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Exoplanet Expeditions: Discovering the Cosmic Diversity Beyond Our Solar System · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:00
Jonti Horner: Hi there.
0:00
Andrew Dunkley: Thanks for joining us yet again. This is
0:02
Space Nuts. My name is Andrew Dunkley. Great
0:05
to have your company one more time. Well,
0:08
hopefully it's more than one more time, but
0:09
on this occasion, uh, now with Fred Watson
0:12
away, uh, we are doing a series of
0:15
little specials and today the focus
0:18
will be on exoplanets.
0:20
We've known about them since the early 90s
0:24
and since then we have found
0:27
thousands of them. But what is there to
0:30
know? I mean, we've got our own planets.
0:32
Surely that just means everything else around
0:34
the galaxy is the same. That's
0:37
probably not true. And we're going to talk
0:40
about all of it today on this, uh, episode of
0:42
space nuts. 15 seconds. Guidance is
0:45
internal. 10, 9,
0:48
ignition sequence.
0:50
Jonti Horner: Star. Space nuts. 5, 4, 3, 2.
0:52
Andrew Dunkley: 1. 2, 3, 4, 5, 5, 4, 3,
0:55
2, 1. Space nuts. Astronauts report
0:58
at and with us while
1:01
Fred Watson is away is Jonty Horner,
1:04
professor of astrophysics at the University
1:06
of Southern Queensland. Hi, Jonty.
1:08
Jonti Horner: Good afternoon. How are you going?
1:09
Andrew Dunkley: I am quite well. And you?
1:11
Jonti Horner: I can't complain. I'm enjoying us having a
1:13
public holiday today, which is great. I mean,
1:15
I'm still off anyway, so it doesn't really
1:17
matter, but it means I'm taking one day's
1:19
less of sick leave, I guess. Uh, well, it's
1:21
all good.
1:22
Andrew Dunkley: I'm retired, so public holidays mean nothing
1:25
to me now. I
1:28
used to so look forward to having a few days
1:30
off or, you know, an extra long weekend if
1:32
they combined the two in April because we
1:35
get, uh, east sometimes, get Easter and Anzac
1:37
Day in April. And if, um, you jam them
1:40
together, you get a nice free holiday. But,
1:43
uh, it doesn't mean squat to me anymore.
1:45
Jonti Horner: I keep finding it bizarre. At least in
1:47
Toowoomba. I'm sure this is reproduced
1:49
everywhere. If the shop shut for one day, the
1:51
day after is absolutely feral. So
1:54
last week we had Anzac Day, which tells you
1:56
how long ago these were recorded, by the way.
1:58
Um, but yeah, last week we had Anzac Day. And
2:01
obviously, Franz, act quite rightly, the
2:03
shops, the supermarkets and everything are
2:04
shut. It's one of the biggest holidays in
2:06
Australia of the lot of them. But we, we tend
2:09
to do our shopping on a Sunday anyway, so it
2:11
didn't really matter. Went to the shops on
2:13
the Sunday and it was almost people fighting
2:14
in the aisles because heaven forfend that one
2:16
day you don't, you know, you don't get food
2:18
for one day and the shops start running empty
2:21
of bread. And it's like people buy more when
2:24
they've had one day without the Shops being
2:25
open, very, very strange phenomenon.
2:28
Andrew Dunkley: They panic by and there's no toilet paper on
2:30
the shelves. Is also.
2:32
Jonti Horner: Well, the best thing about that. That led us
2:34
to subscribing to who Gives a Crap which
2:37
panel started online.
2:40
Um, and they've been brilliant. We've
2:42
recommended them to everyone because it works
2:44
out cheaper than getting it from the
2:45
supermarket and they're better quality. I
2:47
mean it's, it feels like very much a no, uh,
2:49
brainer. And we'd never have come across them
2:51
if it wasn't for Covid and the
2:54
incredibly smart people of Toowoomba going,
2:56
oh my God, Covid's happening. We're going to
2:58
run out of toilet paper. Of all the things
3:00
for the shop to run out of, happened
3:02
everywhere. Why toilet paper? Uh,
3:05
I mean Covid affect my
3:08
memory was that Covid was a, was something
3:11
that made things come out of your head, not
3:12
things that came out anywhere else. It's not
3:14
like there will be an expectation it would
3:15
make you use more. No, bread was
3:18
fine, eggs were fine, perishables were fine.
3:20
But toilet paper, I don't understand.
3:24
Andrew Dunkley: I never, I never got it either. But uh, uh,
3:26
our shelves were devoid of the stuff.
3:29
We better get down to business.
3:30
We're talking exoplanets today.
3:33
And I did a little bit of research. Uh, the
3:35
first exoplanets were confirmed in
3:38
1992. In fact, they suspected they existed
3:41
before that, but they couldn't prove it. But
3:43
1992, uh, they
3:45
found two planets that were later named
3:48
Poltergeist and um, Phobitor
3:52
Phoebe. Uh, so they were
3:55
officially the first two exoplanets. And then
3:58
the first one that was
4:01
orbiting a sun like star was found in
4:03
1995. That was
4:06
um, 51 Pegasi B.
4:08
Jonti Horner: Yes.
4:09
Andrew Dunkley: So, uh, those were the first few. And of
4:11
course now we've reached a point where
4:14
as at 30
4:17
April 2026,
4:19
6278 confirmed
4:22
exoplanets with another 8000
4:25
waiting to be, um, officially
4:28
catalogued. I suppose. So we've
4:31
found a lot of them. And the other thing
4:33
we've been discovering about, um, finding
4:36
these things is how very different
4:39
a lot of solar systems are and how very
4:42
different some of the planets are. Ah,
4:46
what we always thought was basically the
4:49
standard for solar systems,
4:51
which was ours. Doesn't appear to be very
4:54
standard at all.
4:56
Jonti Horner: No, it's an incredible time to live through.
4:58
I think the way I always budge this is we've
5:00
lived through one of the great scientific
5:03
revolutions almost without noticing it.
5:05
And I think it sheds A light into how people
5:08
would have reacted in previous scientific
5:09
revolutions, which is that when it's
5:11
happening in your lifetime, it just happens.
5:13
So we look back and think that was such a
5:15
fundamental change. And at the time it was
5:17
just Tuesday, you know. And
5:19
yes, it's like that with exoplanets. I
5:22
grew up in a world where one of the big
5:25
science questions was, is a solar system
5:27
unique? Are there planets around other stars?
5:29
Or are we alone? And there were good
5:32
reasons for some people to suspect that we
5:34
might be the only planetary system in the
5:36
universe. There were kind of, at that time,
5:38
two broadly competing models of planet
5:40
formation that could both explain the solar
5:42
system as we see it to a fair degree. And one
5:45
was what's almost described as the
5:48
Laplace model, the disc model, which is now
5:51
what we favour, that has developed a lot
5:53
since then. But the other was this idea that
5:55
you had a close encounter between the sun and
5:57
a protostar. Ah, that was close enough that
6:00
the two stars almost collided and a tongue of
6:02
material was pulled out of the sun, which
6:04
went on to condense from the planets. And
6:05
that was championed by people like Martin
6:07
Wolfson of York University, among others.
6:10
At, uh, this time we're talking in the late
6:12
80s, it was kind of widely held that, uh,
6:15
Wolfson's suggestion had problems.
6:18
It was probably not the right solution, but
6:21
it potentially could be. We'd found a few
6:23
debris discs, debris around stars, a bit like
6:25
the asteroid belt around the sun, but much
6:27
more massive in the early 80s. And that
6:30
was kind of hinting that planets could be
6:33
common, that the disc model could be the one.
6:36
But at the time I was growing up, and at the
6:38
time, going into the early 90s, you have
6:40
these two models of planet formation that
6:42
predicted vastly different outcomes. If
6:45
the disc model was right, planets would be
6:47
ubiquitous, planets would just be the
6:49
leftovers from star formation, and
6:51
effectively every star would have planets or
6:53
close to it. If the encounter
6:56
model was right, then planetary systems would
6:58
be exceedingly rare, because to get two stars
7:01
to come sufficiently close together at just
7:03
the right speed for that to draw a tongue out
7:05
and form a planetary system is vanishingly
7:08
unlikely. So that was arguing that we were
7:11
effectively the result of a freak encounter.
7:14
And if that prediction was right, then if
7:17
that method was right, sorry, it would
7:18
predict that planetary systems were
7:20
exceedingly rare and that we wouldn't find
7:22
them. So going into the 90s, you had these
7:25
two theories that could both explain in broad
7:27
brushstrokes, what we see at home, but that
7:30
predicted very, very, very different
7:31
outcomes. And as I say, The Wolfson idea was
7:34
already losing a bit of seam. But in the time
7:37
since we found that planets are under the
7:40
stars and, um, that they are ubiquitous,
7:41
basically every star you see in the night
7:43
sky, no matter how complex system, no
7:46
matter what's that, there are going to be
7:48
planetary objects around it, pretty much all
7:50
cases. And that's a death knell, of course,
7:53
for the Wolfson model of freak planetary
7:55
system formation and its support for the
7:58
model we now know and love, which has been
8:00
refined over the years because of all the
8:02
oddities we found. Now, it's really
8:04
interesting, storey, but it goes way back
8:06
before that. We've got a long history of
8:09
the things that led to finding the first
8:11
planets. What we take it a bit for granted
8:13
now. We're finding so many planets and I have
8:15
the good fortune of getting to be involved
8:17
peripherally in some of the discoveries. I'
8:19
have the very entertaining job of killing
8:21
some planetary systems. So it should be said
8:23
that the number you gave at the start can go
8:25
down as well as going up. Some of
8:28
the planets that get confirmed later on get
8:30
redacted, get killed. And I've probably,
8:32
certainly as lead author, I've never led a
8:35
planet discovery, but I've been involved with
8:36
them. But I've led a number of research
8:38
projects that killed planets that other
8:40
people claimed. So I've probably been net
8:42
responsible as an individual for a negative
8:44
number of planet discoveries that can happen.
8:47
But it's really important that we do that
8:49
kind of work. I've always been really
8:50
passionate about that because all of the
8:52
things that we do to talk about how common
8:55
planets are, to look into how they form and,
8:58
um, further down the line to try and find
9:00
planets that could be like the Earth and to
9:02
try and look for life on them. All of that is
9:04
based on the catalogue of the known. What do
9:06
we know? What's the variety? And so if you've
9:09
got planets that are in that catalogue that
9:11
don't exist, they're polluting that catalogue
9:13
and confusing and obscuring the truth. So
9:15
it's really important to not just accept that
9:18
when a planet is claimed and marked as
9:20
confirmed, that's the end of the storey. But
9:22
we need to follow it up and say, does it make
9:23
sense? Could there be something else going
9:25
on? And in those cases we do learn more about
9:27
it. So it's a fascinating field. I'm really
9:30
fortunate to have gone from being a kid who
9:32
wondered to an adult who gets to be involved
9:34
in the process. That's incredibly
9:36
wonderful for me, but it's a fabulous Storey
9:39
we have lived through a great scientific
9:41
revolution in many ways. One that's as big as
9:44
the acceptance of continental drift or uh,
9:47
the origin of species and Darwin or general
9:49
relativity and Einstein. It's one of those
9:52
revolutions. And when you talk about the
9:53
other ones, you think about how epochal
9:56
and incredible and how they change the world
9:58
and we've just lived through one. Um, it's
10:00
amazing.
10:01
Andrew Dunkley: Yeah, it's incredible. And, and
10:04
will it never end? I mean the thought of
10:06
looking up into the night sky and seeing
10:09
billions of stars and knowing that there
10:12
are probably multi, billions of planets is
10:15
just, it's mind blowing.
10:17
Jonti Horner: And the rest, I mean to me it's a numbers
10:19
game and we talk about this when we talk
10:20
about life elsewhere, but the numbers get
10:23
ridiculous really, really quickly. Now we've
10:26
been heavily biassing what we found to
10:28
finding planets closer to their stars than
10:30
the Earth is to the sun. The overwhelming
10:31
majority of planets. We found a very close
10:33
end, but there will be planets further out as
10:36
well. You're not going to have a situation
10:37
very often where you've got a few planets
10:39
near the star and nothing further out. So a
10:41
lot of the very tentative estimates you get
10:43
of the number of planets in the universe say,
10:46
well, imagine there's just one planet per I.
10:48
Based on what we found so far, I think it's
10:50
fairer to say there are probably nearer to 10
10:52
planets per star. And depending on whether
10:55
Jared Isaacson, the guy who's taken
10:58
over NASA who is not an astronomer, gets his
11:00
way and restores Pluto. If he restores
11:02
Pluto, then you have to argue that Ceres,
11:05
Makemake, Haumea, Eris, all these other
11:07
things are planets in the solar system. You
11:09
could have 20 planets in the solar system. So
11:12
let's assume 10 per star. You
11:15
know whether Pluto is arisen. Leave that for
11:17
aside. I have strong opinions on that. Other
11:19
opinions are available. They're wrong, but
11:20
they're available. As Matt come out always
11:22
says, um, ignoring
11:25
that though, if you assume 10 planets per
11:27
star, because it's going to be nearer to 10
11:28
than when an astronomer's working factors of
11:30
10. In our galaxy alone, um, we have
11:34
somewhere around 400,000 million
11:37
stars. Now that number also is only accurate
11:39
to a factor of 2 or 3. So it could be 200, it
11:41
could be 600, but call it 400,000
11:44
million stars means 10 planets per star.
11:46
You'd have 4 trillion planets in our
11:49
galaxy, ignoring the free floating ones that
11:51
don't have a star to call their own. 4
11:54
trillion planets in our galaxy.
11:56
There are more galaxies in the observable
11:58
universe than there are stars in our galaxy
12:01
by orders of magnitude. Which means you start
12:03
getting to the point which, in the observable
12:05
universe alone, um, ignoring the part of the
12:08
universe that we can't see because that's
12:09
utterly unquantifiable, but just in the part
12:11
we can see, you'll have planets numbered in
12:14
the sextillions of septillions.
12:17
So a trillion is 10 to the 12, a trillion is
12:19
a thousand billion, a quadrillion is 10 to
12:22
the 15, which is a thousand trillion, and so
12:25
on. So these numbers are utterly,
12:28
astonishingly, overwhelmingly, mind boggling.
12:31
And that's where I come to with this thing,
12:33
that if we're the only place with life in the
12:35
universe, then there's something very unusual
12:37
going on.
12:38
Andrew Dunkley: Absolutely, yeah. Um, and
12:41
it was the movie Contact where they said, uh,
12:44
space is really big. So if it's just stuff,
12:47
just us, it seems like an awful waste of
12:49
space.
12:50
Jonti Horner: It is.
12:51
Andrew Dunkley: I always like that line.
12:52
Jonti Horner: Yeah, well, the question of life elsewhere is
12:54
one that really polarises people. I mean,
12:56
everybody's interested to know the answer.
12:58
Arthur C Clarke said something along the
13:00
lines of, there are two possibilities. Either
13:02
we're alone in the universe or we are not.
13:04
Both equally terrifying. Um,
13:08
a lot of people. Stephen Hawking was very
13:10
adamantly, we shouldn't try and contact
13:11
aliens because they will kill us in the face.
13:14
I don't tend to agree with them, but
13:17
it is one of those discussions that really
13:19
fires people up, gets people energised. And
13:22
for me, it would be actually far more
13:24
terrifying to know we're alone in the
13:26
universe, because that means life is such an
13:27
impossible fluke that given planets
13:30
numbering in the sextillions or septillions,
13:33
in the known universe, we're the only one
13:35
with life. Which means that only one planet
13:38
in 10 followed by 20 zeros or more
13:41
gets life on it. And that seems infeasible to
13:43
me, but m. We won't really know until
13:47
we move forward and we actually proceed with
13:50
the search for life elsewhere. And as I've
13:51
said in a previous episode, absence of
13:54
evidence is not evidence of absence. So if we
13:56
find life, then we'll know we're not alone.
13:58
We'll know that life's common in the
14:00
universe. The longer it takes us to find life
14:03
doesn't mean that there is nothing to be
14:05
found, it just means that life is scarcer,
14:08
basically. So the longer we take to find it,
14:10
the better we'll get at doing it. The further
14:12
we'll be able to look, the more planets we
14:14
can Sample. And that will then give us a
14:16
handle for the commonality of life.
14:18
Andrew Dunkley: Life.
14:18
Jonti Horner: So we find life in our lifetime. All well and
14:20
good. If we're still looking in a thousand
14:22
years. I'd be gobsmacked, but that just tells
14:25
you life is a lot rarer than we thought.
14:27
Andrew Dunkley: Indeed. And we will talk about that more in
14:30
another, uh, special episode when we do part
14:32
two of Astrobiology. Uh, we kind
14:35
of had, we didn't have enough time to
14:38
talk about it last time, so we're going to do
14:39
a part two.
14:40
Jonti Horner: But uh, I can talk too much.
14:43
Andrew Dunkley: It's also an area that um, uh, makes
14:45
your brain hurt. So we, we decided to,
14:49
you know, give it a miss this week and go
14:51
back, uh, next week.
14:53
Um, so where do you want to go with this?
14:56
Like, um, everyone knows there's
14:58
exoplanets. Everyone knows there are, um, you
15:01
know, powder puff planets. And um,
15:04
they've actually got names for them. I've got
15:07
named, um. So you know, we can
15:10
officially say that uh, as far as
15:13
planets are concerned, we have
15:15
um, specific types of
15:17
planets in our solar system, and that is
15:20
rocky planets, gas giants, and
15:23
for want of a better term, ice giants. But in
15:25
the exoplanet world there are
15:28
several other types. Um,
15:31
you've got um, uh, Neptunian,
15:34
like planets, super Earths, uh, you've
15:37
got uh, hot Jupiters, you've got super cold
15:40
worlds, you've got pulsar planets, and
15:42
there's even uh, uh,
15:44
circumbinary planets where they're
15:47
orbiting two stars. We don't have that
15:49
thankfully. Uh, that could be messy,
15:51
especially when it comes to trying to predict
15:53
the tides. But um, it's, you know, there's so
15:56
much more going on out there.
15:58
Jonti Horner: There is, and it reflects something that's
16:00
incredibly human. And it again goes back to
16:03
that discussion about Pluto and many other
16:06
things in human experience. What we find
16:09
in every field of study, but you know, in
16:11
astronomy in particular, is you have a
16:14
continuum of things you've got from the very
16:16
small to the very big with no obvious sharp
16:18
gaps. You know, you'll find everything in
16:21
planetary systems from stuff the size of a
16:23
grain of dust to things more massive than the
16:25
sun, depending on the planetary system you're
16:27
in. What we tend to do as humans is we tend
16:30
to break down that which we
16:33
see as a continuum into manageable bite sized
16:36
chunks by grouping like with like in order
16:38
that we can then better study objects.
16:42
And so for example, you'd say that the Earth
16:44
is more like Venus or Mars than it is Like
16:46
Jupiter. So you categorise them into
16:47
different subgroups. For humans, we do this
16:50
all around the world. You've got babies and
16:53
toddlers, children, teenagers, adults,
16:55
retirees, pensioners, and you set boundaries.
16:58
And those boundaries don't always agree from
17:00
country to country. You know, you remember
17:02
the incredible day that you suddenly wake up
17:04
and you're able to drive legally when the day
17:06
before you weren't. And fundamentally you'
17:08
changed as a human. You're one day older out
17:11
of what, you know, several thousand days at
17:14
that point, about 5,000, 6,000 days. But
17:16
miraculously you've crossed this arbitrary
17:18
threshold which we've put there to separate
17:21
people who can't drive and people who can but
17:23
maybe shouldn't. You know, that's kind of
17:25
where the division is.
17:28
We do this as humans all the time to
17:29
categorise things. And that's kind of where
17:32
Pluto fallafal and it's where all these
17:34
groups of different types of planets come
17:36
from. You've got hot Jupiters and warm
17:37
Jupiters, super puff planets and all
17:40
sorts of quirky things. And those terms
17:43
are taking the broad spectrum of planets that
17:46
we've got and trying to group apples with
17:48
apples and oranges with oranges, things that
17:50
are similar to one another. And the diversity
17:53
just continues to ascend, as every time we
17:55
think we've found the most extreme of
17:57
whatever, we find something that's even more
17:58
so. Like I said, we found planets who we
18:01
can calculate their size by how much light of
18:04
their star they block. We can calculate their
18:05
mass by how much they pull their star around.
18:09
We've got a subset of stars and planets where
18:11
we can do both those, uh, things which lets
18:12
us figure out the density. And from them we
18:15
found planets that are less dense than cotton
18:18
candy, which are the super puffs,
18:20
fluffy ones, probably coming towards the end
18:22
of their lives because they're so low density
18:24
that they are probably being stripped away by
18:26
their star stellar winds. We found planets
18:28
that are effectively like comets with tails
18:31
as their atmosphere stripped off. I mean, to
18:33
some degree, actually, the planet Mercury in
18:35
the solar system is a comet. It's got a
18:37
beautiful long sodium tail. One of my
18:39
favourite astrophotos I've ever seen is a
18:42
picture of Mercury near the Pleiades, where
18:44
somebody's done some imaging in a sodium
18:46
filter and you can see Mercury's tail
18:48
visible on the image. It's an astonishing
18:51
thing. So we found planets like comets. We've
18:53
even found planets around pulsars and they
18:55
were the first three planets we found around
18:57
other stars. There were um, Phoebe Toe,
19:00
Poltergeist and Rao, these stars orbiting a
19:03
pulsar named after three kinds of the, um,
19:05
undead. So there's this huge variety that
19:07
worth mentioning actually from the names. The
19:09
names are being allocated by the
19:12
International Astronomical Union, just as
19:13
names of asteroids and names of satellites
19:16
and things like that are. What they're trying
19:18
to do with them is to be very
19:21
democratic globally, to try and represent
19:24
multiple cultures rather than just have all
19:26
the planets draw from a single cultural base,
19:29
a single kind of background. And so they've
19:31
been running a series of competitions over
19:33
the years for the general public where a
19:36
given planetary system is to a given country.
19:39
And, um, then people from that country get to
19:41
nominate names, and then people from that
19:43
country get to vote on it. And I think we've
19:46
now got more than 100 planets named. We've
19:47
had a few of them from Australia named. And
19:49
I'm actually just trying to look up, um, the
19:52
planet names from the iau. They're the
19:54
official ones. Now, what's interesting is
19:56
these are, uh, official names. They're
19:59
the IAU's official names. I
20:01
therefore try to use them in my purpose.
20:04
Um, and I've had pushback from astronomers
20:06
because everyone's so used to the catalogue
20:08
numbers. So what I've been trying to do
20:10
is you give both names, you give the
20:12
catalogue name on the proper now. And I think
20:14
where it will go long term is it'll become a
20:16
bit like comets. You know, I've been trying
20:18
to get images through the cloud and cursing
20:20
the weather of Comet Pan Stars at the minute.
20:22
And we talk about Comet Pan Stars, but it's
20:24
real name that I'd write down, if I'm writing
20:26
it is C20, 26 R3
20:29
brackets, pan stars. And I think
20:32
in the long term, I can see exoplanet names
20:34
going that kind of way once people get used
20:36
to it. So 51 Pegasi B,
20:39
for example, is dimidium. That's the name
20:41
that's been given there. And you can use both
20:44
interchangeably. But because astronomers are
20:46
used to 51 Pegasi B, that's where it
20:49
sticks. Now, the names come from lots of
20:51
different cultures. They come from lots of
20:53
different groups. There are planets that have
20:55
been discovered by Australians that are named
20:57
after Australians. There are planets that are
20:59
named after people. You know, you've got the
21:01
planet Galileo going around 55 Cancri.
21:04
So 55 Cancer's five named planets are all
21:06
named after astronomers. You've got Galileo,
21:08
Brahe, Lipper, Hay Janssen,
21:11
Harriet, and, um, that's it. So Five
21:13
planets, five names. Lots of different names
21:16
from different cultures. We've got names that
21:19
are controversial, names from different
21:21
folklore, names from different cultures all
21:24
around. That list is growing. But you don't
21:26
say, see used all that much yet because a
21:28
planet needs to be confirmed and
21:31
then very confidently there and well studied
21:34
for it to get onto the list for the name. So
21:36
I think like I said, we've got a bit more
21:37
than 100 names and a bit more than 6,000
21:39
planets. Those 6,000 planets, that
21:42
number will go up as well as down, but it's
21:44
not going to be too long until we're 10,000
21:45
plus.
21:46
Andrew Dunkley: Yeah, I figured out why, uh, some of these,
21:49
um, sometimes the number goes down. They're
21:52
the ones that have been discovered by Monty
21:54
Python. It's a planet.
21:55
Jonti Horner: No it's not, it's not.
21:56
Um, so that's why we'll also lose
21:59
some with Gaia. So Gaia has been this
22:02
amazing satellite measuring positions of
22:04
stars and it can measure the
22:07
wobble on the sky side to side of
22:10
stars as a result of their planets. Now
22:12
historically, the two, by far the two most
22:15
successful methods of finding planets are the
22:16
radial velocity method where we measure the
22:19
star speed towards our away from us and see
22:21
it wobbling along the line of sight, and the
22:23
transit method where we see it pass between
22:24
us and the star. And that means the orbit is
22:26
edge on to us. And but for those radial
22:28
velocity planets, we're measuring the
22:30
fraction of the wobble towards or away from
22:32
the observer. And um, the orbit could be
22:35
tilted almost edge on or almost face on to
22:37
give that same amount of wobble along our
22:39
line of sight. Gaia will give us the other
22:41
dimension. It'll give us a side by side,
22:43
which means it'll find us the tilts of all
22:45
those planets. Some of those planets will be
22:48
on orbits very tilted to ours and therefore
22:51
the mass that they have will be much higher
22:52
than that we think they probably have. And
22:55
that there'll be certain amount of attrition
22:56
where planets that we think are planets are
22:58
actually brown water dwarfs. And that is
23:01
another of these arbitrary boundaries which
23:02
we set roughly at 13 Jupiter masses. But we
23:05
will have planets falling off at the top end.
23:08
When Gaia comes out. I suspect he won't see
23:11
the number drop though, because Gaia will
23:12
also lead to so many new discoveries that,
23:14
that will overwhelm the ones that fall, uh,
23:16
off the top end.
23:18
Andrew Dunkley: I, yes, that's a fair point. So, um,
23:20
it's, it's going to be one of those waveforms
23:24
that goes up and down
23:26
as, as situations change. Yeah,
23:29
let's take a. I was going
23:31
Jonti Horner: to say I've been responsible for a number of
23:33
systems getting killed because people propose
23:35
planets in places that they seemed unlikely
23:38
and they didn't make sense from orbital
23:40
mechanics point of view. So I ran simulations
23:42
and showed that if these planetary systems
23:44
are real, wetting them in the last 10 years
23:46
of a 4 billion year lifetime before
23:49
the planets crash into each other or reject
23:50
each other. And that's not feasible. So there
23:52
must be something else going on. So on the
23:53
one hand, hand, boohoo, you've killed a
23:55
planet. That's not good, you naughty boy. Um,
23:57
on the flip side though, it's really cool
23:59
because there's something there creating the
24:01
signal that people have measured and it
24:04
isn't planets, so what is it? So there's
24:06
always. Science always gives you more
24:08
questions.
24:09
Andrew Dunkley: Indeed it does. And you're listening to Space
24:12
Nuts with Andrew Dunkley. Andrew Dunkley, I
24:15
do know my name. And Professor Johnty Horner.
24:19
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26:10
Jonti Horner: Space Nuts.
26:11
Andrew Dunkley: I'm gonna have to write it down so I can read
26:12
it properly.
26:13
Um, Jonty, where do you want to go next? I
26:16
mean, we've found so many, uh, I don't think
26:19
we will ever, never stop finding
26:21
exoplanets, uh, because as
26:24
technology improves they're just going to
26:25
keep stacking up, aren't they?
26:26
Jonti Horner: Yeah. I mean, if we talk about the 6000ish we
26:29
found so far, uh, 6278
26:32
I think it was. We said earlier on there are
26:34
probably 4 trillion give or take in our
26:37
galaxy, which means we've only found about
26:40
one planet for every billion planets
26:43
that are in our galaxy. We've barely
26:46
scratched the surface in doing that. We've
26:48
utterly revolutionised our knowledge of the,
26:51
the variety of planets that'll be out there,
26:53
of how planets form. We have still for
26:56
me, not found something truly Earth like. I
26:58
think that's the next hurdle. Now you'll see
27:00
a number of media articles over the years
27:02
saying the most Earth like planet yet has
27:04
been found. All the bloody.
27:06
Andrew Dunkley: I, I actually read an article yesterday
27:09
which said, uh, oh, super Earth found
27:12
potential life. Da, da, da, da, da. And I
27:14
thought, yeah, here we go again. And I read
27:15
it and of course when you get down to the
27:17
second last paragraph, it says, of course
27:19
there's no confirmation that this is even a
27:21
rocky planet.
27:21
Jonti Horner: But yeah, and to me it's like
27:24
imagining that you're an alien visiting the
27:26
Earth. Ah, and you're flying over the oceans
27:27
and you say, we found the most human like
27:29
animal yet. It's about two metres long, it's
27:31
a couple of hundred kilos, 100 kilos. I mean,
27:33
it's a dolphin, it's nothing like humans, but
27:36
it, you know, it's that kind of thing. And I
27:38
think I understand the urge, uh,
27:41
for scientists to talk about things in the
27:44
context of the habitable zone, in the
27:45
purpose, because that's interesting. Is it
27:47
too warm? Is it too cold? I understand the
27:50
thing of saying this planet has similarities
27:52
to the Earth. It's about the same size, size,
27:54
or it would be about the same temperature.
27:56
What tends to happen though then is that the
27:58
pressure release from the universities gets a
28:00
little bit more hyperbolic in it because they
28:01
want to get the reads and the clicks, want to
28:04
get the word out there. It then gets into the
28:06
media, who again are being more hyperbolic,
28:09
and we're seeing it at, ah, the minute, with
28:11
the articles about the meteor shower that's
28:13
active at the minute, where people are
28:14
building it up and blowing it up to a level
28:16
that is not practical and not observable and
28:19
leads to this point. It's not helped by the
28:22
fact that there are people who are making
28:23
careers out of
28:26
discussing how Earth like planets are that
28:28
they didn't discover, that they weren't
28:30
involved with to get themselves clicked and
28:32
to get money. And a lot of the beautiful
28:33
visuals you get cropping up online about
28:36
Earth like planets come from one resource,
28:38
which is called the Planetary Habitability
28:40
Laboratory in Puerto Rico, which has been
28:43
an ongoing source of frustration for me and
28:45
colleagues because there's been storeys that
28:48
people I know have published about planets.
28:49
And then this entity
28:52
puts out their own press release saying,
28:54
we've calculated this magic number and this
28:56
is the most Earth like planet found and it's
28:57
probably got life. And the scientists who
28:59
discovered it have said none of those things.
29:01
Yeah. Um, and all the coverage is, look
29:04
at this beautiful AI generated artwork. Isn't
29:06
this amazing? So I do, and I
29:09
had a fun storey about this a few months ago.
29:11
I had a. An author get in touch with me,
29:13
asking me to proofread a chapter of the book.
29:14
A book, A book that they're doing. And they'd
29:16
got a little bit in there about all the
29:18
potentially Earth like habitable planets that
29:20
have been found out there. And they use that
29:21
as a resource. And I had to back them off on
29:24
it and say, look, it's brilliant to talk
29:25
about this. Please don't use this as a
29:27
resource. If you use their equations,
29:30
Venus would be the most habitable planet
29:32
we've discovered other than the Earth.
29:35
And I certainly wouldn't want to have a
29:37
holiday there.
29:38
Andrew Dunkley: No, no. Um, you'd need. Need 20
29:41
gazillion plus sunscreen
29:44
for starters or something like
29:46
that. Now that'd be Mercury. But, um, it's.
29:49
Yeah, it's.
29:49
Jonti Horner: It's impossible unless it's impossible, you
29:52
know, and we could live among the clouds.
29:54
That'd be a bit different. But yeah, there's
29:56
a lot of stuff around it. And it. We've
29:59
talked before about other things. We talked
30:01
about interstellar comets and the obfuscation
30:03
of science when it comes to those. And
30:04
they're definitely not aliens. And I'll say
30:06
again, they definitely are not aliens. In
30:09
this case, the exo Earth
30:12
fatigue is real. People in the general public
30:15
are convinced that we found planets like the
30:17
Earth already. And I mean, it's great, it
30:19
keeps people interested, but it also
30:21
diminishes the impact when we finally do,
30:24
you know, astronomers will finally find a
30:25
planet that could genuinely be truly Earth.
30:27
Like. We'll then need to do a lot of work to
30:29
characterise it, but you can imagine in 10
30:31
years time, we get data back from a planet
30:34
that shows not only that it could be Earth
30:37
like, but the surface temperature is right,
30:38
and that there is liquid water in the
30:39
atmosphere. And the scientific community will
30:42
be, wow, this is our best discovery ever.
30:44
This is so cool. And nobody'll care because,
30:46
well, you've done it 10 times already. The
30:48
media told me.
30:49
Andrew Dunkley: So, yeah, I think I've found
30:51
it. Um, a potentially habitable
30:54
new planet has been discovered 146 light
30:57
years away. Um, but then it goes.
31:00
It goes on to say, but it might be minus 70
31:02
degrees Celsius, um, but there's a storey
31:05
like that coming out every other week.
31:07
Jonti Horner: Um, and if you want to play that game, our
31:09
definitions of habitability, based very much
31:11
as we talked about in the previous episode,
31:13
on our understanding of where
31:16
Earth life could thrive and in the solar
31:18
system. We've got potentially habitable
31:20
worlds all over the place. Mars is
31:22
potentially habitable on the borderline.
31:24
Depending on what you think about bacteria in
31:26
the atmosphere, Venus could be habitable for
31:27
that type of life. We've got all the icy
31:30
objects with buried subsurface oceans that
31:32
are habitable, but not detectably habitable
31:34
because there's ice in the way. I don't think
31:37
it. It benefits people to overplay
31:40
these discoveries, even though I fully
31:41
understand the reason why people do,
31:45
and I don't think it does anybody a service
31:47
long term. Um, it is the unfortunate
31:50
reality of what it is. But, hey,
31:53
people are interested. Of course, you'll play
31:55
to that in the kind of modern media cycle.
31:57
Nobody remembers the retraction. They all
31:59
remember the discovery. You know, everybody
32:01
remembers cold fusion back from when I was a
32:03
kid and a teenager. Um, that was, of course,
32:06
published in the Journal of Irreproducible
32:07
Results, otherwise known as Nature. Um,
32:10
these things happen.
32:13
Andrew Dunkley: Yeah, they do.
32:14
Um, so, all right, where to next? With
32:17
exoplanets, with, uh, so many
32:20
discovered, um, that that's provided a
32:22
baseline for the probability that every star
32:25
has at least 10 planets around us.
32:29
Jonti Horner: Um, we're finding them in a growing variety
32:31
of ways. It's instructive a little bit to
32:33
look back at history. You know, if I took you
32:35
back to the early 1800s, our telescopes
32:38
had finally got good enough to measure the
32:41
motion of nearby stars against the background
32:43
stars. Um, that allowed us to start measuring
32:45
the distance to nearby stars using
32:47
trigonometric parallax, where you look at a
32:49
star from one side of the Earth's orbit, then
32:50
the other and see it move against the
32:52
background just like your finger moves if you
32:54
look from one eye or the other. That same
32:56
trick at ah, that time people start measuring
32:59
it and they realise that nearby stars also
33:01
moved through space. They were
33:04
undergoing what we now know as proper motion,
33:06
moving against the background stars in a
33:08
straight line, which is their true space
33:10
movement through the galaxy as seen by people
33:13
on Earth. A guy called Friedrich
33:15
Wilhelm Bessel, who was a fabulous astronomer
33:18
in the early 1800s was doing
33:20
observations of Sirius, which is our, uh, one
33:23
of our class's star systems. It's a brightest
33:25
star in the night sky and he found that once
33:28
he took away the parallax Martian, the wobble
33:30
left and right because of the Earth going
33:31
around the sun, that Sirius was wobbling
33:34
as it moved across the night sky. And it
33:35
looked as though it was being pulled around
33:37
by something as massive as the sun, but you
33:39
could see nothing there. There obviously was
33:42
something there pulling it around. It turns
33:44
out that was the indirect discovery of what
33:46
we now know as Sirius B, the white dwarf
33:48
star. It wasn't the first white dwarf to be
33:50
found, but in this case it was discovered
33:53
indirectly. We saw Sirius doing something
33:55
unexpected. We saw it wobbling and we used
33:58
that to infer the presence of the white dwarf
34:00
star around it. And of course we got another
34:03
example of this a little bit later in the
34:05
1800s with the discovery of Neptune, not
34:08
through direct observation, but initially
34:10
through mathematics, through John, um,
34:13
Couch, Adams and Urban, uh, Le
34:15
Verrier, doing calculations of how Uranus
34:18
was moving across the sky, seeing that it was
34:21
moving as though something we couldn't see
34:24
was pulling on it. Predicting where that
34:26
thing will be in Neptune was duly found. So
34:27
they set this heritage of inferring
34:30
the presence of something we cannot see
34:32
because of its effect on something else. And
34:35
that has been foundational to how we find
34:38
planets around other stars. That's
34:40
fundamentally how for more than 99% of
34:42
them we've discovered them. There have been
34:45
slip ups on the way in the 1940s,
34:48
1950s, Edwin Vanderkamp, who's director of
34:50
Spruill Observatory, thought he'd found
34:52
planets around Barnard's Star, which is a
34:54
star with the biggest proper motion in the
34:56
sky. Turned out that he'd actually discovered
34:58
the cleaner because what was happening was
35:00
that his telescope was getting dirty. He used
35:03
a lens telescope, a refracting telescope
35:06
as the front Objective lens got
35:08
Grottier the way in which it meant red light
35:11
compared to blue light changed, causing
35:13
Barnard's star position to shift against the
35:15
background sounds. And when it got cleaned,
35:16
it all went back to normal. He went very sad.
35:19
But he went to his grave in the 70s convinced
35:22
he was a victim of an injustice and he'd
35:23
found planets around Barnassar. We now have
35:26
found planets around Barnard, sir, but
35:27
they're very different to the ones he
35:29
proposed. We also had the fabulous
35:32
Storey just prior to the pulsar planets
35:34
actually being found, the same researchers
35:37
thought they'd found a planet around a
35:38
different pulsar and announced it at a
35:40
conference. And someone went away and said a
35:42
little bit, bit. Something a bit odd about
35:44
this. What had been done was they were
35:46
measuring the timing of the pulsars. So
35:49
pulsars are super, ah, condensed
35:51
neutron stars, leftovers from the explosion
35:54
of star as a supernova, which have a couple
35:56
of magnetic hotspots on their surface. And as
35:58
they spin, they beam radio waves into space
36:00
like lighthouse beams. And when the beam
36:02
sweeps across as we get pulses of radio waves
36:05
like the ticking of a clock.
36:07
Andrew Dunkley: Yep. With this pulse, they're very, they're
36:09
very precise, aren't they?
36:10
Jonti Horner: Yeah, they're viewed as being the most
36:11
accurate clocks in the universe, aside from
36:13
when they have the old glitch or. And I've
36:15
had plenty of watchers that do that in this
36:18
case, uh, he was observing this pulsar and
36:20
sometimes the pulses arrived a little early,
36:22
sometimes they arrived a little there. And
36:23
this was happening periodically, so
36:26
ruled everything else out. There must be
36:28
something causing the distance between the
36:29
pulsar and the solar system to vary
36:31
periodically though, uh, it must be a planet.
36:34
Turned out that after the conference someone
36:36
said, there's something a little bit odd
36:38
here, maybe you should just do a double
36:39
cheque before you publish it. Went away and
36:41
found a single typo in their code that meant
36:43
they didn't properly account for the motion
36:45
of the Earth around the sun. So they had
36:47
discovered a planet, but they discovered that
36:49
the one that they were set on, they
36:50
discovered the Earth. I mean it's a
36:53
fabulous discovery. Now we laugh about this,
36:56
but it shows how hard these observations are.
36:58
Uh, finding planets around other stars is
37:01
incredibly difficult. We've had the
37:02
wherewithal to understand the methods
37:05
that we would use for a couple of hundred
37:07
years, but it was only in the
37:10
90s it really became feasible to do them. And
37:13
in those early days in particular, there were
37:15
two methods that hugely
37:17
dominated. For the first, probably 10
37:20
years, 12 years of the exoplanet area era,
37:23
the main way we found planets was what you
37:25
call the radial velocity technique, the
37:27
wobble technique, which is using the Doppler
37:29
effect. And you see a distance star. And, um,
37:32
we can measure its light and we can break
37:33
that light to its component colours, seeing
37:35
what we call the Fraunhofel lines littered
37:37
across it, which are dark lines that are the
37:39
chemical fingerprint of what the star's made
37:41
of. And, um, we can measure their positions
37:43
in the lab incredibly precisely. And if the
37:45
star's moving towards us, its light gets a
37:47
bit blue shifted and all those lines move a
37:49
little bit to the blue. And if it's moving
37:51
away from us, they move a little bit to the
37:52
red. And if you can monitor it for long
37:54
enough, you can see the star coming backward
37:56
and forward, it's wobbling. You can infer the
37:59
presence of something massive pulling it
38:01
round. You can figure out the, the orbital
38:03
distance of that object by how
38:06
long it takes for the wobble. So it comes
38:08
towards us, goes away, comes towards us again
38:10
as it does one full lap. That gives you the
38:13
orbital period. You can infer the mass based
38:16
on the size of the wobble. But we're only
38:18
measuring that component along our line of
38:19
sight. So you get a minimum mass that it
38:21
could be, and it could be higher than that.
38:23
So we can learn about the orbit. That's the
38:25
radial velocity technique. And that is an
38:27
indirect method. You see the station wobbling
38:29
and infer the presence of a planet or planets
38:31
around it. The technique that's taken over
38:33
from it is the transit technique. That's
38:36
where a planet's going around its star and
38:38
its orbits just lined up right, that every
38:39
time it goes around, it blocks a bit of the
38:41
star's light. The star dims and then
38:43
brightens again periodically. And, um, by
38:45
measuring the periodic dimming, you can infer
38:47
the presence of something blocking the star's
38:49
light. Again, that gives you the orbital
38:51
period, because you get one dip per orbit and
38:54
it gives you the size, the diameter of the
38:56
planet, because a bigger planet will block,
38:57
block more light. But fundamentally, again,
38:59
it's an indirect method. You see a star doing
39:02
something odd and infer the presence of a
39:04
planet. Now, both these methods
39:08
were known and were used for hundreds of
39:10
years. We saw binary
39:12
stars being observed because of the
39:15
dimming during the eclipses. Um, John
39:18
Goodrick, um, a British astronomer who died
39:20
at a very young age, explained Algol. The
39:22
Wink of Kingdom star has been a binary star
39:24
back in the early 1700s. That is effectively
39:27
the same as A transit technique, it's just
39:29
you've got a bigger, uh, blocker. Problem is
39:32
our eyes are only sensitive to variations in
39:34
light at about the 20% level. Smaller
39:37
variations than that, we just don't pick up.
39:38
Your lights can be flickering by 20% and
39:40
you'll barely notice it. For a binary star,
39:43
the brightness can change by a factor of two
39:45
or more. For an exoplanet, Jupiter,
39:48
uh, blocks about 1% of the light from the sun
39:51
on that is just something you cannot see with
39:53
a naked eye. So to be able to use the transit
39:56
technique, we had to wait for detectors that
39:58
were sensitive enough to measure incredibly
40:00
fine variations in brightness to come along,
40:02
which is why we've only been able to use a
40:04
transit technique this millennium. It wasn't
40:07
really possible before that. Similarly, with
40:09
the radial velocity technique, we could
40:12
measure the wobble of stars from binary
40:14
stars for decades. Because the movement of
40:17
the lines were sufficiently big, you could
40:18
measure it on a photographic plate and you
40:20
could measure speeds of kilometres per
40:21
second. Fairly easy.
40:23
Planets like Jupiter going around the sun
40:25
cause wobbles measured in metres per second,
40:28
maybe 10 metres per second. That is, again,
40:31
this such a small wobble that taking photos
40:33
on photographic plates of the spectral lines,
40:36
the resolution isn't good enough. Our
40:38
spectrograph we've got up at Matt Kent in our
40:41
facility, Merv Ross Rallis. Typically, the
40:43
measurements we're making are measurements of
40:45
a thousandth of a pixel shift
40:48
in a given line. And the only way we can do
40:50
that is because you're seeing thousands of
40:52
lines at once and you can work out
40:54
statistically what they're doing. So even
40:56
with the most modern cameras and most modern
40:58
technology, it's still hard. And that's why,
41:00
even though we had the wherewithal to
41:03
understand the physics and, um, to know how
41:05
to do the techniques, 200 years ago,
41:08
we were stuck in a technology gap. We just
41:10
had to wait for the technology to reach the
41:12
right place. And that's why finding the first
41:14
was hard. But once you found one, you'll find
41:16
tech 10, you'll find 100, you'll find a
41:18
thousand. I'd m point people, incidentally,
41:20
to the astonishingly beautiful videos by
41:23
System Sounds, in partnership with NASA, that
41:25
were put out to celebrate the 4 and 5000th
41:28
discovered exoplanets, where they run the
41:31
discoveries over time on a, on a map of the
41:33
sky where the discoveries are marked with a
41:35
little ring. And every planet gets its own
41:38
musical note, where the musical note tells
41:40
you the orbital period of that planet around
41:42
the star. So a high Pitched note like a ding
41:45
will be a planet really close and going
41:46
around really quick and low pitch note like a
41:48
ding that'll be a planet a long, long way
41:51
away going around really slowly. And um, it
41:53
shows you the diversity we found but it also
41:56
shows you this incredibly accelerating
41:59
rate at which we're getting better at doing
42:01
it because now we've crossed that threshold
42:03
where the technology wasn't good enough. And
42:06
now the technology keeps getting better, we
42:08
get better at doing it and the numbers
42:09
continue m to rise. And depending who you
42:11
talk to, there are people who suggest we may
42:13
well actually we'll certainly cross the
42:15
10,000 count by 2030.
42:18
Might not be long after that before we cross
42:20
100,000 mark. That will all depend on Gaia,
42:22
but also the Nancy Grace Roman telescope
42:24
that's due to launch in a few years time.
42:27
Andrew Dunkley: Yeah, it's going to be amazing. Uh,
42:30
and uh, who knows what we will find.
42:33
And we'll talk about uh, a bit more in a
42:35
moment here on Space Nuts.
42:40
Three, two, one.
42:43
Jonti Horner: Space Nuts.
42:44
Andrew Dunkley: And you're with Andrew Dunkley and Professor
42:46
Jonty Horner. We're talking exoplanets on
42:49
this special episode. Uh, it's
42:52
our last segment. So, um, over to you
42:55
Jonty. Where do you, where do you want to go
42:57
to finish off this particularly interesting
42:59
topic?
42:59
Jonti Horner: Well, I think it's also worth flagging out
43:02
the diversity places that are doing this work
43:04
as well. I mean amateur astronomers are
43:05
contributing a huge amount. We're now at the
43:07
point where, where the technology's moved on
43:09
enough that you can observe and measure
43:12
exoplanet transits using a fairly cheap off
43:15
the shelf telescope. Many amateur astronomers
43:17
will occasionally observe the transit of one
43:19
of our bright planets. There was an article
43:21
on Australia's ABC News recently about some
43:23
amateur astronomers who banded together to be
43:25
involved in planet discovery. I'm
43:29
increasingly proud of the facility we've got
43:32
at Uni sq, which is as far as we know, the
43:34
only dedicated Southern Hemisphere exoplanet
43:37
observatory in the Southern Hemisphere.
43:38
There's a lot of facilities looking for them,
43:40
but we've got our own facility at Matt Kent
43:43
Observatory just outside Toowoomba that all
43:46
it does is look for planets and learn more
43:47
about them. It doesn't split its time with
43:49
other tasks. Its job is planet search.
43:52
And it's really important to stress that
43:54
particularly for the younger listeners from
43:56
Australia, there's this perception
43:59
that the only place you can go to do real
44:01
science and to become a scientist is to go to
44:03
the big cities, the big capital cities, to
44:05
the group Fake Universities and for people in
44:08
regional Australia, and particularly people
44:09
from less prestigious
44:12
backgrounds, lower socioeconomic backgrounds,
44:14
all the rest of it, there's this very much
44:16
feeling that it's a big city thing and you've
44:18
got to go to the right schools. But we're at
44:19
a small regional university in regional
44:22
Australia and we're leading the world in
44:24
this. You know, we have two of my colleagues,
44:27
um, Professor George Zhao and Associate
44:29
Professor Chelsea Huang are, uh, between them
44:31
responsible for 30% of all time Australia
44:34
has ever had allocated on the James Webb
44:36
Space Telescope. And, uh, they've sat to
44:39
study planets around other stars. So I do
44:41
want to stress to people listening that this
44:43
is not just something that's done in the US
44:45
or it's not just something that's done at the
44:47
world's top 10 universities. It's something
44:49
that you can participate in yourself. There's
44:51
some fabulous citizen science programmes out
44:53
there and uh, there is going to be an
44:55
increasing extreme wealth
44:58
of data coming out in the coming years that
45:00
uh, astronomers simply won't have enough
45:02
hands to go through. So I'm sure that, that
45:04
if people keep their eyes out, there will be
45:06
other citizen science programmes pop up in
45:08
the coming years. You know, we've got,
45:10
currently I'm looking at the wonderful NASA
45:12
Rexoplanet archive here, looking at the
45:15
different methods planets have been
45:16
discovered by, and we've now got, I think
45:18
it's 11 different methods that have been
45:20
used. Of our
45:22
6283 planets,
45:25
4640 have been found by the
45:28
transit method. That's overwhelmingly the
45:30
most successful now. And that's because you
45:32
can play a numbers game. You can look at
45:33
thousands of stars at once, looking to see if
45:36
any of them wink. And that's what the Kepler
45:38
spacecraft and more recently NASA's test
45:40
spacecraft did. We've got nearly
45:43
1200 planets found with the radial velocity
45:44
method, the wobbled method. Now should be
45:47
said this is a discovery method and a lot of
45:49
these planets have then been studied using
45:51
other methods. But this is how they were
45:52
found. So between those two were, uh, what,
45:55
5800 of the known
45:58
planets, 6200 were found by those.
46:01
That's 90 odd percent of the
46:03
remainder. We, uh, know of 278 planets that
46:06
were found by microlensing. This is where you
46:08
look at very distant stars like the middle of
46:11
the galaxy and look for planets and stars
46:13
that we can't see passing along our line of
46:15
sight and their mass bending light to
46:18
cause that background star to brighten then
46:20
fade. Very small number found so far.
46:23
But the Nancy Grace Roman telescope will
46:25
likely discover thousands, if not tens of
46:28
thousands of microlensing planets in the
46:30
coming years. Because that telescope's going
46:32
to go and stare at the middle of the galaxy,
46:33
among other things, and should be very useful
46:36
at that. We've got nearly a hundred planets
46:39
now discovered by direct imaging,
46:41
and they're really interesting because
46:43
they're the ones where we actually see the
46:44
planet and we find it by seeing the light
46:46
from the planet. So it's amazing that we're
46:48
nearly at 100 there. And my favourite movie
46:51
of all time Time is really the
46:54
movie of the planets orbiting the star HR
46:57
8799, where observations spanning
46:59
more than decade now have been made, where
47:01
you can see four planets around that star and
47:03
watch them move in their orbits. And you
47:06
think from where we were when I was a kid,
47:08
where we didn't even know if there were any
47:10
planets out there, we can now watch some of
47:12
them go around their stars in real time.
47:15
That's just astonishing.
47:17
There's a lot of other really niche methods
47:19
that have been used news, but they're kind of
47:20
the big four, I'd say. And I think the one
47:23
that's going to grow over the coming decade
47:25
more than any other is astrometry. So at the
47:28
minute there is a grand total of six planets
47:30
that have been discovered by astrometry. This
47:32
is measuring the positions of stars in the
47:34
sky and seeing them wobble side to side. It's
47:36
what Bessel did with Sirius to find Sirius B.
47:39
We've only found six so far, but the Gaia,
47:41
uh, spacecraft observed for a long time,
47:44
finished observing, but we're still getting
47:45
new data releases from. From it. Gaia data
47:47
release number four is coming allegedly in
47:50
December this year. Maybe push back a little
47:52
bit, but that's where they will have enough
47:55
quality and analysis of the data and enough
47:58
time period the data covers to start finding
48:00
planets in the Gaia data doing astrometry
48:04
and people are still predicting that could
48:06
yield tens of thousands of planets. Even if
48:08
you're a pessimist, it's easy that Gaia
48:11
could take over from Kepler and TESS as a
48:14
tool that found the most planets. That's just
48:16
in the next year or two. And what we're doing
48:18
then we're finding more, but where we're
48:21
shifting to is not just finding them, but
48:22
learning more about them, characterising
48:25
them. And that's where the future of
48:27
exoplanet science is. It's not just enough
48:29
now to find a planet, we want to learn more
48:31
about it. What's its atmosphere made of?
48:34
What's its internal composition? What's it
48:36
like? That's where we're going. And
48:39
um, we're making great leaps in that we are
48:42
finding out what chemical species are in the
48:44
atmospheres of different planets. Currently
48:45
only really doing it for the very biggest
48:47
ones because of the easiest to observe. But
48:49
that's very much the future. And that's what
48:51
will lead to the search for life elsewhere,
48:53
which I think is what really hooks a lot of
48:55
people into the subject.
48:57
Andrew Dunkley: Yeah, it's fascinating. For the record, the
48:59
first actual photograph of an
49:02
Exoplanet was in
49:03
2004
49:07
Jonti Horner: and
49:08
Andrew Dunkley: it was 2m, um, 1207b.
49:10
Jonti Horner: Yes.
49:11
Andrew Dunkley: Which apparently is an exoplanet, uh,
49:13
orbiting a gas giant.
49:16
Yes. Which is a big, a big one,
49:18
about five times the mass of Jupiter. So, um,
49:21
yeah, so that was the first one ever
49:23
photographed that we actually got to see a
49:25
picture of rather than just identified
49:28
through some.
49:29
Jonti Horner: I mean we're still just seeing them as a
49:30
single pixel. We're not going to be at the
49:33
point of Star Trek type images of the surface
49:35
for a long, long, long time because the
49:37
resolutions are challenged there. But that
49:39
was a breathtaking thing. And it is worth
49:42
noting that the overwhelming majority of the
49:44
direct imaging planets that we've imaged are
49:46
um, massive and um, young. And the thing
49:49
about them being young is they're still
49:50
hotter, which means they glow brighter and
49:52
therefore are easier to see.
49:54
Andrew Dunkley: M okay, um,
49:57
last chance to talk about exoplanets.
50:00
We're going to wrap it up in a sec. Any, any
50:01
final comments?
50:02
Jonti Horner: Well, I think, I think there is so much more
50:05
we could talk about. I mean like every topic
50:07
we get onto, I talk too much. But we could
50:09
fill several hours worth of excitement
50:10
digging into the nitty gritty. But I think
50:13
the thing that leaps out to me probably even
50:14
more than the ubiquity of planets, the fact
50:17
that they're everywhere, is the diversity.
50:19
You know, when I was growing up, we thought
50:22
that there would be other planetary systems,
50:24
but we weren't sure. But we assumed they'd be
50:25
like the solar system, you know, rocky
50:26
planets on the interior, giant planets on the
50:28
outside. Yeah. And the first planets
50:31
discovered shattered that you had planets
50:33
around a pulsar, which makes no sense.
50:36
Um, we think there are probably a second
50:37
generation of planets. The initial planets
50:39
there were destroyed and new ones formed
50:41
after the supernova, but we're not sure. You
50:43
then found a hot Jupiter, a planet the size
50:45
of Jupiter, going around a star like the sun
50:47
every few days and that was enough to
50:49
revolutionise our understanding of how
50:51
planetary systems form. And with every new
50:53
technique and with every new facility and
50:55
with every new way of finding planets, we
50:58
find planets that are more different to the
51:00
solar system than we could ever possibly
51:02
imagine. The lightest, well, not the
51:04
lightest, the fluffiest planets, the lowest
51:06
density planets are so fluffy that they're
51:08
being torn apart by their stars. We mentioned
51:10
them early on. The highest density
51:13
of any planet in the exoplanet catalogue is
51:16
denser than any metal or mineral or anything
51:18
known on Earth by such a large distance. Uh,
51:21
there is speculation that it could be a
51:22
fragment of a white dwarf or something. That
51:24
it could be actually not a lump
51:27
of iron but a lump of white dwarf material or
51:29
something. We just don't know. And everything
51:32
in between. We're finding that the planets in
51:34
our solar system are pretty
51:37
average. We still don't have a handle on
51:40
how common are planets like the Earth. How
51:42
common are planets on, like the Earth? On
51:44
Earth like orbits. We also don't really have
51:47
a handle yet on how common are ah, planets
51:49
like Jupiter and Saturn, in other words
51:50
called Jupiters planets that take a decade
51:53
um, or more to orbit their star because
51:55
finding them hard you need to watch for a
51:56
long time. So we know much more about planets
51:59
close in and planets very different to our
52:01
own than we do about planet planetary systems
52:04
similar to the solar system. So I think one
52:05
of the big questions now is not is the solar
52:08
system unique but rather how
52:11
unusual or usual is the solar system,
52:14
our planetary systems like our one common or
52:17
are we a bit of an exception? We're not
52:19
really in a position to answer um, that yet.
52:21
It seems that the frequency of
52:24
Jupiter like planets around other stars is
52:26
somewhere between 5 and 20%. And by Jupiter
52:29
like, I mean Jupiter mass on a Jupiter like
52:32
orbit around stars like the sun.
52:34
But that's a big variety of,
52:37
you know, possibilities we just don't know
52:39
yet. And so even though we now
52:42
know that planets are everywhere, we've
52:44
barely scratched the surface. And it's the
52:46
kind of thing where if we had this chat again
52:47
in five years time the numbers would be
52:49
different but there would be whole swathes of
52:51
new knowledge then that we can't even predict
52:54
now. There will be things that surprise us
52:56
just as much in the years to come as hot
52:58
Jupiter's and pulsar planets did at the dawn
53:00
of the era. And that's part of the fun.
53:03
Andrew Dunkley: Yeah, and there'll probably be planets we
53:05
can't even imagine that would
53:08
be discovered that we couldn't have even
53:10
contemplated, contemplated existing.
53:14
Um, and I can't even pretend to make one up
53:17
at the moment. But there will be. Of course
53:18
the search, as you mentioned, is for an Earth
53:21
like planet. A planet, a, uh,
53:24
rocky planet in the right place orbiting a
53:26
star like ours, um, that
53:29
basically duplicates Earth. We just haven't
53:31
found one of those yet, have we?
53:33
Jonti Horner: No, no. With a caveat we may
53:36
have done and it have not been picked up.
53:38
There's more to learn about these things.
53:40
Things I still think of the planets
53:43
we've found so far. Venus is more like the
53:45
Earth than anything we've found so far. I
53:48
also think though, that that's even a
53:51
difficult question because what do we mean by
53:52
it being like the Earth? If you went and
53:54
looked at the solar system 4 billion years
53:57
ago, I don't think you'd have considered the
53:59
Earth an Earth like planet. It would have had
54:01
this incredibly thick atmosphere, very
54:03
different to ours, with a very different
54:04
composition. It would have been outside
54:07
the edge of the habitable zone because the
54:09
sun was that much fainter. But it would
54:11
probably still have liquid water on the
54:12
surface because it had such an intense
54:14
greenhouse effect. So there could
54:17
almost be a philosophical question about how
54:18
long would you consider the Earth to have
54:20
been an Earth like planet?
54:22
Andrew Dunkley: That's a really good point. Yeah. And
54:26
the possibility that we have observed planets
54:28
that just, ah, aren't where we are yet
54:30
because of the time differences in,
54:32
in, in the travel, uh, time of our vision.
54:35
So again, it mightn't be there yet
54:38
and it could be billions of years before it
54:40
is and we won't be around to confirm it.
54:42
There's all sorts of weirdisms that go into
54:45
this. My, the bottom line for me is if they
54:48
find one, it's got to have kangaroos on it.
54:49
Otherwise there's just no Earth like planets.
54:51
Jonti Horner: Oh, absolutely. I mean, would be very
54:53
interesting to imagine kangaroos in space. I
54:55
talk a lot about, um, the Dragonfly mission
54:58
going to Titan, and the fact that Titan is
55:00
the only other body we know of with permanent
55:01
liquid water on the surface. Well, not
55:03
permanent liquid water, permanent liquid on
55:05
the surface. The water there is harder than
55:07
granite frozen solid, but it's got liquid
55:09
methane and Ethernet there. But on Titan,
55:12
unlike on Earth, you could fly under your own
55:14
power. If you strapped a pair of wings on.
55:16
The gravity is low enough in the atmosphere,
55:18
dense enough that you could flap around and
55:21
saw. I have never thought about how a
55:23
kangaroo would react if you took it to Titan.
55:26
It would just, uh, launch itself. Just launch
55:28
itself. Um, it Would, of course, need a very,
55:31
very good space suit because it's so cold
55:33
there and kangaroos are not fans of the cold.
55:35
But, yeah, that would be the shock. If
55:37
Dragonfly hops around, flying around on the
55:39
surface of Titan, and then gets attacked by a
55:41
kangaroo when it comes into land. Like, we
55:43
see some of the videos online of kangaroos
55:45
being territorial. That would be the most
55:47
bizarre discovery of life elsewhere that I
55:48
think I could imagine. Kangaroos on Titan.
55:51
Andrew Dunkley: I wait with bated breath. Although kangaroos,
55:53
uh, do have one particular problem in this
55:56
country. They do not know how to get out of
55:58
the way of a car. Even when they do, they go,
56:00
oh, no, no, hang on, I want to get back in
56:02
front of you. Bang. Okay, see ya. Uh,
56:05
anyway, um, that's our problem. I'm sure it's
56:07
the same in other countries without other
56:09
animals and other planets, probably that
56:11
we're unaware of as yet. Uh, Jonty, that's
56:14
been a lot of fun. It's a, it's a fascinating
56:17
topic and it's one that will keep evolving, I
56:19
think is probably, probably the best way to
56:20
describe it. Thank you so much and we'll
56:22
catch you again real soon.
56:23
Jonti Horner: It's a pleasure and I look forward to it.
56:25
Andrew Dunkley: Professor Jonty Horner from the University of
56:28
Southern Queensland. And thanks, uh, to Huw
56:31
in the studio. Couldn't be with us today.
56:32
Made a fatal error. He's back in hospital. He
56:35
ran into an ex. And, uh, he called
56:37
his ex a planet.
56:40
Think about that. It's terrible. And don't
56:42
forget to visit us online if you dare, at
56:44
spacenutspodcast.com or spacenuts
56:47
IO until next time, thanks for your company.
56:49
We'll see you on the very next episode of
56:51
Space Nuts. Bye.
56:53
Jonti Horner: Bye. You've been listening to
56:55
the Space Nuts podcast,
56:58
available at Apple Podcasts, Spotify,
57:02
iHeartRadio or your favourite podcast
57:04
player. You can also stream on
57:06
demand@bytes.com.
57:08
Andrew Dunkley: this has been another quality podcast
57:10
production from bytes.com.
57:12
Jonti Horner: um,