Welcome back to Launch Pad, I’m 
Christian Ready, your friendly  
neighborhood astronomer. In our 
last video on ESA’s Solar Orbiter,  
we talked briefly about how it 
compares to the Parker Solar Probe.  
But come to think of it, 
it’s been a while since  
we last checked in on Parker. 
It turns out it’s been busy!
For a quick recap, Parker was launched 
in August 2018 to investigate the Sun’s  
outer atmosphere or corona. There’s two 
really weird things about the corona.  
First, it’s millions of degrees 
hotter than the Sun’s surface,  
despite being well above the Sun’s 
surface. Even though its temperature  
was determined in 1940, no explanation 
for the coronal heating problem has  
ever been tested experimentally. 
Another problem is that the solar  
wind is accelerated in the corona 
to millions of kilometers per hour.  
But, it’s not clear how the 
wind is accelerated, either.
In order to understand both of these 
phenomena, you need to trace the flow  
of energy and make measurements in the 
region where all the action happens. But  
that requires being there. In the Sun’s 
corona. Which is really, really hot.
That’s why Parker is protected by a 
heat shield made of carbon composite,  
along with solar arrays 
that are cooled by water,  
and retract as Parker 
swings about the Sun.
During its closest approach, 
Parker will fly to within 9  
solar radii of the Sun’s 
“surface”. That’s about 3.83  
million miles (6.16 million km) 
or just 0.05 astronomical units.
At that distance, the heat shield 
will reach temperatures near 2500  
°F (1400 °C), but the spacecraft’s 
payload will be near room temperature,  
at about 85 °F (29 °C).
However, it’s going to be a while 
before Parker makes its closest approach  
because it has to get rid of some of the 
orbital energy it inherited from Earth.  
So, Parker was launched into an 
elliptical orbit around the Sun. And,  
its launch was timed in such a way as 
to make the occasional flyby of Venus.  
During each of these flybys, some of 
Parker's orbital energy is transferred  
to Venus, and the spacecraft 
descends closer with each orbit.
As it approaches the Sun, 
Parker samples the solar wind,  
while spacecraft like STEREO A and B,  
SDO, and SOHO see the overall 
environment Parker flies through.  
This allows the science team to put 
Parker’s observations in their proper  
context, and understand what the Sun was 
doing when the measurements were made.
Now, even though it won’t make its 
first really close approach until 2025,  
Parker's already come much closer than 
any spacecraft in history. And, Parker’s  
already made some really interesting 
discoveries about the Sun! So, here now,  
are 5 Really Cool Things Parker 
Learned About the Sun, plus something  
else it learned that’s really cool 
that’s not about the Sun at the end.
#1 Evidence for a Dust-Free Zone
The Sun is surrounded by a thin disk of 
dust spread throughout the inner solar  
system. Some of it comes from comets, 
while some are the remains of collisions  
that formed the planets, asteroids, and 
comets billions of years ago. This dust  
scatters sunlight. If you can get to 
a dark enough site on a clear night,  
you’ll see the faint glow of this dust 
in a phenomenon called Zodiacal light.
It’s long been thought 
that close to the Sun,  
the radiation there should 
be high enough to either  
vaporize the dust particles entirely, or 
push them away with radiation pressure.  
But from our vantage point on Earth, we 
cannot discern the disk’s interior edge.
But as it made its way around the 
Sun during its first three orbits,  
It noticed a thinning out of the 
dust starting at about 7 million  
miles (11 million km) from the Sun. 
This decrease in dust continued  
steadily to the limits of WISPR's 
measurements, which at the time  
could see to a little over 4 million 
miles (6 million km) from the Sun.
At the current rate of thinning, it’s 
possible the truly dust-free zone  
may start around 2-3 million 
miles (3-4.6 million km) from  
the Sun's surface. That means 
Parker might see the dust-free  
zone as early as September 2020, 
when it makes its sixth flyby of  
the Sun and closes to within 11.5 
million miles (18.7 million km).
But if that weren’t cool enough, Parker 
also “heard” the dust striking the  
spacecraft as it passed through it at 
250,000 miles per hour (402,000 kph)!
At those speeds, the spacecraft 
doesn't just crash into these  
particles — it obliterates them 
into a plasma that Parker's  
FIELDS instrument can - for 
lack of a better word - “hear.”
[static]
Pretty cool, huh? However,  
each collision chips away a 
tiny bit of the spacecraft.
And this was something the Parker team 
expected to happen. But until now,  
they could only guess at the rate of 
these collisions using models based  
on remote observations. It turns out 
the dust is denser than expected, but  
not enough to pose a concern 
for the mission. Still,  
it’s just one of those things you 
can’t tell for sure until you’re there.
Not only did Parker hear the dust 
impact the spacecraft, but...
#2 Parker hears the 
turbulence of the solar wind
The solar wind is the stream of charged 
particles - or plasma - blowing from  
the corona in all directions. But 
weirdly, the solar wind actually  
speeds up as it leaves the Sun. 
Not only that, but it stays hot,  
even as it travels away from the Sun!
By the time the solar 
wind reaches Earth,  
it mostly flows at a fairly steady 
rate. Any trace of the mechanisms  
that heated and accelerated 
the wind has been smoothed out.
But closer to the Sun, Parker’s 
FIELDS instrument revealed a much  
more chaotic and turbulent system 
even when the Sun is “quiet”.
FIELDS detected thousands 
of waves of plasma  
rippling through the solar 
wind. Such waves would be  
driven by fluctuations in the 
electric and magnetic fields.
It’s kinda like how fluctuations in 
air pressure on Earth create the winds  
that drive rolling waves on the ocean.
In the solar wind, particles can ride 
these plasma waves and are propelled  
to higher speeds. But as they surf those 
waves, the particles interact with each  
other, creating fluctuations in the 
frequency and amplitude of the waves.  
Parker recorded these waves as they 
passed by, and they sound really cool.
These are whistler-mode waves. They're 
caused by energetic electrons bursting  
out of the Sun’s corona. These electrons 
follow magnetic field lines that stretch  
from the Sun out to the solar system’s 
farthest regions. But as they do so,  
the electrons spiral around the 
lines. When a plasma wave’s frequency  
matches the frequency of the spinning 
electrons, they amplify each other.
It’s thought that part of 
the solar wind’s acceleration  
may be due to these escaping 
electrons. It’s also possible  
they may play a role in 
heating the solar wind.
As the plasma waves move 
through the solar wind,  
they quickly shift from one 
frequency to another, creating other 
waves called dispersive 
waves that FIELDS detects.
[windy, chirping sounds]
These dispersive waves are 
rarely detected near Earth,  
so they weren’t thought to be a 
significant driver of the solar wind.  
But near the Sun, dispersive 
waves are everywhere.
It’s yet not clear what causes 
the changes in frequency that  
creates these waves, or how they may 
heat the solar wind. But this is a  
really cool finding that’s going to 
be followed up on with future orbits.
And speaking of funky electromagnetic 
phenomena, Parker also discovered…
#3 Magnetic Switchbacks
During its first couple of orbits,  
Parker’s FIELDS instruments detected 
sudden reversals in the magnetic fields.  
At first, it was thought the 
spacecraft might have been passing  
across a series of magnetic field 
lines with alternating polarities.
But the Solar Wind Electrons Alphas and 
Protons - or SWEAP experiment - made  
measurements of the particles flowing 
along the magnetic field lines.  
SWEAP showed that the outflowing 
wind particles were in fact reversing  
their direction, and then reversing 
again to their original outflow with  
twice the kinetic energy 
of the background wind!
The science team dubbed these 
reversals “switchbacks”.  
Nothing like them have been detected 
before. At Earth’s distance, only the  
occasional wiggle of some magnetic 
field lines have ever been detected.  
But these are full 180 ° reversals that 
pack a ton of energy. It’s like trying  
to do the same thing with a bungee 
cord that’s already pulled taut.  
The more tightly drawn it is, the 
more energy is required to reverse it.
These switchback reversals 
last anywhere from a few  
seconds to several minutes. When field 
reverses, it’s like cracking a whip,  
and the particles pack twice 
their original kinetic energy.
Parker measured clusters of 
switchbacks during its first  
two flybys. But as it flew closer 
to the Sun on subsequent orbits,  
it measured an increase in both the 
number and energy of the switchbacks.
The exact source of the switchbacks 
isn't yet understood, but with each  
new set of measurements, scientists 
can narrow down the possibilities.  
It’s thought that as Parker gets 
closer to the Sun, the switchbacks  
should become more common and stronger. 
If that turns out to be the case, they  
may turn out to be one of the energy 
sources that’s heating the corona!
Parker doesn’t have a camera that faces 
the Sun, because the radiation it faces  
would fry any camera we could put on it. 
But ESA's Solar Orbiter may be able to  
image new features on the Sun that 
can be linked to these switchbacks.
Solar Orbiter already spotted small 
bursts of energy dubbed “campfires”. As  
Solar Orbiter gets closer to the Sun, 
it’ll determine whether or not these  
campfires are the long-theorized “nano 
flares” and if so, are they providing  
the energy needed to generate the 
switchbacks that accelerate the wind?
But the atmosphere and solar wind 
behave differently than we thought  
in a very significant 
way, in particular...
#4 The atmosphere and solar wind rotate 
farther from the Sun than we thought.
The solar wind emerges from the 
corona. Near Earth, the wind streams  
more or less radially from the 
Sun, going out in all directions.  
But the Sun rotates, carrying the corona 
along with it. That means the solar wind  
is initially traveling in curved path 
before switching to a straight one.
It’s a little bit like riding 
a merry-go-round. The farther  
you are from the center, 
the faster you’re moving.  
If you jump off, you would then be 
moving in a straight line outward.
Somewhere between the Sun and 
Earth, the solar wind does the  
same thing and transitions from 
a rotational to a radial flow.  
Exactly where this happens 
has implications for how  
the Sun - and how stars in 
general - slow down over time.
Parker’s SWEAP instrument measured 
this rotational flow for the first time  
when it was still 20 million miles 
(32 million km) from the Sun.  
That’s considerably father 
from the Sun than predicted.  
Not only that, but as Parker 
approached perihelion, the speed  
of the rotation increased to more 
than 10 times faster than predicted!
Not only does this tell us something new 
about our star, but it has implications  
for understanding the lifecycles 
of stars in general, and the  
formation - and even habitability 
- of their planetary systems.
You see, where and how the wind 
transitions affects how rapidly the  
star slows its rotation. The farther 
away the wind transitions, the more  
rotational energy it carries away and 
the more quickly the star slows down.
In general, the slower a star rotates, 
the less magnetically active it is,  
and the more habitable its planets 
are. Perhaps one of the reasons we’re  
here in the first place is because the 
Sun slowed its rotation quickly enough  
to give life a chance to evolve into 
more complex, sophisticated creatures.
Of course, that doesn’t mean the 
Sun is completely without activity.  
Even during the quiet 
times, Parker observed...
#5 Small flares and space weather.
We know that electrons and ions in 
the solar wind are accelerated by  
explosive solar activity. Exactly how 
this happens is not yet well understood,  
but under the right conditions, it can 
create storms of energetic particles.  
Major events on the Sun, such as 
flares and coronal mass ejections,  
can send these particles racing out 
into the solar system at nearly the  
speed of light. That means they can 
reach Earth in under a half an hour.
These particles carry a lot of 
energy, enough to damage spacecraft  
electronics and endanger astronauts. 
When astronauts eventually do return  
to the Moon and head out for Mars, 
they won’t have the protection of  
Earth’s magnetic field and won’t 
have much advance warning, either.
However, Parker’s Integrated 
Science Investigation of the  
Sun - or ISIS - there, I said 
it, I'm taking it back - detected  
several high-energy particle events 
that have never been seen before.  
These events proceeded a 
small coronal mass ejection  
that unleashed a burst of material 
with as much mass as Lake Michigan.  
ISIS detected high-energy particles 
rushing ahead of the ejected mass.
If we can learn more about the nature of 
these phenomena, it may be possible to  
use them as part of an early-warning 
system for future explosions.
Meanwhile, the CME ejecta formed 
structures in the corona and solar wind  
that were captured by the Wide-field 
Imager for Solar PRobe, or WISPR.
High-energy particles slammed into 
WISPR’s cameras, creating these brief  
flashes of radiation “snow" as they 
bombard the detectors. Previously,  
radiation “snow” had only been 
detected by spacecraft like the  
Solar Heliospheric Observatory - or SOHO 
- during major solar eruption events.
But now WISPR is detecting 
them on a much smaller scale  
inside the corona, while ISIS is 
detecting the kinds of high-energy  
particle events that 
may be causing them.
All of these observations demonstrate 
just how active the Sun is,  
even during so-called “quiet” times. 
But Parker, and its sideways-facing  
WISPR cameras in particular, are 
in a position to see some really  
cool things in our solar system that 
aren’t the Sun. Which brings me to
#6 Cool Things Parker detected in 
our solar system that aren’t the Sun.
During Parker’s first solar encounter in 
November 2018, its WISPIR camera picked  
up a really faint structure that’s never 
been seen before: a 60,000 mile- (97-161  
million km-) wide dust trail in the 
orbit of the asteroid Phaethon. Phaethon  
is one of the closest Sun-approaching 
asteroids in our solar system. Its orbit  
is highly elliptical, and reaches 
all the way out past Mars' orbit.
A couple of thousand years ago, 
Phaethon approached the Sun and  
something happened to it. We’re 
not sure what happened to it,  
but it released a long 
debris trail into its orbit.
Every December, Earth passes 
through this debris field,  
and we see them as the 
Geminid meteor shower.
Phaethon comes about as close 
to the Sun as Parker does.  
Every time it does so, it heats 
up and bits of the crust break  
off to form a dust trail. It’s like 
Phaethon is a kind of “rock comet”.
So, was this particular trail of 
dust created in the same event  
that created the Geminid meteor shower  
thousands of years ago, or 
was it created more recently?
To find out, scientists estimated the 
mass of the dust in the Parker images.  
They found that the trail weighs about 
a million tons (1 billion kg). However,  
Phaethon is currently losing 
mass at a rate that is way too  
low to create the amount 
of dust seen in this trail.
However, the amount of dust measured 
is comparable to the estimated amount  
of dust that enters our atmosphere 
every December during the Geminids.
And that’s pretty solid evidence that 
Parker is looking at dust created in  
the same event that created 
the Geminids. In other words,  
Parker saw what a meteor 
shower looks like from space!  
Only, one that’s caused by an 
asteroid instead of a comet.
And speaking of comets, Parker got a 
really nice look at the newly-discovered  
comet NEOWISE on July 5th. On the 
right (correction: left) side of  
the image there is sunlight 
being scattered by dust.  
In fact, there’s a little black 
structure on the lower left of the image  
that's actually a grain of dust 
resting on the camera lens.  
The comet’s broad dust tail is easily 
visible. But, after some processing to  
remove the excess brightness from 
scattered sunlight, the comet’s  
straight ion tail pointing directly away 
from the away from the Sun can be seen.
So yeah, Parker's been busy! And 
now it’s been joined by ESA’s  
Solar Orbiter which orbits a little 
further away. But, unlike Parker,  
it will be just close enough to take 
the closest images of the Sun. In fact,  
ESA just released the first set 
of images from Solar Orbiter,  
and I made a video about them 
and the Solar Orbiter mission,  
so if you haven’t seen it yet, I’ll meet 
you over there when we’re done here.
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