Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / Sunlight Satellites, Near-Earth Asteroids & the 6,000th Exoplanet Revelation

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Sunlight Satellites, Near-Earth Asteroids & the 6,000th Exoplanet Revelation · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:00
Andrew Dunkley: Hi there. Thanks for joining us on another
0:02
edition of Space Nuts, where we talk
0:04
astronomy and space science. My name is
0:06
Andrew Dunkley, your host. It's good to have
0:08
your company as always. Today,
0:11
we're going to start off with something quite
0:12
controversial. And in some
0:15
parts of the world they probably call this
0:17
dumb. But, a proposal to create
0:20
a sunlight service. Yes. Using
0:23
mirrors in orbit. It's a thing.
0:25
also a near miss for Earth involving asteroid
0:28
20, 2025 TF, the
0:30
6,000th exoplanet has
0:33
been discovered. And another potential
0:36
subsurface ocean, this one
0:39
involving the moon Mimas. That's all coming
0:41
up on this edition of Space Nuts.
0:43
Jonti Horner: 15 seconds. Guidance is internal.
0:46
10, 9. Ignition
0:49
sequence. Star. Space Nuts. 5, 4,
0:52
3. 2. 1. 2, 3, 4, 5, 5, 4,
0:55
3, 2, 1. Space Nuts astronauts,
0:57
report.
0:58
Andrew Dunkley: It feels good.
1:00
And joining us, in the stead of Fred
1:03
Watson, we are, joined by Jonti Horner,
1:05
professor of astrophysics at the University
1:06
of Southern Queensland. Hello again, Jonti.
1:10
Jonti Horner: good morning. How are you going?
1:11
Andrew Dunkley: I am well. And we should, just put a
1:14
caveat to this episode. There might be noise
1:16
because you're getting work done at the
1:17
house.
1:18
Jonti Horner: Yes. And of course we organized to record at
1:21
this time prior to the trade is getting in
1:22
touch and saying, you know what, we'll be
1:23
there at 7am on Monday morning. It's like
1:25
great, you know, want this done. Hopefully
1:28
the wonders of the microphone will filter it
1:31
all out. But given that some of the banging I
1:33
can feel through my feet, I suspect the
1:35
vibrations might go all the way through the
1:37
desk and all the way up the microphone and
1:38
we'll occasionally get bang, bang, bang,
1:40
drill, drill, drill. So, yeah, I know.
1:42
Consider it like we've got a craft work gig
1:44
going on or something like that.
1:46
Andrew Dunkley: Well, I can tell you we've, we've heard worse
1:48
from Fred's house. So, yeah, it should, it
1:50
shouldn't sound out of the ordinary, to be
1:52
honest.
1:53
All right, let's get, stuck into these
1:56
stories because we've got a lot to talk
1:58
about. This first one, I know you sent me
2:00
the, information initially that came from, I
2:03
believe, one of your students who's overseas.
2:05
But this is, an idea of a Californian company
2:08
who is applying to the federal,
2:11
communications commission in the United
2:13
States, the fcc, for permission to launch a
2:15
satellite into space to reflect
2:18
sunlight back down on Earth and
2:21
charge people for the privilege.
2:24
Jonti Horner: Yeah. Now I try very hard to be
2:27
even handed and to not be too critical even
2:30
when I'm talking About the people who shall
2:32
not be named. You know, the ones who are
2:34
putting up, Starlink satellites and abusing
2:37
colleagues of mine, or people who are
2:39
claiming that things that are not aliens are
2:41
aliens in order to sell books. You know, I
2:43
try and be even handed and it's very
2:46
hard to talk about this one without getting a
2:48
bit caustic. it reminds me
2:51
of the late, great Terry Pratchett, who,
2:54
in one of the books was talking about a
2:55
certain subset of the landed gentry.
2:58
You know, there's, political things going on
3:01
and this is a time when the city's under
3:03
siege and they're reforming the regiments and
3:06
things like this. And it's talking about the
3:08
boys who were dropped on their heads as
3:10
babies, as this kind of subset of,
3:13
you know, nice but dim gentry. Yeah, they're
3:15
nice, but they're not all there. And this,
3:18
to me, seems like an idea that was dropped on
3:20
its head as a baby. It's so
3:24
overwhelmingly dumb that you think it must be
3:27
April 1st and it isn't. So the idea
3:30
that this company called Reflector Orbital
3:31
have. And it's an idea that has
3:34
led to them getting tens of millions of
3:36
dollars of funding. So it's not like,
3:39
yeah, this is. It's
3:42
not like these are people in the pub saying,
3:44
we've had a few. You know what'd be funny?
3:46
This is a company taking it seriously.
3:48
They're getting interns in, they've got a
3:50
very active social media presence and their
3:53
whole business is. Isn't it sad that it's
3:55
dark at nighttime? Wouldn't it be great if
3:58
you could pay somebody and get sunshine
4:00
delivered to you at night? And that could
4:02
power your solar panels or it could help you
4:04
grow your crops or, you know, help you
4:06
illuminate your sporting event or your
4:08
concert. And the idea that
4:11
they've got is that they will launch
4:12
satellites into low Earth orbit, maybe 400
4:15
kilometers up, that will go around the Earth
4:17
every 90 minutes. So they're going to be
4:19
fleetingly above any given location, above
4:21
the horizon for a few minutes. And if you
4:24
send them a few of your dollary dues, they
4:26
will make their satellite reflect light down
4:29
to your location and deliver
4:32
sunlight to you. Now, there's all sorts of
4:34
problems with this. Firstly, you know, I
4:36
live, in Toowoomba. I'm 27 degrees south and
4:39
I can see satellites that are about 400 km up
4:42
in about the first hour after sunset, the
4:44
first hour before sunrise, the rest of the
4:46
night, those satellites are in shadow too. So
4:49
there isn't any sun to reflect. Oh.
4:51
Andrew Dunkley: So, you know, fair point.
4:53
Jonti Horner: Nobody seems to be really mentioning that in
4:55
the narrative of how this will work. But even
4:57
ignoring that, think about the International
4:59
Space Station going overhead. And you can get
5:01
predictions of this from wonderful websites
5:03
like heavensabove.com and the space
5:06
station becomes visible,
5:09
passes over, and then goes into the shadow.
5:11
And you might get five, six minutes of it
5:13
going overhead, if you're lucky. Yeah. And
5:16
then it's gone. So you have this idea that
5:18
these mirrors, that they're going to launch
5:20
at about that altitude, and
5:23
if you want them to illuminate a single point
5:25
on the ground, they've got to be turning. So
5:27
they keep rotating the light to that point as
5:29
they pass overhead. Mm. When they're
5:32
passed overhead, what do they do? They can't
5:34
just turn off the mirror. So is that
5:37
suggesting that you're gonna have a beam of
5:39
light sweeping across the countryside at
5:41
orbital speed? Like when you're trying
5:44
to entertain a cat and you're shining a laser
5:46
pointer on the floor and the cat's chasing
5:47
it, you've got a beam going across the Earth.
5:49
yeah. Going across the skies of all these
5:51
people who didn't pay for the service. Not
5:54
just that, how do you get enough sunlight
5:56
down to be functional? So
5:59
these satellites are going to be small enough
6:01
to launch. So you're talking about a mirror a
6:03
few meters across, 400 kilometers away,
6:06
trying to reflect sunlight down, and they,
6:08
they talk about how the diameter of the
6:11
beam will be about 5km across.
6:15
So that means if I pay for them to deliver
6:17
light to my backyard, anybody in a five
6:19
kilometer diameter area around me also get
6:22
illuminated as well, for free, whether they
6:24
want to or not.
6:25
Andrew Dunkley: Yeah, but not just that.
6:27
Jonti Horner: The light's not going to be that bright,
6:28
because if you've got a 1 meter sized mirror
6:31
reflecting sunlight, and then you spread that
6:33
light over an area that is 5km in diameter,
6:36
you're spreading that light awfully thin. So
6:38
any area on the ground there is not going to
6:41
see broad daylight. They're going to see
6:43
something that is comparable in brightness or
6:45
a few times brighter than the full moon,
6:48
which is. Okay, that's enough light for you
6:50
to go out and do something in the backyard
6:52
by. But it's not particularly enough light to
6:54
get really effective solar power from. So if
6:57
you want to make this effective, you're going
6:59
to have to launch hundreds of thousands
7:02
of these mirrors, all to work in
7:04
concert to beam towards a given location,
7:07
which doesn't sound that feasible. Add to
7:10
that the fact that these are Big floating
7:12
targets in space that space debris can hit
7:14
and smash, which means that a, you could
7:17
get all this debris scattered off in all
7:19
sorts of different directions, but also that
7:22
it's going to be hard for them to control the
7:23
direction the mirror's pointing. So you've
7:26
got all sorts of problems here. I mean, I
7:28
think there's growing and
7:30
demonstrated evidence, and Fred's talked
7:32
about this to death, about all the negative
7:34
effects artificial light at night has. We've
7:37
got effects on people. You've got increased
7:39
cancer rates, a very bizarre but
7:42
very significant link between light at night
7:44
and an increased risk of breast cancer for
7:46
women. Believe it or not, just as one
7:48
example, you've got the impact in our
7:50
circadian rhythms, the fact that we need it
7:53
to be dark to sleep, then you've got all
7:56
the impact on flora and fauna. Now, I've
7:58
visited some wonderful places on the coast of
8:00
Queensland to do outreach sessions, you know,
8:03
some kind of night sky observing. And a lot
8:05
of these places are places where turtles
8:07
nest. In fact, I'm going next weekend to the
8:10
wonderful Lady Elliot island on the reef to
8:12
do some outreach. And I go there several
8:13
times a year. And all of their resort is
8:16
designed to keep light down and pointed at
8:19
the ground and have lights that get turned
8:20
off because baby turtles, when they hatch,
8:24
they navigate to the ocean by looking at the
8:26
very faint light on the horizon, light
8:28
reflecting off the ocean. And, that's what
8:30
sets their internal compass as they start
8:32
their lives. And if you have stray light,
8:35
they go the wrong way and they end up under
8:37
the buildings and on the road and things like
8:39
this. Yeah, so there's huge impacts on life.
8:42
But I think the biggest concern about this is
8:45
the safety aspect. You know, you're driving
8:47
around and I know here in regional Australia,
8:49
most of our roads don't have street lights
8:51
and that's perfectly fine. It's safer. As
8:53
such, you drive along with your full beam on
8:55
and any kangaroo that you see, you've got
8:57
room to do something about it. So you're
8:59
driving along on this pitch black road and,
9:01
suddenly from nowhere, something brighter
9:03
than the full moon shines full head on in
9:05
your view. You're dazzled. That's
9:07
hugely dangerous. Odd enough, if you're
9:09
driving on the ground, if you're a pilot
9:11
coming in to land, and suddenly somebody's
9:13
trying to spotlight in your face, that's not
9:16
going to be a particularly pleasant outcome
9:19
for you and the passengers in your plane. And
9:22
so there's all these issues there that
9:24
any one of them will be enough for you to
9:26
say, this is a really foolish idea. It
9:29
is not something that is likely to work
9:32
anyway, but it's a really foolish
9:34
idea from the ground up. It's only going to
9:36
work near twilight. You're going to have to
9:38
launch thousands of satellites to make it
9:40
work, but it isn't stopping people funding
9:43
them. And, this company, like I say, has
9:45
applied to the FCC in the US for
9:47
permission to launch the first of these
9:49
satellites, which they've named Earundel 1
9:51
after the light from Lord of the Rings.
9:54
Earundel 1. They're hoping to launch April,
9:57
May time next year, 2026, to
10:00
demonstrate that their wonderful great idea
10:02
can work. And it's just yet another example
10:05
of this kind of Wild west scenario we've got
10:08
with the use of space around the Earth, where
10:10
the use of space is really outstripping our
10:13
ability to regulate and control that use.
10:15
And, people are doing things because it
10:17
seemed like a good idea at the time without
10:18
any real thought about the practicality of
10:21
it, whether it could work. And, normally you
10:23
just think like, say you think this is an
10:25
April Fool's Day kind of prank. But the
10:28
fact that this company has raised tens of
10:30
millions of dollars in kind of venture
10:31
capital, it's supported by A M
10:33
multibillionaire, is really, really
10:36
concerning. And that's why a group of
10:38
astronomers, including Jessica Heim, who's
10:40
doing a PhD with me at UNISQ, have put
10:43
out this fact sheet with lots of information,
10:46
loads of links, number of astronomers in the
10:48
US who people in the media can contact for
10:50
more information and suggestions about what
10:53
people can do to flag up how catastrophically
10:56
dumb this is. And that includes submit
10:58
comments on the application to the Federal
11:00
Communications Commission in the US to demand
11:03
an environmental review of reflected light
11:05
from orbit. Contact government
11:07
representatives, particularly in the US but
11:09
also locally where you live, to try and raise
11:11
noise about this, but also tell people about
11:14
it and point out how dumb it is. Because I
11:16
can understand that if you don't really think
11:18
about this too much, you can think, yeah,
11:20
there are times it'd be really nice to have a
11:22
bit of extra light at night.
11:24
I didn't get round to doing the gardening.
11:25
It'd be good to mow the lawn tonight.
11:27
Wouldn't it be great if I could just turn on
11:28
the spotlight and have half an hour of my
11:30
backyard being daily, at night for me to
11:33
do that job? And you need to talk about it
11:36
and you need to think about it to see why
11:38
this is just so catastrophically
11:41
dumb. In so, so many ways that you
11:44
would have thought it'd be an unstarter, but
11:45
yet they're getting money.
11:48
Andrew Dunkley: I can't see or understand
11:51
any logic in this. And,
11:55
the way in low Earth orbit, as you said,
11:57
there's only going to be a few minutes of
11:58
light. It's not like they can light a stadium
12:01
for four hours straight. Not yet, any. But,
12:04
even if they could, that's going to take a
12:06
lot of hardware up in space. And there's more
12:08
light pollution on Earth.
12:10
Jonti Horner: Which is a big problem.
12:11
Andrew Dunkley: Fred and Marnie are so heavily involved in
12:14
the Dark Skies project. This would just blow
12:16
that out of the water.
12:17
Jonti Horner: Well, it would. And I mean, to light that
12:19
stadium for four hours, you would need
12:21
mirrors going overhead continuously in a
12:24
parade. You'd need that stadium to be near
12:27
enough to the pole on it to be summertime
12:29
that those satellites were always in sunlight
12:32
or you'd need to put them further from the
12:34
Earth. The further you move them from the
12:36
Earth, the more spread out the light will be,
12:38
and so therefore the more satellites you'll
12:40
need, you know. And if you get
12:43
to that stage, if you've got that many
12:45
satellites in orbit around the Earth, you may
12:47
as well build a mirror that
12:50
is held in geostationary orbit that covers
12:52
half of the size of the Earth, and bears the
12:55
entirety of that side of the Earth in
12:57
sunlight. And, you know, while you're at it,
12:59
you're increasing the amount of heat coming
13:00
to the Earth and we'll just speed up global
13:01
warming and kill everybody.
13:04
Andrew Dunkley: Yeah, there is a groundswell of discontent,
13:07
as you mentioned. So people are starting to
13:09
make some noise about this. I hope the fcc,
13:14
you know, looks at both sides of the story.
13:16
how, just quickly, how likely are they
13:19
to get their license and start testing
13:22
this?
13:23
Jonti Horner: I mean, a pessimist would say it's almost
13:25
certain to happen because, you know, the FCC
13:27
are quite happy for sailing to be putting up
13:29
the number of satellites. They are looking at
13:31
42,000 long term. So it
13:34
doesn't seem like there's much thought of
13:36
that. And there's the added concern. I think
13:39
one of the things that is hindering
13:40
legislation is the fact that you can launch
13:42
the space from many, many countries. And so
13:45
companies can quite rightly say to, a given
13:47
legislating body, if you don't give us this,
13:50
we'll just take our business elsewhere and
13:52
someone else will. And, you know, once you're
13:54
launched from a given country, you're above
13:57
all of the countries of the world as you move
13:59
over them in your orbit. So it isn't like
14:01
this thing is just going to affect people in
14:03
the U.S. because it's been launched from the
14:05
U.S. it's going to be going around the Earth,
14:07
like say, running a five kilometer size beam
14:09
of light across the surface of the earth,
14:12
every 90 minutes as it goes round and round
14:14
and round and round.
14:16
Andrew Dunkley: It just doesn't, doesn't make much sense
14:18
really. It sounds like pie in the sky. But,
14:21
yeah, they're actually seriously considering
14:24
doing this. And yeah, hopefully
14:27
common sense will prevail, but, time will
14:29
tell, I suppose we'll know next year whether
14:31
or not they start testing these things.
14:34
I know they did do this some years ago
14:37
with a mirror array up in space and they,
14:40
they lit up a spot on Siberia or something.
14:44
yeah, I don't know why they did that then. I
14:46
can't remember. But, it was, somewhat
14:49
successful, although quite dim. But, This,
14:51
this just. Yeah, I mean, I don't know where
14:54
it stops. there seems to be this,
14:57
this constant tug of war between what
15:00
we need up there and what we don't need up
15:03
there. And the. Yeah,
15:06
it's swinging the wrong way at the moment, I
15:07
suppose, would be the way to describe it.
15:10
But, I dare say this will get a lot more
15:12
press and a lot more pushback and maybe the
15:15
fcc, will look at the
15:18
problems associated with this.
15:20
Jonti Horner: Really hope so. I mean, it reminds me, and
15:22
I'm probably paraphrasing terribly, but
15:23
there's a famous science fiction quote,
15:25
something along the lines of, you know, they
15:27
spent so much time and effort trying to show
15:29
that they could, that they never put any
15:30
thought into whether they should. It feels
15:32
like all of those.
15:34
Andrew Dunkley: Yes, yes, indeed. All right. yeah, it's
15:36
a project, you might find online. It's only
15:39
just sort of starting to emerge. I don't know
15:41
how much press it's got yet, but, it will
15:43
grow. Because it's one of those stories that,
15:47
is also fascinating and they're the ones that
15:49
generally get a lot of attention.
15:51
Jonti Horner: Looking at the website, the company seems to
15:53
have been around for quite a while and I
15:54
think it's probably getting attention now
15:56
because previously everybody thought, well,
15:59
no, this will never fly. This is clearly not
16:02
something we should be worried about. And now
16:04
it's very clear that actually it is, because
16:06
they're in for licenses and they've got a lot
16:09
of money invested.
16:10
Andrew Dunkley: Yeah.
16:10
Jonti Horner: Yeah.
16:11
Andrew Dunkley: And one wonders who's really going to pay
16:13
them to shed a little light on their
16:16
whatever. I mean, what would you use it for?
16:18
Solar panels. You said they won't work.
16:21
Football, matches. Well, we've got lights for
16:23
that. I don't know. I don't know.
16:25
Jonti Horner: We can do a bit of quick mental arithmetic to
16:27
cheer everybody up. I mean, the brightness of
16:29
the full moon to first order very roughly, is
16:31
about magnitude -12 in the wonderful
16:34
complex magnitude system astronomers are so
16:36
fond of. The brightness of the noonday sun's
16:39
about magnitude -27. So that's a 15
16:42
magnitude difference. Now, that magnitude
16:44
system is a logarithmic scale.
16:47
So every five magnitudes you're brighter off
16:49
enter than something is equivalent to a
16:52
factor of 100 influx. So if you're
16:54
15 magnitudes, that's three lots of 100. So
16:57
100 times 100 times 100, that's 100
17:00
becomes 10,000 becomes a million.
17:03
So if the light from this thing is about the
17:06
brightness of the full moon, it's a million
17:08
times fainter than the sun is.
17:11
So if you've got your solar panels that are
17:13
generating in full sunlight, you know, a few
17:16
hundred watts of power, right. they're
17:19
generating a few hundred watts. Divide that
17:22
by a million and you're not
17:24
generating enough to register. Yeah,
17:27
yeah.
17:28
Andrew Dunkley: It would be like putting up a solar panel to
17:30
power a light and using that light to
17:33
generate the power to power that light.
17:35
Jonti Horner: It's just absolutely. Or just holding a
17:37
match, a lit match near your solar panels and
17:40
expecting it to run your entire house. Yeah,
17:42
yeah.
17:43
Andrew Dunkley: Ah, it's crazy stuff. All right, yeah, keep
17:45
an eye out for that story and if you feel
17:47
strongly enough about it, maybe, get
17:49
involved.
17:50
let's move on to our next story. this
17:52
involves a near miss for Earth with asteroid,
17:55
2025 TF just skimming us,
17:58
and we didn't see it till it was too late,
18:01
technically speaking. And, it kind of
18:04
dovetails into the previous story because if
18:07
there's going to be more light up there, it's
18:09
going to make us harder, make things harder
18:11
for us in terms of, you know, getting these
18:13
ready alerts for potential objects that could
18:16
strike Earth. this one wasn't huge,
18:19
but, yeah, it was, it was there
18:21
and it was a detectable object and we didn't
18:24
see it.
18:24
Jonti Horner: Yes. And that's the issue. Now, this
18:27
thing, you know, quite happy to say, straight
18:30
up the size of this thing is such that it
18:32
would have put on a nice light show as it,
18:34
you know, was quite harmlessly destroyed in
18:37
the atmosphere. It was probably about 1 to 3
18:39
meters across.
18:40
Andrew Dunkley: Yeah.
18:40
Jonti Horner: But of the things that have not entered the
18:42
Earth's atmosphere, but have come close, this
18:45
is the second closest on record. Now,
18:48
back in. I'm trying to remember exactly when
18:50
the great daylight fireball was. But in the
18:52
early 1970s, there was a fireball
18:56
observed widely over, North America, which
18:58
was what we call an earth grazing object, and
19:01
it actually hit the atmosphere and skimmed
19:02
back out. That is not counted when people
19:05
talk about these two closest encounters that
19:07
didn't hit Earth because technically that did
19:09
hit the atmosphere. The fact that it skipped
19:11
back out again is beside the point.
19:14
And that was a daylight fireball. It created
19:16
sonic booms over a couple of the US States
19:18
and was really the first kind of fireball
19:20
event that was widely captured because it was
19:22
early in the era of modern holiday
19:25
snaps. And this was a time when people were
19:27
taking photos on holiday, then boring their
19:29
friends when they came home.
19:30
Andrew Dunkley: Yeah, yeah, 1972 it was.
19:32
Jonti Horner: That's the one. Yeah, I thought it was. It
19:34
was, probably something smaller than a house
19:37
that came within about 57 km
19:39
of the surface of the Earth. And put that in
19:42
perspective, that's like, you know, the old
19:44
William Tell thing of shooting an apple off
19:45
somebody's head. That's like shooting the
19:47
arrow at the apple and touching the skin of
19:49
the apple without breaking it. It's coming
19:52
within less than 1% of the diameter of the
19:54
Earth of actually hitting our planet. This
19:56
one wasn't quite that close. But it's an
19:59
object that was discovered by the Catalina
20:02
Sky Survey a few hours after
20:04
its closest approach to the Earth,
20:07
basically whizzed over Antarctica. So I think
20:10
it's one of those that even if it had hit the
20:12
atmosphere and burned up, very few people
20:13
would have seen it, but a lot of penguins
20:15
would have been impressed. at
20:18
its closest, it was 428km above the
20:21
Earth's surface. So that's slightly closer
20:23
than reflector orbital. Want to put their
20:25
mirrors. so if it had come through a few
20:28
years later, we could have hoped it would
20:29
have knocked a few of them out of the way.
20:30
But it's a really close approach.
20:33
And, yes, it's an object that in this case
20:36
wouldn't have been big enough to cause any
20:37
damage, wouldn't have had any impacts felt at
20:40
ground level. It may have, if it was made of
20:43
the right stuff, dropped a few little bits of
20:45
meteorite on the surface, but that's about
20:47
it. But it's a reminder,
20:50
of the fact that as we're looking for things
20:52
that come close enough to the Earth, to pose
20:54
a threat. We haven't found them all yet.
20:57
Now probably about 75% of the threat
20:59
to the Earth, from impacts comes from the
21:01
near Earth asteroids. And they're objects at
21:03
the bottom of the asteroid belt, typically
21:06
rocky or metallic objects moving on orbits at
21:09
a relatively short period in the inner solar
21:11
system. And they're short lived. You know, if
21:12
you come back in a million years, most of the
21:14
ones we currently know will have been
21:16
removed. They'll have been ejected from the
21:18
solar system or collided with a planet or
21:20
fallen apart or fallen into the sun. But
21:22
they're continually being repopulated from
21:24
the asteroid belt. Some of them hide
21:27
closer to the sun than we are and then pop
21:28
out to say hello. We were talking about that
21:30
last week with the objects near Venus.
21:33
But there's this effort to try and find all
21:35
of them. And the earlier you can find them,
21:38
and the earlier you can figure out if there's
21:41
going to be an encounter with the Earth that
21:43
poses a threat, the better the odds of you
21:45
doing something about it. And we saw this
21:48
kind of a bright light shone on this back at
21:50
the start of 2025 with the object
21:53
2024 yr 4. I think the name M was
21:56
that for a while we thought had a
21:58
substantial possibility of hitting the Earth
22:00
in 2032 that we now know is not going to
22:03
hit the Earth, but might hit the moon in
22:04
2032. And that was a big success because we
22:07
found it early enough to get a lot of data.
22:08
and over the course of about a month
22:10
astronomers observed it repeatedly until
22:12
eventually we showed that it definitely
22:14
wasn't going to hit the Earth in eight year
22:16
time. And everybody kind of basically jumped
22:18
up and down and said hooray. And there was
22:19
much rejoicing. So that's like the ideal
22:22
scenario. We find something when it passes
22:24
relatively nearby on one apparition a
22:27
few years before it would realistically pose
22:29
a threat. And that's what we want to achieve.
22:32
And the stated goal of a lot of the agencies
22:35
looking for these things is to find all the
22:36
objects bigger than about 100 meters across
22:39
that could pose a threat to the Earth, and
22:41
catalog them. And we haven't managed
22:44
that yet. We even more haven't managed that
22:46
when you take into account things like
22:48
comets. You know we were talking about, about
22:50
Comet Swan last week, which appeared from
22:53
hiding behind the sun and came and was
22:55
suddenly the brightest comet in the sky.
22:57
Comets are coming in on orbits that take
22:59
hundreds, thousands, sometimes even tens of
23:01
thousands or millions of years to complete.
23:03
So even if we find all the near Earth
23:05
asteroids, we're still going to have comets
23:07
coming in. So we'll have to stay vigilant and
23:09
keep watching forevermore. But this
23:12
is a really good reminder that despite how
23:14
you feel, we're not there yet. We are still
23:17
in a position where these things are
23:20
catching us by surprise. And the worst case
23:22
scenario is what happened in 2013 with the
23:24
Chelyabinsk impactor to a similar
23:27
level of what happened with comets 1 earlier
23:29
this year in that as, ah, the object
23:31
approaches the Earth and eventually gets
23:32
close enough that it was visible in the
23:34
nighttime sky, would be able to detect it.
23:37
It's coming from the sunward side of the
23:38
Earth, so it's hidden in the glare of
23:40
daylight. And so that's why you
23:43
don't want to try and detect something the
23:45
moment it's on an approach to hit you. You
23:47
want to find it well in advance. And with
23:49
Charlie Abinsky, it demonstrated something
23:51
big enough to injure people, damage a city
23:54
we didn't find until it was in the
23:55
atmosphere. And it was kind of too late. It
23:58
was seconds from disaster.
23:59
Andrew Dunkley: Indeed.
24:00
Jonti Horner: Now there's hope. We've got Vera Rubin
24:03
coming online. We saw a beautiful picture
24:05
from that earlier this year. Vera Rubin's
24:07
going to start getting data regularly,
24:09
continuously later this year, early next
24:12
year, that's when the Mayan mission starts.
24:14
And Vera Rubin is going to be an exceptional
24:16
thing finding tool no matter what. The thing
24:18
is, it will find more of them than anybody's
24:20
found before. From a solar system point of
24:23
view. We're really excited because it will
24:25
increase the number of objects we know by a
24:27
factor of several to an order of magnitude
24:29
within a year or two. And it'll be great at
24:31
finding these things, but it'll be less
24:34
great than it would have been thanks to all
24:36
the stuff we keep watching.
24:37
Then this is where it ties into the previous
24:39
story. Also ties in again to the wonderful
24:42
student who sent me the information about the
24:44
reflector orbital stuff. Jessica Heim
24:47
is finishing up her PhD with us at UNESCO.
24:50
She's based in North America and she's
24:53
done a lot of her work about light pollution
24:55
and artificial, light at night and things
24:58
like this. And one of her papers early in a
25:00
PhD that she was a co author on was in
25:03
Nature Astronomy. And they actually did a
25:05
study looking at just the starlink satellites
25:08
that were in orbit at that time, so not the
25:09
predicted number in the future, and tried to
25:12
quantify how much harder they would make
25:15
life for Vera Rubin, and particularly how
25:17
much harder they make it for Vera Rubin to
25:19
find objects like the one we're just talking
25:20
about that was over Antarctica.
25:23
And what they found was the Starlink
25:26
satellites that were in orbit at the time. So
25:28
not the constellation we have now, which is
25:30
big and not the final constellation would
25:32
make it 10% harder for Vera Rubin to do its
25:35
job. So in other words, it would have to
25:36
observe for 10% longer. Roughly. I think the
25:38
number was actually slightly higher than that
25:41
in order to achieve the same results. Now
25:43
when you're talking about a facility that's a
25:44
billion dollar level facility, hundreds of
25:47
millions of dollars to build, having to take
25:50
10% longer to do something is a cost measured
25:52
in tens of millions of dollars. Yeah, that's
25:55
real impact in this. And what it means is
25:57
that things like this are going to be harder
25:59
to find. And our ability to
26:02
detect potential threats is really
26:04
kind of confused and obfuscated by the
26:07
stuff we're putting to hang around in the
26:09
foreground. It's like, I guess it's really
26:12
easy to see a road sign on a clear day, but
26:14
when it's foggy, it's a lot harder to spot it
26:16
until you're right on that side.
26:17
Andrew Dunkley: Yeah, yeah, indeed. And
26:20
if you want to read up on that story, about
26:23
the near miss, you can do so@space
26:25
space.com. this is Space Nuts with Andrew
26:28
Dunkley and John T. Horner.
26:31
Jonti Horner: Three, two, one.
26:34
Andrew Dunkley: Space nuts.
26:35
Now, Johnny, we have found the
26:38
6,000th exoplanet.
26:41
It took us 30 years, which is,
26:44
you know, if you, if you look back at when we
26:46
found the first one, it was quite a surprise
26:49
for a bunch of reasons. mostly because
26:51
we didn't even know they could have existed
26:54
beyond our solar system. Logic suggests, you
26:56
know, if it's. We've got planets around our
26:58
sun, other stars must have planets too.
27:02
And 30 years ago, that was proven. Well, now
27:05
we're up to number 6,000. When are we going
27:07
to stop counting? Because it's going to reach
27:09
a point where we're going to find millions
27:11
upon millions of these things, isn't it?
27:13
Jonti Horner: It is. And even the counting's a little bit
27:15
confused because the resource I
27:18
trust as kind of being the authoritative word
27:20
on this is the NASA exoplanet archive, which
27:23
is a wonderful resource. And they've got a
27:25
certain threshold for what they consider a
27:28
confirmed planet. And we've got all these
27:30
candidate planets as well, of which there are
27:32
thousands more where we're fairly Confident
27:34
there's a planet there, but it doesn't meet
27:36
that rigorous criterion. There is a
27:39
different exoplanet catalog run out of Europe
27:41
that has a number higher because they are
27:43
less strict on their criterion for
27:46
confirmation. part of the reason I'm more
27:48
skeptical about that catalog is that there's
27:50
a number of planetary systems I've helped to
27:52
kill and they've left them in their catalog.
27:55
So we know for a fact those planets aren't
27:56
there. I did some of that work and they still
27:58
include them in their catalog, which puts
28:00
them m on my naughty list. So I prefer the
28:02
NASA one and the NASA one is the more
28:05
cautious of them. It's really
28:07
interesting how this has come though. You
28:09
know, I'm, I'm 47 now. I don't feel it, but
28:11
I'm getting on a little bit. I was a kid who
28:14
was mad about astronomy. You know, like some
28:16
of the people who send in their questions,
28:17
some of the youngsters who send in questions.
28:19
And when I was growing up, one of the
28:21
questions I'd have been asking is do you
28:22
think there are planets around other stars?
28:24
We'd had observations from satellites like
28:27
IRAS in the 1980s that indicated there was
28:30
dust and debris around some stars. But at
28:33
the time our models of planet formation fell
28:36
into kind of two camps. So whereas what's now
28:38
become kind of the standard baseline with
28:40
some tweaks, which was that you get a disc of
28:42
material around every young star and planets
28:45
forming it. So most stars will have planets.
28:47
But there was a competing theory that said
28:50
that the planets were formed by a very close
28:52
encounter between the sun and a passing star
28:54
that pulled material out of the sun like a
28:57
tongue of material, and the planets formed
28:59
from that. and there are people who were
29:02
very strong advocates of that. Now
29:04
the test of those theories
29:08
it would have been, are, ah, there planets
29:10
around other stars, Are they common? Because
29:11
the idea that two stars get close enough
29:13
together to have this tidal interaction pull
29:16
out a ton of material and planets form from
29:18
that would suggest that planets would be
29:20
overwhelmingly rare in the cosmos. So
29:22
likelihood of 2 stars getting that close
29:24
together and having exactly the right
29:25
conditions would mean that planets were
29:28
pretty much non existent, that they were a
29:31
fluke of nature. The other model
29:34
suggested that planets are common. And so one
29:36
of the goals in the early 1990s with the
29:39
search for planets elsewhere was to see
29:41
whether there were any at all. And we just
29:43
didn't know. The discovery of
29:46
three planets around a pulsar in the early
29:48
1990s broke everybody's heads. Those
29:51
planets have now, incidentally, been called
29:53
drow, Phoebeta and poltergeist, which are
29:56
names of different types of undead from
29:57
different cultures around the world. And I
29:59
think that's kind of cute because you've got
30:00
zombie planets around a dead star. That's all
30:03
good. But 30 years ago, and actually 30 years
30:06
ago last week on the 6th of October
30:08
1995, we saw the announcement
30:11
of the first confirmed planet around a star
30:13
like the sun. And that planet was 51 Pegasi
30:16
b. So it's a planet going around the south 51
30:19
Pegasi. And it immediately broke
30:22
everybody's heads because it was not what we
30:23
expected. So both our models of planet
30:25
formation that were based on a grand total of
30:28
one planetary system, our own, predicted
30:31
you'd have rocky planets close to the star
30:33
and big gas giants a long way from the star,
30:35
because that's what we see at home. And that
30:37
makes sense. So to find a planet
30:40
similar to Jupiter, but going around its star
30:42
every four days with a surface temperature in
30:44
excess of a thousand degrees C was not
30:47
what was expected, I think would be the
30:49
polite way to put it. Now, that forced people
30:51
to immediately go back and start revisiting
30:54
and improving that disk model of planet
30:56
formation, which has kind of led us to where
30:58
we are now. But that was kind of
31:00
fundamental and foundational. For the first
31:04
decade or so after that
31:06
discovery, new planets were found in dribs
31:09
and drabs, and the rate at which they were
31:11
discovered gradually increased. And in that
31:12
first decade, the best technique for finding
31:15
planets, the one that was most successful,
31:17
was what we call the radial velocity method,
31:20
which Australia really played a leading role
31:22
in with the Anglo Australian Planet Search.
31:24
There was this beautiful spectrograph
31:26
attached to the 3.9 meter telescope at Siding
31:28
Spring, which I know Fred loves daily. It's a
31:31
real icon of Australian astronomy. And, that
31:34
telescope was used to point at one star,
31:36
measure that star speed, then point at
31:38
another, and gradually survey this collection
31:41
of stars and then keep coming back to them
31:43
every now and again and measure their speed
31:44
again. And, by measuring the speed of these
31:46
stars to the level that you can see them
31:49
wobbling with changes of
31:52
speed measured in a few meters per second. So
31:54
comparable to speed, people walk or jog
31:56
around stars that are trillions or
31:59
quadrillions of kilometers away, measuring
32:00
their wobbles to a precision of meters per
32:02
second. That just makes my head hurt. But by
32:05
doing that, you can spot the telltale wobble
32:07
of a star rocking back and forward in space
32:09
and infer the presence of a planet. But it's
32:12
a really time consuming, challenging
32:15
method where you can only observe a few stars
32:17
at once, because you've got to gather light
32:18
for an hour or more to get enough
32:21
light, to get an accurate enough spectrum to
32:23
get a single measurement. And you can only
32:25
point at one star at once. By
32:28
the late part of the first decade of the
32:30
21st century, the transit method started to
32:33
take over. And this is where we look at a lot
32:35
of stars all at once and look for the
32:38
few of them that are winking at us. So
32:40
they've got a planet going around them that's
32:42
lined, up just right that every time it goes
32:43
around that star, it will block a bit of that
32:45
star's light and the star will dim and then
32:47
brighten again. And that started to
32:50
take over from the radial velocity method
32:52
purely because of the numbers. Again, because
32:54
you can look at a large number of stars at
32:56
the same time. And even if only
32:58
1% of those stars have a planet oriented in
33:01
the right direction for you to have it line
33:03
up and give us a dip by looking at 100,000
33:06
stars at once, you'll have plenty of
33:08
candidates. The Kepler spacecraft
33:10
launched in about 2008 and became
33:13
this first census of the night sky. And
33:16
it discovered on its own more than 3,000
33:18
planets around other stars using this transit
33:20
method. So we've got better and better at
33:23
doing it. And over time what's happened is
33:25
we've not only found the low hanging fruit,
33:27
the really big planets close to their stars
33:29
that give a whopping great signal that you
33:31
can find, but with each generation of new
33:33
instrument that's gone up there, we've got
33:34
better at finding planets that are further
33:36
from their stars, better at finding planets
33:38
that are ever smaller, finding planets that
33:40
are weird, or other techniques are coming
33:43
online that allow us to do things another
33:44
way. And I still think one of the greatest
33:46
movies that never won an Oscar are, ah, the
33:48
wonderful Images of the SAHR 8799 that
33:51
shows four planets going around it. And we've
33:54
got kind of a live movie of those planets
33:56
orbiting that star that runs back more than a
33:59
decade now. It's just breathtaking.
34:00
Andrew Dunkley: Yeah, I saw it.
34:02
Jonti Horner: Yeah, it's awesome. And we've basically lived
34:05
through this awesome scientific
34:07
revolution without really realizing it. You
34:10
know, we've gone from a world where nobody
34:12
knew if there were planets around other stars
34:14
to a fact that there is nobody younger than
34:16
the age of 30 now who grew up in that world
34:18
that you and I grew up in, where we wondered
34:21
if there were planets around other stars.
34:22
It's absolutely breathtaking. We've had
34:25
real big involvement with this here in
34:27
Australia. The Anglo Australian Planet Search
34:29
was one of the leaders for the first 10 or 15
34:32
years of this exoplanet era. We've got a
34:34
facility here in Queensland that is now
34:36
leading the way, one of the leading
34:38
facilities in the entire planet. You
34:40
know, the only dedicated exoplanet search
34:43
facility in the Southern hemisphere. And we
34:45
work with NASA to do this. We've been
34:47
directly involved with 41 planet discoveries
34:50
in the last couple of years, using NASA's
34:52
test mission and working with them. But it's
34:55
this kind of ongoing exploration, this
34:57
ongoing search. And, you know, what will the
35:00
next 30 years bring? That's kind of what I
35:02
wonder. Where will we go with it? And
35:05
it's not so much when will we stop counting,
35:08
but when will we start to get things that
35:11
really potentially could be like the Earth?
35:13
And I've said this before, I don't think
35:15
we've found an Earth like planet yet. We
35:16
found things about as big as the Earth that
35:18
are very different. Like saying, I went
35:21
swimming last week and I saw the most human
35:23
like creature I've ever seen. And it was a
35:24
dolphin. It was about the same size and
35:26
weight as a human, but it's fundamentally not
35:28
a human being. Yeah, but we're going to be
35:30
moving forward and we're going to be moving
35:32
from just finding these things to learning
35:33
more about them. We're moving into this era
35:35
of characterization and I think the number's
35:38
going to gradually lose importance.
35:39
You know, when we find 10,000 or 100,000,
35:43
the difference will be a lot less significant
35:45
than the difference between 0 and 1. But
35:48
it'll start being which of the planets we
35:50
know the most about. What are they like? What
35:52
can we learn about them? And that's, I think,
35:55
the journey for the next 30 years.
35:56
Andrew Dunkley: Yes. And finding, and as you said, finding
35:59
that, one planet that is so
36:02
like ours in size and proximity,
36:05
orbiting a sun like ours,
36:09
maybe with liquid water, et cetera, et
36:11
cetera.
36:11
Jonti Horner: Yeah.
36:12
Andrew Dunkley: that's the golden goose, isn't it, really?
36:15
Jonti Horner: Absolutely.
36:15
And we've got this really interesting
36:18
question about how long has the
36:20
Earth being in a condition that if we looked
36:23
at it, it would look like the Earth. So in
36:25
other words, how long has the Earth been an
36:27
Earth like planet? Because when we're talking
36:29
about a planet like the Earth, when it's
36:32
something like the Earth is today, with, you
36:33
know, beautiful blue sparkling oceans and A
36:35
thin oxygen rich atmosphere and life
36:38
teeming in abundant continents that are
36:40
mottled brown and green and icy polar
36:43
caps. But for the vast majority of the
36:44
Earth's history it has looked nothing like it
36:47
does now. It's had an entirely different
36:49
atmosphere. It's not had free
36:51
oxygen in the atmosphere. It's had periods
36:53
when it was an enormous snowball, you know,
36:56
snowball Earth episodes. So it's quite likely
36:58
that for the majority of the Earth's history
37:01
we wouldn't recognize it as an Earth like
37:03
planet because it would look totally, totally
37:05
different.
37:06
Andrew Dunkley: Yeah, that's an interesting point. And that
37:08
could exist elsewhere in the
37:11
universe. And we may have seen a planet
37:14
already that could one day be like
37:16
ours, but it might be tens of thousands or
37:19
hundreds of thousands of years before it
37:20
reaches that point. So
37:23
that's a really interesting factor to bring
37:26
into the equation.
37:28
you said some odd planets. I thought I'd do a
37:30
bit of a search. these exoplanets that we've
37:32
discovered in the last 30 years. Wasp
37:34
76B. It's a hot
37:37
Jupiter which rains molten iron. I think Fred
37:40
and I talked about that one. Wasp,
37:42
107B. A gas giant, with
37:45
a density so low it's been described as a
37:47
marshmallow planet.
37:50
HD,
37:51
189773B. It's a planet
37:54
with an atmosphere that contains clouds of
37:56
molten glass.
37:58
Jonti Horner: Yeah, that's often described as a blue marble
38:00
planet, I think.
38:01
Andrew Dunkley: Yeah, yeah. Hat P7B is an ultra
38:04
hot Jupiter that's so dark it's nearly
38:06
charcoal and 5,
38:09
5 Cancri E I think it's
38:12
pronounced a, super Earth with a lava world,
38:15
and sparkling skies. And there's probably
38:18
more weird ones out there. We yet defined
38:20
that, defy explanation. It's a really
38:22
fascinating part of astronomy.
38:24
Jonti Horner: it is. And it's that realization that the
38:26
diversity of things that are out there is far
38:28
greater than we could have possibly imagined.
38:30
And it really forces us to revisit
38:33
and refine our definitions of what a planet
38:35
is. So we historically people have this
38:38
idealized boundary at 13 Jupiter masses where
38:41
if you're more massive than that, you're a
38:42
brown dwarf and you're a fail star. And if
38:44
you're less massive than that, you're a
38:46
planet.
38:46
Andrew Dunkley: Yeah.
38:47
Jonti Horner: And we're now finding things that people are
38:48
claiming a brown dwarfs that are only twice
38:50
the mass of Jupiter and things people are
38:52
claiming are planets that are 20 Jupiter
38:54
masses. You know, there's a real blurring of
38:56
that Boundary. You've then got one weird
38:59
object. If you look at what the most dense
39:01
planet we found is, there's one planet that
39:04
has a density that is something like
39:07
150 times the density of water or something
39:09
like this. And it's a few Jupiter
39:12
masses. And we know the density, we know the
39:15
size because of transits and we know the mass
39:17
because of radial velocity. And if you've got
39:18
the size and the mass, you get the density.
39:21
This thing is so dense so that it doesn't
39:23
confirm with any known material.
39:26
You know, it's many times denser than the
39:28
densest metal. Gravity pulling things in
39:30
can't explain it. And so
39:33
is it really a planet? There is some
39:35
speculation that it's actually something that
39:38
was probably a white dwarf that has somehow
39:40
been bombarded and fractured. So there's only
39:42
a few Jupiter masses left.
39:46
So it's not a planet. You know,
39:49
if it was a white.
39:50
Andrew Dunkley: Dwarf that's been culver, I would say no, but
39:53
gosh, yeah, there's.
39:54
Jonti Horner: All these other things. Planets that are less
39:56
dense than cotton candy and yeah, it's
39:59
awesome from a speculation point of view. And
40:02
it's a, a lot of the planets we've found are
40:04
things that if you saw them in an episode of
40:05
Star Trek or you know, any of these sci fi
40:08
series, you'd think that they jumped the
40:11
shark, that that kind of thing just wasn't
40:13
possible anymore. They'd obviously been
40:15
enjoying themselves a little bit too much in
40:17
the pre writing session. And yet we're
40:20
finding these objects are just so diverse
40:23
and bonkers. It's untrue. That's part of the
40:25
fun of it. You never know what we're going to
40:26
find next.
40:27
Andrew Dunkley: Absolutely not.
40:28
and that sort of takes us into our final
40:30
story because this is an object that
40:33
a little bit weird in our solar system.
40:36
It's the moon Mimas. But it's also been
40:39
called the Death Star because it does have
40:42
that Death Star look about it. It's got a
40:44
dish like depression, in it where it
40:47
must have got hit at some stage. But the
40:49
reason it's in the news now is because it
40:52
is yet another object in our solar system
40:55
that may contain a subsurface
40:58
ocean.
40:59
Jonti Horner: Yes. And it's probably of all the moons where
41:01
subsurface oceans have been suspected or
41:04
detected, it is the smallest of them and
41:07
it's probably the most surprising of the lot.
41:10
The evidence for this has built up over
41:13
a bit more than a decade and comes from the
41:15
Cassini mission that Spent all that time
41:17
orbiting Saturn making wonderful discoveries,
41:20
most famously, of course, being the geysers
41:23
of liquid water erupting from the south pole
41:25
of another of the small icy moons, Enceladus,
41:27
which was a shock because Enceladus is so
41:29
small that it should be frozen to the core.
41:31
So it's a bit of a surprise there's liquid
41:33
water there. Mimas is even smaller.
41:36
It's the smallest object in the solar system
41:39
that is spherical because its gravity has
41:42
overcome the strength of the material it's
41:44
made from. And when you look at the
41:47
calculations people have made at what the
41:49
minimum size something would have to be to be
41:52
in hydrostatic equilibrium to be an object
41:54
where gravity overcomes the strength. Mimas
41:56
is actually a little bit smaller than that,
41:59
which is interesting. It's a real edge case.
42:02
And, you know, the fact that it is spherical
42:05
like it is would suggest that at some point
42:07
it has not been that strong in the past. So
42:08
it was probably fairly liquid early on in its
42:11
formation. But any ocean it had when it was
42:14
born should have frozen out
42:17
long, long, long, long, long ago. And, that's
42:19
kind of borne out when you see the photos
42:21
that are taken of Mimas. It doesn't look like
42:23
Enceladus. It doesn't look like AR were
42:26
talking about last week. It doesn't look like
42:27
Europa. They're all places that have
42:30
obviously been resurfaced, that have flat
42:32
areas with cracks that look like ice that has
42:35
been broken by plate tectonics. Because it's
42:37
floating on an ocean, Mimas just looks like
42:39
another cratered ice ball.
42:41
Andrew Dunkley: Yes.
42:41
Jonti Horner: So there's a few oddities that have built up.
42:43
One of them is that, enormous crater,
42:45
Herschel. Now, Herschel, as a crater, is
42:48
almost big enough that the impactor could
42:50
have shattered me. And if it had been only
42:52
slightly larger, Mimas would have been
42:54
destroyed. So it's right at the limit of
42:57
how big a crater can be before things get
42:59
seriously bad. But a lot of calculations
43:02
have shown that if the Herschel crater had
43:05
formed when the Moon was frozen solid to its
43:08
core, it shouldn't have a central peak.
43:11
But it has a central peak. Now, that suggests
43:14
that Mimas was a bit slushy. But if you do
43:16
the calculations and assume Mimas had a very,
43:19
very well developed ocean, that
43:22
crater wouldn't look like it did either,
43:23
because it would have dug down into the ocean
43:25
and splashed liquid water everywhere. So
43:27
there are suggestions that the Herschel
43:29
crater formed when Mimas was slushy rather
43:32
than ocean, when it was fluid enough to get
43:34
this central peak form, but not so fluid that
43:37
an ocean was breached. And with the size of
43:38
that M impact, it would have breached one if
43:40
one was there. Now I've seen some suggestions
43:42
from that saying that Herschel must therefore
43:44
be a young crater because it's tied
43:47
to this young ocean that is thought to be
43:49
there on Mimas. Now that's one of the
43:52
suggestions. I'm not necessarily sure that's
43:53
the case. It may be that Herschel may be
43:55
older than there was an ocean in the past.
43:57
That's still to be sorted. But aside from
44:00
that, there's been a lot of the data from
44:02
Cassini linked to how Mimas is
44:05
rotating and wobbling, suggested that
44:07
it couldn't be solid to the core unless the
44:10
core was not in her static equilibrium. The
44:12
core was elongated and pancake shaped. and
44:15
that just doesn't make sense. And as they got
44:17
more and more data, more and more
44:18
observations, that just doesn't work. And
44:21
so from the rotation and the wobble of this
44:23
moon, it suggests that as much as
44:25
50% of its volume is liquid water.
44:28
Wow. Which is an enormous subsurface ocean.
44:31
That's an absolutely incredible ocean. But
44:34
because of the thermodynamics of it, that
44:36
ocean can't be old because if it was old, it
44:38
would have frozen out already. Now, part of
44:41
the supporting evidence for this is that the
44:43
orbit of Mimas around Saturn is not perfectly
44:45
circular. It's actually a little bit more
44:48
eccentric than the orbit of the Earth around
44:50
the Sun. That is not a
44:52
situation that's tenable long term. The orbit
44:55
should be circularized by tidal
44:57
effects with Saturn. And so the suggestion
45:00
seems to be that at some point, probably in
45:02
the last 15 million years, something
45:05
happened to stir, Mimas's orbit upper Mechi
45:08
more eccentric, to actually make it a bit
45:10
more elongated. That increased
45:13
eccentricity means that Mimas now experience
45:15
a significant tidal heating
45:18
from being squashed and squeezed effectively
45:21
by the gravity of Saturn and also by the
45:23
other moons. It's in mean motion resonance
45:25
with a couple of the other saturnian moons.
45:28
And all of that means that you're going to
45:29
get a significant amount of heat dumped into
45:31
the interior of Mimas, melting that interior
45:34
and creating this ocean. And the argument
45:37
for the fact that the surface is not yet
45:39
smooth and resurfaced is that a, that
45:42
ocean is young and it's a still developing
45:44
situation. But also that the crust of
45:47
Mimas is 20 or 30 kilometers thick and
45:50
that's thick enough that it hasn't yet
45:52
responded to the liquid underneath
45:55
and so you've almost got this hidden ocean in
45:57
a place you wouldn't expect, but where all
46:00
our observations, all our data is suggesting
46:03
that the only explanation that works for all
46:05
of the different things we've observed for it
46:07
is that this is yet another of this growing
46:09
catalog of places where there's a huge volume
46:12
of liquid water buried beneath an icy
46:14
surface. It's absolutely breathtaking work
46:16
and it's a really good example of the
46:18
iterative nature of science because it's not
46:21
like this is a new discovery this week.
46:23
There've been whispers about this for years
46:25
and papers published about it for years and
46:28
alternative hypotheses proposed and
46:30
disproved and all the rest of it. And all
46:33
the way through we're getting more and more
46:35
certain that this ocean's there. We're
46:37
learning more about the history. And I guess
46:40
again, not only are we learning that liquid
46:41
water is more common than the solar system,
46:43
but we're getting reminded once again that
46:45
the solar system's a very dynamic place. And
46:48
it's not like everything of interest happened
46:50
four and a half thousand million years ago.
46:52
And now we're in the kind of mop up phase
46:54
where nothing interesting happens. There's
46:56
still a lot going on. And the solar system's
46:59
dynamic in a way that if we were around when
47:01
the dinosaurs walked the Earth, it would have
47:03
looked like a very different place than the
47:05
place we see today. It's that changeable.
47:07
Andrew Dunkley: Yeah, absolutely. Yeah. And
47:10
Mimas is also,
47:13
if indeed it is another,
47:17
water moon, let's say ice moon, whatever you
47:19
want to call it, it's starting to show that
47:22
it's probably more normal than we ever
47:24
thought. You've got so many others that are
47:27
starting to be found. obviously
47:30
Europa Enceladus would be the top two, but
47:33
Ganymede's now in there.
47:37
Andrew Dunkley: Most of the dwarf moons,
47:39
or dwarf planets in the outer solar system
47:41
are starting to show these signs. So
47:45
it could be quite normal here. And
47:48
as we've already discussed, you know, there
47:50
was a time where we weren't sure whether or
47:52
not there were other planets in other solar
47:55
systems in the universe. Well, it's
47:57
probably going to be discovered that there
48:00
are probably a lot more ice moons out there
48:02
than we could possibly imagine. So.
48:05
Jonti Horner: Absolutely. And the other interesting thing
48:07
about this to me is it's not just suggesting
48:08
that you get oceans and the oceans go away.
48:11
It's suggesting you can get episodic oceans
48:14
because m. If this Ocean is only 10 or 15
48:16
million years old. We've had a lot of 10 and
48:19
15 million year old windows
48:22
in four and a half thousand million years of
48:24
time. And, what is the likelihood that we
48:27
just happen to be in the only one of those
48:29
windows where you've got two temporary oceans
48:31
at the same time, Where Enceladus and
48:34
Mimas have temporary transient oceans that
48:37
have only formed in recent times. And for
48:39
both of them, the logic is the same. They're
48:41
too small to have had this ocean since
48:43
they're formed. It's got to be a recent
48:44
thing. What is the likelihood that we catch
48:47
two of them going off at once, just by
48:48
random, when there have never been any
48:50
others? So that's suggesting that these
48:52
subsurface oceans on the smaller moons come
48:54
and go and come again, which means
48:57
that again, from the point of view of life
48:59
elsewhere, life that can
49:02
survive the long freeze is ready to take over
49:05
during the short summer. And we see that on
49:07
Earth. It's a really interesting thing that
49:10
if this is a temporary transient ocean now,
49:13
it's possibly been there multiple times in
49:15
the past. And that's why I
49:18
suspect that the Herschel Crater may not have
49:20
formed with the latest recent ocean. But
49:23
maybe it's a previous episode of it. We will
49:25
only know when we get more studies. And of
49:27
course, it's a really good reason to go back
49:29
to Saturn to find out.
49:30
Andrew Dunkley: Absolutely true. Yes, indeed. All right, if
49:32
you want to read about that story and the,
49:34
previous story, about exoplanets, you
49:37
can go to space.com
49:40
and we are done. Jonti, thank you so much.
49:44
Jonti Horner: It's a pleasure. It's a lot to talk about.
49:45
It's always good fun.
49:46
Andrew Dunkley: It is great fun. Good, to see you. that's
49:49
Jonti Horner, professor of Astrophysics at
49:51
the University of Southern Queensland. And
49:53
don't forget to visit our website while
49:55
you're online and check us out. you can do
49:58
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50:02
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check it all out on our, space,
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nutspodcast.com, website.
50:33
and I would say thanks to Huw in the studio.
50:36
But he's out counting, exoplanets. And he got
50:39
to 10, and you can't count any higher.
50:41
And from me, Andrew Dunkley, thanks for your
50:43
company. We'll see you on the next episode of
50:44
Space Nuts real soon. Bye. Bye.