Once again, it’s time to take a look at the Sun. You know, ongoing thermonuclear explosion of fusing hydrogen that’s right over there. Fortunately, there’s a fleet of spacecraft and ground observatories ready to give our best ever view of the Sun.
PODCAST: Ep. 30: The Sun, Spots and All (Astronomy Cast)
Solar neutrino problem (Wikipedia)
Solving the mystery of the missing neutrinos (Nobel Prize)
PODCAST: Ep. 32: The Search for Neutrinos (Astronomy Cast)
What’s a neutrino? (FNAL)
Dark Matter (CERN)
Parker Solar Probe (JHUAPL)
What Is the Sun’s Corona? (NASA)
The Transition Region (NASA)
Alfvén Waves – Basic (NASA)
Parker Solar Probe Timeline (JHUAPL)
Solar Minimum; Solar Maximum (NASA)
Solar Orbiter (ESA)
Solar Wind (NOAA)
Solar Dynamics Observatory (NASA)
What was the Carrington Event? (NOAA Scijinks)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, Episode 628: The Sun Revisited. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos where we help you understand not only what we know but how we know what we know.
I’m Fraser Cain, publisher of Universe Today. With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey, Pamela. How are you doing?
Dr. Gay: I am doing well enough. I am currently trying to cut back on caffeine. And, wow, this is gonna be a caffeine light episode, everyone. You are warned.
Fraser: We need to warn everybody that you are dangerously under-caffeinated today.
Dr. Gay: It is true.
Fraser: And that could have serious consequences. So, if it seems like I’m sort of having to boost her awake again every now and then, it’s fine. It’s fine. She’ll get over this.
Dr. Gay: It’s true.
Fraser: I think you have always just had so much coffee flowing in your system.
Dr. Gay: Yeah. I’m definitely one of those people that when the doctor asks, “How much coffee do you drink?” if I say two, it means pots, not cups. And I had gotten better for a while so that I was down to like 60 ounces of coffee a day.
Fraser: So, 60 fluids ounces of coffee.
Dr. Gay: Yeah, yeah – which is a lot.
Fraser: So, I drink about a third of that. I drink two cups of coffee a day. So, that’s crazy.
Dr. Gay: So, I was only having three cups, but they were 20-ounce cups. So, I realized over Christmas that because I was so acclimated I had to go up to five 20-ounce cups a day just to have it really take an effect, at which point the anxiety kicks in.
Fraser: Yeah, yeah, and your heart is going.
Dr. Gay: And in the modern world we live in, no one needs added anxiety.
Dr. Gay: So, I am back to 20 ounces of coffee a day –
Dr. Gay: – and regretting all my life choices, all of them.
Fraser: Yeah, that’s not enough. That’s not enough. This is madness. But, anyway, we’ll see how you do. All right.
So, once again, it’s time to take a look at the sun – you know, that ongoing thermonuclear explosion fusing hydrogen that’s right over there. Fortunately, there’s a fleet of spacecraft and ground observatories ready to give us our best-ever view of the sun so we can watch it, always watching.
All right, Pamela, the sun. Again, we covered this on our tour of the solar system 1000 episodes ago – almost, actually. We’re in the 600s, and I say 1000 episodes ago. Actually, we’re within various error bars.
Dr. Gay: Order of magnitude.
Fraser: Yeah, error bars are starting to come in line here. When my hyperbole lines up with reality, we know there’s a problem.
So, we’re gonna stick to the newish stuff. Obviously, we know the sun, ball of hydrogen and helium fusing in the core, releasing the energy, radiated pressure, different layers inside, really hot inside, less hot on the surface. It’s gonna last for a while, and then it’s gonna die.
Now, what’s new about the sun that is really interesting?
Dr. Gay: So, the thing that got me the most prepping for today’s episode is when we first started this show and first did that tour through the solar system, everyone was like – so, for decades we thought there was a solar neutrino problem, and we think we might’ve figured it out. We think maybe the neutrinos are changing flavors and this could explain it. And nowadays, they don’t even mention the solar neutrino problem because, yeah –
Fraser: It’s not a problem.
Dr. Gay: – neutrinos have identity crises on a regular basis and just oscillate their variety to whatever suits them at the moment. So, the sun is giving off all the neutrinos it is supposed to. And then many of those neutrinos are deciding to be a different kind of a neutrino.
Fraser: Right. All right. So, we’re just gonna call this now the solar neutrino thing – the solar neutrino reality? Anyway, all right. So, we’ve done whole shows on neutrinos.
Dr. Gay: Yes.
Fraser: But give us just sort of a quick version of what a neutrino is.
Dr. Gay: A neutrino is a basic particle that can’t be broken down any further. And they generally carry the bits of stuff that have to be conserved in a reaction.
Dr. Gay: So, if you have a reaction involving an electron, it will often give off an anti-electron neutrino just to make sure that all the bits and pieces of the reaction –
Fraser: Like the rounding errors.
Dr. Gay: Yeah, exactly.
Dr. Gay: So, in the core of the sun where nuclear reactions are going on, where hydrogen is getting transformed into helium, neutrinos that should be electron neutrinos are getting created.
And for the longest time, we were only detecting – and we continue to only detect – a fraction of the number of expected neutrinos. And if a particle is made up of no mass, it can travel at the speed of light, and its identity is pretty well locked in – so, think photon. And for decades, it was thought that neutrinos maybe had no mass, were traveling at the speed of light.
And then it was realized some neutrinos appear to have mass. Shoot. All neutrinos appear to have mass. And that means they’re able to swap around what ratio of their identity is tied up into energy versus mass, and that electron neutrino can now become a tau neutrino, a muon neutrino. And those are detected in different mechanisms. So, we weren’t seeing them in the original datasets. And now we realize, okay, neutrinos are weird.
Dr. Gay: And the solar neutrino problem is not a problem.
Fraser: So, we knew the math said a certain amount of neutrinos should be getting thrown out from the sun.
Dr. Gay: Yes.
Fraser: But we were only detecting a very precise fraction of those neutrinos because our detecting equipment only allowed us to see one flavor of neutrino.
Dr. Gay: Which is the only flavor that originally leaves the sun – they just change on their way here.
Fraser: Right. So, they’re all leaving the sun in this one flavor. They’re changing into different flavors, and then they’re passing through the Earth. And we finally have the capability to detect the other flavors.
Dr. Gay: Yes.
Fraser: It’s so weird but so cool. I wanna just rabbit hole for one second. All the time – I’m sure you get this too. People have this instinctual I don’t like dark matter. It seems made up. What’s this nonsense that astronomers are trying to figure out?
Dr. Gay: Right.
Fraser: But search and discovery of neutrinos are just a beautiful analogy for dark matter that you’ve got this theoretical particle that should be there but astronomers were not able to detect it, that didn’t interact with regular matter in any way. We know the neutrinos can go through a light year worth of lead and not interact; that they’re out there and all right responsible for some of the processes that we know; but, yet, astronomers are not able to detect them.
So, they had to develop multiple different capture mechanisms to finally figure out a way to detect them. And they were dark matter, and now they’re a known particle.
Dr. Gay: And the thing is – it’s not even so much a capture mechanism. You can’t lay a trap out for a neutrino and put food in the center and you’ll end up with a neutrino in your cage.
Dr. Gay: We have to actually hope that in vast vats of liquid a neutrino will just happen to collide with something just right that it triggers a flash of light. So, it’s no clear cut and dried. It’s a – well, this happens to match this exactly.
Fraser: So, you have countless – and I forget the number now – countless neutrinos passing through your body from the sun right now. And almost none of them are interacting with the particles in your body. And, yet, we know experimentally with incredible precision that these things are there, that there are particles fully able to do this.
And no one dismisses the idea that neutrinos exist. It’s accepted physics. And dark matter is the same thing just 10 years back, 20 years back on the discovery experiment pipeline. And we’ll get there.
Yeah, it’s funny to me when people have that conversation. And I’m just like, well, how do you feel about neutrinos? And they’re like, well, what about them? I’m like – you got this particle that is passing through, doesn’t interact with regular matter. Is that okay? Are you okay with that particle? Anyway, let’s move on because this is starting to feel like a soapbox.
Dr. Gay: I wanna put just a little bit of numbers to that. So, the sun is fusing 600 million tons of hydrogen per second. Each one of the reactions involved in all the atoms that add up to that six million tons is producing a neutrino as part of the reaction.
Dr. Gay: And that is admittedly getting spread out over a sphere. But that’s all, nonetheless, getting blasted out from the sun every second.
Fraser: And, again, they’re rounding errors. They are a tiny amount of matter compared to the mass of the sun, the mass of the atoms in the sun. And, yet, we can detect them, and they were predicted, and then they were detected. And that’s how science works.
But since we did that episode of the show, whatever, 15 years ago, there have been a fleet of spacecraft launched and an incredible ground observatory designed to help us understand the sun better. The most famous of which, of course, is probably the Parker Solar Probe. So, can we talk just a bit about what that spacecraft is gonna be doing?
Dr. Gay: So, the Parker Solar Probe – as we are recording this on January 24th, 2022, it’s getting ready to start its next perihelion run into the sun where it’s expected that today it’s going to rotate to have its heat shield into the sun so that you can go and check out what temperature it’s at at the website.
And orbit after orbit, it’s getting itself a little bit closer and a little bit closer so that we’re able to actually acquire data from within the sun’s corona. And this is that part of the sun that is enigmatically hot for – well, pick which reason you believe the most.
Fraser: So, that part is amazing. That Parker Solar Probe is passing through the atmosphere of the sun.
Dr. Gay: Yes.
Fraser: And when you watch an eclipse and when you’re not completely clouded out like what we experienced, that hazy glow around the sun is the corona. Parker Solar Probe is passing into that region. It’s that close.
Dr. Gay: In this region of the sun, the energy in the individual particles has a temperature of two to five million degrees. Now, the catch is that there are very, very few particles. So, it’s not totally going to destroy our poor innocent spacecraft.
But every few years, it has seemed like there was a new press release, usually coming out at an American Astronomical Society meeting that said, “We now understand why the transition zone is only 40,000 degrees and the chromosphere below it is 10,000 to 36,000 degrees. And then the corona at the very top is suddenly two to five million degrees.” It’s always been something to do with magnetic fields.
And with Parker Solar Probe, they think they actually figured out exactly what the mechanism is. And here, if you have a better pronunciation than I, please correct me. But from what I’ve been able to hear, the pronunciation is the Alfven waves.
And these are where you have magnetic fields going though plasma, and the plasma gets distorted away from the magnetic field line. And it oscillates as it comes back to the field line releasing energy as it does. And it’s thought that it’s these Alfven waves that are releasing the energy that is heating up the corona.
Fraser: And it’s really bizarre. Just the fact that, as you said, the surface of the sun is, say, just shy of 6000 degrees. The lower atmosphere rises into the tens of thousands of degrees. And then you kick up into millions of degrees. It’s been the biggest unsolved mystery in solar astronomy.
And now we’re at the point where it’s largely understood that you’ve got these weird resonant magnetic waves pulsing through the plasma of the sun powered by the magnetism of the sun releasing this energy in a way that keeps these temperatures so high. Bizarre.
Dr. Gay: And beyond just that, with Parker Solar Probe going in so close, they’ve been able to start to measure the transitions in how the spacecraft is interacting with the magnetic field that tells them they have gone from the point where the solar winds are free of the magnetic and gravitational pull of the sun and able to fly their happy way across the solar system to being inside that line and into an area where the gas is bound by magnetic fields and gravity.
And we now know where this transition is. It’s about 18 solar radii out from the center of the sun. And we’re also finding that there’s quiet once the mission gets in there and just this idea that if you go in far enough things quiet back down. It’s often likened to passing within a storm. So, that outer part is a storm. And as you get closer, it actually quiets.
Fraser: And Parker Solar Probe is gonna be getting closer still?
Dr. Gay: Yes. We’re looking at it getting down to less than 10 solar radii out. With every orbit, it’s getting a little bit closer, a little bit faster. It’s actually starting to get to the point as it gets – well, in 2025 – to perihelion 24. We’re still down at seven. It’s going to be hitting speeds where folks start talking about – well, it is a fraction of a percent of a speed of light. And it is not an embarrassingly bad percentage.
Fraser: Yeah, it’s moving at relativistic speeds.
Dr. Gay: Yes. That is kind of awesome. And with each different passage, they’re hoping to probe not just the sun as a function of distance, but we’re also experiencing a fairly significant portion of the solar cycle. We finally started making these perihelions in 2018. And that was about solar minimum. Exactly one solar minimum is something you’d find out about after the fact.
We are now heading into the next solar maximum. It should be sometime around 2025. It’s unclear if it is going to be earlier than normal or if it’s going to be a higher number of sunspots than predicted. We just know at this moment in time we’re seeing more solar activity than was expected.
And Parker Solar Probe is going to be there getting closer and closer as the sun gets more magnetically tied up and more magnetically tied up so that as the sun is hitting maximal chaos, Parker Solar Probe is also getting its tightest in orbits.
Fraser: That’s gonna be amazing. All right. Let’s talk about Europe’s companion to the Parker Solar Probe.
Dr. Gay: So, with Solar Orbiter, there’s this interesting bifurcation of plans that they originally had for a solar mission. Back in the 90s, folks were thinking about planning a solar probe that would go into a beautiful orbit over the poles of the sun getting there via Jupiter, taking the long journey with lots of instrumentation.
And under NASA administrator Sean O’Keefe, it and a whole lot of other programs got zeroed out. And that idea that we need to see the sun not just equatorially, which is easiest to do with the kind of orbit that uses the Earth and Venus and Mercury, all those things for gravitational assist. For something like that, you want to stay in the plane of a disk.
If you’re just gonna hop off Jupiter and dive straight in, you can come in over the pole. So, we’re getting the equatorial observing more with Parker Solar Probe. And Solar Orbiter coming in on the European Space Agency side, it made its first encounter in November of 2021. It has that more polar orbit that’s going to allow us to see the other parts of the magnetic field. And it’s also there for, well, essentially solar maximum as it gets closer and closer in over time.
Fraser: And it’s not getting as close as Parker?
Dr. Gay: No, no.
Fraser: A nice healthy distance away.
Dr. Gay: Yeah. And it’s carrying a different suite of instruments. And this is where we have to remember that all of these different things have their own costs. So, you can either spend a whole lot of money on a heat shield or a whole lot of money on your cameras and instrumentation.
And with Solar Orbiter, they were going for the instrumentation. They have a solar wind plasma analyzer, an energetic particle detector. They’re doing all sorts of different remote sensing where they’re looking in the ultraviolet. They’re doing spectral imaging. They have their own chronograph. And with all these different instruments, they’re gonna get as close as they can safely get and give us that polar perspective on what the sun is actively doing.
Fraser: On the one hand, you’re making your remote observations. But as you said, it’s got instruments on board to detect the material flowing past it, the solar wind, the plasma, all of that. So, it’s gonna be both watching it from afar but also swimming upstream through the solar wind and detecting it.
But I love this idea of a spacecraft being able to finally look at the top of the sun. It’s a part of the sun that we’ve literally never seen. We have no idea. There could be just a big hole at the top of the sun, and we’ve never seen it.
Dr. Gay: There’s not a hole at the top of the sun. There could be a vortex.
Fraser: Maybe. Ooh, that would be great.
Dr. Gay: It would be amazing.
Fraser: Yeah, it could be just a big black circle at the top of the sun. We don’t know. We don’t know.
Dr. Gay: I’m gonna go with a no on that one.
Fraser: Fine. We suspect no, but we’re about to have a confirmed no. And it’s great because now you have these two spacecrafts that can coordinate their observations of the sun and see an event from two different perspectives.
Dr. Gay: But wait, there’s more.
Dr. Gay: So, in addition to these two missions that have these spiraling inward orbits that are each taking their own route to get in, we also have the Solar Dynamic Orbiter, which is hanging out at the Lagrange point between the Earth and the sun. And there’s also all of our ground-based systems.
Dr. Gay: So, you add in SOHO. You add in the Solar Dynamic Orbiter.
Dr. Gay: All these other missions. There is literally a fleet out there. And they each do their own special thing. And the thing about studying the sun is you really want to get as many different perspectives as possible because the sun is oscillating on a variety of different scales. So, this is something that was first really measured by the GONG system here on the surface of the planet.
In addition to having all of these oscillatory modes, its magnetic field is capable of bunching up in spots and creating the sunspots that are so cool to see in solar projections and with proper filtering on a solar telescope.
But the sun, as much as it’s capable of doing these cool things, it’s also able to create great violence. There was what was called the Carrington Event in the 1800s, which oscillated the Earth’s magnetic field so much that it generated electricity in telegram lines.
Fraser: So, now, with these instruments, all of the spacecraft and ground-based observatories – we didn’t even talk about the Daniel K. Inouye, which is the extremely large telescope for solar observing, which has come online.
Dr. Gay: Right.
Fraser: You’ve got this ability to predict dangerous solar flare events with more notice than we’ve ever had. We can literally now start to see the sun preparing to release a flare in our direction, not just detecting it after the fact. Our understanding of the sun has just grown in leaps and bounds.
Dr. Gay: And what I love is with Solar Dynamic Orbiter and SOHO we have the full disk perspective and the full corona perspective. With the Parker Solar Probe and ESA Solar Orbiter, we have the insitu, which is just a weird thing to say, observations of what’s going on
And then with the Daniel J. Inouye – pronunciation apologies – telescope here on the surface of the Earth, we have the most zoomed in capacity that we have for anywhere. So, it gives us that complete – let’s look at the whole thing, and zoom in on what we care about.
Fraser: It’s funny. This episode – we didn’t mention a few things that we’ve newly discovered. But I think the take-home is Earth has amassed an enormous number of science instruments, focused them at the sun. And when we’re ready to do another revision episode, we will have a mountain of fascinating discoveries about the sun to share with you that we have learned. All of the pieces are in place, and now the sun will give up its secrets.
Dr. Gay: We just need to make it through solar maximum, and it’s the other side of the solar maximum that I think we’re gonna have some really cool information.
Fraser: Sounds good. All right. Thanks, Pamela.
Dr. Gay: Thank you, Fraser.
Fraser: Do you have some names?
Dr. Gay: So, as always, we are here thanks to the generous contributions of folks like you.
This week, I wanna thank in particular Robert Wenger, Daniel Loosli, Randa, marco iarossi, Alex Cohen, Jim Schooler, Phillip Walker, Matthias Heyden, The Lonely Sand Person, Justin Proctor, Paul L. Hayden, Gregory Singleton, Brian P. Cox, Tim McMackin, Jeff Willson, Nial Bruce, Cooper, Steven Shewalter, Kenneth Ryan, Nate Detwiler, Benjamin Müller, Jordan Turner, Eran Segev, Paul Disney, Alex Raine, Omar Del Rivero, NinjaNick, Micheal Regan, Matt Rucker, Scott Briggs, Don Mundis, Karthik Venkatraman, Dean McDaniel, Jeremy Kerwin, Benjamin Carryer, Frode Tennebø, Janelle Duncan, Moose and Deer, J. AlexAnderson, Father Prax, Bruce Amazeen, Michelle Cullen, Kimberly Rieck, Anitusar, Mark Steven Rasnake, Jim McGihon, Mark H. Widick, Brent Kreinop, John, Philip Grand, Dustin A. Ruoff, Cemanski, Dwight Illk, and planetar.
And thank you so much. You make this possible.
Fraser: Thanks, everyone. We’ll see you next week.
Dr. Gay: Bye-bye.
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