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February 21, 2023 50 mins

Daniel and Jorge talk about the daring and dangerous mission of the Parker Solar Probe and what it might reveal about the Sun.

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Speaker 1 (00:08):
Daniel, how did you get into physics in the first place.
You know, it's kind of embarrassingly cliche. It was basically
staring up at the night sky and just wondering about
the stars and everything out there. That's not really cliche,
you know. I think that's what gets most people interested
in physics. But it doesn't make me wonder about something.
You're wondering about my wondering. Well, if everyone's wondering about stars,

(00:29):
why don't they focus more on the star that's closest
to us, the Sun. I think it's a little bit
more dangerous to stare at the Sun than it is
to stare at the night sky. Why I didn't know
physics was so dangerous. You're living on the edge, the
edge of the Solar system. I'm taking lots of risks,
napping in my office every day. It was like a
sunny job. You got there. Hi am Orhand cartoonists and

(01:05):
the creator of PhD comics. Hi. I'm Daniel. I'm a
particle physicist and a professor at you see erline, and
I'm a big fan of the sunshine. Oh yeah, you're
a big sun bather. You like having a tan said
with those reflective mirrors. I don't embody every Southern California stereotype,
but I do enjoy a sunny day, you know, just

(01:27):
like lifts my mood. I've lived in places where it's
cloudy every day and it's just not as fun. Yeah,
the sun is pretty warm out here in Southern California,
and it's interesting because it means we're getting bathed by
science every day almost as sent the time. It certainly
affects our life. It grows all of our plans, that
controls the weather. It basically is in charge of everything

(01:49):
that happens on the surface of the Earth. And so
you think we might understand it a little bit better
than we do. Are you saying we need to shed
some sunlight on the sun? We need to uminate those mysteries.
Welcome to our podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we try
to shine a light on everything we do and don't

(02:09):
know about the universe. Our curiosity knows no bounds as
it flies from the surface of the Earth down to
the tiny particles all the way out to the workings
of the Sun. At the heart of our solar system,
the fiery fusion engine that powers everything, including life on
Earth and the sparkling stars in our sky. We dig

(02:30):
into all of those mysteries and try to explain all
of them to you as best we can. Yeah, because
it is a bright and sunny universe, shining bright with
amazing knowledge. We're ready for us to bathe in it
and take it in and become an intent our brains,
I guess, to make them more colorful and knowledgeable about
how things work and why things are the way they are.
I really like that picture of the universe as sending

(02:53):
us information, is beaming us clues about how the universe works. Because,
as we've often limited, we are trapped here on this
little rock, mostly unable to physically explore the universe, but
we can decode those signals. The universe is zapping us
information about what's going on elsewhere, letting us put the
pieces together to try to build a mental model of

(03:13):
what is happening far far away. Yeah, and it's pretty amazing.
We are in a little tiny corner of a galaxy,
in a tiny corner of a supercluster of galaxies, in
a tiny corner of the universe, and yet just from
the light we get from other suns out there in
the universe were able to kind of piece together a
huge picture of the entire universe. It really is incredible
how much we do know about things happening far far away.

(03:36):
We have models of little stars and big stars, and
star lifetimes and star deaths and star explosions and star implosions,
all just from watching from this little rocky perch in
the suburbs of the Milky Way. And that knowledge has
been developed over many, many years, people staying up late
at night, freezing their bones to look up in the
night sky and take careful notes, and developing fancy new

(03:58):
technology to take better pictures of what's going on out there,
and more recently actually sending probes out to explore our
neighborhood and try to learn a little bit closer up
what's going on. Yeah, because we can learn a lot
about stars and also about the star that's closest to us,
the Sun. It's kind of easy to forget that the
Sun is a star. You know, like, if you're an

(04:19):
alien in another planet and you look up at the
sky and you see a tiny pinpoint shining bright in
the darkness, that could be us, That could be our sun.
Sending them information about the universe in US. Yeah, and
I think the phrase solar system is sort of underappreciated.
It's not just that we have a star and it's
at the center of the system. We really are part

(04:41):
of our star. In some sense, we are living in
the atmosphere of our star. It really does dominate the
Solar system in a way I think people don't really understand.
It's of the mass of the Solar System is in
that star, and it's sending out enormous waves of energy
and particles all throughout the Solar system. So you could

(05:02):
say we're just sort of like flying high in the
very outskirts of the solar atmosphere. You know, we are
a tiny little part of the Solar system. It is
basically the Sun, the whole Solar system. We're almost like
little tiny moons on a giant exploding ball of fire. Yeah,
you could say that we live on the Sun. You know,
in some sense. The edge of the Sun is not

(05:23):
really something that's well defined. You could say the whole
Solar system is basically just the Sun, and we are
part of it. Yeah. And even though it is the
closest start to our system, and it provides light for
us and heat and which powers all of life on
this planet. There's a lot that we surprisingly don't know
about our own son. It is fundamentally important to everything

(05:44):
we do. It's the best example of a process that
happens all over the universe, and it's really important for
the universe looking the way that it does. And yet
we still have basic questions about what's going on inside
our star, how it all works, and how it's even
stable for it to get so hot. Yeah, and it
seems like an important question right to understand this giant

(06:05):
exploding ball of nuclear powered fusion happening right next to us,
you know, like, is gonna keep doing that? Is it
going to go out? Is it gonna explode? What's going
to happen to it? It It seems like important to find
out what's going on there. Yeah, if I lived right
next to a fusion reactor, I want to understand pretty
well if it was going to blow up or if
it was going to fail, or what it was going
to do, and why it's it's suddenly so hot. There

(06:27):
are lots of practical reasons to understand the Sun. It's
also just a great mystery, like it's doing so much cool,
amazing important stuff, huge tubes of plasma, superheated, incredibly powerful
magnetic fields. It's just a great laboratory for understanding, like
what can the universe do? After all? How do all
these forces come together in extreme environments to create such

(06:50):
a dramatic and beautiful display. Yeah, I'm not sure I
would call what the Sun is doing cool. It's more
like maybe little. It's sisslingly hot. Yeah, there's a lot
we don't know about the Sun, and so today on
the podcast, we'll be asking the question what will the
Parker Solar Probe teachers? I'm guessing things about the Sun? Yeah,

(07:15):
the Parker Solar Probe is a really fun piece of
technology that humanity designed, build and launched out to go
and explore, to visit up close the Sun and to
try to get some answers to some pretty basic questions
about how the Sun works. Yeah, it's a pretty cool
NASA project, one which I made a comic about last year.

(07:36):
I don't know if you know those for Physics magazine.
Oh no, awesome, I didn't see that. Yeah. I had
to interview a bunch of scientists for it, and I
put out a comic of your Google, peachd Comics and
Parker Solar Probe. You will find it in case you
need like a visual companion to this episode. Awesome. I
encouraged everyone to check that out. Jorges cartoons explaining signs
are always super well done and the visual is always

(07:58):
very helpful. Yeah, it is a pretty your sting and
fascinating project over at NASA there and so, as usually,
we were wondering how many people had heard about the
Parker Solar Probe and what they know about it. So
thank you very much to everybody who volunteers for this
segment of the podcast. We'd love to hear your voice
as well. If you've been listening for a while but
never screwed up the courage to write in, please don't

(08:18):
be shy reach out to me at questions at Daniel
and Jorge dot com. So think about it for a second.
Have you heard the Parker Solar Probe. Here's what people
have to say. I actually learned some things about the
Parker Solar Probe recently, and that that well, study the
older atmosphere of the Sun or the outer corona, and
to learn why it is hotter actually then the surface

(08:42):
of the Sun. I believe the Parker Solar Probe is
designed to investigate some of the physics behind the fusion
of our Sun and perhaps try to explain why there
is a temperature differential whereby the gases that are expelled
or the atmosphere of the Sun that is farther away

(09:04):
from the surface actually heats up as it leaves the
surface of the Sun. So I guess it's going to
the Sun, the Parker Solar Probe. So I feel like
I could probably tell us about pangnetic field or maybe
solar flares or um and stuff like that. I have
absolutely no idea speculating. I would imagine that it would

(09:26):
be something that would go out into the Solar system
in order to collect information on things that we otherwise
can't infer, such as particles in space, radiation from this
point in space, or perhaps a different perspective that we
can't get from Earth. I have no idea what the
Parker Solar Probe is. I don't know I would get
something to do with like temperature radiation, have no clue,

(09:48):
maybe solar flares. Not a lot of name recognition, but
I think people are sort of pieced together that it's
probing the Sun Yeah, but people seem excited to learn
about what the Parker Solar Probe might teach us about
the mystery of the source of all energy and life
on Earth. Yeah, and so let's dig into it, or
I guess, let's go out into the Sun with this idea.

(10:08):
First of all, what is the Parker Solar Probe? So,
the Parker Solar Probe is a really cool project. It's
a spacecraft launched from Earth to go investigate the Sun. Basically,
to do a bunch of really close fly bys close
sort of by solar standards, and measure a bunch of
things about the Sun, to try to get a handle
on some long standing mysteries about how the Sun works,

(10:32):
what's going on inside it, how it gets so hot,
and the solar wind that flies out from it. And
so in the end, it's just a satellite that we
launched from here. It zooms around Venus a few times
and makes a bunch of approaches to the Sun and
gathers a bunch of data about what's going on. Well,
you can't just call it a satellite. It's more like
a spaceship, right, spacecraft, that's right. It's not a satellite

(10:52):
in the sense that it's orbiting the Earth, it will
be orbiting the Sun, so in that sense, it's a
satellite of the Sun. But yeah, spacecraft is definitely cool, ruler,
and this one contains a lot of really cool technological
advances to let it like survive getting so close to
the Sun. It's going to get closer to the Sun
than any human object ever has and it's going to
have a velocity with respect to the Sun greater than

(11:14):
any human object has achieved. Super cool. But this is
not the first spacecraft we sent to the Sun, right
for the first spacecraft we've used to study the Sun.
This is kind of the latest and most awesome and
the one that's going to get to the Sun the closest. Yeah,
the last spacecraft to go visit the Sun before this
was the Helios two in nineteen seventy six. So it's

(11:35):
been a few decades since we've visited the Sun. It's
been a lot of planning, a lot of technological advancements,
a lot of ideas, a lot of arguing at NASA
budget meetings. So it's exciting to get to go back
to the Sun with new technologies and upgraded instruments and
to get closer as you said than ever before. Yeah,
it's a hot mission, and it's a long mission to write.

(11:55):
It's didn't just take decades to get it going, but
the mission itself office is several years. It was launched
in August of two eighteen, and you know, even when
it launched, it was already unique for a couple of reasons.
One is that it was named after a living person.
Eugene Parker, who's a famous theorist about how the Sun works,
was alive at the time it was launched, even though

(12:16):
he was ninety one, and he was on hand to
observe the launch, which is really cool. Also, it contained
the names of more than a million people who wanted
their name to sort of touch the Sun. NASA let
people submit their names and they wrote down more than
one point one million submissions, put it on a memory
card and slapped it on the outside of the probe,
so those people could sort of ride along and go

(12:38):
visit the Sun with them. No kidding, for real, They
just like duct tape a little flash drive to the outside. Yeah,
there was a memory card mounted on the plaque so
that all those people could feel like they went to
visit the Sun. Pretty cool, but you're right, there's gonna
be like twenty four solar orbits in a seven year mission.
So it's going to zip around the Sun a bunch
of times, and it goes sort of between the Sun

(13:00):
and Venus and the Sun and Venus, and some of
those visits are closer to the Sun and some of
them are further from the Sun. Also, remember that the
Sun has a weird cycle of its own. It's about
eleven years, so the mission lasts long enough to allow
us to sample the Sun several times in different places
in its own internal cycle. M what do you mean
the Sun has a cycle like it It's it's not moving.

(13:20):
I mean it's moving through space, but it's not really
were respective the solar system. It's more like has cycles
of its temperature and size. Right. Yeah, people have been
noticing over the last few hundred years that there's an
eleven year cycle of the Sun. Over eleven years, you
see like the number of sun spots rise and then fall.
And people have been recording this four hundreds of years.

(13:40):
It's something we've known about it for quite a while.
And so the number of like solar flares and corona
loops increase and then fall, and actually they think that
this cycle has been pretty stable for like hundreds of
millions of years. They see evidence of this going back
to like the impact on ancient tree rings that have
they dung up, like fossilized tree rings from hundreds of

(14:02):
millions of years ago show these same kind of cycles.
Are you saying the trees are the original scientists, solar
scientists of Earth. It's incredible how sensitive life on Earth
is to like the mood of the Sun. As the
Sun gets hotter, it changes the weather on Earth in
a way that we can measure hundreds of millions of
years later because of the impact on the trees. And

(14:24):
it's not just the Sun's weather. The Sun's magnetic field
also flips every eleven years. Remember, the Earth's magnetic field
also flips, but it's very irregular. Sometimes it flips every
fifty thousand years, sometimes every million years. The Sun's magnetic
field flips every eleven years. So that's all part of
the solar cycle that people want to understand. And so

(14:44):
the mission is like seven years long to try to
gather data from different parts of that solar cycle. Yeah,
super interesting. Now for the probe. One thing that I
found interesting when I talked to scientists about this was
that it's actually really hard to get close to the Sun.
Like you would have thought that sending something to design,
you just kind of put it in space and then
the gravity makes it fall towards the Sun. But actually
you need a lot of energy to slow down your

(15:06):
space graph in order to get close to the Sun. Yeah,
as you fall towards the inner Solar System, you speed
up because you're trading gravitational potential energy for kinetic energy,
and so you likely to sort of like whizz around
the back of the Sun. That's true because you have
angular momentum and it doesn't go away, right, and so
you need to use some energy to basically lose angular
momentum if you want to actually fall into the Sun.

(15:29):
And that's why it goes around Venus, right. It kind
of uses Venus's gravity to slow itself down exactly, uses
Venus as like a gravity assist and it's gonna do
like five different flybys of Venus to try to shed
some of that energy so we can get closer to
the Sun. There were previous designs for this mission back
in earlier iterations, when it was going to use Jupiter

(15:50):
as a gravity assiste. And also have like a bunch
of nuclear power on board to try to help it
get even closer. So previous designs, we're going to get
even closer to the Sun than the actual spacecraft that
they launched, but it wasn't going to be near the
Sun as long. It was gonna be like a very
fast close fly by. So they opted for this approach,
which is cheaper, didn't require nuclear power, and give them
a longer visit to the Sun, even though it's a

(16:12):
little bit further than the original design. Yeah, and so
it's on this kind of elliptical orbit where it's kind
of swinging between Venus and the Sun. You can imagine
like in the ellips Like one end of the ellipse
is really close to the Sun, and that's the fly
by they do close to the Sun to take data
from the Sun exactly. So it's going around. Remember this
is like a multi year mission. It's gonna be like

(16:32):
twenty four solar orbits. As of October two, it's done
thirteen of those so far, and so it's like more
than halfway through its life, but there's a lot more
coming and we're all looking forward to it getting closer
to the Sun. It hasn't yet reached its closest approach,
and also it's sampling the solar maximum, which is going

(16:53):
to happen in around five that's when the Sun is
like at its peak of solar activity. Mm. Yeah, because
every time it goes near the Sun, it gets a
little bit closer each time, right, Like the orbits are
getting smaller and smaller. Yeah, if you look at a
map of the orbits, you see it's sort of cork
screwing around in this elliptical path, as you say, between
the Sun and Venus, so sort of like zooming in

(17:15):
on the Sun. Yeah, it's pretty cool that we can
like navigate a spacecraft around the Solar System like that,
like swinging between the Sun and then on the planet. Yeah.
It requires really precise knowledge of where everything is in
the Solar System and also a really detailed understanding of gravity.
You know, these are also really exquisite tests of our
understanding of how gravity works, because you're talking about throwing
a rock and basically predicting where it's going to be

(17:38):
in ten years right as everything is flying around the
Solar System. So it's incredible precision and really awesome sort
of control over the physics of the Solar system and gravity. Yeah,
you don't want to fall short on that knowledge of
gravity when you're sending something close to the Sun. Yeah,
and so this thing is going to get closer than
anything has ever gotten to the Sun before by actor

(18:00):
of seven though when you say the number doesn't actually
sound that impressive. It's going to get within four million
miles of the Sun. It's like just under five of
one au the distance from the Sun to the Earth.
But that is seven times closer than any previous mission,
and it's going to be within ten times the radius

(18:20):
of the Sun. Yeah, it sounds like a lot, but
it's actually super different close to the Sun and super
dangerous and in fact, people I think one of the
ways they described is that it's actually gonna touch the
Sun in a way, and we'll talk about that later
about what that means. Yeah, it's cool to think about
touching the Sun. That we can of course argue about
what it means to touch it, because like where is
the edge of the Sun In some definitions, we're already

(18:43):
in the Sun. And it's definitely fascinating to get nearer
to the Sun and to study up close what's going
on with its magnetic fields and its corona and the
solar wind and maybe even understanding what's going on inside
it to generate all these cycles. Yeah, and as the
sent this probe to the Sun to learn about its mysteries,
there are still a lot of things we don't know
about the Sun, and so we'll get into those. But

(19:05):
first let's take a quick break. All Right, it's the
sunny day here in southern California, and we're talking about
the Sun and the probe that NASA has sent to

(19:26):
study it, the Parker Solar Probe, launched in August, and
it's been making closer and closer passes to the Sun,
getting us closer to what's going on there in the
inside of the Sun and in its atmosphere, to learn
about some of the deep mysteries we still have about
how it works and what's going on inside there and
outside of it. Yeah, you think that after studying the

(19:47):
Sun for hundreds or thousands of years, that we might
understand better this fusion engine at the heart of our
solar system, the thing that's basically making all life on
Earth possible. And while we do have some understand of
how stars work in general, there are a lot of
big mysteries remaining about basic facts about the sun. Yeah,

(20:07):
like why don't my kids like to put on sun block?
It's a huge mystery to me. The fight to the death.
Maybe you should move somewhere less sunny, Maybe you should
get them into the habit of wearing hats. Perhaps, But
the Sun does have a lot of interesting and pretty
deep mysteries about it that we still don't know, and
so let's dig into those, Daniel, what are some of
the unknowns about the Sun or the sun knowns? One

(20:27):
of my favorite mysteries about the Sun is just why
the outside of it is so hot. You know, the
Sun is of course very very hot. It's thousands of
degrees at its surface, and that's where the light that
you see is generated. Remember we talked on the podcast
several times about the connection between temperature and wavelength. Everything
in the universe radiates light, and the light that it

(20:48):
radiates depends on its temperature. And the Sun is several
thousand degrees kelvin and at that temperature you tend to
radiate in the visible spectrum. And it's no coincidence, of course,
that the Sun tends to give off light in the
visible spectrum. Our eyes evolved in this environment in order
to see the light typically given off by the Sun.
And so the sun itself is several thousand degrees kelvin.

(21:10):
But around the sun is something called the corona, which
is much much hotter than the Sun itself. And that's
a really big mystery how that gets so hot and
how it stays so hot. Yeah, it's a really weird thing,
and it's a little bit hard to wrap your head
around because the Sun itself is not one temperature, right, Like,
the core of the Sun is super duper, duper duper
hot because that's where all the fusion is going on.

(21:32):
But as you get closer to the surface, it's sort
of cools off, right, Like the surface of the sun
is much cooler than the center of the Sun. But
then if you keep going out further past the surface,
it actually starts to get hotter. Again. It's like having
a light bulb where the air around the lightbulb is
hotter than the surface of the light bulb itself. Expect
the hottest point to be the center. This is the

(21:54):
source of the heat where most of the fusion is
happening until the star gets much much older, of course,
but in a star the to the age of our Sun.
Mostly you have hydrogen fusion at the core which is
driving it, and then it cools off, as you say,
as you get to the outer regions. But then it
weirdly spikes again. So this part the corona is hotter
than the actual surface of the Sun itself. It can

(22:14):
be like hundreds of times hotter. The corona is like
millions of degrees kelvin. Yeah, it's super weird. It's like
you said, it's like you can imagine the air around
a light bulb hotter than the actual surface of the
light bulb. Like, what's going on there? How is that possible?
It's a big mystery, and it's been a mystery for
more than a hundred years. People who have been studying

(22:36):
the Sun, like in the eighteen hundreds were looking at
the light that comes from the Sun and they noticed
something really weird when they looked at the spectrum, Like
they took the light from the Sun and they asked,
what is the wavelength of all the photons that we get.
That's sort of the spectrum, and it peaks in the
visible range as you expect, But there's also one particular line,
this green line from the Sun at a very strange

(22:57):
wavelength that they couldn't explain. The only way to explain
this line, The only thing that tends to give off
light at this particular frequency is a weird form of iron,
iron that's been ionized thirteen times. So iron has like
twenty six protons and twenty six electrons, and in extremely
hot situations, it can get so ionized that it loses

(23:19):
thirteen of its electrons. So this is iron thirteen plus
and this is capable of making that green line. But
it only exists in situations that are super duper hot,
like multimillion degree plasmas. So they spotted this in eighteen
sixty nine and it was a real puzzler. Yeah, it
tells us that the corona of the Sun is a

(23:39):
lot harder than the surface of the Sun. And now,
to give pe pose some context, I think you maybe
mentioned that the corona is It's like the Sun is
about one point four million kilometers. Why, but the corona
extends eight million kilometers around the Sun, right, It's like
a much wider circle that they call the corona of
the Sun. That's right. And if you just like had

(24:01):
a hot blob of gas around the Sun, that was
hotter than the Sun, than that heat would flow in
it would cool down. This is not like an equilibrium situation.
In order for this to persist, you need some source
of heat. But if the source of heat is the
Sun itself, you would expect it to be hotter in
the core. So really nothing about this makes sense. There
needs to be some way to heat the corona, and

(24:22):
it doesn't seem like it can come from the inside, right,
And so it's a very strange situation. Somehow heat seems
to be flowing out, violating the second law of thermodynamics,
from something cooler, which is the surface of the Sun,
to the corona, which is hotter. Right. He doesn't usually
flow from a cooler surface to a hotter surface, right. Well,
there's some subtleties. I think then maybe we need to

(24:43):
go over like, for example, you're talking about temperature, not
overall energy, Like the corona is hotter than the surface
of the Sun, but it's a lot sparser. So this
is one of those situations where it's like it's not
like there's more energy outside of the Sun, it's just
that the particles that are there are moving fast for
than the particles at the surface of the Sun. Right,
that's exactly right. It's much less dense than the surface

(25:06):
of the Sun, but the temperatures are higher. In the
same way that you can have very high temperature plasmas
between galaxies, places where if we dropped you without a
space who you would instantly freeze. Though technically you're in
a very high temperature plasma. It's just very dilute. So
there are fast moving particles, just not very many of them.
So I think the same thing is true here. The

(25:26):
corona is definitely hotter than the surface of the Sun.
They're faster moving particles, but they're not as many of them,
so there is less energy. Yeah, but it's still kind
of I guess the mystery is like, why are these
particles around the Sun moving faster than the particles just
coming off of the Sun, Right, that's kind of the mystery. Yeah,
exactly where did they get this energy? Because by a

(25:47):
standard heat diffusion process, that shouldn't happen. You shouldn't get
this weird spike where things suddenly get hotter further from
the source of the heat. Now, could it just be
like a situation where it's just the gas around the
Sun is absorbing the heat from the Sun and getting
that heat building up, you know, like kind of like
if I put a black blanket around a light bulb,

(26:08):
but it's gonna get hot. It is gonna get hot,
but it's not going to get hotter than the light bulb. Right,
That's the weird thing that's happening here. The air is
already a blanket around the light bulb, and it doesn't
get hotter than the light bulb. The heat diffusion equations
tell you that the heat flows from the higher temperature
to the lower temperature. So you need something else to
explain this. You need some way to like pump energy

(26:29):
out from the Sun, some other kind of process, not
just diffusion of energy, all right, So that's a huge mystery.
There are also other mysteries about the solar wind. Yeah,
this is sort of connected in the sense that there
are mysterious high speed particles. The solar wind is something
that actually is kind of well named because when you
think about a wind on Earth, you're thinking about like

(26:49):
high speed particles pushing on you, bouncing off you, transferring
their momentum. Well, the solar wind is sort of similar.
The Sun doesn't just put out photons, it also puts
out particles, protons, electrons, all these things moving at very
very high speeds, like hundreds of kilometers per second. So
this is what we call the solar wind, and it
flies out through the whole solar system. Right, you get

(27:11):
the solar wind even out here on Earth, and it's
far out of Jupiter and Neptune. It's like it's not
just light, it's actual like stuff flying from the Sun. Right. Yeah,
the Sun is sort of throwing itself at us. This
is one reason people say that we're sort of in
the atmosphere of the Sun, because we are in this
envelope of gas that the Sun is basically produced and
it's sitting in the middle of Yeah, so then what's

(27:32):
the mystery about the solar wind. The mystery is how
the solar wind gets so fast, Like a four hundred
kilometers per second is very very high speed for these particles.
If you build a model of the Sun and just
think about like particles at the edge of the Sun
boiling off based on the temperature of the Sun, then
you don't get particles this high speed. Like the Earth

(27:54):
has an atmosphere, right, and it's losing its atmosphere because
things at the very top of the atmosphere are moving
at high speeds and gravity is lower, and they just
sort of like fly off they reach escape velocity. So
the Earth is boiling off hydrogen the same way the
Sun is boiling off particles of itself. But if you
do the calculations and predict how fast those particles should
boil off, you get like a hundred and fifty kilometers

(28:17):
per second, But what we see are things like four
hundred kilometers per second. So there's some mechanism we don't understand.
It's like accelerating these particles over a really short distance
just from like the surface of the Sun boom out
through the corona and out into the rest of the
Solar system. You're saying the solar wind is faster than
what you would expect. Now, is that related to also

(28:39):
why the corona is harder, Because the corona beaming harder
also means that the particles there are moving faster than
what we expect. Yes, we think that these might all
be connected mysteries, and the answer to them might lie
somehow in the magnetic fields, because Sun isn't just a
hot ball of gas the way the Earth is has
very very powerful magnetic fields that are driving is happening

(29:00):
inside of it, and also that are driven by what's
happening inside of it. And these mathetic fields contain a
lot of energy. And so if essentially you're getting little
pumps or these magnetic fields are breaking, then those are
various theories we have about how these particles might get
accelerated really fast. And it also might explain how the
corona is getting heated so much cool Now, you mentioned

(29:22):
solar cycles before the cycles that the Sun goes through.
There are some mysteries about that too. Yeah. I think
this is one of the most incredible mysteries in the
solar system, which is that the Sun's magnetic fields flips. Right,
I mean, it blew my mind when I learned that
the Earth's magnetic fields flips. First of all, that it
isn't just static. It isn't just like point the same direction,
like wanders around a little bit, but that every fifty

(29:44):
thousand years or million years, it changes direction. North becomes south,
south becomes north. If that's not weird enough for you,
the Sun does that also, but it doesn't like clockwork.
Every eleven years it flips. I can't overstate how much
energy is involved here because the song one is enormous
and whatever is causing its magnetic fields are very very powerful.

(30:05):
For that entire thing to flip over, it's like turning
a football stadium upside down, right, and it does it
every eleven years. Yeah, it's pretty amazing. And so you're saying,
we don't quite know why they flip, or we don't
know what's causing it to flip every eleven years. Both,
we don't even know why it flips. We don't know
why the Earth's magnetic field flips either. But we definitely

(30:27):
don't know why the Sun's magnetic field flips, and we
don't know why it's so regular. We have a bunch
of different theories for why the Sun's magnetic field flips,
some of which are pretty awesome and hilarious. Is it
like an eleven year old kid at the switch, just
going click click click click, click click plick. I don't
think eleven year old kids are that regular over a
seven hundred million year timeline. It's amazing. The first thing

(30:50):
to understand is how you get a magnetic field anyway.
For the Earth, we think it comes from like motion
of fluid metals inside the Earth. Right, Essentially, you're having
the flow of charge particles creates a magnetic field that
pushes the charged particles. You get more flow, which gives
you more magnetic field. It's called the dynamo. And we
have a whole podcast episode about where the Earth's magnetic

(31:10):
field comes from. It might be that the Sun's magnetic
field also comes from something similar. But these dynamos, these
flows of plasma within the Sun could be affected by
other things. Like for example, it could be that gravity
from the other planets like Jupiter and Saturn and even
the Earth are tugging on these things, and as they
move around the Sun, their collective gravity could like create

(31:33):
an instability which flips the whole thing over. Yeah, it's
like a giant generator basically inside of the Sun and
the Earth where you have like a all these kind
of like magnetic materials kind of swirling around and creating things.
And so I guess if the overall flow changes and
the overall magnetic field changes to Another possibility is that
it could be due to differential rotation. Like the Sun rotates,

(31:55):
but it doesn't rotate the same speed all over. It's
not a firm object the way the Earth is, right,
and so for example, at the equator, it takes about
thirty five days for the Sun to rotate, and it's
twenty five days to rotate closer to the polls, And
so the magnetic field lines might be getting like twisted
and pinched, and it might take like eleven years for
enough tension to build up for everything to sort of

(32:17):
like snap and reassemble upside down. That's another possibility. And
there's a third possibility for what might be explaining the
Sun's weird magnetic field, which is that the plasma currents
inside the Sun that are generating these magnetic fields might
be moving sort of like in a huge donut of plasma.
Like imagine not just a donut, but a donut now

(32:38):
with layers in it. Like what do they call that
when you have a croissant and a donut together, a chronut, right,
So imagine a donut with all these layers in it.
And every eleven years, instead of these plasma currents going
sort of around the outside of the donut, they flip.
So now they're going like around the short side of
the donut. Briefly before it's flipping around and going the
other direction. So we have like lots of very different

(33:00):
weird ideas about what's going on inside the Sun, and
the problem is we just haven't gotten close enough to
make the measurements we need to understand what's going on. Yeah,
because it is pretty hard to get close to the Sun,
as I think Icarus and his father learned, it's hard
to touch the Sun, and obviously also a little bit
dangerous because the Sun is so hot and putting out

(33:21):
so much radiation and light and heat. And so let's
get into what it takes to build the spacecraft to
get that close to the Sun to solve some of
these mysteries. But first let's take another quick break. All right.

(33:44):
We're talking about the Parker Solar Probe, which is the
fastest or it's going to be the fastest moving spacecraft
that humankind has ever built, and it's also going to
get closer to the Sun than anything we've ever build.
Some say it made it's sort of in a way
touches the Sun. That makes me think of that kid
on a Christmas story who puts his tongue on the

(34:04):
life post and gets it stuck. Yeah, it does sound
like a cautionary till the people who try to touch
the Sun. Yeah, and I love this description of it
as the fastest thing ever built, and that sounds really
impressive until you kind of hear the number is going
to go zero point zero six four of the speed
of light relative to the Sun, and that's really really fast.
It's like six thousand kilometers per hour, six hundred and

(34:29):
ninety kilometers per hour. Thousand kilometers per hour. That is insane, right, because, um,
as you go down the highway, you're going at like
a hundred kilometers per hour. Does is six kilometers per hour? Yes,
it's much much faster than I hope any of our
listeners are traveling on their commute. But it's also such

(34:50):
a tiny fraction of the speed of light, just another
sense for like how vast the universe is and how
extreme the conditions are out there, and how like quiet
and cozy things are in our neighborhood. It's still a
pretty amazing achievement. And it's also a huge achievement to
send something that close to the Sun because the Sun
is hot, like it's hot here on Earth, Like if

(35:13):
you stand in the sun in the desert, maybe you're
going to get heat through, but we're millions of kilometers
away from the Sun. Imagine being like super close to
the Sun, You're just getting so much more of the
radiation and heat and particles trying to kill you. Right. Yeah,
it's a very intense environment and, as you say, an
incredible technological achievement to build a spacecraft that can survive

(35:34):
these visits. Yeah. Do you know how they did it? Yeah,
they have a bunch of like really cutting edge thermal
engineering advances. They have a complex solar shield. Basically, the
thing is diving towards the Sun, but most of the
instruments are protected by a shield. So the thing is
like diving towards the Sun, but it's doing a sort
of shield first. Behind that shield are a bunch of instruments,

(35:56):
and the shield itself is very fancy and very technological.
It's made of two panels of reinforced carbon composite with
like a carbon core foam, and a lot of really
complicated engineering and modeling went into like how to bleed
this energy off, how to make sure that the stuff
behind the shield doesn't get fried. Yeah. I think if

(36:16):
you look at a picture of the park or solar probe,
you'll see that like half of it is basically the
heat shield. It's almost like you know, like when Captain
America jumps out of a building and he's you know,
it's covered behind his shield. That's kind of what this
probe is doing. It's it's not that it's covered all
the way around. It just has a one shield in front,
and so it's always going to be facing the Sun
with the shield, otherwise it's gonna get fried. Yeah, and

(36:38):
the shield can withstand temperatures up to like thirteen or
fourteen hundred celsius, but the instruments have to be kept
at like thirty celsius otherwise they'll get fried. And you know,
this is a complicated maneuver. It's not just diving towards
the Sun and done as you said, it's orbiting the
Sun a bunch of times, so has to orient itself
to always keep the shield between the instruments and the Sun.

(37:00):
So that means like turning right. If these things are
exposed to the intense radiation near the Sun for like
tens of seconds, they're fried. So over like a ten
year mission, you can't have ten seconds of exposure to
the Sun. So this thing has a lot of computing
on board to make sure that the shield is always
in place. They call it one of the most autonomous

(37:23):
spacecraft ever flown. Because it's so far away that like
nobody on Earth can drive it in real time. It
would take too long for the signals to get back
and forth. So basically has to fly itself. And it
doesn't just have to fly by itself because it's far away.
It's because it's at some point it goes behind the sun, right, like,
at some point it's on the other side of the Sun,
and there's like no way it can send a signal

(37:44):
to us or we can send a signal to it,
so it has to be pretty much autonomous and always
face the shield towards the Sun. Yeah, that's a really
good point. We cannot control anything on the other side
of the Sun. No signals we send could be received there.
So every time it goes behind the Sun, we just
sort of sit and wait and hope that it comes
back around the other side in good condition. Yeah, they

(38:06):
told me that. Apparently there are three computers on board,
and the way that the probe makes decisions is that
the three computers are independent and they vote on what
the probes should do at any point when it's independent,
and then they take a vote and whoever whichever decision
wins gets the most votes. Is what the probe does.
That's awesome. Are they all running Windows? No? I think

(38:27):
one of them is like iOS. When of them to
Linux or unux, just to be safe, you know, would
download the Windows computer. But it's also interesting because like
the probe needs to shield itself from the sun when
it's closed because the sun is so hot. But when
it's far away from the sun, it meets the Sun's
energy to power and its batteries. So it has like

(38:47):
these retractable solar panels that when it's far away from
the sun, it like puts out these panels, but when
it's getting closer, it tucks them in, kind of like
one of those jets that tucks its wings in. Yeah,
it's like a hawk diving right as it gets to
very high speeds, it tucks itself in. It's really very awesome,
and my applause to everybody who worked on this project
and designed it. And it must be really nail biting

(39:09):
to see actually out there and flying and implementing the
programming that you put into it and trusting these autonomous
systems to make these decisions with your baby. I mean,
you work on this project for like a career. This is,
you know, not a one project you work on and
then you move on to another one the next week.
This is a decades long project. So these people are
biting their nails every time it goes around the Sun. Yeah,

(39:32):
it's a lot of trust to put into or a
majority vote, but you know, to get answers to the
physics questions that we want, you really do have to
get near the Sun. Sometimes you can learn things about
what's happening really far away just by sampling the photons
that get here, but sometimes they're scrambled, and that's the
case here. To understand what's going on in the Sun's corona,
in the acceleration of the solar wind and the magnetic field,

(39:54):
you have to get as close as possible to the
Sun because things tend to get scrambled by the time
they're already here on Earth. And so part of what
the probe is doing is getting those measurements really close
to the Sun, which we know it's really hard, but
they seem to be doing it. And so the idea
is to, as you said, to study the electromagnetic field
to the Sun because maybe that's where a lot of
these mysteries can be explained. Yeah, they have a bunch

(40:16):
of instruments on board. One of them measures the electromagnetic fields,
another one measures the velocity of the particles of the
solar wind, and there's also a camera they can just
like take pictures of solar activity. Um. But it's this
one that like measures the electromagnetic fields that I think
is really going to provide the clues that help us
understand and build like a deeper model of what's going

(40:36):
on inside the Sun, because fundamentally, the Sun is a
ball of plasma. Remember, a plasma is just a gas
that's so hot that the electrons are free, they're flying around,
so everything in the plasma has an electric charge. So
instead of just being like any other blob of hot gas,
now affected by electromagnetic fields and it generates electromagnetic fields.

(40:57):
So it's very chaotic. It's very difficult to understand this
part of why fusion is so hard to do here
on Earth, because plasmas are chaotic and very intense, and
so measuring those electromagnetic fields close up will give us
a sense for like what's going on inside the Sun.
How are these things flipping? Are these magnetic tubes like
reconnecting and snapping to accelerate particles. That really is part

(41:18):
of the core of the mission of the spacecraft. Yeah, because,
as you mentioned before, the maybe the sort of two
big mysteries about the Sun that we don't know right now.
Why the outside of the Sun, the solar corona is
hotter than the surface of the Sun. And also what
is making the solar winds so fast, faster than it
should be if it was just coming off of the Sun.
And so it seems like maybe a big explanation is

(41:39):
what's going on with the magnetic fields outside of the
Sun right exactly, And it might be connected to another mystery,
which is the mystery of these solar flares. You know,
the Sun is bright and hot, but it's not always static,
right There are suns spots and sometimes it injects a
lot of energy and even like huge blobs of plasma.
These things are called coronal massage actions and solar flares,

(42:01):
and something we want to understand because it affects life
on Earth, because these particles sometimes even reach Earth and
can damage our electronics. And they think that these solar
flares might be caused by disruptions in the magnetic field
of the Sun. Like when these magnetic tubes get pinched
off and collapse, it can cause a little eruption. That's
an idea for what might be explaining these solar flares,

(42:21):
and a related idea might solve these questions of the
solar wind and the heat of the corona. As you
were saying this, this theory of like nanoflares that instead
of like always having huge, big flares, maybe the Sun
is constantly having a lot of these little magnetic disruptions
that caused nanoflares that dump out energy from the surface
of the Sun to the solar wind and to the corona. Yeah,

(42:45):
because I think an interesting concept here is that the
Sun isn't just the gas that's on fire. It's not
just the circle that's shining bright kind of like part
of the Sun is also the invisible magnetic fields that
the Sun is creating, and that it's there are extending
out past a visible surface, right, because these magnetic fields
are huge, right, they are there are millions of kilometers

(43:08):
more wider than the actual visible width of the Sun,
Like it has invisible fingers. Yeah, and it's sort of
like a duet, right, or like a dance. There's two
partners there. The magnetic fields push on the particles and
change how they behave and where they go and how
much energy they have. And the particles, because they have charges,

(43:29):
also generate electric fields. It's this very nonlinear behavior that
can easily generate runaway effects that can get very very extreme,
and they power each other, like these dynamos inside the
Sun or inside the Earth that generate our magnetic field.
And so, as you say, this like one partner in
that dance that we can't always see directly with our eyes,
but it plays a really big role in what's happening.

(43:51):
It controls how all this plasma flows and where the
energy is deposited. And so instead of just thinking about
the sun is like a hot ball of gas where
the energy is diffusing out from the second law of thermodynamics. Instead,
now we're imagining like all these little magnetic tubes that
are like leaching energy out from the Sun more intensely,
and those could be like heating up the particles and

(44:11):
speeding them away in the solar wind to get them
really really fast and making the corona hot as well. Yeah,
because the other thing is that it's kind of like
a dynamic environment around the Sun, right, like, the Sun
is churning, things are moving, like you said before, Uh,
there are flows inside of the Sun of these particles,
and the stuff in the Sun is changing and flowing

(44:33):
and churning, and so these magnetic fields outside of the
Sun are also moving and changing, and sometimes they crash
into each other. And that's kind of I think one
of the other explanations for maybe what makes the corona
so hot is that these magnetic fields are basically crashing
and exciting the corona more than you would think. Yeah,
and it's Eugene Parker who sort of came up with
this idea. Before him, people thought about the Sun's atmosphere

(44:56):
sort of like static, the way the Earth's is. It's,
you know, maybe boiling off a little bit at the top,
but it's basically just floating there, held by gravity. But
he wrote the first paper suggesting that the Sun's atmosphere
is could of dynamic and has all these magnetic components
and generates this really powerful wind to explain these high
speed particles. And his original paper was like rejected a
million times, sort of like the way like the Harry

(45:19):
Potter manuscript was rejected by dozens of people before it
was published, but he was right, and it was confirmed
later by like the Mariner mission that measured the solar
wind to be these really high speed and so, yeah,
the Sun's atmosphere is much more complex in the Earth's
atmosphere because it's a big magnetic ball of hot plasma.
Is lots of crazy things happening. These magnetic tubes are
breaking and clipping and reversing and smashing into each other.

(45:41):
It's like magnetic weather. Yeah, it's good that his theory
finally saw the light of day. But I think also
that could also maybe explained the solar wind. Right, it
could be these like thrashing, moving magnetic fields around the
Sun that are maybe causing or accelerating particles in the
solar wind. Yeah, these are all mechanism sums for taking
energy from the inside of the Sun and dumping it

(46:04):
out into the corona, accelerating those particles into the solar
wind and heating up the corona. Remember, to solve this mystery,
we need something other than just the second loftterm agynamics.
We need some pump that's like pulling energy from the
Sun and accelerating these particles. And as you say, these
magnetic fields and they're crazy behavior might just do that.
And early results from the Parker Solar Probe are suggestive.

(46:25):
They've made a bunch of measurements of these magnetic switchbacks,
like sudden reversals in the magnetic field, much more dramatic
than anything you would expect otherwise. They're like frequent and
short lived changes in the magnetic field. That's suggesting that
it's sort of like a chaotic magnetic environment. And these
magnetic pumps, these nanoflares at the surface of the Sun

(46:47):
caused by this crazy magnetic behavior could be with heating
up the corona and accelerating the solar wind. Yeah. I
think that was the whole point of the Parker Solar Probe,
is to get in there, in those magnetic fields and
measure what's going on in there. And that's kind of
what they mean when they say that probe kind of
touches the Sun because it's it's sort of in there.
It actually gets to the point where it's right in

(47:07):
the middle of those magnetic fields, which in a way
are kind of the Sun itself, right. I mean, it's
not touching the visible surface of the Sun, but it
is touching it's magnetic fingers. Yeah, when you're building a
model of the Sun, you have to match the data
you see from the outside, but it's always ambiguity about
what's going on inside. So which you really want is
data from the inside, from where all the action is happening,

(47:28):
right from the inside out. As you say, Parker is
going to give us this measurement of what's going on
very very close to the Sun and can help us
constrain these models, tell us which ideas are wrong and
which ideas do actually describe what's happening in the Sun.
So that's pretty exciting in a way. It's sort of
like the probe is not really touching the Sun. It's
more like it's getting to the point where the Sun
touches it. Touched by the Sun. That's going to be

(47:51):
the name of its memoir when it's done with its trip,
and hopefully it didn't make it's a heat shield out
of wax and feathers, because we know that's a bad idea.
And there's also exciting room for surprises. Right, we have
these ideas about what might be happening inside the Sun
and near its edge, but remember that every time we
send something out into the universe or develop a new
kind of eyeball. We're surprised by what we learned. The

(48:13):
universe doesn't just say yes or no to our theories.
It says yes but or actually, something totally different is happening.
And so the Parker Solar Probe is going somewhere nobody's
gone before, and it might discover things that totally surprise us.
The universe is not big into improv theory. It's not
a yes and kind of thing. It's a yes, but

(48:35):
it's a sorry about the theory you've been developing for decades,
but you were totally wrong. Well that's when we have
to improvise. I guess all right, Well, the probe is
out there, it's flying close to the Sun. Uh. There's
data coming in all the time now and new papers
coming out of it, and so as it gets even
closer to the Sun, we'll learn more and more about
what's going on in there, and so stay tuned for

(48:56):
more news about the Sun. I'm saying that pro has
a lot of any days ahead of it, exactly, And
so thank you to everybody at NASA who developed these
things and sweated over it and launched it so that
we could all learn more about what's going on at
the heart of our solar system. Yeah, and thanks to
the scientists who talked to me to make my comic
about the Parker Solar Probe and all of this solar signs. Again,

(49:19):
if you want a visual companion to this episode, just
google PhD Comics and Parker Solar Probe. You'll see it
on Physics Magazines website. All right, well, we hope you
enjoyed Dad, Go out there and get some sun if
you can. Thanks for joining us, See you next time.

(49:41):
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of I Heart Radio. For
more podcast from My Heart Radio, visit the I Heart
Radio app, Apple Podcasts, or wherever you listen to your
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