The Supermassive Podcast - 56: We Made It To Mercury!
Episode Date: September 4, 2024Izzie and Dr Becky complete their tour of the solar system with a trip to Mercury, the space spirograph (copyright: Dr Becky). Join them as they explore what we know about the planet so far and what E...SA's current mission, BepiColombo, is hoping to find. Plus, Dr Robert Massey is on hand to answer your questions. Special thanks to guests Dr David Rothery from the Open University and Dr Simon Lindsay from the University of Leicester. Don't forget to send your questions to the team via podcast@ras.ac.uk or Instagram @SupermassivePod The Supermassive Podcast is a Boffin Media production for the Royal Astronomical Society. The producers are Izzie Clarke and Richard Hollingham.Â
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it's day it's twice as long as its year why is it so dense then it's got to have so much iron
in its core to make it that heavy and mercury certainly moves pretty quickly around the sun
but it's an odd little planet
hello and welcome to the supermassive podcast from the royal astronomical society
with me,
science journalist Izzy Clark and astrophysicist Dr. Becky Smethurst.
We are finally completing our tour of the solar system this month with a trip
to Mercury. Izzy, I mean, it's about time. I actually, I looked back, right?
Oh no, don't.
We first did Jupiter in March 2023. So it's only took us 18 months to do a trip around this little stuff.
Well, how long would an actual mission time take?
It's not bad in terms of missions.
Yeah.
We're still quicker than most.
And I swear, if anyone writes in to be like, what about Pluto?
I'll be like, no, no.
Anyway, what do we know about Mercury?
And what is the latest mission on its way to study the planet further?
And as always, Dr. Robert Massey, the Deputy Director of the Royal Astronomical Society is here.
So, Robert, what is Mercury like as a planet?
Well, you could sum it up as hot, small and close to the sun or hot and cold and small and close to the sun.
And in many ways, it looks a lot like our moon.
If you look at all the photographs from space probes.
It's got a really bleak, cratered surface.
And it's not that much bigger than the moon either.
It's only 5,000 kilometres across, got no atmosphere to speak of.
And it also has this sort of like baked Alaska quality.
So for those of us who ate that dessert in the 1980s,
it's the closest planet to the sun.
It's very hot. It gets up to 400 degrees C. But also, because there's no atmosphere, the shadow regions, it goes down to minus 200 C.
So, you know, minus 200 Celsius. Imagine this huge contrast in temperatures and there might
even be water ice in the poles. Now, one of the things people often ask is, you know, how can you
see it in the sky? Because it is one of the naked eye planets and it's definitely something that our
ancestors would have seen, you know, and been aware of.
But it's always a bit of a challenge,
because it's quite close to the sun in the sky,
as well as being close to the sun in reality.
But as it happens, you can catch it before sunrise in early September 2024.
So if you're listening to this episode early on after it goes out,
you've got a chance of being able to do that.
You can also see it in the morning at the end of the year.
I'm thinking of this from a UK and Northern Hemisphere perspective. It's reasonably bright. You need to know, it helps to have one of the apps to do that. You can also see it in the morning at the end of the year. I'm thinking of this from a UK and Northern Hemisphere perspective.
It's reasonably bright.
You need to know, it helps to have one of the apps to find it.
A good telescope shows you maybe a phase that changes like Venus does
because it's moving between the Earth and the Sun.
So to do better than that, we really needed space probes.
And after all, that's what this episode is about,
to find out more about that, and you'll hear later.
What a perfect setup.
Yes, Robert, we'll catch up with you later in the show for some more questions and this month's stargazing tips. this episode is about to find out more about that and you'll hear later what a perfect setup yes
robert we'll catch up with you later in the show for some more questions and this month's stargazing
tips so if we turn to the history books mercury is the messenger of the roman gods zipping around
from place to place which is how the planet got its name and mercury certainly moves pretty quickly
around the sun but it's an odd little planet. And it's over to our pal,
planetary scientist, Dr. David Rothery from the Open University to tell us more.
Well, Mercury is the smallest of the planets, but it's bigger than the moon. It's 2,400 and
something kilometres in radius. It's a rocky body. It's the closest planet to the sun and it's the
most elliptical orbit. At its closest, it's 30% of the Earth's sun distance planet to the sun and it's the most elliptical orbit.
At its closest, it's 30% of the Earth-Sun distance away from the sun.
At its furthest, it's 40% of the Earth-Sun distance away from the sun.
So it's quite an elongated orbit.
The surface is very hot by day, as you would expect being that close to the sun,
400 degrees Celsius or thereabouts. But at night, it gets very cold
because there's no atmosphere. So it just radiates all that heat away to space. So big temperature
extremes. And its day length is weird because, let's get this right, its day, it's twice as long
as its year. It rotates three times for every two orbits around the sun and the
combined effect of that means sunrise to sunrise takes two orbits of the sun to achieve. So it has
nights which are 88 Earth days in length so it's dark for a long time which is why it's able to
get so cold at night because there's a long time for all that daytime heat to be radiated back to space yeah we briefly covered mercury before as well and we talk
about it i think someone described it as it's 80 core so you know we've got these huge temperature
changes it's a rocky body so what's it like on that surface? Well, you're right, Izzy. It has a
very big core. We think it lost most of its rock in a giant impact during its formation process.
So that stripped away most of the rock, but there's enough rock left to give it a rock covering about
300 kilometres depth on top of its big iron core. And that rock is surprisingly interesting.
I'm a geologist and I'm great about this.
It's a really fascinating place for geology.
You'd expect the rock just to be some kind of parched cinder,
but no, it's not.
It's got volatile elements in considerable abundance.
The crust that we see today was largely formed
by volcanic eruptions of lava flows,
stuff oozing out and flooding across the surface,
layer after layer of lava flows,
which have been intensely created by impact.
But the most recent volcanism has been explosive volcanism,
blasting holes in the crust.
And you don't get that unless the rising molten rock, the magma, has got
volatiles in it that will turn to gas. Or else maybe we're encountering the volatiles as the
magma nears the surface. Maybe there's a volatile rich layer just below the surface. But either way,
when the magma is not confined by much weight of overlying rock, the gas comes out of solution and it goes bang and you get explosive eruptions.
And that's a wonderful history for a volcanologist like me.
And we've also got patches where volatiles are escaping even today.
It looks moth-eaten in places.
It's a process that we call hollow formation.
These hollows are 10 metres, 20 metres deep and hundreds of metres wide.
They're flat-bottomed, steep-sided depressions where stuff is just dissipating away to space.
And we don't know what's being lost. We know Mercury's rocky, but in places it's so rich in
volatiles that the chemical bonds can be broken and the atoms just drift away to space, leaving
you these strange flat-bott bottom depressions in the ground.
It's weird. There's stuff going on today that we didn't expect.
I mean, I love hearing you talk about this.
But I mean, so when we talk about volatiles, those are those chemical elements,
chemical compounds that are, you know, vaporized, essentially.
So what chemical elements are they? Like like what can we know about the chemical
composition of mercury and then what impact does that have you know for it as a planet
we don't know what all the volatiles are we do know that there's a lot of sulfur on mercury two
to four percent sulfur wherever you look that's a result from nasa's messenger probe which orbited mercury 2011 to 2015 had an x-ray spectrometer which could detect the sulfur we don't think it's
sulfur as elemental sulfur it's in compounds it's calcium magnesium sulfide something like that
as well as sulfur we've got a lot of sodium and potassium and chlorine. And we think probably that what's being lost
in the volcanic explosions is gases containing sulphur.
It could be carbon disulfide.
It could be hydrogen sulphide.
I doubt that because we're not expecting much hydrogen.
It could be sulphur dioxide.
We're not sure.
But gases containing sulphur,
because the deposits that we see on the ground around these explosive volcanic vents are deficient in sulphur.
So they've lost their sulphur. It's been turned to vapour.
Maybe that was a vapour that was driving the explosion.
Where the hollows are forming, where we've got passive, gradual, non-explosive loss of material, and that's got to be by breaking chemical bonds
we don't understand it and we're going to understand the chemical composition of mercury
much better two years from now when we have the european space agency's probe beppy colombo
in orbit with its british built x-ray spectrometer called mix mercury imaging x-ray spectrometer called MIX, Mercury Imaging X-ray Spectrometer, that will measure 20 or thereabouts
chemical elements with spatial resolutions as fine as about 10 kilometres. So we'll get
very detailed chemical mapping and then we'll begin to understand what's being lost.
Mercury, obviously it's our planet is closest to the sun. Can it protect itself from, you know,
that is closest to the sun, can it protect itself from the impact of the sun in any way?
Well, Mercury has a magnetic field. We've mentioned its large core, and the outer part of that is molten and generating a magnetic field. So it has a magnetosphere, and the solar wind streaming out
from the sun, mostly protons, will hit the magnetic field and be deflected around the planet.
So the solar wind doesn't hit the surface most of the time.
Now, when there's a solar storm, the edge of a magnetic field,
or the magnetopause, if we want to be technical,
gets pushed down to Mercury's surface.
So at those times, charged particles from the sun do impinge on the surface.
So if you think the aurora here is pretty, on
Mercury, when there's a big solar storm, you've got stuff coming right down to the surface and
irradiating the ground. And that's another process that could be responsible for forming Mercury's
hollows when the solar wind reaches the ground. That's another way to break chemical bonds.
So it is a very hostile environment. There's no atmosphere, really.
There are atoms associated with Mercury, but the atmosphere is so diffuse
that molecules are more likely to drift off to space or bounce back to the surface
rather than bumping into each other.
So there's no atmospheric pressure on Mercury, really.
It's just called an exosphere.
Thank you to David Rothery. So Becky,
what's Mercury's density and how do we know that? So Mercury's density is just a bit less than
Earth's. It's around about 98% of the density of Earth at around about 5.4 grams per centimeter
cubed. It actually makes it the second most dense planet in the solar system. The Earth
is the densest, right right and that's actually really
interesting especially if we think about it in comparison to our moon as robert said it looks
very similar to the moon it's just a little bit bigger than the moon as well and yet it is five
times more massive than the moon which is what makes it so dense right and that's really interesting
to think about like okay why is it so dense then it's And that's really interesting to think about like,
okay, why is it so dense?
Then it's got to have so much iron in its core to make it that heavy and that dense as well.
Now, as for how we know this,
we need two things, right, to work out density.
You need to work out the planet's like diameter
or its radius, its size across,
and then its mass, right?
So the diameter we get from knowing how far away it is from us and its radius, its size across, and then its mass, right? So the diameter
we get from knowing how far away it is from us and its apparent size in the sky, but mass is
a little bit trickier to work out. If planets have moons, it's really easy because you can just get
it from how the moons orbit the planet with Kepler's laws. But Mercury doesn't have a moon,
so how do you do this? Really, you've got to send a satellite to it
to get a really accurate measurement of this to like measure essentially its gravitational pull
on the satellite. And then you can work out, okay, what's its mass, how heavy it is.
And the Mariner mission to Mercury actually did this back in the 1970s. And that's what then led
to the determination of its density and it being so dense and this idea that it must have
this huge iron core we're talking like 85 percent of mercury's got to be made of iron to explain
how heavy it is and how dense it is and so then you start thinking well how did it get
so much iron like is it because there just happened to be that much iron in that area of
the solar system after the sun formed like heavier elements perhaps sank towards the center or is it because of another like giant impact between two planets that occurred
in the early solar system in the same way that we think that our moon was formed through a giant
impact with another planet in the earth in the early solar system and do we see planets like
mercury in other solar systems or are we special well we've seen super mercuries is what
people call it like you must have heard this before like we find super earths and like super
neptunes we find super mercuries right they are a very similar density but they are bigger than
mercury right there's no as far as i know it there's no mercury analogs that have been found
now even though we haven't found them i don't think that means that they don't exist right i As far as I know it, there's no Mercury analogs that have been found.
Now, even though we haven't found them, I don't think that means that they don't exist, right?
I don't think that means that our solar system is special because we've got a Mercury kind of planet so close to the sun. And I think that's because our ways of finding planets are really biased to more massive planets like Jupiter-, that orbit really close to their star.
So that their orbits are maybe once every month
or once every few days,
which means that when we find planets
through the transit method,
which is when they pass in front of their star
and block some of the star's light,
that's a lot easier if they do it more often
so we can spot the signal more often
and if they're bigger because they block more light.
And then the other way that we've got of finding planets
is the tug that they have on their star, right?
They don't orbit the star.
The star's not static.
The star and the planet orbit each other.
So there's this like a center of mass between them.
So for example, Jupiter, as it orbits the sun,
pulls that center of mass between them
outside of the surface of the sun.
So the sun orbits that little point outside of its surface.
So it wobbles around on the sky. and we can spot if there's planets like Jupiter in orbit around stars
because they wobble. Mercury, however, is not going to give you a wobble that's going to be
anywhere near noticeable in terms of if you have a similar planet around a star elsewhere in the
universe as well, just because it is so small. Again, it doesn't block a lot of light either
for a transit. So it's unlikely that we'll find those as well. So I don't think we're unique in the fact that
we have Mercuries. I think they must exist out there. It's just that we haven't ever found any
Mercury analogs. There is some hope though with the Habitable Worlds Observatory that's, you know,
NASA is in planning stages for now. Not going to launch till like the 2040s, but the idea is that
you have a good enough imager on board that you could image at least Earth-like planets.
Probably capture Venus as well.
Whether you'd be able to get Mercury if it's further away from its star, maybe.
But I think that's a big, big question.
I think the focus is more on Earth-like planets than Mercury-like planets, sadly.
Okay. But Mercury's orbit is an interesting one
and it helped to explain general relativities.
So can you explain that one?
Yeah, yeah.
So, I mean, the best way to describe
what Mercury's orbits,
I mean, most planets' orbits look like
is, you know, a spirograph.
Do you remember spirograph from when we were kids?
Right?
The little game where you put your pen in a little cog
and you'd like turn it around in a circle. Yeah, yeah, exactly. Pretty it around yeah yeah pretty patterns yeah so basically if you don't know what we're talking about
essentially like you think about a planet making a loop around its star and just tracing that same
path over and over again but actually once it's made the loop it doesn't really join up
with where it was before and it does another loop of its orbit sort of next just next to where it
was before and you can see how that sort of spirals out to make almost like a pattern like a like almost like a petals of a
flower right it's what it ends up sort of looking like right and this is like scientific term for
this is perihelion precession perihelion means the closest point uh to us to the sun in a planet's
orbit essentially what it means is that that point is is moving around a circle really is what's
happening it's where your pen is in your paragraph basically right all planets do this process ever
so slightly and that can be explained by newton's laws of gravity and kepler's laws of motion and
things like that but for mercury the effect is so pronounced like it's so much bigger than for the other planets,
because it's so close into the sun and the pull of the sun's gravity, that this is what gives it
this sort of bigger, more pronounced effect when this happens. The Newton's laws of gravity can't
explain this. You have to start considering all of the relativistic effects that come from the
fact that you're in a stronger gravitational field because you're closer to the sun, which is where
Einstein's theory of general relativity comes in, which explains gravity
in terms of relativistic effects. And it was actually one of the very first proofs of general
relativity when Einstein was actually like putting together his new theory of gravity.
It was like, oh, well, here's this one problem that no one's been able to explain for ages,
you know, like Mercury's orbit. Let's see if it fits. And it does. It fits really, really well.
but let's see if it fits.
And it does.
It fits really, really well.
We've seen two missions travel to Mercury before. We had NASA's Mariner 10 spacecraft in the 70s,
making the journey for the very first time,
and it made three flybys.
And then we had NASA's Messenger mission,
which studied Mercury from 2011 to 2015.
So what did they show us?
And what is ESA's latest mission, BepiColombo, aiming to find?
It's something that I asked Dr. Simon Lindsay from the University of Leicester, who's the
instrument scientist of MIX, which is one of the instruments on board of the spacecraft.
We knew almost nothing about it before those missions went there. So Mariner was able to find
that had a magnetic field, which is very odd.
It's imaged about half of the surface. It measured this temperature differential, but it was only
able to do so much. You've got these three flybys, they each last a few hours. And that was the whole
of the mission. Messenger is the source of basically everything we know now. So it was
orbiting more or less north to south. It mapped the whole surface
for the first time. It measured the composition of the surface. It mapped out the magnetic field.
It took all sorts of altitude measurements that allowed us to build up this topographic map of
the planet. And yeah, pretty much everything else we know comes from that mission. Yeah. And now
we've got BepiColombo, which launched in 2018.
So what was the aims of this mission?
What can you tell me about BepiColombo?
So BepiColombo has a few sort of USPs.
One of our unique points is there are two spacecraft,
well, two science spacecraft that make up BepiColombo. So we have European NPO, Mercury Planetary Orbiter,
which goes into a low orbit.
It's polar like Messenger, maps the surface.
So it's got objectives to do with the composition of the planet, the formation of the planet.
It also maps its magnetic field at low altitude.
And then we have MEO, the Magnetospheric Orbiter, which orbits further out from the planet.
That's there to map out the magnetic environment, to look at the
interaction of the planet and the solar wind, to measure the planet's exosphere, all these sorts
of things. We are trying to answer these sort of quite fundamental questions about the planet. It's
this weird, unusual planet. It's the closest to the sun. We call it an end member of the solar
system. So it's the smallest planet. It's the closest to the sun. It call it an end member of the solar system. So it's the smallest planet. It's the
closest to the sun. It's the extreme in quite a lot of ways. And Bepi is very much looking at
what that means about the formation of Mercury and its properties now and what that means for
the solar system as a whole. And so what's on board? How is it going to find out all of this
information? Because there's a lot packed in there.
Yes, yes, absolutely. So there are a lot of instruments, exactly how many depends on how you define them, but there's about 16. So on MPO, the instruments are kind of focused around the
surface, but not exclusively. On MPO, we have visible camera, we have an infrared camera,
exclusively on MPO we have visible camera we have an infrared camera we have a suite of exospheric instrument we have a magnetometer we have a gamma ray spectrometer we have a x-ray
spectrometer which I work on and I am sure I'm leaving someone out but that's the ones I can
remember I mean you've done well to list as many as you have to be fair thank you thank you very
much and then uh on M mio i could say they're a
little bit more focused on magnetospheric stuff so there's a magnetometer again there's a plasma
wave instrument and then there's a large number of different particle instruments electrons protons
and and ions and so forth and measures how they move around inside the environment of the system yeah and you work on an instrument called mix so what is that
doing so mix stands for uh mercury imaging x-ray spectrometer which is very confusing because it's
mixed with an s and i when we first started before we started recording i was like can i just check
how we pronounce this absolutely everyone calls it mixes the first time. So you will only understand the name properly if you speak Finnish.
So we are part of a suite of two instruments.
We're a pair with another instrument called SIX, which is Finnish.
Hence this whole thing.
SIX stands for Solar Intensity X-ray Spectrometer.
And this is a pun if you know Finnish because mixy is Finnish for why
sixy is Finnish for because I love that that's very good we often talk about this like the way
that scientists and physicists name things I love a pun yeah like that we are addicted to acronyms
okay so what is mix doing and how does it work okay so it's an X-ray spectrometer. And what that means is it's measuring X-rays.
That's the obvious part.
The reasoning behind this is that X-rays are continuously being put out by the sun.
Those X-rays get absorbed in any material you put in the way.
So in our case, that's the surface of Mercury.
Mercury has no atmosphere.
So that means none of those X-rays get absorbed on the way in.
They get absorbed in the surface of the planet. Atoms in the surface gain energy from these x-rays.
An electron gets promoted or ejected from the atom leaving a gap and then that gap is filled
by an electron from a higher shell in that atom and in the process it emits an x-ray.
And that's the x-ray that we're measuring. And the reason that this is interesting is that the energy of the X-ray will tell you what atom it came from.
So if you're able to measure that energy, you can say that came from silicon, calcium, magnesium, whatever.
So that's what we do.
We fly around connecting these X-rays, tracing them back to where they came from on the surface and saying there is these
elements in this location on the surface and that means that we can build up a map of the composition
at the surface. I mean that makes total sense so where is BEPI now? It is rapidly approaching
Mercury right now the trajectory of the the mission is very very long it launched in 2018
and it's still a couple of years
till it gets there. This trajectory has several flybys in it. So we flew past Earth, we flew past
Venus twice, flew past Mercury three times so far, and then we will fly past again on the 4th of
September. That will be the 4th of six flybys. We've got two more Mercury flybys to go before we
finally go into orbit. I mean, that sounds really exciting. And so we've got, you said a few more years until
Bepi actually reaches Mercury. So is there anything a bit more specific than that? And
then what will it be getting started on? So it gets started in 2026, a science mission begins.
We expect it to last a year. We hope it will last two years. We expect
to be cooked before too long. But in that time, we are really sort of poised because we know we've
got this short mission and we've been waiting a very long time to get that data down. So we're
very poised to spring into action as soon as this data starts coming down and make the best
we can with the data we get back. Thank you to Simon Lindsay from the University of Leicester.
This is the Supermassive podcast from the Royal Astronomical Society with me,
astrophysicist Dr Becky Smethurst and science journalist Izzy Clark.
This month is all about Mercury, so let's dive into some listener questions.
Becky at Kashetid on Instagram wants
to know, and I hope I've said that handle correctly. They want to know, why doesn't
the gravity of the sun and other planets cause Mercury to fall into the sun?
Well, it's because it's in orbit, essentially. So it's moving with enough speed in its orbit to
keep it there, despite the fact that the sun is still pulling on it due
to gravity like i always like to think about you know when we put uh things like satellites into
orbit around earth right we have to give them enough energy so that we throw them so they're
almost making this like perfect circle around the earth so that like they're falling to earth but
they're always just falling past it yes yeah yeah it's like it's like a similar thing right for
planets orbits as well if if you
were you know wanting to actually cause mercury to fall into the sun which you know let's let's
go easy on the little guy let's just say we were evil villains and we had this power yeah yeah um
and we had some minions um we would need to like nudge with enough energy to like you know remove
energy from from mercury like or give it
some energy to change its orbit in some way so you could do that with maybe like a again like a
collision between mercury and a massive object like only an asteroid would have enough energy
to do this but you know another planet maybe would give it enough energy to change its orbit in some
way and as soon as you change the orbit you make it unstable and that's when then the pull of the
sun's gravity might start to win out and pull it
towards the sun.
But for now, it's just sort of falling perfectly around the sun.
So it never falls into the sun.
Okay, thanks, Becky.
And Robert, iMusic sent an interesting question about averages.
And they say, on average, Mercury is the closest planet to Earth.
Do you find it counterintuitive? So
let's look into this a little bit more. Is that true? And can you explain it?
Yeah, so iMusic, yes, I definitely found it counterintuitive. And I was thinking,
so I had to do a bit of sense checking and reading around. And there was an article in
Physics Today describing this work, I think it was five or six years ago now.
And the crucial point is the average distance between the planets.
And what that's taking into account using their method is the fact that, say, Venus, although it gets closer to the Earth
than any other planet, and then Mars and so on,
spends an awful lot of the time further away as well
and goes around the sun slowly.
So when you crunch the numbers you find
that on average and only on average mercury is closer to the earth so is it counterintuitive
definitely yes does it tell us a lot about the layout of the solar system or not to my mind
because you know the order of the planets and the sun is still the same or at least the order of the
planetary orbits it just says that you know sometimes a bit or a lot of the time mercury
is closer to the earth than venus just because venus happens to a bit or a lot of the time mercury is closer to the earth
than venus just because venus happens to be on the other side of the sun so it's it's a curiosity
more than anything else but yes one i was glad to find out about because i have a feeling somebody
else will ask me that having read the article as well i was gonna say do you not remember when this
the animation of this hit the internet like a few years back and like i just remember seeing this
like collective minds blow
it's overturning everything we learned in primary school isn't it you know
it's because we all think about it again as static yeah totally yeah completely i had to deal with
pluto being demoted from a planet and now there's this what else is coming if you need five minutes
robert will understand i'll take a moment and becky elise
asks why isn't mercury the hottest planet in the solar system despite it being the closest to the
sun yeah great question elise i think it just it shows how important atmospheres are for planets
holding on to heat right because mercury barely Mercury barely has an atmosphere, Venus, incredibly thick
atmosphere. So Mercury, what happens is radiation from the sun just hits the surface of Mercury and
bounces straight back off again and is lost to space, right? That heat is not held onto,
it is just lost to space, right? So you can sort of instantaneously heat the surface where you are
in sunlight in that sort of way when, you know, sort of like it could be a cooler winter day and the air could be cold.
But if you feel the sun on your face, it feels warm because you have the energy hitting into you.
It's that kind of a sort of heat that Mercury has.
And that's because, like I said, Mercury's atmosphere is so thin.
The actual only atmosphere that Mercury has is stuff from the surface
that's bounced up off the surface
as radiation from the sun hits into it.
Yeah.
Right, so it's almost like little bits of like rock and stuff
that is the atmosphere.
It's so incredibly, incredibly thin.
It's a hundred trillion times thinner
than Earth's atmosphere.
Yeah.
It's just crazy to think about, right?
Right, yeah.
Whereas Venus's atmosphere is 93 times thicker than Earth's, right?
So all that gas in Venus's atmosphere can absorb all that reflected light
that's come back off the surface, right?
And so it can store it there in the atmosphere.
So the atmosphere warms up and that's what makes Venus the hottest planet
compared to Mercury because it has both that incident sort of heat that's on it
but also the atmosphere to keep it warm too.
And Elise, I would recommend that you listen to our Venus episode as well.
Robert, we've also had a question about life on Mercury from Fiona, and she asks,
what's the likelihood of life being found on Mercury with the knowledge from Earth life?
Well, Fiona, I think sadly, it's really quite close to zero.
And the reason is, look, it's the things we've been talking about,
that Becky was just mentioning, no atmosphere does not help.
You know, huge variations in temperature as a result,
so incredibly hot and also incredibly cold in different places.
Lack of liquid water, which is seen as not necessarily
an absolute prerequisite for life but certainly
helpful and you know never say never maybe but if there was life there it would have to be hiding in
some very much more benign environment under the surface that we don't think we're really aware of
exists at all so it seems really unlikely i guess you know thinking about this could you have
something that some very specialized bacteria or something perhaps but it's
to my mind it's very difficult to see how they'd get started in the first place you know i could
imagine somebody doing some genetic engineering on earth and making something that could live
under the surface of mercury but it seems very unlikely it ever arose there at least to me
happy to be contradicted by an astrobiologist but i think it's a it's a long shot or robert
don't forget what jeff goldblum taught us from last episode as well life finds a way exactly from jurassic park channel jurassic park yeah i guess you've got
to think about like you know we've shown that the tardigrades the little what people call them
water bears those little things they've survived on the outside of the international space station
so clearly like you know no atmosphere and high radiation intense environments
certain types of life can obviously survive it.
But like you say, it's the trigger to get it started.
Yeah.
Yeah.
Like, that's the weird thing.
I think we could probably like contaminate Mercury's surface and see if life survived.
But I probably wouldn't get that past the ethics board.
Yeah, exactly.
I really hope that doesn't happen.
Exactly.
Yeah.
It's evolution, you know, just know just like yes starting point is life
evolves to these extreme environments but it must be a struggle to get started there yeah okay so
thank you to everyone who sent in questions and if you want to send in any questions for a future
episode then you can email podcast at ras.ac.uk or find us on instagram at super massive pod uh feel free to slide into the dms on that
one so shall we finish with some stargazing robert what can we see in the night sky this month yeah
quite a lot as it happens the nights are drawing in equinox is on the 22nd of september so for
those of us in the northern hemisphere you know we're moving into the autumn and winter because
it's getting properly dark so you can see things like the milky way after sunset much more much
more easily than in the summer keep looking out for things like t corona borealis this
star that might just go nova we just don't know when predicted too soon you just have to keep an
eye on that it'll only be really bright for i think about half a day so social media seems like
the way to find that and also planets are coming back so we had sort of months where they were
really difficult to see so venus is just visible after sunset easier to find with binoculars saturn is at
opposition so it's best for the year opposite the sun in the sky on the 8th of september good
throughout the month and really through the rest of the year the constellation of aquarius and the
quirky thing about it is it won't look much like saturn if you look through a telescope because
its rings are almost edge on they've almost disappeared disappeared. And I've put in my notes in the script,
has anybody told Becky about this?
You know, Saturn without its rings.
David taught me about it.
Honestly, I'm not even, I'm sad, first of all,
that they're going to disappear for a while.
Second of all, I'm more just preparing for the headache
of when we do public stargazing with kids and they're like,
but it doesn't look like Saturn.
Exactly.
And you're like, well.
So anyway, yes, it'll come back.
It'll come back.
Be patient.
A couple of years.
Mars is good after midnight, but it is best in January.
You know, a nice opposition, close and bright in the sky then.
Neptune is at opposition as well on the 20th of September, but that's faint.
It's, you know, it's the most distant planet.
You need a pair of binoculars to find it.
A telescope shows it as a disk, and that's about it.
But, you know, if you want the satisfaction of doing that, then get some charts and try.
And Mercury, as we mentioned earlier, is in the morning sky at the start of the month and best on the 5th of September and okay for about a week after that so you need
to get up about an hour before sunrise to try and or look from an hour before sunrise to try and
find that looking over towards the northeast there's also a partial lunar eclipse very partial
on the 18th of September but you have to be watching that
from about 3am onwards, and only about 8% of the moon will be covered by the darkest bit of the
Earth's shadow, so it's not very spectacular, but it'll look like a weird red bite has come out of
the moon. And then two final things, one is, and thinking of the timing of the episodes, we might
be able to reference this in the October one, but's also a comet a potentially bright comet called comet Sushenshan Atlas it's behind the sun at the time of recording so we don't know
how bright it's going to be but it's predicted that it could be easily visible to the naked eye
who knows you know the problem with comets is that it's often said they're like cats they've
got tails and they do exactly what they want so we will see but do look out for that and you know
we'll be flagging on social media and all these things i think there'll be a lot of interest around that and the last
thing i'm gonna notice i've got to reference the fact sunspot maximum the sun is really spotty if
you've got the equipment to look at it safely there's loads to see at the moment there so
really nice time to be observing our nearest star well i think that's it for this one we have
finally completed our tour of the solar system if you missed any of them then just go back into the
supermassive archive because they're all in there we promise we did do them all not in the right
order there's a few feature more than others hey it's what it is we'll be back with another bonus
episode in a few weeks time and then after that we're doing a big topic and we are exploring the
mysterious cosmic web i'm so excited for that one.
Yeah, not to be confused with James Webb space telescope.
No, very different thing.
Very different thing.
And of course, contact us if you try some astronomy at home.
It's at supermassivepod on Instagram
or you can email your questions to podcast at ras.ac.uk
and we'll try and cover them in a future episode.
But until next time, everybody, happy stargazing.