0:01

It's day, it's twice as long as

0:04

its year. Why is it so dense?

0:06

Then it's got to have so much

0:08

iron in its core to make it

0:10

that heavy. And Mercury certainly moves pretty

0:12

quickly around the sun, but it's an

0:14

odd little planet. Hello

0:20

and welcome to the Supermassive

0:22

podcast from the Royal Astronomical

0:24

Society with me, science journalist

0:26

Izzy Clark and astrophysicist Dr.

0:28

Becky Smithers. We are

0:30

finally completing our tour of the solar

0:32

system this month with a trip to

0:34

Mercury. Izzy, I mean, it's about

0:36

time. I actually, I looked back, right? Oh

0:39

no, don't. We first did Jupiter in March

0:42

2023. So it only took us 18 months to do a

0:44

trip around the solar system. Well,

0:47

how long would an actual mission time look

0:49

like? It's not bad in terms of missions. Yeah. We're

0:53

still quicker than most anyway. And I swear, if anyone writes

0:55

in to be like, what about Pluto? I'd be like, no,

0:57

no. Anyway,

1:02

what do we know about Mercury and

1:04

what is the latest mission on its

1:06

way to study the planet further? And

1:09

as always, Dr. Robert Massey, the deputy director

1:11

of the Royal Astronomical Society is here. So

1:14

Robert, what is Mercury like as a

1:16

planet? Well, you could sum it up as

1:18

hot, small and close to the sun or hot and cold and

1:20

small and close to the sun. And in many ways, it looks

1:23

a lot like our moon. If you

1:25

look at all the photographs from space probes, it's got a

1:27

really bleak, cratered surface. And it's not that much bigger than

1:29

the moon either. It's only

1:31

5000 kilometers across, got no atmosphere to

1:33

speak of. And it also

1:35

has this sort of like baked Alaska quality. So

1:38

for those of us who ate that dessert in the 1980s, it's

1:40

the closest planet to the sun. So it's

1:42

very hot. It gets up to 400 degrees C. But

1:45

also, because there's no atmosphere in the shadowed regions,

1:47

it goes down to minus 200 C. So,

1:50

you know, it's 200 Celsius. Imagine this huge contrast

1:52

in temperatures and it might even be waterized in

1:54

the poles. Now, one

1:57

of the things people often ask is, you know, how can you see it

1:59

in the sky? because it is one of

2:01

the naked eye planets and it's definitely something that

2:03

our ancestors would have seen and been aware of.

2:06

But it's always a bit of a challenge because it's quite close to the

2:08

sun in the sky as well as being close to the sun in reality.

2:11

But as it happens, you can catch

2:13

it before sunrise in early September, 2024.

2:16

So if you're listening to this episode early on after it goes

2:18

out, you've got a chance of being able to do that. You

2:21

can also see it in the morning at the end of the

2:23

year. I'm thinking of this in the UK and Northern Hemisphere perspective.

2:25

It's reasonably bright. You

2:27

need to know, it helps save one of the

2:29

apps to find it. The good telescope shows you

2:31

may be a phase that changes like Venus does

2:33

because it's moving between the earth and the sun.

2:36

So to do better than that, we really needed space

2:38

probes. And after all, that's what this episode is about,

2:40

to find out more about that and you'll hear later.

2:43

What a perfect setup, she asks Robert. We'll catch

2:45

up with you later in the show for some

2:47

more questions and this month's Stargazing Tips. So

2:50

if we turn to the history books, Mercury

2:52

is the messenger of the Roman gods zipping

2:54

around from place to place, which is how

2:56

the planet got its name. Mercury

2:59

certainly moves pretty quickly around the sun,

3:01

but it's an odd little planet and

3:03

it's over to our pal planetary scientist,

3:05

Dr. David Rothery from the Open University

3:08

to tell us more. Well,

3:10

Mercury is the smallest of the

3:12

planets, but it's bigger than the

3:14

moon. It's 2,400 and something kilometers

3:16

in radius. It's a

3:18

rocky body. It's the closest planet

3:20

to the sun and it's the most elliptical

3:24

orbit. At its closest,

3:26

it's 30% of the earth's sun distance

3:28

away from the sun and its furthest,

3:30

it's 40% of the earth's sun distance

3:32

away from the sun. So

3:34

it's quite an elongated orbit. The

3:36

surface is very hot by day, as

3:38

you would expect being that close to the

3:40

sun, 400 degrees Celsius

3:43

or thereabouts, but at night it

3:45

gets very cold because there's no

3:47

atmosphere. So it just radiates all

3:49

that heat away to space. So

3:51

big temperature extremes and

3:53

its day length is weird

3:55

because let's get this right.

3:58

It's day. twice as long

4:01

as its year. It rotates

4:03

three times for every two orbits

4:05

around the Sun and the combined

4:07

effect of that means sunrise to

4:09

sunrise takes two orbits of the

4:11

Sun to achieve. So it

4:13

has nights which are

4:16

88 Earth days in length so it's dark

4:18

for a long time which is why it's

4:20

able to get so cold at night because

4:23

there's a long time for all that daytime

4:25

heat to be radiated back to space. Yeah

4:28

we briefly covered mercury before as well

4:30

and we talk about it I think

4:33

someone described it as its

4:36

80% core so you know

4:38

we've got these huge temperature

4:40

changes it's a rocky body

4:42

so what's it like on that surface? Well

4:45

you're right Izzy it has a very

4:47

big core we think it lost most

4:49

of its rock in a giant impact

4:51

during its formation process so that strips

4:53

away most of the rock but there's

4:55

enough rock left to give it a

4:57

rock covering about 400 kilometres depth

5:00

on top of its big iron core and

5:03

that rock is surprisingly

5:05

interesting I'm a geologist and I'm great

5:08

at this it's

5:10

a really fascinating place for geology. You'd expect

5:12

the rock just to be some kind of

5:14

parched cinder but no it's not

5:17

it's got volatile elements

5:19

in considerable abundance. The

5:22

crust that we see today was largely

5:24

formed by volcanic eruptions of lava flows

5:27

stuff oozing out and flooding across the

5:29

surface layer after layer of lava flows

5:32

which have been intensely created by impact

5:34

but the most recent volcanism

5:37

has been explosive volcanism blasting holes

5:39

in the crust and

5:41

you don't get that unless the

5:44

rising molten rock the magma has

5:46

got volatiles in it that will turn

5:48

to gas or else maybe we're

5:51

encountering the volatiles as

5:53

the magma nears the surface maybe there's a

5:55

volatile rich layer just below the surface but

5:57

either way when

6:00

the magma is not confined by much

6:02

weight of overlying rock, the gas comes

6:04

out of solution and it goes bang

6:06

and it gets explosive eruptions. And that's

6:08

a wonderful history for a volcanologist like

6:10

me. And we've also got patches where

6:13

volatiles are escaping even today. It

6:15

looks moth-eaten in places. It's a

6:18

process that we call hollow formation.

6:20

These hollows are 10 meters, 20

6:22

meters deep and hundreds of meters

6:25

wide. They're flat bottom steep-sided depressions

6:27

where stuff is just dissipating away

6:29

to space. And we don't

6:31

know what's being lost. We know mercury is

6:33

rocky but in places it's so

6:36

rich in volatiles that the chemical bonds can

6:38

be broken and the atoms just drift

6:40

away to space leaving you these

6:43

strange flat bottom depressions in the

6:45

ground. It's weird. There's stuff going

6:47

on today that we didn't expect.

6:50

I love

6:52

hearing you talk about this. I

6:54

mean so when we talk about volatiles

6:56

those are those chemical elements, chemical compounds

6:58

that are vaporized

7:01

essentially. So what

7:03

chemical elements are they? What can

7:05

we know about the chemical composition

7:07

of mercury and then what impact

7:09

does that have for it as

7:11

a planet? We don't

7:13

know what all the volatiles are. We do

7:15

know that there's a lot

7:17

of sulfur on mercury, 2 to 4

7:20

percent sulfur wherever you look. That's a

7:22

result from NASA's messenger probe which orbited

7:24

mercury 2011 to

7:26

2015. It had an x-ray spectrometer

7:28

which could detect the sulfur. We

7:30

don't think it's sulfur as elemental

7:32

sulfur. It's in compounds. It's calcium,

7:35

magnesium, sulfide, something like that. As

7:37

well as sulfur we've got a

7:39

lot of sodium and potassium and

7:42

chlorine and we think probably

7:44

that what's being lost in

7:46

the volcanic explosions is

7:49

gases containing sulfur. It

7:52

could be carbon disulfide. It could be

7:54

hydrogen sulfide. I doubt that because we're

7:56

not expecting much hydrogen. It could be

7:58

it could be sulfur. oxide. We're

8:00

not sure, but gases containing sulfur,

8:02

because the deposits that we see

8:05

on the ground around these explosive

8:07

volcanic vents are deficient in

8:09

sulfur. So they've lost their sulfur, it's

8:11

been turned to vapor. Maybe

8:13

that was a vapor that was driving the explosion.

8:16

Where the hollows are forming, where we've

8:18

got passive, gradual,

8:21

non-explosive loss of material, and that's

8:23

got to be by breaking chemical

8:25

bonds, we don't understand and

8:27

we're going to understand the chemical composition

8:30

of mercury much better two

8:32

years from now, when we have

8:35

the European Space Agency's pro-Bepi Colombo

8:37

in orbit, with its British built

8:39

x-ray spectrometer called MIX, Mercury Imaging

8:42

X-ray Spectrometer. That will measure 20

8:44

or very about chemical

8:46

elements with spatial

8:49

resolutions as fine as about

8:51

10 kilometers. So we'll get very

8:53

detailed chemical mapping and then

8:55

we'll begin to understand what's being lost.

8:58

Mercury, obviously our planet is closest

9:00

to the Sun, can it protect

9:02

itself from the impact

9:04

of the Sun in any way? Well, Mercury

9:08

has a magnetic field. We've mentioned

9:10

its large core and the

9:12

outer part of that is molten and

9:14

generating a magnetic field. So it has

9:16

a magnetosphere and the solar wind streaming

9:18

out from the Sun, mostly protons, will

9:21

hit the magnetic

9:23

field and be deflected around the planet.

9:25

So the solar wind doesn't hit the

9:27

surface most of the time. Now, when

9:29

there's a solar storm, the

9:31

edge of a magnetic field or the magneto

9:34

pores, if we want to be technical, gets

9:36

pushed down to Mercury's surface. So those times

9:39

charged particles from the Sun do impinge

9:41

on the surface. So

9:43

if you think the aurora here is

9:46

pretty on Mercury, when

9:48

there's a big solar storm, you've got stuff

9:50

coming right down to the surface and

9:53

irradiating the ground. And that's another process

9:55

that could be responsible for forming Mercury's

9:57

hollows when the solar wind reaches the

9:59

ground. another way to break chemical

10:01

bonds. So it is

10:03

a very hostile environment. There's no

10:05

atmosphere really. There are atoms associated

10:08

with mercury but the

10:10

atmosphere is so diffuse that molecules are

10:12

more likely to drift off to space

10:14

or bounce back to the surface rather

10:16

than bumping into each other. So there's

10:18

no atmospheric pressure on mercury really. It's

10:20

just called an exosphere. Thank

10:23

you to David Brodery. So

10:25

Becky, what's mercury's density and

10:27

how do we know that?

10:30

So mercury's density is just a bit less than

10:32

Earth's. It's around about 98% of the density of

10:35

Earth at around about 5.4 grams

10:38

per centimeter cubed. It actually makes it the second

10:40

most dense planet in the solar system. The Earth

10:43

is the densest, right? And that's

10:45

actually really interesting, especially

10:47

if we think about it in comparison to

10:49

our moon. As Robert said, it looks very

10:51

similar to the moon. It's just a little

10:54

bit bigger than the moon as

10:56

well. And yet it is five times

10:58

more massive than the moon, which is

11:00

what makes it so dense, right?

11:02

And that's really interesting to think about like,

11:04

okay, why is it so dense? Then it's

11:06

got to have so much iron in its

11:09

core to make it that heavy and

11:11

that dense as well. Now, as

11:14

for how we know this, we

11:16

need two things, right? To work out density.

11:19

You need to work out the planet's like

11:21

diameter, its radius, its size across, and then

11:23

its mass, right? So the diameter we get

11:25

from knowing how far away it is from

11:27

us and its apparent size in the sky,

11:29

but mass is a little bit trickier to

11:32

work out. If planets have moons,

11:34

it's really easy because you can just get

11:36

it from how the moons orbit the planet

11:38

with the Kepler's laws. But

11:40

mercury doesn't have a

11:42

moon, so how do you do this? Really,

11:44

you've got to send a satellite to it

11:46

to get a really accurate measurement of this

11:48

to like measure essentially its gravitational pull on

11:51

the satellite and then you can work out, okay,

11:53

what's its mass, how heavy it is. And the

11:55

Mariner mission to Mercury actually did this back in

11:57

the 1970s and that's what then

12:00

led to the determination of its density and

12:02

it being so dense and this idea that

12:04

it must have this huge

12:06

iron core. We're talking like 85% of Mercury's got

12:08

to be made of iron to explain how heavy

12:11

it is and how dense it is. And so

12:13

then you start thinking, well, how did it get

12:15

so much iron? Like, is it because

12:18

there just happened to be that much

12:20

iron in that area of the solar system after

12:22

the sun formed, like heavier elements perhaps sank towards

12:24

the center? Or is it because

12:26

of another like giant impact between two planets that

12:28

occurred in the early solar system in the same

12:31

way that we think that our moon was formed

12:33

through a giant impact with another planet in the

12:35

earth in the early solar system? And

12:38

do we see planets like Mercury

12:40

in other solar systems or are

12:42

we special? Well,

12:46

we've seen super-Mercuries is what

12:48

people call it. Like you must have heard

12:51

this before, like we find super-Earths and like

12:53

super-Neptunes. We find super-Mercuries, right? They are a

12:56

very similar density, but they are bigger

12:58

than Mercury, right? There's no, as far

13:00

as I know it, there's no Mercury

13:02

analogues that have been found.

13:04

Now, even though we haven't found

13:06

them, I don't think that means that they don't

13:08

exist, right? I don't think that means that our

13:11

solar system is special because we've got a Mercury

13:13

kind of planet so close to the

13:15

sun. And I think that's because our ways

13:17

of finding planets are really

13:19

biased to more massive planets,

13:21

like Jupiter sized, that orbit

13:23

really close to their star

13:26

so that, you know, that their orbit, so, you

13:28

know, maybe once every month or once every few

13:30

days, which means that when we find planets through

13:32

the transit method, which is when like they pass

13:34

in front of their star and block some of

13:36

the star's light, that's a lot easier

13:38

if they do it more often so we can spot the

13:40

signal more often and if they're bigger because they block more

13:43

light. And then the other way that

13:45

we've got of finding planets is the tug that

13:47

they have on their star, right? They don't orbit

13:49

the star, the star's not static, the star and the planet

13:51

orbit each other so there's this like a center of mass

13:54

between them. So for example, Jupiter as it

13:56

orbits the sun pulls that center

13:58

of mass between them outside. of the surface

14:00

of the sun. So the sun orbits

14:02

that little point outside of its surface, it

14:04

wobbles around on the sky and we can

14:06

spot if there's planets like Jupiter in orbit

14:09

around stars because they wobble. Mercury

14:11

however, is not

14:13

gonna give you a wobble that's gonna be anywhere

14:15

near noticeable in terms of if you

14:17

have a similar planet around a star elsewhere in

14:19

the universe as well. Just because it is so

14:21

small, again it doesn't block a lot of light

14:23

either for a transit, so it's unlikely it will

14:25

find those as well. So I don't

14:28

think we're unique in the fact that we have

14:30

Mercurys. I think they must exist out there, it's

14:32

just that we haven't ever found any Mercury analogues.

14:34

There is some hope though with the habitable worlds

14:37

observatory that's, you know, NASA is in planning stages

14:39

for now, not gonna launch until like the 2040s,

14:41

but the idea is that you have a good

14:43

enough imager on board that you could image

14:47

at least Earth-like planets, probably

14:50

capture Venus as well, whether

14:52

you'd be able to get Mercury if it's

14:54

further away from its star maybe, but I

14:56

think that's a big big question. I think

14:58

the focus is more on Earth-like planets than

15:01

Mercury-like planets sadly. Okay, but

15:03

Mercury's orbit is an interesting one and

15:05

it helped to explain general relativity, so

15:07

can you explain that one? Yeah, yeah,

15:09

so I mean the best way to

15:11

describe what Mercury's orbits, I mean most

15:13

planets' orbits look like is, you know,

15:15

a spirograph. Do you remember spirograph from

15:18

when we were kids, right? The little

15:20

game where you put your pen in

15:22

a little cog and you'd like turn

15:24

it around in a circle. Yeah, so

15:26

basically, if you don't know what we're

15:28

talking about, essentially like you think

15:30

about a planet making a loop around its star

15:32

and just tracing that same path over and over

15:34

again, but actually once it's made the loop, it

15:36

doesn't really join up with where it

15:39

was before and it does another loop

15:41

of its orbit, sort of next, just next to where it

15:43

was before and you can see how that sort of spirals

15:45

out to make almost like a pattern, like a, like almost

15:47

like a petalism of flower, right? It's what it ends up

15:50

sort of looking like, right? And this

15:52

is like scientific term for this

15:54

is perihelion precession. Perihelion means like

15:56

closest point to us to the

15:58

sun in a planet. orbit,

16:00

essentially what it means is that that

16:02

point is moving around a circle, really,

16:04

is what's happening. It's where your pen

16:07

is in each paragraph. All

16:09

planets do this, process ever so slightly,

16:12

and that can be explained by Newton's laws of

16:14

gravity and Kepler's laws of motion and things like

16:16

that. But

16:18

for Mercury, the effect is

16:21

so pronounced, like it's so much bigger

16:23

than for the other planets because it's

16:25

so close into the sun and the

16:27

pull of the sun's gravity that

16:30

this is what gives it this bigger, more

16:32

pronounced effect when this happens. The Newton's laws

16:34

of gravity can't explain this. You

16:36

have to start considering all of the relativistic

16:38

effects that come from the fact that you're

16:40

in a stronger gravitational field because you're closer

16:42

to the sun, which is where Einstein's theory

16:44

of general relativity comes in, which explains gravity

16:47

in terms of relativistic effects. And

16:49

it was actually one of the very first proofs

16:51

of general relativity when Einstein was actually putting together

16:53

his new theory of gravity. It was like,

16:55

oh, well, here's this one problem that no one's

16:57

been able to explain for ages, you know, like

16:59

Mercury's orbit. Let's see if it fits. And it

17:01

does. It fits really, really well. We've

17:05

seen two missions travel to Mercury before.

17:08

We had NASA's Mariner 10 spacecraft in

17:10

the 70s, making the

17:12

journey for the very first time, and it

17:14

made three flybys. And then we

17:16

had NASA's messenger mission, which studied Mercury from 2011

17:18

to 2015. So what did they show us? And

17:20

what is

17:24

ESA's latest mission, Bepi Colombo,

17:26

aiming to find? It's

17:28

something that I asked Dr. Simon Lindsay

17:30

from the University of Leicester, who's the

17:32

instrument scientist of MIX, which is one

17:34

of the instruments on board of the

17:36

spacecraft. We knew almost nothing

17:39

about it before those missions went there.

17:41

So Mariner was able to find that it

17:43

had a magnetic field, which is very odd.

17:46

It's imaged about half of the surface. It

17:48

measured this temperature differential, but it was only

17:51

able to do so much. You've got these

17:53

three flybys. They each last a few hours,

17:55

and that was the whole of the mission.

17:57

Messenger is the source of basics. clear

18:00

everything we know now. So

18:02

it was orbiting more or less North to

18:04

South. It mapped the whole surface for the

18:06

first time. It measured the composition of the

18:08

surface. It mapped out the

18:11

magnetic field. It took all sorts

18:13

of altitude measurements that allowed us to build up

18:15

this topographic map of the planet and yeah, pretty

18:17

much everything else we know comes from that mission.

18:20

Yeah. And now we've got

18:22

Beppe Colombo, which launched in 2018. So

18:25

what was the aims of this mission? What

18:28

can you tell me about Beppe Colombo? So

18:31

Beppe Colombo has a few sort of USPs.

18:34

One of our unique points is there

18:36

are two spacecraft make up, well, two

18:38

science spacecraft that make up Beppe Colombo.

18:40

So we have European MPO, Mercury Planetary

18:42

Orbiter, which goes into a low orbit.

18:45

It's polar like messenger, maps

18:47

the surface. So it's got objectives to

18:49

do with the composition of the planet,

18:51

the formation of the planet. It also

18:53

maps its magnetic field at low altitude.

18:56

And then we have MIO, the magnetospheric

18:58

orbiter, which orbits further out from the

19:01

planet. That's there to map out the

19:03

magnetic environment, to look at the interaction

19:06

of the planet and the solar wind

19:08

to measure the planet's exosphere, all these

19:10

sorts of things. We are trying

19:13

to answer these sort of quite fundamental questions

19:16

about the planet. It's this weird, unusual

19:18

planet. It's the closest to the sun.

19:21

We call it an end member of the solar system. So

19:23

it's the smallest planet. It's the closest to

19:26

the sun. It's the extreme in quite a

19:28

lot of ways. And Beppe is

19:30

very much looking at what that means about

19:32

the formation of Mercury and its properties now

19:34

and what that means for the solar system

19:37

as a whole. And so what's on board?

19:39

How is it going to find out all of

19:41

this information? Because there is there's a lot packed

19:43

in there. Yes, yes,

19:45

absolutely. So there are

19:48

a lot of instruments, exactly

19:50

how many depends on how you define them. But there's

19:52

about 16. Okay. So

19:55

on MPO, the instruments are

19:57

kind of focused around the surface, but

19:59

not exclusively on

20:01

MPO. We have visible camera. We have

20:03

an infrared camera. We have

20:05

a suite of exospheric instrument. We have

20:08

a magnetometer. We have a gamma-ray spectrometer.

20:10

We have a X-ray

20:12

spectrometer, which I work on.

20:14

And I am sure I'm leaving someone

20:16

out, but that's the one I can remember. I mean, you've

20:18

done well to list as many as you have, to

20:20

be fair. Thank you. Thank you very much. And

20:24

then on MIO, like I say, they're

20:26

a little bit more focused on magnetospheric

20:28

stuff. So there's a magnetometer again, there's

20:31

a plasma wave instrument, and then there's

20:33

a large number of different particle instruments,

20:35

electrons, protons, and ions and

20:37

so forth, and measures how they move

20:39

around inside the environment of the system.

20:42

Yeah. And you work

20:44

on an instrument called MIX.

20:46

So what is that doing?

20:49

So MIX stands for

20:51

Mercury Imaging X-ray Spectrometer.

20:53

Which is very confusing, because it's MIX with

20:55

an S. And I, when we first started, before

20:57

we started recording, I was like, can I

20:59

just check how we pronounce this? Absolutely, everyone

21:02

calls it MIXes the first time. So

21:05

you will only understand the name properly if you

21:07

speak Finnish. So we

21:10

are part of a

21:12

suite of two instruments. We're a pair

21:14

with another instrument called SIX, which is

21:17

Finnish, hence this whole thing. SIX stands

21:19

for Solar Intensity X-ray Spectrometer. And this

21:21

is a pun, if you know Finnish,

21:24

because MIX-y is Finnish for Y, SIX-y

21:26

is Finnish for because. I love that,

21:29

that's very good. We often

21:31

talk about this, like the way that

21:33

scientists and physicists name things, I

21:35

love a pun. Like the... We

21:37

are addicted to acronyms, really. Okay,

21:40

so what is MIX doing and how does

21:42

it work? Okay, so it's an X-ray spectrometer.

21:44

And what that means is it's measuring X-rays,

21:46

that's the obvious part. The reasoning

21:48

behind this is that X-rays are

21:51

continuously being put out by the sun.

21:54

Those X-rays get absorbed in any material you

21:56

put in the way. So in our

21:58

case, that's the surface of MIX. Mercury

22:01

has no atmosphere, so that means none of those

22:03

x-rays get absorbed on the way in. They get

22:05

absorbed in the surface of the planet. Atoms in

22:07

the surface gain energy from these

22:09

x-rays and electron gets promoted or ejected

22:12

from the atom, leaving a gap. And

22:15

then that gap is filled by an electron from a

22:17

higher shell in that atom.

22:19

And in the process it emits an x-ray

22:22

and that's the x-ray that we're measuring. And

22:24

the reason that this is interesting is that

22:26

the energy of that x-ray will

22:28

tell you what atom it came from.

22:31

So if you're able to measure that

22:33

energy you can say that came from

22:36

silicon, calcium, magnesium, whatever. So that's what

22:38

we do. We fly around connecting these

22:40

x-rays, tracing the vector where

22:42

they came from on the surface and saying

22:44

there is these elements in this location on

22:46

the surface. And that means that we can

22:48

build up a map of the composition at

22:50

the surface. I mean that

22:53

makes total sense. So where is

22:55

is Beppy now? It

22:57

is rapidly approaching Mercury right now. The

22:59

trajectory of the mission is very very

23:01

long. It launched in 2018 and it's

23:03

still a couple of years till it

23:05

gets there. This trajectory has

23:07

several flybys in it. So we flew

23:09

past Earth, we flew past Venus twice,

23:11

flew past Mercury three times so far

23:13

and then we will fly past again

23:16

on the 4th of September. That will

23:18

be the 4th of 6 flybys. So

23:20

we've got two more Mercury flybys to

23:22

go before we finally go into orbit.

23:24

I mean that sounds really exciting and

23:26

so we've got, you said a few

23:28

more years until Beppy actually

23:31

reaches Mercury. So is there anything a

23:33

bit more specific than that and then

23:35

what will it be getting started on?

23:37

So it gets started in 2026, a

23:40

science mission begins. We expect

23:42

it to last a year. We hope it

23:44

will last two years. We expect to be

23:46

cooked before too long. But

23:48

in that time we are really sort

23:50

of poised because we know we've

23:52

got this short mission and we've been waiting a

23:54

very long time to get that data down. So

23:56

we're very poised to spring into action as soon

23:58

as this data's set. starts coming down and make

24:01

the best fish we can with the data we

24:03

get back. Thank you to

24:05

Simon Lindsay from the University of Leicester. This

24:11

is the Supermassive podcast on the

24:13

Royal Astronomical Society with me, astrophysicist

24:16

Dr. Becky Snaath-Est and science journalist

24:18

Izzy Clark. This month is all

24:20

about mercury. So let's dive into

24:22

some listener questions. Becky at Kashiteed

24:24

on Instagram wants to know, and

24:27

I hope I've said that handled

24:29

correctly. They want to

24:31

know, why doesn't the gravity of the

24:33

sun and other planets cause mercury to

24:35

fall into the sun? Well, it's because

24:37

it's in orbit essentially. So it's moving

24:40

with enough speed in its orbit to

24:42

keep it there, despite the fact that the sun

24:44

is still pulling on it due to gravity. Like

24:47

I always like to think about, you know, when

24:49

we put things like satellites into orbit around earth,

24:51

right? We have to give them enough energy so

24:53

that we throw them so that they're almost making

24:55

this like perfect circle around the earth so that

24:57

like they're falling to earth, but they're always just

24:59

falling past it. Yes. Yeah. Yeah. It's like, it's

25:02

like a similar thing, right? For planets orbits as

25:04

well. If, if you were, you

25:06

know, wanting to actually cause mercury to fall

25:08

into the sun, which, you know, let's, let's,

25:10

let's go easy on the little guy. Let's

25:12

just say we were evil villains and we

25:15

had this power. Yeah. Yeah. And

25:17

we had some minions. Um, we would need

25:19

to like nudge with enough

25:21

energy to like, you know,

25:24

remove energy from, from mercury, like, or give it

25:26

some energy to change its orbit in some ways

25:28

you could do that with maybe like a, again,

25:30

like a collision between mercury and a massive object.

25:32

Like I don't know, an asteroid would have enough

25:34

energy to do this, but you know, another planet

25:36

maybe would give it enough energy to change its

25:38

orbit in some way. And as soon as you

25:40

change the orbit, you make it unstable. And that's

25:43

when then the pull of the sun's gravity might

25:45

start to win out and pull it

25:47

towards the sun. But for now it's just sort of falling

25:50

perfectly around the sun. So it never

25:52

falls into the sun. Okay. Thanks, Becky.

25:55

And Robert, iMUSIF sent an interesting

25:57

question about averages and they say.

25:59

on average, Mercury is the closest

26:01

planet to Earth. Do you find

26:04

it counterintuitive? So let's look into

26:06

this a little bit more. Is

26:08

that true? And can you explain

26:11

it? Yeah. So I'm music.

26:13

Yes, I definitely found it counterintuitive. And I

26:15

was thinking, so

26:18

I had to do a bit of sense checking and reading

26:20

around. And there was an article in Physics Today describing this

26:22

work, I think it was five or six years ago now.

26:25

And the crucial point is the average distance

26:27

between the planets. And what that's taking into

26:29

account using their method is the fact that

26:31

say Venus, although it gets closest to the,

26:33

closer to the Earth than any other planet

26:36

and then Mars and so on, spends

26:39

an awful lot of the time further away as

26:41

well and goes around the sun slowly. So when

26:43

you crunch the numbers, you find that on average

26:46

and only on average, Mercury is closer to the

26:48

Earth. So is it counterintuitive?

26:51

Definitely yes. Does it tell us a lot about the

26:53

layout of the solar system? Well, not to my mind,

26:55

because you know the order of the planets and the

26:57

sun is still the same or at least the order

26:59

of the planetary orbits. It just

27:01

says that sometimes, or a

27:03

lot of the time Mercury is closer to the Earth

27:05

than Venus, just because Venus happens to be on the

27:07

other side of the sun. So it's a curiosity more

27:09

than anything else. But yes, one I was glad to

27:11

find out about because I have a feeling somebody else

27:13

will ask me that having read the article as well.

27:16

I was going to say, do you not

27:18

remember when the animation of this hit the

27:21

internet like a few years back? And I

27:23

just remember saying this collective minds blow. Like,

27:25

yes, the internet is everyone's like, wait, what?

27:28

It's overturning everything we learned in primary school,

27:30

isn't it? Yeah, because we all think about

27:32

it again as static, like all lined up

27:34

and like... I had to deal with

27:36

Pluto being demoted from a planet and now there's this. What

27:39

else is coming? If you need five minutes, Robert,

27:42

we'll understand. Yeah, I'll take a moment. And

27:45

Becky, Elise asks, why isn't Mercury

27:47

the hottest planet in the solar

27:49

system despite it being the closest

27:51

to the sun? Yeah,

27:53

great question, Elise. I think it just shows

27:56

how important atmospheres are

27:58

for Pluto. holding

28:00

on to heat, right? Because

28:04

Mercury barely has an atmosphere,

28:06

Venus, incredibly thick atmosphere. So Mercury, what

28:08

happens is radiation from the sun just

28:11

hits the surface of Mercury and bounces straight

28:13

back off again and is lost to space,

28:16

right? That heat is not held onto, it

28:18

is just lost to space, right? So you

28:21

can sort of instantaneously heat the surface where you

28:23

are in sunlight in that sort of way when

28:25

you know sort of like

28:27

it could be a cooler winter day and the

28:30

air could be cold, but if you feel the

28:32

sun on your face, it feels warm because you

28:34

have the energy hitting into you. It's that kind

28:36

of a sort of heat that Mercury has. And

28:39

that's cause like I said, Mercury's atmosphere is

28:41

so thin. The actual only atmosphere that Mercury

28:44

has is stuff from the surface that's bounced

28:46

up off the surface as radiation from the

28:48

sun hits into it, right? So

28:50

it's almost like little bits of like rock

28:52

and stuff that is the atmosphere. It's so

28:55

incredibly, incredibly thin. It's a hundred trillion times

28:57

thinner than Earth's atmosphere. Yeah.

28:59

It's just crazy to think about, right? Right,

29:02

yeah. Whereas Venus's atmosphere is 93 times

29:04

thicker than Earth's. Right?

29:09

So all that gas in Venus's atmosphere can

29:11

absorb all that reflected light that's come back

29:13

off the surface. Right? And so

29:15

it can store it there in the atmosphere. So the

29:17

atmosphere warms up and that's what makes Venus the hottest

29:19

planet compared to Mercury because it has

29:21

both that incident sort of heat that's on it

29:24

but also the atmosphere to keep it warm

29:26

too. And Elise, I would recommend that you listen

29:28

to our Venus episode as well. Yeah. Yeah.

29:32

Robert, we've also had a question about

29:34

life on Mercury from Fiona and she

29:36

asks, what's the likelihood

29:38

of life being found on Mercury with

29:40

the knowledge from Earth life? Well,

29:44

Fiona, I think sadly it's really quite close

29:46

to zero. And the reason is, look, it's

29:48

the things we've been talking about, Becky was

29:50

just mentioning, no atmosphere does not help, you

29:52

know, huge variations in

29:54

temperature as a result. So incredibly hot

29:57

and also incredibly cold in different places.

30:00

of liquid water, which is seen as

30:02

not necessarily an absolute prerequisite for

30:04

life, but certainly helpful. And

30:06

you know, never say never, maybe, but if there

30:09

was life there, it would have to be hiding

30:11

in some very much more benign environment under the

30:13

surface that we don't think we're really aware of

30:15

exists at all. So it seems really unlikely. I

30:18

guess, you know, thinking about this, could you

30:20

have something that some very specialized bacteria or

30:22

something perhaps, but it's, to my man, it's

30:25

very difficult to see how they'd get started

30:27

in the first place. You know, I could

30:29

imagine somebody doing some genetic engineering on earth

30:31

and making something that could live under the

30:33

surface of mercury, but it seems very unlikely

30:35

ever arose there, at least to me, happy to

30:37

be contradicted by an astrobiologist. But I think it's

30:40

a long shot. Or Robert, don't forget what Jeff

30:42

Goldblum taught us from last episode as well. Yes.

30:45

Life finds a way. Exactly. From

30:47

Jurassic Park. Channel Jurassic Park. Yeah.

30:50

I guess you've got to think about like,

30:52

you know, we've shown that the tardy graze,

30:54

the little, what people call them water beds,

30:56

those little things, they've survived on the outside

30:58

of the International Space Station. So clearly, like,

31:01

you know, no atmosphere and high radiation intense

31:03

environments, certain types of life can

31:05

obviously survive it. But like you say, it's

31:07

the trigger to get it started. Yeah. Yeah.

31:10

Like that's the weird thing. I think we

31:12

could probably like contaminate Mercury surface and see

31:14

if life survived, but I probably wouldn't get

31:16

that past the ethics board. Yeah, exactly.

31:18

I really hope that doesn't happen.

31:20

Exactly. Yeah. It's evolution, you know,

31:22

just like, yes, starting point is

31:25

life evolves to these extreme environments, but it

31:27

must be a struggle to get started. Yeah.

31:30

Okay. So thank you

31:32

to everyone who sent in questions. And

31:34

if you want to send in any

31:37

questions for a future episode, then you

31:39

can email podcast at ras.ac.uk or find

31:41

us on Instagram at supermassivepod. Feel free

31:44

to slide into the DMs on that

31:46

one. So shall we finish with

31:48

some stargazing? Robert, what can we see in

31:50

the night Skyless Month? Yeah, quite a lot

31:52

as it happens. The nights are drawing in equinoxes

31:54

on the 22nd of September. So

31:57

for those of us in the Northern Hemisphere, you know, moving into the

31:59

autumn and winter.