ways that would be. And that would be something like
130,000 times the mass of our
galaxy. So stupidly
big numbers it is spread over a
distance. It's a big long feature, about
400 megaparsecs long. So one
parsec is perversely the
distance that an object would
be away from the Earth if its
parallax, as the Earth goes around the sun, was
1/ arc second. It's a really obscure unit of
measurement. It makes sense when you're doing the
maths of measuring distance, but it's not particularly user
friendly. It's a bit like talking in feet. Light
years is a bit like talking in meters. Same kind of thing.
Most people find light years more straightforward to
visualize, but where one light year is the time it takes
light to travel in one year, and there are
3.26 light years in one parsec.
So 400 megaparsecs is
1.3 billion light years long. So
in other words, light leaving one end of this structure will
take 1.3 billion years
or, uh, 1300 million years to go from one end
to the other. So it's an enormous, enormous
structure. Now, that's all well and good, and
it's fabulous cataloging the biggest and the most massive and the
brightest. And I know a lot of people, I do this occasionally. Look
up Wikipedia articles like, what's the most massive star? What's the
most luminous star? Things like that. But it's
also really valuable to know this kind of stuff because if you study
these big structures, that gives us information that
we can compare to the models that are based on
our current understanding of the universe to see
if those models make sense. And, uh, the good thing is that
the current models of how the universe work
predict structures like this. So this is very much
in line with what people expected to see. And
that's a really good part of how science works. It's very much a
case of our models predicted this and now you've
seen it, that makes us happy because it means the models are working
correctly. It also is the kind
of information that's really useful for people studying
the Big Bang and more ancient universe. Because
structures like this are sufficiently massive,
then they will influence our view of what is beyond.
You get gravitational lensing from the big objects.
You also even get. And, um, I don't fully understand how this
works, but you also get the pollution of
the cosmic microwave background, which is the
last hiss of the Big Bang. It's
our image of the last surface 300,000
years after the Big Bang, where the universe became transparent.
And we found little bits of structure in that which
are important for us understanding how the modern
structure of the universe formed. But that structure is
polluted by the influence of these
foreground objects by something called
the integrated Sachs Wolfe effect. And I have no idea how
that works, to be brutally honest. But
if you've got something like that, that pollutes our view of
what's beyond. And we want to understand what's
beyond. The better we can see the foreground, the better
we can account for it when we're studying the background. So
getting studies of this a. It's fascinating. It's a
really good test for our models. But it also
allows us in the future to get a better handle
on how things like the cosmic microwave background really
look when you filter out the foreground mess.
And I guess the equivalent here will be like having a
light pollution filter for people who are astronomy
photography enthusiasts. You've got a murky,
light polluted sky, but if you put a light pollution filter on the front of
your lens, you can cancel out that foreground mess and
get a much better view of what's beyond. This
will enable us to do that same kind of filtering when we're looking at the
microwave background.
So I think it's a fabulous story, full of
numbers what make your head hurt. Quite.
Andrew Dunkley: They're massive numbers. It's just uh,
just incredible. Now why is
it called Quipu?
Jonti Horner: This is partially because of the structure. So it looks
like a long thick filament with thinner filaments branching
off the sides of it. The authors of this
paper noticed that this looks very similar
to the traditional counting instrument of the Incan
people in Peru. Um, which was essentially they
did their counting using knotted ropes and ah, that
knotted rope counting device was a Quipu. So
it's quite a nice nod to the traditional culture of
that area in Peru. Again, I'm not an
anthropologist or an archaeologist, I don't really know much more
about it than that, but I think it is a really nice
nod to a different culture. And
as we've talked about in previous weeks, this idea of embracing
all the cultures of the Earth in our studies going forward is
really gaining traction. It's a really nice way of doing things, I
think.
Andrew Dunkley: Absolutely, yes, I'd agree. And uh, the
Incans have a, um, strong history
with astronomy so uh, that ties
in well too. So yeah, fascinating.
If you would like to chase up that story. It was published
in Astronomy and Astrophysics, the journal. You can
also read about it at the
arxiv.org website. That's
arXiv. I learned that last week.
arxiv.org uh, yes,
there was um, um, a lot of involvement from
the Max Planck Institute in um, in
running this. The author was Hans
Boehringer. So uh, you might want to look that
up.
Space nuts.
Uh, now, uh, let's move on to our next
story. This is a pet peeve peeve story,
um, which Jonti wanted to talk about. And look,
I'm not surprised that bothers
some people, uh, because I, I have
often referred to the popular press when
doing this podcast and how they latch onto
something that isn't quite the story
but it makes a great headline and that's what this is.
Overselling the potential for life on
exoplanets.
Jonti Horner: Yeah, yeah, it's.
Andrew Dunkley: And one in particular in the news at the moment.
Jonti Horner: Well it's something that's niggled at me for a while. It should be said that
the criticism here is not of the research done by these authors.
They've done a fabulous bit of research and if you look at the paper,
they've got the balance right. That's fine. But there
is a very common trend, particularly among press
offices at universities and also
around a lot of media sites that rely on clicks for their
income, to talk about
the most habitable planet ever discovered. We found the
most Earth, uh, like, planet ever. And the reports on this planet
are not quite that bad, but they have been talking about
potentially habitable planet discovered around nearby
star, because that gets the clicks. And
before we dig into this story, the reason that this niggles at
me is that people are getting exo Earth
fatigue and also life elsewhere fatigue.
So by reporting things when we haven't
actually found what the reports are saying, it creates this opinion that
the science is already done. We've already discovered the
autumn stuff. So when we finally find a planet that really does
have life on it, or when we finally find a planet that
genuinely is Earth, ah, 2.0.
That'll be exciting. I'll be thrilled. We've finally got something to talk about
and everybody will be kind of the boy who cried wolf. Well, you've told us that
you've done this a million times already. Yeah, and it's easy.
Why are you interested? You know, it's
also the fact that we
basically don't know enough to make these statements yet. So when you
see a headline like, we found the most Earth, uh, like, planet
ever. What it's actually telling you is we found a
planet that's about the same diameter as the Earth, and
that's it. So it's like me being an alien and
visiting the Earth and scanning the oceans and saying, I
found the most human, like, creature ever. It's about the same length and
it's about the same weight and it's about the same size. It's called a
dolphin. Nothing like a human
whatsoever, but it's about the same size and about the same
mass. So it's the most human, like, animal ever.
So I get a bit grumpy. And there's a lot that goes into habitability
that I can talk about a little bit later on, which is
why I think this is a much more complex problem. And for me, that
makes it much more interesting, a lot more research to do.
But it does mean that when you get a claim saying, potentially
habitable planet, or the most habitable planet we've ever
found yet People even publishing articles about super
habitable planets that are more suitable for life than Earth.
I don't think you can say any of that. Aha.
Uh, in this particular case, it is an interesting
story. There is a star called 82
Erudani, which also goes by the name HD
20794. You know, astronomers love
our acronyms and our barcodes. This
is a star that you can see with the naked eye in the constellation of
Eridanus, but it's not particularly bright. It's about magnitude 4,
4 and a half. And for a while we've known it had
two planets around it. But it's been monitored by
the High Accuracy Radial Velocity Planet Search
for Spectrograph HARPS in Chile. And
HARPS is an incredible instrument.
It allows you to measure the velocity of a
star. So you take the light from a star, you
break it up into its component colors, and laced
across that spectrum is a series of dark lines.
And those dark lines, which we call the Fraunhofer absorption
lines, are, uh, the fingerprint of all the different
atoms and molecules in the star's outer atmosphere.
Every atomic species, every molecular species absorbs
light at a very specific, unique set of
wavelengths. And it imprints this dark set of
lines across the star spectrum. Now, if the star's
moving towards us, its light will be blue shifted.
So all of those lines will move a little bit to the blue because of the
Doppler effect. If it's moving away from us, the light will be
redshifted. So it'll move a bit to the red again with the
Doppler effect. And I've talked about this before, this is the
equivalent of having the siren coming towards you and
hearing it high pitched and fast with Nino, Nino,
Nino and uh, then it moving away and you're hearing it low
pitched and slow with Nino, Nino to do
with the waves getting stretched or compressed
essentially. Now what that means is if we
measure the positions of these lines accurately enough, we can measure the
change in the speed of the star as it moves around
by seeing those lines move. So we can look at
stars and see them wobbling and infer the presence of planets
that we can't see by how those planets pull those
stars around. But there are limits to this. There's a
lot of challenges involved. So facility like the one
we've got at the University of Southern Queensland, which is actually
the Southern hemisphere's only dedicated exoplanet search
facility, we can get an accuracy
where we can measure the wobble of stars down to about two or three
Meters a second. So we could see a star, ah,
changing in speed by about as much as someone going at a
very gentle jog. What that means is
we could not find these particular planets, they're just
much too hard. But the HAARP spectrograph is on
a much bigger telescope in a much better
location and it's an incredibly accurate piece of
kit. So it lets you get down to sub meter
per second measurements, which is
breathtaking. Put that in perspective. We're looking at stars
here whose distances are quadrillions ah,
of kilometers away. Again using the units from before.
These are stars where the light has taken decades to
reach us and we are able to measure their
velocity so accurately that we can see changes in that
velocity of 50 centimeters a second.
Wow, that's just astonishing precision
and that's what the team have done. So they've observed this star, uh,
HD 20794 for
a number of years with haps getting more and more data
tracking how the speed changes. And in the past they'd found
two planets and hints of a third and they've now
confirmed that third one. That third planet,
HD2.0, uh, 794-D is
making the star wobble with its speed changing
by just 50cm a second plus and
minus over a period of about 700
days. So you're watching for 700 days,
you get rid of all the other noise, the star wobbling around
itself, just oscillating like a shruk
bell. You get rid of the orbits of the two inner planets which
are causing it to wobble by a similar amount with a different
period and you're left with a tiny wobble of plus or
minus 50cm a second that takes 700 days
to complete once. And that's what they found. So this
is our planet. It's a planet about six
times the mass of the Earth, at least might be
more than that. We don't know how edge on or tilted the orbit
is because we're not seeing it transit. If it's tilted by
30 degrees, the mass of this planet will be higher.
If it's tilted by 60 degrees instead of being 6 earth
masses, it'll be 12 earth masses. So this is a minimum
mass. So it's what we call a
super Earth, ah, or a mini Neptune. It's much
more massive than our planet and certainly larger than our
planet. It's moving on an orbit
that if you calculated its semi
major axis, the length of the
ellipse, half the length of the ellipse, which sets a period
that will put it in the habitable zone, um,
that's what the paper says. Now, the habitable zone I'll get into in a
second. But this planet moves on a very
elongated orbit, so its distance from its star
is changing by a factor of two from its closest to the star
to the furthest away. Now, if you scale that up to
the solar system and put it in the same place, temperature wise,
as it is in its system. Now, if you put it in the solar
system so that its orbit had that same temperature
range, that would mean when it's closest to its star, it's as
close as Venus. When it's furthest from its star, it's
further out than Mars. You're going to
have extreme, extreme temperature
variability on this planet. Now, the habitable
zone, um, is always thrown out for these planets. It's
that Goldilocks idea. If you have a planet that's at the right
distance from a star, the temperature will be not too
hot and not too cold, and it'll be just right for liquid water on the
surface. The subtle implication
buried in this is not actually what I
just said, but it's rather. If you took the Earth
as the Earth is today, and dropped
it where this planet is, would the Earth, uh, still have liquid
water on its surface? Now, that's a subtle
difference. But to illustrate it, if you think about the solar
system, the boundaries of the habitable
zone are usually set by looking at Venus and Mars. That's what's
motivated this. The calculations are more robust, uh, now,
but that's about where it washes out. Venus, closer
to the sun than us, is super hot. 450 degrees
centigrade on the surface and clearly not habitable.
Mars is super cold. It's too cold for life. It's outside
the habitable zone. The Earth's in the middle, and it's just right.
But to illustrate why it's not so simple, imagine a thought
experiment where you swap Venus and Mars around. If
you put Mars where Venus is, it's got a thinner atmosphere than we
do, so it's got less of a greenhouse effect. So
it would probably remain clement where Venus
would overheat. Similarly, if you put Venus where Mars
is, Venus has this incredibly thick atmosphere with an
incredibly strong greenhouse. It will probably still
be habitable. It would still be warm enough where Mars
wouldn't. So this habitable zone is a much woollier
concept than I think most people
realize. And it's just not really
a guideline. It's just an indication that this could
be somewhere worth looking at. It's not more than that, but it tends to get
played up as being the Holy Grail. And
one is in the habitable zone. It must therefore have
the potential to be habitable. Whereas in fact, what you're
saying is if you put the Earth on the orbit that this planet is
on, it might still look like the Earth, except with
the planet we're talking about at the minute. If you put the Earth on that
orbit at, um, perihelion, when it was
closest to the sun, it would receive a flux from
the sun as high as Venus does. So the oceans would start to
boil. Fortunately, it doesn't spend long at
perihelion. We move quickest when we're closest to the
object. We swing out through the habitable zone,
probably everything's fine. But you've got bonkers weather
because you're dealing with all that heat you've just been given. Then
you get to your furthest point from the star and that's when you move
the slowest. So this planet spends probably more than
50% of its time further from its star
than the outer edge of that habitable zone by calculation. So
those oceans would freeze and you get this deep, Game
of Thrones style winter. You'd have everybody going, oh, look, winter is
coming. Everybody's doomed. And then it would
swing back into the star and have a brief furnace like summer,
and then a long cold winter again. It doesn't sound
particularly clement.
You add to that, though, the fact that this planet is six times the mass of
the Earth means it's going to have a very
substantial atmosphere, and I should say at least six times the mass of the
Earth. A much thicker atmosphere means a much stronger
greenhouse effect, which means the
results of that extreme insolation, the extreme
radiation at, uh, pericentre when it's closest to the
star, is even more pronounced. So I don't
think it's at all fair to say that this planet could be potentially
habitable. And in fact, the authors of the paper
themselves don't really say that. What they do say is, is that
this planet crosses the habitable zone. And, um, because it's a
bit bigger and, um, because it has this big variation in existence
from the star and, um, because it's around a nearby
star, could be a really good test case for us to
practice our observation techniques to learn
more about atmospheres of planets this size before
we really look at ones that could be habitable enough
like. But this planet certainly isn't it.
And even then there's a whole heap of Other things that will impact
habitability, which we may or may not have time to go into
today. But the habitable zone really is just
the first of an incredibly long list of
variables that you can slide around that could
influence a habitability. Because all it's saying is, how hot would
the Earth be if you put it there? Essentially?
Andrew Dunkley: Yeah, yeah. And at six times the size of the Earth,
at least gravity has to be a factor as well,
doesn't it?
Jonti Horner: It does. I mean, if you estimate that
this thing is twice the Earth's diameter and M, we don't know that
because this thing doesn't transit its star,
or we've never seen it transit its star. So its orbit is almost
certainly not edron, which means its mass is probably a bit higher
than we say that minimum is. But it means we have no way of
measuring the size. Now, at six Earth
masses or a bit heavier, it's near this boundary between what we call
super Earth or mini Neptune. Super Earth
is a rocky object with a big thick atmosphere, and
mini Neptune is a big thick atmosphere with a rocky core.
So you can see how that transitions between them. But if you
estimate for a minute that it is a super Earth with a bit of a thick
atmosphere, you could say, well, maybe it's twice the
diameter of the Earth. Uh, and, uh, that would kind of make
sense density wise. That would place it a little
bit less dense than the Earth. But that might make sense because it's
a little bit cooler for a lot of its orbit.
Even in that scenario, the acceleration due to
gravity on its surface will be 50% higher than that we
have on the Earth right now. You know, so gravity
will be stronger. We'd probably all, if we were there, be squat
and dumpy and grumbling about how heavy we
feel and all the rest of it. You know, I'm heavy enough already without giving
me 50%.
Andrew Dunkley: Yes, no, that's a fair point. But,
uh, yeah, these, these stories are not uncommon now.
And you make a very valid point that people will just, you
know, when the day comes that we've genuinely got an Earth
like planet Earth 2.0, uh, that
could harbor life. People will go, yeah,
right. Oh, ah, heard it all before.
Jonti Horner: And it's dangerous. And quite often the
researchers involved don't have control of that story.
That's one of the reasons I love working
with websites, like the conversation, where I control the narrative when I
write articles. But it's also why I really appreciate our
media team here at unisq because they
actually talk to us when they're writing media releases and a lot of
the bigger universities, the media team get hold
of a paper and they write their own interpretation of it with, with a couple
of quotes from the authors, but they don't let the authors read the
release. Then you get journalists who read the media
release and spin it further and you end up from an
article that says, we found a planet that is interesting to being
new. Earth planet has been found. Life 2.0
is there. And that's not what anybody actually
said.
Andrew Dunkley: No, no, but it's a good way.
Jonti Horner: To get hits and links to your university's website.
Andrew Dunkley: Exactly. Yeah. Okay. If you'd like to
read up on that, uh, the genuine article I'm talking
about, uh, you can find it in the journal
Astronomy and Astrophys. You
feel better now that you've got that off your chest, Jon?
Jonti Horner: This is a perpetual rant of mine. I actually did
with my former mentor, Barry Jones, who passed away
about a decade ago now. Um, we wrote
my first ever review paper back in 2010 where I
dug into this. So it always used to bug me that it
was just, it's in the habitable zone, right? That's job
done. And so we wrote this paper where we looked at all
of the other things people have proposed that could make a planet more
habitable or less habitable, more suitable. And for
me, the thing here is, when we get to
do observations to look for life on these planets,
which is still a bit beyond us, but we're getting towards that
point, those observations are going to be the
hardest observations humanity's ever had to carry out. You're
talking hundreds or thousands of hours on the biggest
space telescopes, really competitive time.
You're not going to be able to look at them all. So you're going to have to find a way
to pick the best target. You're going to have to find a way to whittle down
a list of hundreds or thousands into the best two or three.
And you can't just use the habitables on there. So I thought, let's look
at all the different things that can impact habitability
to see if you can turn them almost into the volume sliders on
the mixing desk of the dj, right? You can turn them
up, turn them down, and see which planet
gets the best score overall when you factor all of them in.
And, um, some of them are things we can't yet observe. Some of them are things you
might have to model with computer modeling, like I
do. But it can be everything from the nature of the
star itself, how Variable it is all the way
through to the other planets in the system, what their gravity does,
how much debris there is, and even down to the planet
itself. Whether it has plate tectonics, whether it has a magnetic field,
all of these things will factor in. It's not just as
simple as where do you place it? Is it in the right
spot?
Andrew Dunkley: Valid point. All right. Uh, yeah, as
I said, you can uh, chase that story up at Astronomy and
Astrophysics. Uh, you could probably find it just about
anywhere online. Uh, there's an article on
Space.com as well. This is Space Nuts
with Andrew Dunkley and John Horner.
Space Nuts, right.
Our next story, which uh,
we've uh, done before, we did it a week
ago, uh, about uh, the comet
2024 yr. Uh 4. I happen to be
playing our uh, podcast in the car.
I always like to listen to it just to see how it sounds
and you know, decide whether or not I'm doing a good
job or not. Did it in radio, do it with the
podcast. But I, I was picking up our
grandchildren from school and uh,
Nathaniel who um, is
10, uh, years old, um, he was listening
and he said to me, is a comet going to
hit Earth? And I had to kind
of explain to him what was going on without alarming
him. Uh, and now an
update on the story. Last week we were saying
um, there was a 70 to
77% chance of this thing, um,
hitting the atmosphere in 2032.
Uh, sorry, yeah, see that's,
that was a popular press comment. One in seven.
But now that number's dropped as at
now. But that could change again.
Jonti Horner: Absolutely. So as of today, so when I sent you
notes through yesterday, it was at 1 in
43. It's now fallen back to 1 in 48.
This number is changing every day. And what we
will see and what we'll continue to see is most likely
those odds of an impact gradually
increasing until eventually they
most likely drop to zero. Ah. And the reason
for that is we're getting more observations with every day that passes.
And so with every day that passes we get a refined
estimate of the orbit of this thing.
That then means that uh, the exact location of the
object on 22nd of December
2032 has a smaller uncertainty. So
that big area of space that we think it will be
in with each day's observations get smaller and
smaller. Now if the Earth is still in that area
of space, the Earth is a bigger fraction of
that total volume of space. And so the
probability of impact is going up because we're a bigger
fraction of the total area that thing could be in. But at some
point, as that volume of space shrinks down, the
Earth could fall out of it. And at that point, the probability
immediately drops to zero. So it isn't a reason
to panic at all. This is exactly the behavior you would
expect to see. But that probability
will continue to change day by day. It wouldn't surprise me if it
keeps getting higher. Now, this asteroid we're
probably going to lose track of in about April. It'll be too far
away to observe, but then we won't see it
again till 2028. People are digging back through
archival observations from
2016, 2012, 2008,
because this thing comes roughly near the earth every four years or
so. If we find it by chance
on one photograph from one of those previous years,
this probability will change dramatically and we'll probably drop to
zero straight away. If not, we'll have to wait till
2028. And until then we'll see this continual
slight more wobbling around as each day's observations come
in and it gets recalculated. So
fundamentally, nothing has changed. This thing still
poses a threat. Do not panic. Even if it were to hit us,
it's not really going to cause a problem anyway, to be brutally honest.
But it is fascinating to watch this happen
and to see that evolution in real time.
Andrew Dunkley: Absolutely. Yeah. I think I said comet, I meant asteroid.
But, um, yeah, 2024, uh,
if you do a search on Google or whatever your favorite
search engine is, you'll find plenty of information.
And you. I would advise filtering the
popular press comments because,
uh, they've been going hammer and tongs on this one.
Jonti Horner: Absolutely.
Andrew Dunkley: Um, but, yeah, uh, like, uh,
Jonti said on the previous story, it's clickbait,
isn't it? Um, that's really it. But, uh,
I did reassure my grandson because as soon as I
finished explaining it, he wanted to talk about
Pokemon. So I think I was successful in deflecting
him there.
To, uh, our final story, Jonti, and this
one is about stuff that's hitting the atmosphere.
We're talking specifically about the,
um, turnover of SpaceX
satellites. They've been starting
to rain down on Earth, uh,
fairly regularly. In fact, uh, the Space Nuts podcast
group on Facebook has been,
um, discussing this. They put an article on there
that the listeners were
discussing, and some were quite
surprised by the kinds of numbers we're talking about.
But this is just going to get more and more
significant as time goes on because they haven't finished
deploying their entire, uh, fleet
or whatever. You want to call them of, uh, SpaceX
satellites.
Jonti Horner: Yeah. This is yet another multifaceted story.
So I know a lot of people who get very passionate
in their defense of SpaceX and Elon Musk and many others who
have very negative views of them. And I always try and be
somewhere in the middle. It's like in literature if
you ever read a book, very few people are
purely evil or purely good. Everybody's somewhere in the middle
unless it's a bad book. And it's the
same with things like this. There's a lot of good about this and a lot of bad about
it. Now SpaceX are putting up their Starlink
satellites to deliver Internet
access, which is a great benefit to people in the
regions. I've heard plenty of stories of
people who are living remotely in Australia who can't get a good
Internet connection on Starlink as been revolutionary to them.
Andrew Dunkley: Yeah. And cruise ships use Starlink.
Jonti Horner: Absolutely. Because they're always.
Andrew Dunkley: They're in remote areas a lot.
Jonti Horner: Yeah, it is a really incredible
technological development. On the other hand, you've got all the concerns about the
light pollution from these things and
the fact that they launched them without anybody really being able
to regulate it or say boot about
it. It's a multifaceted
problem and there's good things and bad things about it.
In much the same way, this story is both a
good and bad story. You've got all these satellites up
there and they have finite lifetimes.
They are low down because you need them to be
in low Earth orbit in order to get good latency. If you put these at
geostationary orbit, you've got the light travel time there
and back again, you've got a long way to go and
that puts a significant ping, which means for the people playing
Twitch games and first person shooter games,
they can't play and sulk. Um, but everybody
wants a faster Internet connection with the lowest latency possible.
So these things are in low Earth orbit, which means that they
are moving through a significant chunk of the Earth's
atmosphere. The Earth's atmosphere doesn't just stop, it just gets thinner and
thinner and thinner the further you go away. Technically, the moon
is still encountering bits of the Earth's atmosphere. It should by that point it's so
thin as to be irrelevant. But at the altitude of these
Starlink satellites, they are actually traveling into
a headwind. So without something to
bump them up, they would eventually come down naturally anyway.
But also they are a fixed
term thing. They typically, I think thinking about
an individual satellite having about A five year lifetime.
Andrew Dunkley: Yeah.
Jonti Horner: Now it's about five years since the Starlink satellite started getting
launched, which means the very first generation of them
are now in their retirement phase.
What is really good about this is
that SpaceX and Starlink are being
very aggressive in the retirement in that they
are controlling these things and deliberately putting them back in the
atmosphere to burn up in a controlled fashion. So they're
controlling where they drop them into the atmosphere to minimize the
risk to air travel and the risk of them
dropping on a city and things like this. And that
is really good governance. It's really important to say that there's a lot
of stuff up there that will come down of its own
accord, at its own time, with no control over it.
And that's a risk. And people are talking about the fact
that there's probably as high as a 26% chance
that in a given year from now on space debris will
fall through a populated airspace
m which is problematic. There's even studies saying there's a 1
in 10 chance that within the next decade somebody will
die as a result of space debris hitting them.
So that's a concern. And by deliberately
deorbiting these things in a controlled fashion, they're mitigating
those risks, putting things down in a safe
fashion. But because of how many satellites they're
putting up there, that means we've got an increasing number of them coming
back down. There are currently 7,000
Starlink satellites up there. The goal is to get up
to 42,000. That is their stated end.
So that's the factor of six times more.
Andrew Dunkley: Yeah, that's just Starlink, because there are many
others.
Jonti Horner: There are. If you look at all of the proposed mega
constellations, I think the current number is that there
could be as many as 550,000 satellites in orbit
within a decade. Which makes me, as an amateur
astronomer, the kind of part of me that goes out and observes meteor
showers and stuff just makes me weep because we'll lose the night
sky to such a degree. But that's a slightly
separate thing. With 7,000 up there at
the minute, the retirements of those first gen ones are now coming at a
rate of four or five satellites per day.
So that means four or five satellites are burning up somewhere
over the Earth, uh, every single day of
the calendar year. That's only going to go
up because if you increase the number of satellites up there by a factor of
six times, then you'll increase that number of
reentries per day by a factor of six times. So within
five Years, we could well be looking at
something nearer to 25 or even 30 satellites per
day coming back into the atmosphere. Now, these are coming in
in a controlled fashion. So, uh, they're trying to drop them in the
atmosphere away from things that would be threatened
by lumps of metal hitting the Earth's atmosphere,
essentially. Yeah. But there is now a growing
concern about the pollution side of this.
Andrew Dunkley: That's the thing that I was getting. Yeah, that's
the. That's the big if, isn't it?
Jonti Horner: And it's a difficult one because it's not an experiment that's ever been
done before. Things have re entered. Um, but in
the past, we've not been putting much up in space. So it's been a very
rare thing. A little bit of extra material dumped into the
atmosphere. A tiny amount compared to the amount that
comes in naturally through meteors and meteorites,
um, stuff hitting the Earth's atmosphere, naturally. But we're now getting
to a stage where this is a significant amount of
material entering the Earth's atmosphere. Each of these
Generation 1 satellites is several hundred kilos of
material. So when you've got five of them
coming in a day, that's a couple of tons of material
being ablated and added to the atmosphere, mainly
in the form of heavy metals. There
is a fact that I've pulled out of an interesting article.
India Today of all places, have got a fairly good article about
this. And, um, one thing they point out is that each
individual one of these Generation 1 Starlink satellites,
when it burns up in the atmosphere, when it ablates,
deposits about 30 kilos of aluminum
oxide into the upper atmosphere, about
where the ozone layer is. Now that's a problem
because aluminium oxide is a compound that is known to
be very devastating to the ozone layer.
It's a real problem. Now, if each satellite is dumping
30 kg into the atmosphere, that has a
potential to destroy a large amount of ozone.
If you're suddenly dumping five of them in per day, that's
150 kilos per day.
We go up to the 25. Obviously, that
goes up again from 150 kilos to what, five
times 150, 750. 50
nil. Your ton of aluminium oxide per
day. Something that can damage the ozone layer.
And we've only just got out of the time where we did an incredible job
of preventing us killing the ozone layer. Yeah, we're
about to start it again. People have
tried to do some computational studies of the effects of adding
all this metal to the upper atmosphere. And, uh, nobody really
knows what's going to happen? Some studies have said
that it could accidentally help to slightly mitigate climate
change because it might increase the albedo of the Earth's atmosphere.
It might cause more clouds to form, so it could reflect a bit
more sunlight or could be good. But other studies have
suggested the opposite, that it could actually lower the amount of clouds we've
got and also add a bit more greenhouse nastiness
to the mix. So it could have an impact on our climate. We
don't know which way it'll go. It could have an impact on the ozone
layer. We just don't know yet. And so what's
happening with this is we're effectively running a
science experiment like the ones you do in the lab, the ones you do at
school without ever done it, without ever having
done it before. And we're running it on the planet that
is our own home. Um, so I guess it's a bit like,
you know, you've got two unruly toddlers running around
with, um, insects, prey. Like the stuff you've got
to get rid of. The mosquitoes. Yeah. Running around
emptying can after can of that in your house. And you just said, yeah, well,
let's do it. What's the worst that can happen? And you just don't know.
Andrew Dunkley: Yeah. Uh, 42,000
satellites, when they're ultimately all up there, coming back down
into the atmosphere, will deposit 1.26
million kg of
aluminium oxide. So, and that's going
to be continuous because it's not just
42,000. Uh, as they come down, they'll replace
them and add more to get to their full
structure. So it'll be an ongoing
thing, multiplied by however many
constellations are created to do the same thing. So.
Jonti Horner: But it isn't also like, that is easily recoverable.
That's a lot of resources that we're just losing.
Andrew Dunkley: Yeah, exactly.
Jonti Horner: Um, now, I could imagine a much further
future where instead of things being retired by
deorbiting them, you retire them by boosting
them to kind of graveyard orbits and have something there
collecting them and melting them down for the materials.
That's why in the future, because that will be a lot more expensive.
It's cheaper at the minute m to just throw them away. I mean, we
see with recycling efforts that there's not much motivation to
recycle when making things from new products is
still cheaper.
Andrew Dunkley: Yeah, well, if they could solve the latency problem, that
would maybe help cure it as well.
But how do you do that? Relay stations on Earth? I don't
know. I Don't know. But, uh, yeah, that's a
really fascinating story. I know Fred and I have talked about it before, but
it's worth revisiting. And, uh, yeah, the information
just keeps evolving over time
and we're not nearly at
capacity yet with these constellations. If you'd like to read it,
uh, as Jonti said, it's, uh, on the website
India today.in
that brings us to the end of the show. Don't forget to visit our
website or our social media sites. Plenty of things to see and
do there. Uh, if you have any thoughts on any of the
things we've discussed, by all means, uh, send us a message
via our website. Just, there's a little, uh, button up the top of
our homepage, um, ama, where you
can send us messages and audio questions or whatever
you like. Uh,
spacenutspodcast.com or
spacenuts IO is the place to
go. John D. Thank you so much. We're at the end. We'll
catch up with you real soon.
Jonti Horner: It's absolute pleasure. Thank you for having me.
Andrew Dunkley: Uh, John D. Horner, professor of Astrophysics at the University of
Southern Queensland. Thanks to Huw in the studio, who,
um. Well, he couldn't be with us today because he
got hit by a piece of SpaceX
satellite. Uh, no. No, he
didn't. Maybe he did. I don't know. I haven't seen him for
ages. And from me, Andrew Dunkley, thanks very much for your company.
We'll catch you on the next episode of Space Nuts.
Bye for now.
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