Andrew Dunkley: Hello, thanks for joining us. This is Space
Nuts. My name is Andrew Dunkley, and we're
here to talk astronomy and space science. And
on this episode, we are going to look at a
study into Jupiter's role in shaping
our solar system. What shape is that?
It's rhomboid. No, we don't know. we're also
going to look at a, white dwarf star that's
chowing down on a planetesimal. Sounds
appetizing. observing a rapidly
developing ring system, and it's not far
away. And if we've got time, an exoplanet
that in inverted commas may
be a life candidate. That's all coming up on
space nuts. 15 seconds. Guidance is
internal. 10, 9.
Ignition sequence start. space nuts. 5, 4,
3, 2. 1, 2, 3, 4, 5, 5,
4, 3, 2, 1.
Jonti Horner: Space nuts.
Andrew Dunkley: Astronauts report it feels good. And it's
good to have Jonti Horner back with us again.
Professor of astrophysics at the University
of Southern Queensland. Hi, Jonti.
Jonti Horner: Good evening. How are you going?
Andrew Dunkley: I am well. Good to see you.
Jonti Horner: Oh, it's good to be back. Although I'm
admittedly a bit of a zombie, so I warn
everybody, I've had less sleep than I should
have done in the last couple of days because
of the weather. we had some weather happen on
Sunday, which led to the power here being
knocked out for 24 hours during a mini heat
wave. So I didn't get much sleep then. And
then this morning I've got a colleague from
Japan visiting, so I had to pick him, his
wife and their two lovely daughters up from
Brisbane Airport. So I've had six hours of
driving today off the back of two nights of
not much sleep. So if I seem less coherent
than normal, and I appreciate I'm normally
not that coherent to begin with, you know
why, of course.
Andrew Dunkley: Yes, we've all been there. we've had dreadful
weather here too. But it hasn't been the
extreme heat, it's been the extreme wind.
I got woken up, last night about
1am by the Fly, screens rattling. It
was so windy. Yes, they, they were just
shuddering. And I thought, I can't live with
this.
Jonti Horner: So I went outside.
Andrew Dunkley: It was freezing cold, supposed to be late
spring here, and I
just jammed some wood chips
into the. I just went off to the
garden and grabbed some mulch and shoved it
in the wind in, in the fly screens to stop
them rattling.
Jonti Horner: It worked.
Andrew Dunkley: I've done it better during the day, but,
well, that's just Been ridiculous.
Jonti Horner: I know your parents. I mean having said that
we had heat wave conditions and couldn't
sleep because of the heat, I'm happ confess
that I've had the wood serve on today because
having had 36, 38 degrees so
that's around 100 for our American friends
last few days. Today has been a toasty kind
of 15 degrees. and we've got a rain event
happening. so we've had everything in the
last week we've had kind of almost tornadic
storms, we've had hailstones the size of your
fists, we've had under a kilometer an hour
gusts and now we've got random cold that
makes me feel like I'm back in the uk. So
yeah, all happening. And this is why
Australia is an interesting place to live
even to the extent that with the
thunderstorms. We had got an email through
yesterday that our wonderful observatory,
Queensland's only professional astronomical
observatory in Mount Kent was closed
yesterday. We weren't allowed to go there
because there was a bushfire within 10km of
it that had been sparked by the lightning
from the storms and fanned by the heat wave
in a place that got lightning but no rain. So
ah, it's all happening here.
Andrew Dunkley: Yes, dry storms are not uncommon where I am.
We we do get quite a few storms every year
with lightning and thunder and nothing else.
and they, yeah, they're very well known for
sparking bushfires.
Jonti Horner: Yeah.
So while we're on the diversion of the
weather, actually I'll apologize for Maya the
dog chirping in the background but my
partner's just got home. But we're also
sitting here with an incredibly heartbreaking
record, record breaking storm in the
Caribbean. Yes, I know she's just come
home. Thank you for joining me with the
podcast Happy Dog. but yeah, there's
borderline record breaking storm in the
Caribbean which is going to be a Category 5
hurricane hitting Jamaica and doing a, ah,
hell of a lot of damage. And it's one of
these that from a scientist point of view,
fascinating watching it looking at the radar
footage and all the satellite footage and on
one hand you've got this thing of incredible
exceptional beauty and on the other hand the
devastation it's going to cause. So the
people in the, in the firing line for that.
Andrew Dunkley: Yeah, I saw the satellite images this
afternoon. It is enormous.
Jonti Horner: Yeah, you look at the false color one
with the color of the clouds which is an
indication of the severity of the storm and
the shape and it's the kind of thing that you
only see with the strongest storms we've ever
seen, typically in the Pacific. So for this
thing to not only be happening in the
Atlantic, which is less common, but
to be, you know, crosshairs on Jamaica,
which has had a bit of a charmed life with
some sacks of the high mountains that tend to
bounce and go around a bit. This one looks
like it's not so much going to bounce a
splat.
Andrew Dunkley: So yeah, when we were in Panama earlier
this year, we did the Panama Canal and
they were saying that they never get
hurricanes ever.
Jonti Horner: Too equatorial is my understanding. You need
to be far enough away from the equator to get
enough spin so. So it's very rare that you
get storms getting right up to the equator
because coriolis force and things like that.
Andrew Dunkley: Yeah, yeah, it's interesting, isn't it?
Very interesting. Okay, we better get
on with what we came here to get on with. And
we're going to start with a study that's
been released into Jupiter's role in shaping
the solar system. Now I do recall Fred
mentioning that Jupiter, if Jupiter
didn't exist we wouldn't. And this study
basically adds a lot of fuel to that claim.
Jonti Horner: It does. Now where Fred said,
Fred and other people talk about if Jupiter
didn't exist then we probably wouldn't. Ties
into something that's a pretty big
myth in science communication, Ansel in
science papers and stuff, which is the idea
of Jupiter shielding us from impacts. And my
most favorite piece of research I ever did in
my career is proving that to be a lot of
cobblers and it's actually a lot more
complicated. Jupiter throws things at us as
well as protecting us. So I've always got a
bit of an eye on any study that says, hey
guys, if Jupiter wasn't there, neither would
we. But this is a really interesting one that
looks an entirely different aspect of
Jupiter, which is the role that Jupiter
played on the formation and evolution of the
early solar system, the formation of the
planets. And I've actually been teaching
planet formation this week to my undergrad
students. I've just, prior to recording this,
had a two hour tutorial with them where I've
been talking about planet formation and
brought this story up because it
really highlights the fact that when we
often see in documentaries and the stuff we
get taught at school, we get the impression
that everything's solved, that we know the
answers, that we know full well how the
planets formed in microscopic detail and
we've got everything figured out and the
Reality is that we haven't. We have a really
good broad picture and we're getting better
and better at understanding the processes
that went on. But there's still a lot to
learn. And part of that is that while we've
known the solar system since the year dot,
we've only known other planetary systems for
the last 30 years. And in reality we're still
learning an awful lot about the planetary
systems we find elsewhere. And learning about
them is cool and all, but it also gives us
insights that help us better understand our
planetary system and how it formed. And that
ties into this because the more we
study those other planetary systems, the more
we're getting observations of really
beautiful things like planetary systems that
are in formation, where you've got a
protoplanetary disk. And we're getting these
gorgeous images from things like the
ALMA array, the Ataccama Large Millimeter
Array that shows disks of planet
forming material around stars with gaps in
them and ripples in them and bands in them,
and all these beautiful structures. And some
of these have been previous astronomy.
Picture of the days where this ties into the
solar system is if you imagine that kind of
stereotypical image of a
protoplanetary disk, a disk of gas and dust
around a young star like the sun, where
material is feeding in through that disk to
the star. So while the gas and dust is
orbiting the star, there is this kind of
sense of inward motion where the stars kind
of nominating at the inner edge of the disk,
materials falling in, and more material from
outside flowing in to replace it. Yeah, and
some of the models of the formation of the
solar system struggle to make the terrestrial
planets as a result of that. Because the
material in the inner solar system is
destined to fall onto M the star. And how do
you stop that happening to let that material
hang around to actually form into planets?
Now it's been pretty well established for a
long time that the first planet that formed
in the solar system and got to a good size
was Jupiter. And there's good reasons for
that. It formed far enough away from the sun
that the temperature was cold enough that the
disk was rich in ice, which at, the
distance the Earth is from the sun, all that
ice would be gas. when you're forming solid
objects, you need solid objects to feed from.
And so when you've got a lot of ice, you've
got a lot more solids. So things grow
quicker, there's a lot more to eat. And it's
only when you get to about 10 or 12 times the
Mass of the Earth that You're massive enough
to effectively start gobbling up the gas as
well. So Jupiter formed beyond this point
called the snow line, where there's a lot
more solid material. It got to grow really
quickly. It grew quicker than things further
out because the further out you go, the
slower things happen. So Jupiter was very
much in the sweet spot, grew really quickly
and eventually got big enough that it started
clearing the gas and the dust it could gather
the gas as well. And it opened up a gap in
the disk. And that's very analogous to what
we're seeing with these beautiful images from
ALMA places like this. So the team of
researchers behind this work have run some
really in depth computer modeling of the
formation of the solar system formation of
Jupiter, and showed that when Jupiter opens
up the gap in the disk, its gravity will
also have an impact on the inner solar
system. It'll effectively create the
gravitational equivalent of speed bumps,
creating areas where the dust that's
spiraling inwards can pile up and be
stopped from traveling further in.
Effectively. It also creates
a gap between the in run out of solar system
that nothing crosses because if anything gets
in that gap, Jupiter noms on it. And that's
really interesting because some studies that
have looked at primordial material we've
found from in the solar system suggests that
there is a bit of a chemical difference
between material that formed in the inner
solar system and material that formed in the
outer solar system. So this gap
dividing the two gives a natural way for that
to happen. But the really big exciting result
from this is really that modeling of
the structure that Jupiter would have imposed
on the inner solar system. These kind of pile
up regions where you get more m dust and
debris than normal, the structures that, that
would carve out ripples in the disk
effectively and how that would then
contribute to the formation of the
terrestrial planets. and therefore suggesting
that not only did Jupiter help the
terrestrial planets form by creating sweet
spots where material could pile up, but it
may also have had a really strong influence
on the architecture of the inner solar system
by setting where the planets would form,
which then would go through a bit of a
randomization phase as everything collides
with each other. But it kind of possibly set
the blueprint for the inner solar system. And
therefore, if Jupiter hadn't formed where it
did and how it did, the Earth would look
very, very different and we might not be
here.
Andrew Dunkley: Yeah, it's truly fascinating. And
when you look at other systems that
we've discovered, exoplanet solar systems,
ours is starting to look a little bit more
unusual than normal. and
Jupiter may be the reason.
Jonti Horner: It could well be. And it's one of those
things, I'm reminded of the Monty Python
thing. I think it's in Life of Brian, where
you've got that thing of we're all
individuals. Yes, we're. No, we're not. I'm
not. Every
planetary system is going to be unique
because it is influenced by
such a wide variety of things going on. Even
the stars that form in the local
neighborhood, whittling it away from the
outside, it all starts going on. But what
we're seeing is there's a commonality among a
lot of the planetary systems that we find
that look very different to ours.
The thing that gives us a little bit of pause
though, is that we have these observational
biases that make us more likely to find
systems that are different to ours than we
are to find systems like ours. And so you've
always got that question of do we look
unusual because we are unusual,
or do we look unusual because we're not yet
very good at finding places that look like
home? and that's where colleagues of mine,
like professor, Rob Wittenmayer, my colleague
at unisq, have done really interesting
work where what they
do is look at what we found, but work
out what doesn't exist
based on what we haven't found yet. So they
can start getting an estimate of how common
our, ah, planetary systems like ours based on
the fact we haven't found them yet. And it's
a really kind of weird type of science where
the absence of finding thing places limits on
how common that thing is. So if you said
that every star had a planet exactly like the
Earth, on an orbit that's one year long that
is exactly the same size as us and all the
rest of it, then we can work out
statistically, based on how good our
telescopes are and our techniques are, how
many of those planets we would have found.
And we wouldn't have found anywhere near all
of them because it's really hard to do. But
we'd have found X amount. And the fact that
we've only found a very small number smaller
than that places an upper limit on how common
things can be. So you get this perverse
science where you get the observations
that tell us what we found and what we've
seen, but you can also put inferences on
what isn't there and what is there based on
what we haven't found yet, which allows you
to put limits on how common things are that
you couldn't really find very easily. Which,
if that makes your head hurt. it makes my
head hurt a little bit as well. But it's a
really kind of clever use of the data we get
to extrapolate further and draw more
conclusions. And the net result of that is
that the solar system is not hugely rare, but
it's not common either. It's usual.
And, that's really cool. And that probably
extends to everything. Like I say, we're all
individuals. The Earth, even though it's
peeing it down outside at the minute, the
Earth's actually a very dry planet. If you
took all the water off the Earth and made a
little blob of it next to the Earth, that
blob would be fairly tiny. And everybody
views the Earth as being very wet, but I view
it as being very dry because water is such a
common compound in the universe. It's made of
the first and third most common atom. You put
them together. Yet water waters everywhere.
So for the Earth to be as dry as it is is
telling you a lot about the uniqueness of the
solar system. And maybe that's partially
because of Jupiter. Not, necessarily
shielding us from impacts, but preventing
that icy material spiraling in, preventing
us from becoming an ocean world. It's also
partly down to the moon forming impact. The
moon forming impact would have stripped a lot
of the primordial Earth's water away because
it walked as light and sits near the surface.
So a lot about our Earth and a lot about the
solar system is down to the random nature of
the events around us. When we formed the moon
forming impact, a nearby star going
supernova and lacing our solar system with
radioactive aluminium. Things like this.
There's all these oddities that made our
solar system unique, but if those
hadn't happened, other things would have
happened and we'd have still ended up with
something unique because of other random
things happening.
It's all fascinating and I just love this
stuff.
Andrew Dunkley: Yeah. And it adds more and more weight to the
theory that we are just a freak accident.
Jonti Horner: Yes.
Andrew Dunkley: And probably a one off in the universe.
That's one argument. So, yeah,
who knows if, if we find a
solar system just like ours, with a planet
just like ours, orbiting a
star just like ours. That would be
the, you know, one of the greatest
discoveries in astronomical history, I
imagine. But no, we do that.
Jonti Horner: We would have to get in touch with the planet
builders at Magrathea and demand that money
back. Because we thought we had a limited
edition.
Andrew Dunkley: Yes, yes. weren't they the white mice? Was
that the white mice?
Jonti Horner: Yes, it was.
Andrew Dunkley: Yeah. All right, if you want to read all
about it, you can find, the paper,
which was published in the journal Science
Advances.
Jonti Horner: Roger, your labs are here. Also space nuts.
Andrew Dunkley: now, Jonti, let's move on to our next story.
And this one is about a planetismal,
that appears doomed. According to the, paper
I'm reading, it's a white dwarf that's
chowing down very, very hungry, hungry
individual is this one.
Jonti Horner: It is. So just to remind the audience, a
white dwarf is the kind of little husk
that's left after a cell like our sun comes
to the end of its life, burns all its
hydrogen, becomes a red giant, and then
eventually blows off its outer layers. And it
leaves a big chunk of the star's mass
compressed into an object about the size of
the Earth. That whole process will
have a fairly hefty impact on the
planetary system that star's got around it.
And of course, as we just discussed, we now
know that pretty much every star has planets.
The expectation is that when the sun reaches
this stage, unfortunately it's in about 7
billion years, so nothing to worry about.
Immediately it will swell up and it will
chow down on Mercury and chow down on Venus.
They'll just be swallowed up and gone. Yeah,
There is some debate over whether the Earth
will be swallowed up or will survive. Just
all the models of star, evolution suggest
that the sun will swell up to be about the
radius of the Earth's orbit. But whether the
Earth is there to nominal or not is still
open for debate. It may be that the loss of
mass from the sun in the time before may just
mean that the Earth nudges far enough away to
survive as a burnt husk rather than be
devoured. It still would be ideal
to be around when that wouldn't be pleasant.
I mean, that said, the Earth is going to
become uninhabitable a lot sooner than that
because the Sun's getting brighter and the
Earth's oceans will boil and it'll all go
downhill. But after all that process
happens when the sun sheds its outer layers,
that'll have a pretty cataclysmic event on
the planets and the debris that are left. So
suddenly the sun goes on the ultimate kind of
weight loss kick loses mass. And that
will mean that all of the objects going
around the sun will be held less strongly.
And so therefore their orbits will move
outwards because the gravity pulling them in
gets weaker. Now, if you suddenly Press the
button and vanished half of the mass of the
Sun. What had happened is that the speed that
any of the objects are going in their orbit
will be too quick for that orbit to be
circular. So at that instant, at that
point, they'd now be at their new perihelion,
they'd be at their closest point to the sun,
and they'd all move out onto much more
elongated orbits with a longer orbital
period, but orbits that would then cross one
another. So if you imagine you lose half of
the Sun's mass, Jupiter moves onto an orbit
where its perihelion is 5 au from the sun,
but its aphelion could be 15 au from the Sun.
Saturn at the same time would have perihelion
at 10 au and aphelion at say 20 au. And I'm
making the numbers up a bit here. So suddenly
Jupiter and Saturn are on orbits that
cross one another. Their orbits
will probably still have the same ratio of
orbital periods, so 12 years to 29 years. But
they'd scale up to be something like, I don't
know, 30 to 70 or something like that,
because they've both moved out by the same
amount. But suddenly you've got these planets
that are on orbits that cross each other and
therefore can really strongly interact. They
can stir everything else up because all of
the objects in the asteroid belt, all of the
objects beyond Neptune, this happens to
everything. Now the mass loss is a bit more
gradual than that in actuality. So what
happens is you get the orbit spiraling out,
but getting perturbed, being made more
eccentric. You've also got these objects
moving through the headwind of possibly half
a solar mass of material being blown
outwards. That provides friction and so
causes them possibly to spiral inwards a bit.
Causes Jupiter potentially to gather mass as
it numbs on all that gas that's going out. At
the same time, its atmosphere is probably
being blasted away by all this wind blowing
past. All of this complexity means
that you couldn't predict with absolute
certainty what the solar system would look
like at the end of this, but certainly
there'd be a period of chaos. A lot of stuff
would survive, but it would survive on orbits
that are now much more unstable. So you get a
lot of material flung inwards and, some of
that will be flung inwards far enough for it
to impact on the Earth sized object in the
middle and, for the white dwarf to get a
snack. Now all that's expected to happen
really early on. And over time everything
stabilizes out, things get flung around and
clean up happens a bit like the
solar system. You know, we were talking early
on about the early stages of planet
formation. Everything gets flung around and
by the time you get to now, four and a half
billion years down the road, it's fairly
quiet. There's a bit going on, but most of
the drama's finished. So the
expectation is you'd see white dwarfs that
are very young occasionally eating things
because things get flung in and they get a
bit of a snack. And the material from that
snack will be spattered over the surface of
the white dwarf and be visible in its
spectrum as anomalous added
solid material, heavy elements.
But that signal would only last a short time
because the outer layer of the white dwarf is
kind of a hydrogen soup and heavier elements
would sink down. So any given time you'd eat
something. The evidence for that meal would
only remain for a few tens of thousands of
years, SOPs before it goes away. Okay, so
the fact is we've seen some white dwarfs
which have these anomalous heavy element
readings in their atmospheres. We can tell
they're eating stuff, but typically they're
young. So you'd expect that.
The quirky thing here is that this white
dwarf, which goes by the name of
lspm, which I think is a survey name,
m followed by
J020733331.
So that's a coordinate on the sky. So that's
telling you where in the sky this is. It's
catalog number. Yeah, this thing is an old
white dwarf. It's thought to be about 3
billion years old. So in other words, the
star that formed it died 3
billion years ago and it's been sitting there
minding its own business. That's old enough
that you'd expect everything to have calmed
down around it. But what the new
observations have shown is evidence of
13 different heavy elements,
including carbon, chromium,
strontium, titanium, a lot of these different
elements, roughly in the kind of abundance as
you'd see on the Earth, added, to this white
dwarf's atmosphere. So it's
obviously just had a meal and we know it's a
case of just had a meal rather than it's been
a leftover from a long time ago, because this
stuff will sink and disappear over the next
few tens of thousands of years. So what
that means is that this white dwarf
has just had a snack. Now it might have had
that snack 30,000 years ago, or it
may still be in the process of eating as
we speak. Now what the team have been able to
do is look at the amount of material you'd
need to give the strength of signal you've
got in the spectrum of the star. And, what
they've calculated is that to get this amount
of material you'd need to eat an asteroid
about 200 kilometers in diameter.
So that's comparable to some of the larger
asteroids in the asteroid belt, but not the
largest by any means. It's within the bounds
of possibility of what we see here at home.
But the real question is why is it eating it
now? Why is this happening now when you'd
expect the system to have had plenty of time
to calm down? What
it suggests to me, and it suggests in the
paper, it suggests in the articles about this
as well, is that the only way you can get
something eating this late, after 3 billion
years have passed, is if you've still got a
number of planet mass objects in the system
serving things up, which is what we've got
in the solar system. If we look at the inner
solar system, fragments of comets and
asteroids are falling onto the sun all the
time. We've got near Earth asteroids, short
period comets and long period comets whizzing
around. And, they're being bounced around by
the planets. Jupiter's throwing a lot of
stuff away. Their orbits are constantly
getting tweaked. And so therefore the sun
is still getting this rain of solid material
falling on it as a result of the planets
stirring things up. Even though the solar
system mostly quietened down, the planets are
still injecting material to the inner solar
system, which is why we're getting meteorites
and it's why the sun occasionally gets to
numb some stuff. The idea here is
that this star reached the end of its life.
Puff dots with its outer layers. You have
this really chaotic period where everything
had got stirred up, then it settled down. But
because you still got planet mass objects
there, they're still bouncing around what
debris is left. And we're just catching this
white dwarf just at the right time, when
another asteroid has been flung inwards close
enough to be torn apart by the star's gravity
and to give it a snack. So in other words,
seeing this snack happening this late in the
life of this white dwarf is fairly strong
evidence that planets survived the death of
its star, have lived there for 3 billion
years, which a is really cool in of itself.
But it also means that here is a star that we
should look at when the Gaia data release
comes next year. Gaia Dr. AH4,
which will have been measuring this star's
position on the sky. And if there Are planets
there, we'll be able to detect the wobble and
confirm them. So it's also holding up a flag
to exoplanet people saying,
hey, folks, here's a target for you to look
at when the data release comes out where you
might be able to find some planets, because
we think there's a smoking gun here that the
planets are feeding the white dwarf, giving
it little snacks every now and again.
Andrew Dunkley: Okay, wow. All right.
so are there many white dwarf
stars out there? What, do they, sort of,
percentage wise, inhabit the star field?
Jonti Horner: There would be a fair few of them. So the
more massive a star is, the shorter its life
is. And, that's a really rapid function.
Where that works is, if your star's more
massive, its gravitational pull is stronger,
so its ability to pull material into
the middle of the star is higher, which means
that that star's got to give off a lot more
energy to balance that gravitational pull.
And so stars in the main sequence part of
their life are in equilibrium. The radiation
coming out from the nuclear fusion in the
middle balances gravity pulling in. The
more massive you are, the hotter and denser
you get in the middle, so the more energy you
give off. And the result of that is that it
roughly, it varies a little bit by star's
mass, but roughly the brightness of a star,
the luminosity of a star is proportional to
the mass of the star to the power
4.3.54. Which means if you
double the mass of a star, it'll get between
10 and 16 times brighter.
So twice the mass, Call it a factor of 10
just to keep it easy. If it's 10 times
brighter, that means it's burning its fuel 10
times quicker to produce 10 times as much
energy. But it's only twice the mass, so it's
only got twice as much fuel, so its
life will be a factor of five times shorter.
And the more massive you get, the shorter the
life gets. Now, stars of different masses
have different. A star like Proxima
Centauri will never swell up to become a red
giant. It'll just be a dull, glowing ember
and eventually go out. But even the
oldest stars like Proxima Centauri are still
really in their youth because they're burning
their fuel so slowly. Stars that are more
massive eventually get stars like the sun,
which are what form like dwarfs. And, they
eventually swell up to become a red giant,
puff off their outer layers. And for a star
of the Sun's mass, that process from
forming to the end of its life is thought to
be about 12 billion years. It used to be 10
billion models seem to have refined. So
people nowadays seem to say it's about 12
billion years. So a star of
the mass of the sun that formed when our,
Milky Way was very young will have lived and
died and become a white dwarf more than a
billion years ago. But stars more massive
than the sun can form white dwarfs as well,
up to maybe two or even three times the mass
of the sun, depending how effective it is at
shedding mass at the end. Yeah, the maximum
mass for white dwarf, you can get about 1.4
times the mass of the Sun. If stars lose half
their mass, that gives you something about
three times the mass of the sun before you
start it. Three times the mass of the sun.
Three to the power four is three times three
times three times three. That's 81 if my
mental arithmetic is correct. So three times
the mass of the sun burns its fuel 81 times
as quickly, which means it would live a 27th
as long. Which means instead of 12 billion
years, you get down to, 1.2 billion years,
you get down to or like, 600 million years,
500 million years. So there will have been a
lot of stars that were more m massive than
the sun that have lived and died and created
white dwarfs. And so there's going to be a
lot of white dwarfs out there. I saw
someone talking a while back about how old
the oldest white dwarf will be in how dim it
will be, because white dwarfs just cool and
gradually go from being blue to white to
yellow to red. You know, gradually dim down.
Yeah. but what that all means is that there
are probably a really large population of
white dwarfs out there. We know quite a large
number, but we won't know anywhere near
as many of them as we do stars that are
actually the mass of the sun, that are in the
prime of their life because they're much
fainter and harder to spot because they've
got a much smaller surface area. So even
though they're hot, they're tiny and,
therefore they're faint. and the best example
of that, of course, is a white dwarf that is
a companion to Sirius. Sirius is the
brightest star in the night sky. It's more
massive than the Sun. It's also nearby. Its
white dwarf companion is something
like a factor of a million times fainter than
Sirius is. So even though the white dwarf is
comparable in Master Sirius A,
it is like a million times dimmer because
it's so tiny. And that's why they're Hard to
find.
Andrew Dunkley: Yeah, even though there's probably a hell of
a lot of them out there. Okay, if you would
like to read more about this particular white
dwarf star that is, you know, got a case of
the munchies, probably spent too much time
smoking the juju. you can read all about it
in the Astronomical Journal. This is Space
Nuts with Andrew Dunkley and Jonti Horner.
Jonti Horner: Okay, we checked all four systems and being
with the jerk space nets,
Andrew Dunkley: Don'T know why we went down that road.
Let's go to our next story. And this
one is, this one's close to home.
a, an object that is rapidly developing
a ring system and it's it's in
the outer solar system.
Jonti Horner: It is, this is an object called Chiron,
which was the first of the centaurs to be
discovered. And I always like to talk about
the centaurs because they're what I studied
for my PhD, so, so I was at one
point, 20 odd years ago, one of the world's
experts in how these things move around the
solar system. And then science has moved on
and I haven't, so I probably can no longer
claim that. But Chiron is
an interesting object. It's an icy object,
bit more than 200km across. It was
one of, if not the first object to get both a
classification as an asteroid and as a comet.
So it was initially discovered as a tiny
speck of light moving around. It's discovered
by Cowell I think in 1970,
moving on an orbit that spends nearly all its
time between the orbits of Saturn and Uranus.
At the minute. Long term it's an unstable
orbit. There's about a, ah, one in three
chance that this will eventually end up in
the inner solar system at some point in the
next few million years. And that's part of
the work I did during my PhD was running
simulations of where this thing's going to
go. That in itself is interesting because
it's about a bit more than 200km across.
So if this thing got trapped in the inner
solar system, it will be, be a comet like
nothing we've seen in recorded history. Hale
Bopp, which was ridiculous, had a 50
kilometer nucleus. If this thing's 250
kilometers across, that's five times the
radius, which means it's something like 25
times the surface area, which means it will
be a lot more impressive. So it's obviously
an interesting object. Back in
2011, team of scientists
traveled across the world to gather to
watch Chiron block out the light from a
background star. So as this thing's moving
through space, it just happened to pass in
front of a star, from a subset of locations
across the Earth. Now the distant stars are
effectively so far away, we can consider the
light coming in perfectly parallel. And
so a 200 kilometer
centaur will cast a shadow on the earth
that's 200 kilometers across. And that shadow
will whip across our planet. As the object
and the Earth move around the sun, the shadow
moves, the Earth moves through it. And so you
get a 200 kilometer roughly scale band on the
Earth where that star will disappear, then
reappear. We know how fast everything's
moving. So if you can get in that location,
have a lot of telescopes spread out in a
line, you can observe that
occultation event and, by how long the star
vanishes from different locations, you can
actually figure out the shape and the size of
the centaur because you can essentially map
that shadow. And if you're near the edge, the
star will disappear and reappear really
quickly. If you're near the middle, you'll
get a longer period where it vanishes. So
these kind of, ah, occultation observations
are really valuable to scientists. What
happened in 2011 was they set their
telescopes up and started watching a bit
early to make sure they were looking at the
star. And they noticed the star flickered on
and off a couple of times before it properly
disappeared for the main occultation. Then
after it reappeared, it flickered on and off
again a couple of times. And that's really
weird. Now there was a kind of
precedent for this with observations that
were made in 1977, I believe,
of Uranus, which was being observed from, I
think it was the Kuiper Airborne Observatory
doing one of these occultations. And they'd
observed Uranus for this occultation because
they wanted to understand the atmosphere of
Uranus. And they figured as a stalwart behind
Uranus, you'd see it not just disappear, but
actually fade out as the light passed through
the atmosphere. So you could measure the
atmosphere and with that occultation of
Uranus, occultation by Uranus, sorry, they
got this flickering on and off thing. And
that was the discovery of Uranus, of ring
system. So basically the star vanished behind
the rings, then reappeared, then vanished
again, then reappeared, then went behind the
planet. Right. So with this
2011 event, the same kind of thing applied.
It was the discovery of a ring system around
this icy object. So this is a tiny thing,
smaller than even Mimas, that we talked about
last week with the subsurface ocean,
something so small that its gravity is
probably not strong enough to make it
spherical. It's probably peanut shaped or
rugby ball shaped or something like this.
It's probably not spherical. Around this
object, it seems that there is a system of
rings where there are three or four narrow
rings at various distances. I think the
distances are something like 273, 325, 438
and 1400 kilometers from the
center of Chiron. Got this ring
system and it's been observed again since
they did observations in 2018, 2022 and
2023, where they again figured
out that the shadow of Chiron was going to
scan across the planet, got a load of
telescopes, went on a road trip and observed
it happen to get more information about the
rings. Because having a ring system around an
object that isn't a planet is really cool.
Andrew Dunkley: Yeah.
Jonti Horner: And how did it form? How long has it been
there? What's going on? How common are ring
systems like this? Incidentally, a former PhD
student of mine, Jeremy Wood, did some really
cool dynamical studies that basically showed
that the ring system could be
primordial. It could be as old as the solar
system. From the point of view of Chiron has
never been close enough to one of the planets
to disrupt the rings. So that
doesn't put an edge limit on it, but it was
still quite cool. What the new observations
have shown though, is that, the ring system
now seems to be different to how it was in
2011. In other words, the ring
system is evolving before our very
eyes and it actually seems to be a denser,
stronger ring system now than it was 10 or 15
years ago. So it's possible that we're
actually witnessing this ring system as it is
forming or as it's changing over time.
Now I know Chiron has been quite active,
it's been outgassing because it's been closer
to the sun, hence the cometary type
classification it got. Maybe some
of the material it's ejecting in that
outgassing is being ejected gently enough
that it doesn't escape from Chiron and,
that's repopulating the rings. We just don't
know. But the only way we'll find
out is by doing more of these observations.
But I think it's just really exciting and
it's a really good reminder again that we
always kind of imagine the solar system as a
very sad and boring, placid place where not
much changing anymore because it's four and a
half billion years old. And as you get older,
you Get a bit more sedentary and not much
happens. But in fact it's a reminder that
the solar system's a really dynamic place and
things are constantly influenced, constantly
changing. We talked about it last week. The
ocean on Mimas that is possibly
only 15 million years old. Now, 50 million
years sounds like a really long time, but in
a system that's four and a half thousand
million years old, that's like something
that has happened to me in the last couple of
weeks. That's a new feature, not something
I've had since birth. And this is yet another
example of the fact that the solar system
just seems to be continually rapidly changing
and evolving.
Andrew Dunkley: Yeah, yeah, it's a really interesting
situation. how far out is chiron?
Jonti Horner: It varies. So it's closest to the sun, It's a
little bit closer to the sun than the orbit
of Saturn. at its furthest, it's a bit
further away than the orbit of Uranus. And
that's an unstable orbit. So it bounces
around over time, it will have encounters
with them that fling it around. But at the
minute it's in the outer solar system
between the orbits of Saturn and Uranus most
of the time. Unstable solution. It probably
originated out beyond the orbit of Neptune.
And it's one of this population called the
Centaurs that are, the future parents of the
next generation of short period comets.
Effectively in the same way that the near
Earth asteroids have their origin in the
asteroid belt, short period comets have their
origin in the Transeptunian region. But to
get here from there, they've got to pass
through the outer solar system. And that's
what the Centaurs are.
Andrew Dunkley: Okay. Fascinating. Yeah, it's really
interesting and probably not one that,
too many people would be aware of. I remember
when it was making the news some
years ago, and that's why the name stuck when
you, when you sent the story to me. But, you
don't really hear much about it. But now
we've got a very good reason to look at it.
if you would like to look into that
particular paper, it's been published in
the Astrophysical Journal Letters.
Our final story, Jonti, is,
an exoplanet that the popular press are going
to say has got, some kind of life on it. it's
a, it's a maybe life candidate, story,
this one. And Yeah, but they're still
using the term super Earth.
Jonti Horner: Yeah, I'll keep this one a little bit short
and try not to get too grumpy. But one of my
big bug bears all the way through my career
is a good way for people to get media
coverage of their new planet discovery is say
it could be habitable. It's in the Goldilocks
zone. Hooray.
Andrew Dunkley: Using the L word.
Jonti Horner: Rumble, rumble, grumble, grumble.
Andrew Dunkley: It's a four letter word too, that one.
Jonti Horner: It is, and it's one of the terrible four
letter words. Part of the problem here is
there's this concept of the Goldilocks zone,
of the habitable zone, which has become
really entrenched in the popular
consciousness. And it's always viewed as
being this sweet spot for life. And the idea
is that if you have a planet in the habitable
zone, it will have liquid water on its
surface and all sorts of happy life things
will happen and everything will be good.
What it actually means is that if you took
the Earth, as it is today and put it where
that planet is, the Earth would still
maintain its liquid water because planets are
really diverse. If you took Venus and put
Venus where the Earth is, With Venus's
current atmosphere, Venus will be too hot to
have liquid water. But if you observe the
solar system from a long long way away and
you discovered Venus on the Earth's
orbit, it wouldn't look any different to the
Earth. it's a planet about the size of the
Earth, sat in the habitable sun. We, it's
habitable. Hooray. Whereas Venus is actually
so hot that on the surface it had melt lead.
And I certainly wouldn't want to visit there.
It's even hotter than my room was the other
night when the power cut had happened. And
that was bad enough and brutal enough. so
what this means is that ah, people
have become very fond of
find a planet around a star, you can work out
where the boundaries of the habitable zone
will be based on a few assumptions. And this
is work going back about a decade of the
definitions we use now. And you've got the
conservative and the optimistic habitable
zone, which are basically loosely based
around the fact that if you're as close to
the star that you get an amount of radiation
coming in comparable to Venus, you'll be too
hot. If you're about where Mars is, you'll be
too cold, but in the middle you'll be just
right m. and that's about it.
Now that definition doesn't really take any
account of the mass of the planet or its
atmosphere. What that
means is that ah, when you find a planet that
is a super Earth that Is four times the mass
of the Earth. That is almost certainly
nothing like our planet at all.
You'll do a calculation and say it sits in
the optimistic habitable zone. So there is a
potential it could have liquid water on its
surface. That's full of a whole heap
of assumptions. But to me it's a really long
stretch from saying it could have life.
Andrew Dunkley: A.
Jonti Horner: You're assuming it's got the right kind of
atmosphere to have liquid water where it's
four times the mass of the Earth. So its
atmosphere is almost certainly much, much m
thicker, Therefore
likely has a much stronger greenhouse effect,
Therefore probably runaway greenhouse. Not
good.
The other thing with this particular planet,
GJ 251C is it's a super
Earth orbiting a red dwarf star, ah,
nearby, less than 20 light years away. And
that's part of why people are excited. It's
near enough that we'll learn a lot more about
it in the future. However,
planet orbiting a red dwarf star means that
to be in the habitable zone, it's got to be
close in. This thing goes around its star
every 54 days, which means that it is
closer to its star than Mercury is to the
sun. And given the difference in the masses,
it's actually much closer in than that. That
means it's up close and personal with a red
dwarf star, which are notorious for being
active and flary and noisy, Particularly when
they're young. They're tempestuous teenagers
in their early days with mega stellar flares
and stuff like this. So it seems to be
fairly widely accepted that planets around
red dwarf stars that are close enough to be
warm enough to have liquid water will have a
hard time holding onto their atmospheres,
Particularly when the stars are young,
because it'll be having all sorts of
bonkers fun. And that's kind of borne out
with the planets around Trappist 1, which for
years have been people saying these are the
most Earth like planets ever and we'll find
life on them and hooray. And then when they
finally got to use the James Webb space
telescope and look at those planets, none of
them have an atmosphere. Now I don't know
about you, but I kind of like to breathe.
It's a fairly important part of living. And a
planet without an atmosphere is not going to
have liquid water on the surface because if
you take the atmosphere away, there's no
pressure, the oceans boil and then are blown
away by the red dwarfs, which makes that
planet a desiccated husk, which not
particularly habitable. The reason I Get
energized and activated about this. It's a
lovely discovery. It's a really interesting
planet. We'll, learn a lot more about planets
elsewhere. If there is an atmosphere, it's
around us now that's near enough to us that
with James Webb, we'll be able to study it,
learn more about the atmosphere. We'll learn
a whole heap from it. But I get really
energized about this because there's only so
many times that people can hear a story that
says we found the most Earth like planet ever
before they think we found the Earth before
they think we found life elsewhere. And that
then really devalues it. When we finally do
find planets that are, ah, properly like the
Earth, when we do find signs of life
elsewhere, scientists will be getting really
excited because we've finally done it. And
everybody will be like, well, why bother?
You've done this a million times before. The
whole boy who cried wolf thing
again, a big bugbear. And something that's
really critically important these days is
trust in science and trust in scientists. We,
we've got all the controversies about topics
that, are much more controversial than we're
talking about with astronomy, with vaccine
denial, with climate change denial, with
people refusing to evacuate in the path of a
hurricane that's coming because they don't
believe the scientists. Anything that
makes people less trusting of scientists
because they're overblowing stories is
damaging now far more than it has been in
decades past. It's part of why I get so
frustrated with Avi Loeb and Three Eye Atlas.
It's why get frustrated with the media
coverage of stories like this and the
scientists pushing, I think, somewhat
unethically an argument that this could be a
habitable planet because it makes
the rest of us look like fools. And it makes
people, it gives them ammunition to say,
well, scientists lie to us when they're not.
They're saying that this meets the criteria
for the Habitable Zone paper that was
published 10 years ago. But
it weakens that trust in science, which is so
important now more than it ever has done. And
I said I wouldn't go on a run and I'm now
waving the flag and banging the table and all
the rest of it. But it's a frustration that's
wider than this story. And this story is
lovely. It's an awesome discovery. They found
a planet going around a star. That's very
cool. We'll learn a lot more about it. It's a
brilliant result. You don't need to tag every
result like this and say that this planet
could have life.
Andrew Dunkley: And yet that's what, that's what happens.
it's sort of like, what artificial
intelligence is doing to social media. You
don't know. You don't know what you're
looking at anymore. And my
trust levels have dropped significantly in
recent months.
Jonti Horner: My dad is, 80, and
he's still on Facebook. And he doesn't like
it, but he's on it because it's a way to
communicate with people back in the uk. Moved
over here a few years ago and he's constantly
saying to me, he's getting so frustrated with
these AI stories and fake news things that he
doesn't know what to trust on there anymore
because he'll see a story that some famous
actors died and then he'll look up on
Wikipedia and they're still alive and kicking
and they've got a film coming out. But
there's this thing of, you'd never believe
the tragic photos. And it's
bizarre. And at a time when we need fidelity
and trust in our news and trust in our
science, we've got to be careful about how
much hyperbole we put into stories. I think.
Andrew Dunkley: I totally agree. Yes. If you'd like to read
about that, particular exoplanet, you can,
pick up that yarn through the Astronomical
Journal where they publish the paper. Or you
can read up on all the stories we've talked
about
today@space.com
and I'm sure a few other, platforms have
published them as well.
and that brings us to the end of, this
program. Jonti, thank you so much.
Jonti Horner: It's a pleasure. It's lovely to chat. Thanks
for bearing with me, being a bit flighty and
flirty thanks to the power cuts and the
weather.
Andrew Dunkley: You've done well. You've done well. We'll,
catch you on the next program, a Q and A
program. Johnty, Horn, a professor of
astrophysics at the University University of
Southern Queens. And thanks to Huw in the
studio, who couldn't be with us today
because he never tells me. I
have no idea. I just make up the reasons he's
not here. I honestly don't know why he didn't
turn up this week. Probably because we didn't
tell him when we were recording.
Jonti Horner: That might have been it.
Andrew Dunkley: and from me, Andrew Dunkley, thanks for your
company. Catch you on the very next episode
of Space Nuts. Bye.
Jonti Horner: Bye.
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