Jonti Horner: Hi there.
Andrew Dunkley: Thanks for joining us yet again. This is
Space Nuts. My name is Andrew Dunkley. Great
to have your company one more time. Well,
hopefully it's more than one more time, but
on this occasion, uh, now with Fred Watson
away, uh, we are doing a series of
little specials and today the focus
will be on exoplanets.
We've known about them since the early 90s
and since then we have found
thousands of them. But what is there to
know? I mean, we've got our own planets.
Surely that just means everything else around
the galaxy is the same. That's
probably not true. And we're going to talk
about all of it today on this, uh, episode of
space nuts. 15 seconds. Guidance is
internal. 10, 9,
ignition sequence.
Jonti Horner: Star. Space nuts. 5, 4, 3, 2.
Andrew Dunkley: 1. 2, 3, 4, 5, 5, 4, 3,
2, 1. Space nuts. Astronauts report
at and with us while
Fred Watson is away is Jonty Horner,
professor of astrophysics at the University
of Southern Queensland. Hi, Jonty.
Jonti Horner: Good afternoon. How are you going?
Andrew Dunkley: I am quite well. And you?
Jonti Horner: I can't complain. I'm enjoying us having a
public holiday today, which is great. I mean,
I'm still off anyway, so it doesn't really
matter, but it means I'm taking one day's
less of sick leave, I guess. Uh, well, it's
all good.
Andrew Dunkley: I'm retired, so public holidays mean nothing
to me now. I
used to so look forward to having a few days
off or, you know, an extra long weekend if
they combined the two in April because we
get, uh, east sometimes, get Easter and Anzac
Day in April. And if, um, you jam them
together, you get a nice free holiday. But,
uh, it doesn't mean squat to me anymore.
Jonti Horner: I keep finding it bizarre. At least in
Toowoomba. I'm sure this is reproduced
everywhere. If the shop shut for one day, the
day after is absolutely feral. So
last week we had Anzac Day, which tells you
how long ago these were recorded, by the way.
Um, but yeah, last week we had Anzac Day. And
obviously, Franz, act quite rightly, the
shops, the supermarkets and everything are
shut. It's one of the biggest holidays in
Australia of the lot of them. But we, we tend
to do our shopping on a Sunday anyway, so it
didn't really matter. Went to the shops on
the Sunday and it was almost people fighting
in the aisles because heaven forfend that one
day you don't, you know, you don't get food
for one day and the shops start running empty
of bread. And it's like people buy more when
they've had one day without the Shops being
open, very, very strange phenomenon.
Andrew Dunkley: They panic by and there's no toilet paper on
the shelves. Is also.
Jonti Horner: Well, the best thing about that. That led us
to subscribing to who Gives a Crap which
panel started online.
Um, and they've been brilliant. We've
recommended them to everyone because it works
out cheaper than getting it from the
supermarket and they're better quality. I
mean it's, it feels like very much a no, uh,
brainer. And we'd never have come across them
if it wasn't for Covid and the
incredibly smart people of Toowoomba going,
oh my God, Covid's happening. We're going to
run out of toilet paper. Of all the things
for the shop to run out of, happened
everywhere. Why toilet paper? Uh,
I mean Covid affect my
memory was that Covid was a, was something
that made things come out of your head, not
things that came out anywhere else. It's not
like there will be an expectation it would
make you use more. No, bread was
fine, eggs were fine, perishables were fine.
But toilet paper, I don't understand.
Andrew Dunkley: I never, I never got it either. But uh, uh,
our shelves were devoid of the stuff.
We better get down to business.
We're talking exoplanets today.
And I did a little bit of research. Uh, the
first exoplanets were confirmed in
1992. In fact, they suspected they existed
before that, but they couldn't prove it. But
1992, uh, they
found two planets that were later named
Poltergeist and um, Phobitor
Phoebe. Uh, so they were
officially the first two exoplanets. And then
the first one that was
orbiting a sun like star was found in
1995. That was
um, 51 Pegasi B.
Jonti Horner: Yes.
Andrew Dunkley: So, uh, those were the first few. And of
course now we've reached a point where
as at 30
April 2026,
6278 confirmed
exoplanets with another 8000
waiting to be, um, officially
catalogued. I suppose. So we've
found a lot of them. And the other thing
we've been discovering about, um, finding
these things is how very different
a lot of solar systems are and how very
different some of the planets are. Ah,
what we always thought was basically the
standard for solar systems,
which was ours. Doesn't appear to be very
standard at all.
Jonti Horner: No, it's an incredible time to live through.
I think the way I always budge this is we've
lived through one of the great scientific
revolutions almost without noticing it.
And I think it sheds A light into how people
would have reacted in previous scientific
revolutions, which is that when it's
happening in your lifetime, it just happens.
So we look back and think that was such a
fundamental change. And at the time it was
just Tuesday, you know. And
yes, it's like that with exoplanets. I
grew up in a world where one of the big
science questions was, is a solar system
unique? Are there planets around other stars?
Or are we alone? And there were good
reasons for some people to suspect that we
might be the only planetary system in the
universe. There were kind of, at that time,
two broadly competing models of planet
formation that could both explain the solar
system as we see it to a fair degree. And one
was what's almost described as the
Laplace model, the disc model, which is now
what we favour, that has developed a lot
since then. But the other was this idea that
you had a close encounter between the sun and
a protostar. Ah, that was close enough that
the two stars almost collided and a tongue of
material was pulled out of the sun, which
went on to condense from the planets. And
that was championed by people like Martin
Wolfson of York University, among others.
At, uh, this time we're talking in the late
80s, it was kind of widely held that, uh,
Wolfson's suggestion had problems.
It was probably not the right solution, but
it potentially could be. We'd found a few
debris discs, debris around stars, a bit like
the asteroid belt around the sun, but much
more massive in the early 80s. And that
was kind of hinting that planets could be
common, that the disc model could be the one.
But at the time I was growing up, and at the
time, going into the early 90s, you have
these two models of planet formation that
predicted vastly different outcomes. If
the disc model was right, planets would be
ubiquitous, planets would just be the
leftovers from star formation, and
effectively every star would have planets or
close to it. If the encounter
model was right, then planetary systems would
be exceedingly rare, because to get two stars
to come sufficiently close together at just
the right speed for that to draw a tongue out
and form a planetary system is vanishingly
unlikely. So that was arguing that we were
effectively the result of a freak encounter.
And if that prediction was right, then if
that method was right, sorry, it would
predict that planetary systems were
exceedingly rare and that we wouldn't find
them. So going into the 90s, you had these
two theories that could both explain in broad
brushstrokes, what we see at home, but that
predicted very, very, very different
outcomes. And as I say, The Wolfson idea was
already losing a bit of seam. But in the time
since we found that planets are under the
stars and, um, that they are ubiquitous,
basically every star you see in the night
sky, no matter how complex system, no
matter what's that, there are going to be
planetary objects around it, pretty much all
cases. And that's a death knell, of course,
for the Wolfson model of freak planetary
system formation and its support for the
model we now know and love, which has been
refined over the years because of all the
oddities we found. Now, it's really
interesting, storey, but it goes way back
before that. We've got a long history of
the things that led to finding the first
planets. What we take it a bit for granted
now. We're finding so many planets and I have
the good fortune of getting to be involved
peripherally in some of the discoveries. I'
have the very entertaining job of killing
some planetary systems. So it should be said
that the number you gave at the start can go
down as well as going up. Some of
the planets that get confirmed later on get
redacted, get killed. And I've probably,
certainly as lead author, I've never led a
planet discovery, but I've been involved with
them. But I've led a number of research
projects that killed planets that other
people claimed. So I've probably been net
responsible as an individual for a negative
number of planet discoveries that can happen.
But it's really important that we do that
kind of work. I've always been really
passionate about that because all of the
things that we do to talk about how common
planets are, to look into how they form and,
um, further down the line to try and find
planets that could be like the Earth and to
try and look for life on them. All of that is
based on the catalogue of the known. What do
we know? What's the variety? And so if you've
got planets that are in that catalogue that
don't exist, they're polluting that catalogue
and confusing and obscuring the truth. So
it's really important to not just accept that
when a planet is claimed and marked as
confirmed, that's the end of the storey. But
we need to follow it up and say, does it make
sense? Could there be something else going
on? And in those cases we do learn more about
it. So it's a fascinating field. I'm really
fortunate to have gone from being a kid who
wondered to an adult who gets to be involved
in the process. That's incredibly
wonderful for me, but it's a fabulous Storey
we have lived through a great scientific
revolution in many ways. One that's as big as
the acceptance of continental drift or uh,
the origin of species and Darwin or general
relativity and Einstein. It's one of those
revolutions. And when you talk about the
other ones, you think about how epochal
and incredible and how they change the world
and we've just lived through one. Um, it's
amazing.
Andrew Dunkley: Yeah, it's incredible. And, and
will it never end? I mean the thought of
looking up into the night sky and seeing
billions of stars and knowing that there
are probably multi, billions of planets is
just, it's mind blowing.
Jonti Horner: And the rest, I mean to me it's a numbers
game and we talk about this when we talk
about life elsewhere, but the numbers get
ridiculous really, really quickly. Now we've
been heavily biassing what we found to
finding planets closer to their stars than
the Earth is to the sun. The overwhelming
majority of planets. We found a very close
end, but there will be planets further out as
well. You're not going to have a situation
very often where you've got a few planets
near the star and nothing further out. So a
lot of the very tentative estimates you get
of the number of planets in the universe say,
well, imagine there's just one planet per I.
Based on what we found so far, I think it's
fairer to say there are probably nearer to 10
planets per star. And depending on whether
Jared Isaacson, the guy who's taken
over NASA who is not an astronomer, gets his
way and restores Pluto. If he restores
Pluto, then you have to argue that Ceres,
Makemake, Haumea, Eris, all these other
things are planets in the solar system. You
could have 20 planets in the solar system. So
let's assume 10 per star. You
know whether Pluto is arisen. Leave that for
aside. I have strong opinions on that. Other
opinions are available. They're wrong, but
they're available. As Matt come out always
says, um, ignoring
that though, if you assume 10 planets per
star, because it's going to be nearer to 10
than when an astronomer's working factors of
10. In our galaxy alone, um, we have
somewhere around 400,000 million
stars. Now that number also is only accurate
to a factor of 2 or 3. So it could be 200, it
could be 600, but call it 400,000
million stars means 10 planets per star.
You'd have 4 trillion planets in our
galaxy, ignoring the free floating ones that
don't have a star to call their own. 4
trillion planets in our galaxy.
There are more galaxies in the observable
universe than there are stars in our galaxy
by orders of magnitude. Which means you start
getting to the point which, in the observable
universe alone, um, ignoring the part of the
universe that we can't see because that's
utterly unquantifiable, but just in the part
we can see, you'll have planets numbered in
the sextillions of septillions.
So a trillion is 10 to the 12, a trillion is
a thousand billion, a quadrillion is 10 to
the 15, which is a thousand trillion, and so
on. So these numbers are utterly,
astonishingly, overwhelmingly, mind boggling.
And that's where I come to with this thing,
that if we're the only place with life in the
universe, then there's something very unusual
going on.
Andrew Dunkley: Absolutely, yeah. Um, and
it was the movie Contact where they said, uh,
space is really big. So if it's just stuff,
just us, it seems like an awful waste of
space.
Jonti Horner: It is.
Andrew Dunkley: I always like that line.
Jonti Horner: Yeah, well, the question of life elsewhere is
one that really polarises people. I mean,
everybody's interested to know the answer.
Arthur C Clarke said something along the
lines of, there are two possibilities. Either
we're alone in the universe or we are not.
Both equally terrifying. Um,
a lot of people. Stephen Hawking was very
adamantly, we shouldn't try and contact
aliens because they will kill us in the face.
I don't tend to agree with them, but
it is one of those discussions that really
fires people up, gets people energised. And
for me, it would be actually far more
terrifying to know we're alone in the
universe, because that means life is such an
impossible fluke that given planets
numbering in the sextillions or septillions,
in the known universe, we're the only one
with life. Which means that only one planet
in 10 followed by 20 zeros or more
gets life on it. And that seems infeasible to
me, but m. We won't really know until
we move forward and we actually proceed with
the search for life elsewhere. And as I've
said in a previous episode, absence of
evidence is not evidence of absence. So if we
find life, then we'll know we're not alone.
We'll know that life's common in the
universe. The longer it takes us to find life
doesn't mean that there is nothing to be
found, it just means that life is scarcer,
basically. So the longer we take to find it,
the better we'll get at doing it. The further
we'll be able to look, the more planets we
can Sample. And that will then give us a
handle for the commonality of life.
Andrew Dunkley: Life.
Jonti Horner: So we find life in our lifetime. All well and
good. If we're still looking in a thousand
years. I'd be gobsmacked, but that just tells
you life is a lot rarer than we thought.
Andrew Dunkley: Indeed. And we will talk about that more in
another, uh, special episode when we do part
two of Astrobiology. Uh, we kind
of had, we didn't have enough time to
talk about it last time, so we're going to do
a part two.
Jonti Horner: But uh, I can talk too much.
Andrew Dunkley: It's also an area that um, uh, makes
your brain hurt. So we, we decided to,
you know, give it a miss this week and go
back, uh, next week.
Um, so where do you want to go with this?
Like, um, everyone knows there's
exoplanets. Everyone knows there are, um, you
know, powder puff planets. And um,
they've actually got names for them. I've got
named, um. So you know, we can
officially say that uh, as far as
planets are concerned, we have
um, specific types of
planets in our solar system, and that is
rocky planets, gas giants, and
for want of a better term, ice giants. But in
the exoplanet world there are
several other types. Um,
you've got um, uh, Neptunian,
like planets, super Earths, uh, you've
got uh, hot Jupiters, you've got super cold
worlds, you've got pulsar planets, and
there's even uh, uh,
circumbinary planets where they're
orbiting two stars. We don't have that
thankfully. Uh, that could be messy,
especially when it comes to trying to predict
the tides. But um, it's, you know, there's so
much more going on out there.
Jonti Horner: There is, and it reflects something that's
incredibly human. And it again goes back to
that discussion about Pluto and many other
things in human experience. What we find
in every field of study, but you know, in
astronomy in particular, is you have a
continuum of things you've got from the very
small to the very big with no obvious sharp
gaps. You know, you'll find everything in
planetary systems from stuff the size of a
grain of dust to things more massive than the
sun, depending on the planetary system you're
in. What we tend to do as humans is we tend
to break down that which we
see as a continuum into manageable bite sized
chunks by grouping like with like in order
that we can then better study objects.
And so for example, you'd say that the Earth
is more like Venus or Mars than it is Like
Jupiter. So you categorise them into
different subgroups. For humans, we do this
all around the world. You've got babies and
toddlers, children, teenagers, adults,
retirees, pensioners, and you set boundaries.
And those boundaries don't always agree from
country to country. You know, you remember
the incredible day that you suddenly wake up
and you're able to drive legally when the day
before you weren't. And fundamentally you'
changed as a human. You're one day older out
of what, you know, several thousand days at
that point, about 5,000, 6,000 days. But
miraculously you've crossed this arbitrary
threshold which we've put there to separate
people who can't drive and people who can but
maybe shouldn't. You know, that's kind of
where the division is.
We do this as humans all the time to
categorise things. And that's kind of where
Pluto fallafal and it's where all these
groups of different types of planets come
from. You've got hot Jupiters and warm
Jupiters, super puff planets and all
sorts of quirky things. And those terms
are taking the broad spectrum of planets that
we've got and trying to group apples with
apples and oranges with oranges, things that
are similar to one another. And the diversity
just continues to ascend, as every time we
think we've found the most extreme of
whatever, we find something that's even more
so. Like I said, we found planets who we
can calculate their size by how much light of
their star they block. We can calculate their
mass by how much they pull their star around.
We've got a subset of stars and planets where
we can do both those, uh, things which lets
us figure out the density. And from them we
found planets that are less dense than cotton
candy, which are the super puffs,
fluffy ones, probably coming towards the end
of their lives because they're so low density
that they are probably being stripped away by
their star stellar winds. We found planets
that are effectively like comets with tails
as their atmosphere stripped off. I mean, to
some degree, actually, the planet Mercury in
the solar system is a comet. It's got a
beautiful long sodium tail. One of my
favourite astrophotos I've ever seen is a
picture of Mercury near the Pleiades, where
somebody's done some imaging in a sodium
filter and you can see Mercury's tail
visible on the image. It's an astonishing
thing. So we found planets like comets. We've
even found planets around pulsars and they
were the first three planets we found around
other stars. There were um, Phoebe Toe,
Poltergeist and Rao, these stars orbiting a
pulsar named after three kinds of the, um,
undead. So there's this huge variety that
worth mentioning actually from the names. The
names are being allocated by the
International Astronomical Union, just as
names of asteroids and names of satellites
and things like that are. What they're trying
to do with them is to be very
democratic globally, to try and represent
multiple cultures rather than just have all
the planets draw from a single cultural base,
a single kind of background. And so they've
been running a series of competitions over
the years for the general public where a
given planetary system is to a given country.
And, um, then people from that country get to
nominate names, and then people from that
country get to vote on it. And I think we've
now got more than 100 planets named. We've
had a few of them from Australia named. And
I'm actually just trying to look up, um, the
planet names from the iau. They're the
official ones. Now, what's interesting is
these are, uh, official names. They're
the IAU's official names. I
therefore try to use them in my purpose.
Um, and I've had pushback from astronomers
because everyone's so used to the catalogue
numbers. So what I've been trying to do
is you give both names, you give the
catalogue name on the proper now. And I think
where it will go long term is it'll become a
bit like comets. You know, I've been trying
to get images through the cloud and cursing
the weather of Comet Pan Stars at the minute.
And we talk about Comet Pan Stars, but it's
real name that I'd write down, if I'm writing
it is C20, 26 R3
brackets, pan stars. And I think
in the long term, I can see exoplanet names
going that kind of way once people get used
to it. So 51 Pegasi B,
for example, is dimidium. That's the name
that's been given there. And you can use both
interchangeably. But because astronomers are
used to 51 Pegasi B, that's where it
sticks. Now, the names come from lots of
different cultures. They come from lots of
different groups. There are planets that have
been discovered by Australians that are named
after Australians. There are planets that are
named after people. You know, you've got the
planet Galileo going around 55 Cancri.
So 55 Cancer's five named planets are all
named after astronomers. You've got Galileo,
Brahe, Lipper, Hay Janssen,
Harriet, and, um, that's it. So Five
planets, five names. Lots of different names
from different cultures. We've got names that
are controversial, names from different
folklore, names from different cultures all
around. That list is growing. But you don't
say, see used all that much yet because a
planet needs to be confirmed and
then very confidently there and well studied
for it to get onto the list for the name. So
I think like I said, we've got a bit more
than 100 names and a bit more than 6,000
planets. Those 6,000 planets, that
number will go up as well as down, but it's
not going to be too long until we're 10,000
plus.
Andrew Dunkley: Yeah, I figured out why, uh, some of these,
um, sometimes the number goes down. They're
the ones that have been discovered by Monty
Python. It's a planet.
Jonti Horner: No it's not, it's not.
Um, so that's why we'll also lose
some with Gaia. So Gaia has been this
amazing satellite measuring positions of
stars and it can measure the
wobble on the sky side to side of
stars as a result of their planets. Now
historically, the two, by far the two most
successful methods of finding planets are the
radial velocity method where we measure the
star speed towards our away from us and see
it wobbling along the line of sight, and the
transit method where we see it pass between
us and the star. And that means the orbit is
edge on to us. And but for those radial
velocity planets, we're measuring the
fraction of the wobble towards or away from
the observer. And um, the orbit could be
tilted almost edge on or almost face on to
give that same amount of wobble along our
line of sight. Gaia will give us the other
dimension. It'll give us a side by side,
which means it'll find us the tilts of all
those planets. Some of those planets will be
on orbits very tilted to ours and therefore
the mass that they have will be much higher
than that we think they probably have. And
that there'll be certain amount of attrition
where planets that we think are planets are
actually brown water dwarfs. And that is
another of these arbitrary boundaries which
we set roughly at 13 Jupiter masses. But we
will have planets falling off at the top end.
When Gaia comes out. I suspect he won't see
the number drop though, because Gaia will
also lead to so many new discoveries that,
that will overwhelm the ones that fall, uh,
off the top end.
Andrew Dunkley: I, yes, that's a fair point. So, um,
it's, it's going to be one of those waveforms
that goes up and down
as, as situations change. Yeah,
let's take a. I was going
Jonti Horner: to say I've been responsible for a number of
systems getting killed because people propose
planets in places that they seemed unlikely
and they didn't make sense from orbital
mechanics point of view. So I ran simulations
and showed that if these planetary systems
are real, wetting them in the last 10 years
of a 4 billion year lifetime before
the planets crash into each other or reject
each other. And that's not feasible. So there
must be something else going on. So on the
one hand, hand, boohoo, you've killed a
planet. That's not good, you naughty boy. Um,
on the flip side though, it's really cool
because there's something there creating the
signal that people have measured and it
isn't planets, so what is it? So there's
always. Science always gives you more
questions.
Andrew Dunkley: Indeed it does. And you're listening to Space
Nuts with Andrew Dunkley. Andrew Dunkley, I
do know my name. And Professor Johnty Horner.
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Jonti Horner: Space Nuts.
Andrew Dunkley: I'm gonna have to write it down so I can read
it properly.
Um, Jonty, where do you want to go next? I
mean, we've found so many, uh, I don't think
we will ever, never stop finding
exoplanets, uh, because as
technology improves they're just going to
keep stacking up, aren't they?
Jonti Horner: Yeah. I mean, if we talk about the 6000ish we
found so far, uh, 6278
I think it was. We said earlier on there are
probably 4 trillion give or take in our
galaxy, which means we've only found about
one planet for every billion planets
that are in our galaxy. We've barely
scratched the surface in doing that. We've
utterly revolutionised our knowledge of the,
the variety of planets that'll be out there,
of how planets form. We have still for
me, not found something truly Earth like. I
think that's the next hurdle. Now you'll see
a number of media articles over the years
saying the most Earth like planet yet has
been found. All the bloody.
Andrew Dunkley: I, I actually read an article yesterday
which said, uh, oh, super Earth found
potential life. Da, da, da, da, da. And I
thought, yeah, here we go again. And I read
it and of course when you get down to the
second last paragraph, it says, of course
there's no confirmation that this is even a
rocky planet.
Jonti Horner: But yeah, and to me it's like
imagining that you're an alien visiting the
Earth. Ah, and you're flying over the oceans
and you say, we found the most human like
animal yet. It's about two metres long, it's
a couple of hundred kilos, 100 kilos. I mean,
it's a dolphin, it's nothing like humans, but
it, you know, it's that kind of thing. And I
think I understand the urge, uh,
for scientists to talk about things in the
context of the habitable zone, in the
purpose, because that's interesting. Is it
too warm? Is it too cold? I understand the
thing of saying this planet has similarities
to the Earth. It's about the same size, size,
or it would be about the same temperature.
What tends to happen though then is that the
pressure release from the universities gets a
little bit more hyperbolic in it because they
want to get the reads and the clicks, want to
get the word out there. It then gets into the
media, who again are being more hyperbolic,
and we're seeing it at, ah, the minute, with
the articles about the meteor shower that's
active at the minute, where people are
building it up and blowing it up to a level
that is not practical and not observable and
leads to this point. It's not helped by the
fact that there are people who are making
careers out of
discussing how Earth like planets are that
they didn't discover, that they weren't
involved with to get themselves clicked and
to get money. And a lot of the beautiful
visuals you get cropping up online about
Earth like planets come from one resource,
which is called the Planetary Habitability
Laboratory in Puerto Rico, which has been
an ongoing source of frustration for me and
colleagues because there's been storeys that
people I know have published about planets.
And then this entity
puts out their own press release saying,
we've calculated this magic number and this
is the most Earth like planet found and it's
probably got life. And the scientists who
discovered it have said none of those things.
Yeah. Um, and all the coverage is, look
at this beautiful AI generated artwork. Isn't
this amazing? So I do, and I
had a fun storey about this a few months ago.
I had a. An author get in touch with me,
asking me to proofread a chapter of the book.
A book, A book that they're doing. And they'd
got a little bit in there about all the
potentially Earth like habitable planets that
have been found out there. And they use that
as a resource. And I had to back them off on
it and say, look, it's brilliant to talk
about this. Please don't use this as a
resource. If you use their equations,
Venus would be the most habitable planet
we've discovered other than the Earth.
And I certainly wouldn't want to have a
holiday there.
Andrew Dunkley: No, no. Um, you'd need. Need 20
gazillion plus sunscreen
for starters or something like
that. Now that'd be Mercury. But, um, it's.
Yeah, it's.
Jonti Horner: It's impossible unless it's impossible, you
know, and we could live among the clouds.
That'd be a bit different. But yeah, there's
a lot of stuff around it. And it. We've
talked before about other things. We talked
about interstellar comets and the obfuscation
of science when it comes to those. And
they're definitely not aliens. And I'll say
again, they definitely are not aliens. In
this case, the exo Earth
fatigue is real. People in the general public
are convinced that we found planets like the
Earth already. And I mean, it's great, it
keeps people interested, but it also
diminishes the impact when we finally do,
you know, astronomers will finally find a
planet that could genuinely be truly Earth.
Like. We'll then need to do a lot of work to
characterise it, but you can imagine in 10
years time, we get data back from a planet
that shows not only that it could be Earth
like, but the surface temperature is right,
and that there is liquid water in the
atmosphere. And the scientific community will
be, wow, this is our best discovery ever.
This is so cool. And nobody'll care because,
well, you've done it 10 times already. The
media told me.
Andrew Dunkley: So, yeah, I think I've found
it. Um, a potentially habitable
new planet has been discovered 146 light
years away. Um, but then it goes.
It goes on to say, but it might be minus 70
degrees Celsius, um, but there's a storey
like that coming out every other week.
Jonti Horner: Um, and if you want to play that game, our
definitions of habitability, based very much
as we talked about in the previous episode,
on our understanding of where
Earth life could thrive and in the solar
system. We've got potentially habitable
worlds all over the place. Mars is
potentially habitable on the borderline.
Depending on what you think about bacteria in
the atmosphere, Venus could be habitable for
that type of life. We've got all the icy
objects with buried subsurface oceans that
are habitable, but not detectably habitable
because there's ice in the way. I don't think
it. It benefits people to overplay
these discoveries, even though I fully
understand the reason why people do,
and I don't think it does anybody a service
long term. Um, it is the unfortunate
reality of what it is. But, hey,
people are interested. Of course, you'll play
to that in the kind of modern media cycle.
Nobody remembers the retraction. They all
remember the discovery. You know, everybody
remembers cold fusion back from when I was a
kid and a teenager. Um, that was, of course,
published in the Journal of Irreproducible
Results, otherwise known as Nature. Um,
these things happen.
Andrew Dunkley: Yeah, they do.
Um, so, all right, where to next? With
exoplanets, with, uh, so many
discovered, um, that that's provided a
baseline for the probability that every star
has at least 10 planets around us.
Jonti Horner: Um, we're finding them in a growing variety
of ways. It's instructive a little bit to
look back at history. You know, if I took you
back to the early 1800s, our telescopes
had finally got good enough to measure the
motion of nearby stars against the background
stars. Um, that allowed us to start measuring
the distance to nearby stars using
trigonometric parallax, where you look at a
star from one side of the Earth's orbit, then
the other and see it move against the
background just like your finger moves if you
look from one eye or the other. That same
trick at ah, that time people start measuring
it and they realise that nearby stars also
moved through space. They were
undergoing what we now know as proper motion,
moving against the background stars in a
straight line, which is their true space
movement through the galaxy as seen by people
on Earth. A guy called Friedrich
Wilhelm Bessel, who was a fabulous astronomer
in the early 1800s was doing
observations of Sirius, which is our, uh, one
of our class's star systems. It's a brightest
star in the night sky and he found that once
he took away the parallax Martian, the wobble
left and right because of the Earth going
around the sun, that Sirius was wobbling
as it moved across the night sky. And it
looked as though it was being pulled around
by something as massive as the sun, but you
could see nothing there. There obviously was
something there pulling it around. It turns
out that was the indirect discovery of what
we now know as Sirius B, the white dwarf
star. It wasn't the first white dwarf to be
found, but in this case it was discovered
indirectly. We saw Sirius doing something
unexpected. We saw it wobbling and we used
that to infer the presence of the white dwarf
star around it. And of course we got another
example of this a little bit later in the
1800s with the discovery of Neptune, not
through direct observation, but initially
through mathematics, through John, um,
Couch, Adams and Urban, uh, Le
Verrier, doing calculations of how Uranus
was moving across the sky, seeing that it was
moving as though something we couldn't see
was pulling on it. Predicting where that
thing will be in Neptune was duly found. So
they set this heritage of inferring
the presence of something we cannot see
because of its effect on something else. And
that has been foundational to how we find
planets around other stars. That's
fundamentally how for more than 99% of
them we've discovered them. There have been
slip ups on the way in the 1940s,
1950s, Edwin Vanderkamp, who's director of
Spruill Observatory, thought he'd found
planets around Barnard's Star, which is a
star with the biggest proper motion in the
sky. Turned out that he'd actually discovered
the cleaner because what was happening was
that his telescope was getting dirty. He used
a lens telescope, a refracting telescope
as the front Objective lens got
Grottier the way in which it meant red light
compared to blue light changed, causing
Barnard's star position to shift against the
background sounds. And when it got cleaned,
it all went back to normal. He went very sad.
But he went to his grave in the 70s convinced
he was a victim of an injustice and he'd
found planets around Barnassar. We now have
found planets around Barnard, sir, but
they're very different to the ones he
proposed. We also had the fabulous
Storey just prior to the pulsar planets
actually being found, the same researchers
thought they'd found a planet around a
different pulsar and announced it at a
conference. And someone went away and said a
little bit, bit. Something a bit odd about
this. What had been done was they were
measuring the timing of the pulsars. So
pulsars are super, ah, condensed
neutron stars, leftovers from the explosion
of star as a supernova, which have a couple
of magnetic hotspots on their surface. And as
they spin, they beam radio waves into space
like lighthouse beams. And when the beam
sweeps across as we get pulses of radio waves
like the ticking of a clock.
Andrew Dunkley: Yep. With this pulse, they're very, they're
very precise, aren't they?
Jonti Horner: Yeah, they're viewed as being the most
accurate clocks in the universe, aside from
when they have the old glitch or. And I've
had plenty of watchers that do that in this
case, uh, he was observing this pulsar and
sometimes the pulses arrived a little early,
sometimes they arrived a little there. And
this was happening periodically, so
ruled everything else out. There must be
something causing the distance between the
pulsar and the solar system to vary
periodically though, uh, it must be a planet.
Turned out that after the conference someone
said, there's something a little bit odd
here, maybe you should just do a double
cheque before you publish it. Went away and
found a single typo in their code that meant
they didn't properly account for the motion
of the Earth around the sun. So they had
discovered a planet, but they discovered that
the one that they were set on, they
discovered the Earth. I mean it's a
fabulous discovery. Now we laugh about this,
but it shows how hard these observations are.
Uh, finding planets around other stars is
incredibly difficult. We've had the
wherewithal to understand the methods
that we would use for a couple of hundred
years, but it was only in the
90s it really became feasible to do them. And
in those early days in particular, there were
two methods that hugely
dominated. For the first, probably 10
years, 12 years of the exoplanet area era,
the main way we found planets was what you
call the radial velocity technique, the
wobble technique, which is using the Doppler
effect. And you see a distance star. And, um,
we can measure its light and we can break
that light to its component colours, seeing
what we call the Fraunhofel lines littered
across it, which are dark lines that are the
chemical fingerprint of what the star's made
of. And, um, we can measure their positions
in the lab incredibly precisely. And if the
star's moving towards us, its light gets a
bit blue shifted and all those lines move a
little bit to the blue. And if it's moving
away from us, they move a little bit to the
red. And if you can monitor it for long
enough, you can see the star coming backward
and forward, it's wobbling. You can infer the
presence of something massive pulling it
round. You can figure out the, the orbital
distance of that object by how
long it takes for the wobble. So it comes
towards us, goes away, comes towards us again
as it does one full lap. That gives you the
orbital period. You can infer the mass based
on the size of the wobble. But we're only
measuring that component along our line of
sight. So you get a minimum mass that it
could be, and it could be higher than that.
So we can learn about the orbit. That's the
radial velocity technique. And that is an
indirect method. You see the station wobbling
and infer the presence of a planet or planets
around it. The technique that's taken over
from it is the transit technique. That's
where a planet's going around its star and
its orbits just lined up right, that every
time it goes around, it blocks a bit of the
star's light. The star dims and then
brightens again periodically. And, um, by
measuring the periodic dimming, you can infer
the presence of something blocking the star's
light. Again, that gives you the orbital
period, because you get one dip per orbit and
it gives you the size, the diameter of the
planet, because a bigger planet will block,
block more light. But fundamentally, again,
it's an indirect method. You see a star doing
something odd and infer the presence of a
planet. Now, both these methods
were known and were used for hundreds of
years. We saw binary
stars being observed because of the
dimming during the eclipses. Um, John
Goodrick, um, a British astronomer who died
at a very young age, explained Algol. The
Wink of Kingdom star has been a binary star
back in the early 1700s. That is effectively
the same as A transit technique, it's just
you've got a bigger, uh, blocker. Problem is
our eyes are only sensitive to variations in
light at about the 20% level. Smaller
variations than that, we just don't pick up.
Your lights can be flickering by 20% and
you'll barely notice it. For a binary star,
the brightness can change by a factor of two
or more. For an exoplanet, Jupiter,
uh, blocks about 1% of the light from the sun
on that is just something you cannot see with
a naked eye. So to be able to use the transit
technique, we had to wait for detectors that
were sensitive enough to measure incredibly
fine variations in brightness to come along,
which is why we've only been able to use a
transit technique this millennium. It wasn't
really possible before that. Similarly, with
the radial velocity technique, we could
measure the wobble of stars from binary
stars for decades. Because the movement of
the lines were sufficiently big, you could
measure it on a photographic plate and you
could measure speeds of kilometres per
second. Fairly easy.
Planets like Jupiter going around the sun
cause wobbles measured in metres per second,
maybe 10 metres per second. That is, again,
this such a small wobble that taking photos
on photographic plates of the spectral lines,
the resolution isn't good enough. Our
spectrograph we've got up at Matt Kent in our
facility, Merv Ross Rallis. Typically, the
measurements we're making are measurements of
a thousandth of a pixel shift
in a given line. And the only way we can do
that is because you're seeing thousands of
lines at once and you can work out
statistically what they're doing. So even
with the most modern cameras and most modern
technology, it's still hard. And that's why,
even though we had the wherewithal to
understand the physics and, um, to know how
to do the techniques, 200 years ago,
we were stuck in a technology gap. We just
had to wait for the technology to reach the
right place. And that's why finding the first
was hard. But once you found one, you'll find
tech 10, you'll find 100, you'll find a
thousand. I'd m point people, incidentally,
to the astonishingly beautiful videos by
System Sounds, in partnership with NASA, that
were put out to celebrate the 4 and 5000th
discovered exoplanets, where they run the
discoveries over time on a, on a map of the
sky where the discoveries are marked with a
little ring. And every planet gets its own
musical note, where the musical note tells
you the orbital period of that planet around
the star. So a high Pitched note like a ding
will be a planet really close and going
around really quick and low pitch note like a
ding that'll be a planet a long, long way
away going around really slowly. And um, it
shows you the diversity we found but it also
shows you this incredibly accelerating
rate at which we're getting better at doing
it because now we've crossed that threshold
where the technology wasn't good enough. And
now the technology keeps getting better, we
get better at doing it and the numbers
continue m to rise. And depending who you
talk to, there are people who suggest we may
well actually we'll certainly cross the
10,000 count by 2030.
Might not be long after that before we cross
100,000 mark. That will all depend on Gaia,
but also the Nancy Grace Roman telescope
that's due to launch in a few years time.
Andrew Dunkley: Yeah, it's going to be amazing. Uh,
and uh, who knows what we will find.
And we'll talk about uh, a bit more in a
moment here on Space Nuts.
Three, two, one.
Jonti Horner: Space Nuts.
Andrew Dunkley: And you're with Andrew Dunkley and Professor
Jonty Horner. We're talking exoplanets on
this special episode. Uh, it's
our last segment. So, um, over to you
Jonty. Where do you, where do you want to go
to finish off this particularly interesting
topic?
Jonti Horner: Well, I think it's also worth flagging out
the diversity places that are doing this work
as well. I mean amateur astronomers are
contributing a huge amount. We're now at the
point where, where the technology's moved on
enough that you can observe and measure
exoplanet transits using a fairly cheap off
the shelf telescope. Many amateur astronomers
will occasionally observe the transit of one
of our bright planets. There was an article
on Australia's ABC News recently about some
amateur astronomers who banded together to be
involved in planet discovery. I'm
increasingly proud of the facility we've got
at Uni sq, which is as far as we know, the
only dedicated Southern Hemisphere exoplanet
observatory in the Southern Hemisphere.
There's a lot of facilities looking for them,
but we've got our own facility at Matt Kent
Observatory just outside Toowoomba that all
it does is look for planets and learn more
about them. It doesn't split its time with
other tasks. Its job is planet search.
And it's really important to stress that
particularly for the younger listeners from
Australia, there's this perception
that the only place you can go to do real
science and to become a scientist is to go to
the big cities, the big capital cities, to
the group Fake Universities and for people in
regional Australia, and particularly people
from less prestigious
backgrounds, lower socioeconomic backgrounds,
all the rest of it, there's this very much
feeling that it's a big city thing and you've
got to go to the right schools. But we're at
a small regional university in regional
Australia and we're leading the world in
this. You know, we have two of my colleagues,
um, Professor George Zhao and Associate
Professor Chelsea Huang are, uh, between them
responsible for 30% of all time Australia
has ever had allocated on the James Webb
Space Telescope. And, uh, they've sat to
study planets around other stars. So I do
want to stress to people listening that this
is not just something that's done in the US
or it's not just something that's done at the
world's top 10 universities. It's something
that you can participate in yourself. There's
some fabulous citizen science programmes out
there and uh, there is going to be an
increasing extreme wealth
of data coming out in the coming years that
uh, astronomers simply won't have enough
hands to go through. So I'm sure that, that
if people keep their eyes out, there will be
other citizen science programmes pop up in
the coming years. You know, we've got,
currently I'm looking at the wonderful NASA
Rexoplanet archive here, looking at the
different methods planets have been
discovered by, and we've now got, I think
it's 11 different methods that have been
used. Of our
6283 planets,
4640 have been found by the
transit method. That's overwhelmingly the
most successful now. And that's because you
can play a numbers game. You can look at
thousands of stars at once, looking to see if
any of them wink. And that's what the Kepler
spacecraft and more recently NASA's test
spacecraft did. We've got nearly
1200 planets found with the radial velocity
method, the wobbled method. Now should be
said this is a discovery method and a lot of
these planets have then been studied using
other methods. But this is how they were
found. So between those two were, uh, what,
5800 of the known
planets, 6200 were found by those.
That's 90 odd percent of the
remainder. We, uh, know of 278 planets that
were found by microlensing. This is where you
look at very distant stars like the middle of
the galaxy and look for planets and stars
that we can't see passing along our line of
sight and their mass bending light to
cause that background star to brighten then
fade. Very small number found so far.
But the Nancy Grace Roman telescope will
likely discover thousands, if not tens of
thousands of microlensing planets in the
coming years. Because that telescope's going
to go and stare at the middle of the galaxy,
among other things, and should be very useful
at that. We've got nearly a hundred planets
now discovered by direct imaging,
and they're really interesting because
they're the ones where we actually see the
planet and we find it by seeing the light
from the planet. So it's amazing that we're
nearly at 100 there. And my favourite movie
of all time Time is really the
movie of the planets orbiting the star HR
8799, where observations spanning
more than decade now have been made, where
you can see four planets around that star and
watch them move in their orbits. And you
think from where we were when I was a kid,
where we didn't even know if there were any
planets out there, we can now watch some of
them go around their stars in real time.
That's just astonishing.
There's a lot of other really niche methods
that have been used news, but they're kind of
the big four, I'd say. And I think the one
that's going to grow over the coming decade
more than any other is astrometry. So at the
minute there is a grand total of six planets
that have been discovered by astrometry. This
is measuring the positions of stars in the
sky and seeing them wobble side to side. It's
what Bessel did with Sirius to find Sirius B.
We've only found six so far, but the Gaia,
uh, spacecraft observed for a long time,
finished observing, but we're still getting
new data releases from. From it. Gaia data
release number four is coming allegedly in
December this year. Maybe push back a little
bit, but that's where they will have enough
quality and analysis of the data and enough
time period the data covers to start finding
planets in the Gaia data doing astrometry
and people are still predicting that could
yield tens of thousands of planets. Even if
you're a pessimist, it's easy that Gaia
could take over from Kepler and TESS as a
tool that found the most planets. That's just
in the next year or two. And what we're doing
then we're finding more, but where we're
shifting to is not just finding them, but
learning more about them, characterising
them. And that's where the future of
exoplanet science is. It's not just enough
now to find a planet, we want to learn more
about it. What's its atmosphere made of?
What's its internal composition? What's it
like? That's where we're going. And
um, we're making great leaps in that we are
finding out what chemical species are in the
atmospheres of different planets. Currently
only really doing it for the very biggest
ones because of the easiest to observe. But
that's very much the future. And that's what
will lead to the search for life elsewhere,
which I think is what really hooks a lot of
people into the subject.
Andrew Dunkley: Yeah, it's fascinating. For the record, the
first actual photograph of an
Exoplanet was in
2004
Jonti Horner: and
Andrew Dunkley: it was 2m, um, 1207b.
Jonti Horner: Yes.
Andrew Dunkley: Which apparently is an exoplanet, uh,
orbiting a gas giant.
Yes. Which is a big, a big one,
about five times the mass of Jupiter. So, um,
yeah, so that was the first one ever
photographed that we actually got to see a
picture of rather than just identified
through some.
Jonti Horner: I mean we're still just seeing them as a
single pixel. We're not going to be at the
point of Star Trek type images of the surface
for a long, long, long time because the
resolutions are challenged there. But that
was a breathtaking thing. And it is worth
noting that the overwhelming majority of the
direct imaging planets that we've imaged are
um, massive and um, young. And the thing
about them being young is they're still
hotter, which means they glow brighter and
therefore are easier to see.
Andrew Dunkley: M okay, um,
last chance to talk about exoplanets.
We're going to wrap it up in a sec. Any, any
final comments?
Jonti Horner: Well, I think, I think there is so much more
we could talk about. I mean like every topic
we get onto, I talk too much. But we could
fill several hours worth of excitement
digging into the nitty gritty. But I think
the thing that leaps out to me probably even
more than the ubiquity of planets, the fact
that they're everywhere, is the diversity.
You know, when I was growing up, we thought
that there would be other planetary systems,
but we weren't sure. But we assumed they'd be
like the solar system, you know, rocky
planets on the interior, giant planets on the
outside. Yeah. And the first planets
discovered shattered that you had planets
around a pulsar, which makes no sense.
Um, we think there are probably a second
generation of planets. The initial planets
there were destroyed and new ones formed
after the supernova, but we're not sure. You
then found a hot Jupiter, a planet the size
of Jupiter, going around a star like the sun
every few days and that was enough to
revolutionise our understanding of how
planetary systems form. And with every new
technique and with every new facility and
with every new way of finding planets, we
find planets that are more different to the
solar system than we could ever possibly
imagine. The lightest, well, not the
lightest, the fluffiest planets, the lowest
density planets are so fluffy that they're
being torn apart by their stars. We mentioned
them early on. The highest density
of any planet in the exoplanet catalogue is
denser than any metal or mineral or anything
known on Earth by such a large distance. Uh,
there is speculation that it could be a
fragment of a white dwarf or something. That
it could be actually not a lump
of iron but a lump of white dwarf material or
something. We just don't know. And everything
in between. We're finding that the planets in
our solar system are pretty
average. We still don't have a handle on
how common are planets like the Earth. How
common are planets on, like the Earth? On
Earth like orbits. We also don't really have
a handle yet on how common are ah, planets
like Jupiter and Saturn, in other words
called Jupiters planets that take a decade
um, or more to orbit their star because
finding them hard you need to watch for a
long time. So we know much more about planets
close in and planets very different to our
own than we do about planet planetary systems
similar to the solar system. So I think one
of the big questions now is not is the solar
system unique but rather how
unusual or usual is the solar system,
our planetary systems like our one common or
are we a bit of an exception? We're not
really in a position to answer um, that yet.
It seems that the frequency of
Jupiter like planets around other stars is
somewhere between 5 and 20%. And by Jupiter
like, I mean Jupiter mass on a Jupiter like
orbit around stars like the sun.
But that's a big variety of,
you know, possibilities we just don't know
yet. And so even though we now
know that planets are everywhere, we've
barely scratched the surface. And it's the
kind of thing where if we had this chat again
in five years time the numbers would be
different but there would be whole swathes of
new knowledge then that we can't even predict
now. There will be things that surprise us
just as much in the years to come as hot
Jupiter's and pulsar planets did at the dawn
of the era. And that's part of the fun.
Andrew Dunkley: Yeah, and there'll probably be planets we
can't even imagine that would
be discovered that we couldn't have even
contemplated, contemplated existing.
Um, and I can't even pretend to make one up
at the moment. But there will be. Of course
the search, as you mentioned, is for an Earth
like planet. A planet, a, uh,
rocky planet in the right place orbiting a
star like ours, um, that
basically duplicates Earth. We just haven't
found one of those yet, have we?
Jonti Horner: No, no. With a caveat we may
have done and it have not been picked up.
There's more to learn about these things.
Things I still think of the planets
we've found so far. Venus is more like the
Earth than anything we've found so far. I
also think though, that that's even a
difficult question because what do we mean by
it being like the Earth? If you went and
looked at the solar system 4 billion years
ago, I don't think you'd have considered the
Earth an Earth like planet. It would have had
this incredibly thick atmosphere, very
different to ours, with a very different
composition. It would have been outside
the edge of the habitable zone because the
sun was that much fainter. But it would
probably still have liquid water on the
surface because it had such an intense
greenhouse effect. So there could
almost be a philosophical question about how
long would you consider the Earth to have
been an Earth like planet?
Andrew Dunkley: That's a really good point. Yeah. And
the possibility that we have observed planets
that just, ah, aren't where we are yet
because of the time differences in,
in, in the travel, uh, time of our vision.
So again, it mightn't be there yet
and it could be billions of years before it
is and we won't be around to confirm it.
There's all sorts of weirdisms that go into
this. My, the bottom line for me is if they
find one, it's got to have kangaroos on it.
Otherwise there's just no Earth like planets.
Jonti Horner: Oh, absolutely. I mean, would be very
interesting to imagine kangaroos in space. I
talk a lot about, um, the Dragonfly mission
going to Titan, and the fact that Titan is
the only other body we know of with permanent
liquid water on the surface. Well, not
permanent liquid water, permanent liquid on
the surface. The water there is harder than
granite frozen solid, but it's got liquid
methane and Ethernet there. But on Titan,
unlike on Earth, you could fly under your own
power. If you strapped a pair of wings on.
The gravity is low enough in the atmosphere,
dense enough that you could flap around and
saw. I have never thought about how a
kangaroo would react if you took it to Titan.
It would just, uh, launch itself. Just launch
itself. Um, it Would, of course, need a very,
very good space suit because it's so cold
there and kangaroos are not fans of the cold.
But, yeah, that would be the shock. If
Dragonfly hops around, flying around on the
surface of Titan, and then gets attacked by a
kangaroo when it comes into land. Like, we
see some of the videos online of kangaroos
being territorial. That would be the most
bizarre discovery of life elsewhere that I
think I could imagine. Kangaroos on Titan.
Andrew Dunkley: I wait with bated breath. Although kangaroos,
uh, do have one particular problem in this
country. They do not know how to get out of
the way of a car. Even when they do, they go,
oh, no, no, hang on, I want to get back in
front of you. Bang. Okay, see ya. Uh,
anyway, um, that's our problem. I'm sure it's
the same in other countries without other
animals and other planets, probably that
we're unaware of as yet. Uh, Jonty, that's
been a lot of fun. It's a, it's a fascinating
topic and it's one that will keep evolving, I
think is probably, probably the best way to
describe it. Thank you so much and we'll
catch you again real soon.
Jonti Horner: It's a pleasure and I look forward to it.
Andrew Dunkley: Professor Jonty Horner from the University of
Southern Queensland. And thanks, uh, to Huw
in the studio. Couldn't be with us today.
Made a fatal error. He's back in hospital. He
ran into an ex. And, uh, he called
his ex a planet.
Think about that. It's terrible. And don't
forget to visit us online if you dare, at
spacenutspodcast.com or spacenuts
IO until next time, thanks for your company.
We'll see you on the very next episode of
Space Nuts. Bye.
Jonti Horner: Bye. You've been listening to
the Space Nuts podcast,
available at Apple Podcasts, Spotify,
iHeartRadio or your favourite podcast
player. You can also stream on
demand@bytes.com.
Andrew Dunkley: this has been another quality podcast
production from bytes.com.
Jonti Horner: um,