- So take it away. Holly.

- [Holly] Great. Thank you both Alex and I are thrilled to be here to talk to you about heliophysics and just as a very brief background for myself, I joined the National Center for Atmospheric Research about nine months ago. And before that I was at NASA Goddard for about 13 years. The last of those years, I was the Director of the Heliophysics Science Division there. So heliophysics certainly is one of my favorite topics to talk about, and I'm going to provide a very high level overview. And then Alex is going to go into some more detail and relevancy to exoplanets. So before I go into the overview, let's just start with basic, or basic mission in heliophysics. What are we trying to do? We're really trying to understand not what's just happening on the Sun, but how that impacts and interacts with the Earth and the other planets throughout the solar system. And this really includes the area of space weather, which is essentially the looking at the impact of the solar variability and activity on the planet, but significantly on the Earth. Now, of course it has different implications for us here on Earth and other planets and especially exoplanets. But of course it all begins at the Sun. We are looking at beautiful movies from the solar dynamics observatory. We're looking at different wavelengths and which is showing basically different temperatures of the solar atmosphere. And this is really necessary because there are different layers in the atmosphere are showing different things. And as you can see, there's a lot of dynamic activity. There's some small-scale stuff. There's some large eruptions. These magnetic field lines are high or illuminated by the hot plasma. Some of this plasma is hotter than others. This is probably about 10,000 to 100,000 degrees. The others were like 2 million degrees. So anyway, the point being that this is a very dynamic complex environment and not only are these eruptions happening on the, on the Sun that we have to worry about, but there's a constant solar wind being accelerated away from the Sun. And that's also something that we have to worry about because we're embedded in that solar wind at the Earth and the rest of the planets as well. Alex will actually talk about some enhanced stellar winds aspect. The reason we have to say that it's inherently interesting, but of course it also influences us here on the Earth as I have already mentioned, it impacts Earth, impacts the solar system instead of... That is why. And here is an example. This is just a movie showing a recent data, but there was a major event that happened in 1859 called the Carrington Event and in fact, it was such a big event that there's a drawing of a flare that Carrington was able to draw on just seeing this happen on the Sun. And this was really kind of the beginning of where we realize that the Sun and the Earth are a coupled system. The impact at the Earth during that event was that the Northern lights, or the Aurora, were basically reaching all the way towards the equator. So very significant event happening on the Sun created influence on the Earth. And so that was probably the beginning of looking at how is this coupled system work? Well, importance of space weather is even more so now because our technology is impacted. So there was an event in 1989 that had a huge impact on our grid. So a large swath of the U.S. and Canada lost power. This is just an animation of that. But again, it's not just the grid that we have to worry about. It's our technology. It's our satellites flying over the whole regions of Earth. Because we're more susceptible to the stuff that's coming from the Sun. So again, we, we try to predict the forecast, just like weather here on Earth. It's important to do so far for space weather. Another major event happened in 2012 and shown here. Luckily, this was not pointed at the Earth. What we're seeing is data from NASA STEREO, which is not near the Earth at the time, but you can see that it was significantly impacted by this large coronal mass ejection and associated flare on the Sun. And you can see the cosmic rays hitting the detector. Now, if this had been directed at the Earth, it's estimated that could have caused a lot of infrastructure damage, possibly costing a lot of money. But I want to mention that, you know, this impact is not necessarily given, even if it is directed at the Earth. It is very complex. It depends on what orientation magnetic field has in the storm. It depends on a lot of things between, that happen between the Sun and the Earth. So even though we could say, yeah, it just may have been a catastrophe. We still have to study a lot of different things to even know... So again, title impact that we're worried about, not necessarily for exoplanetary research. The same event was modeled on if it had hit the Earth. So this is the first magnetic flow, and you can see that it was such an extreme event that this is possibly what would have happened if that storm hits the magnetosphere. It distorts it really, really badly. And in fact, just basically strips off off the magnetosphere. What we're seeing here is density. So you can see the importance of, again, trying to understand when you're trying to fight. Now, another key aspect of this is that in heliophysics, we integrates the models and the observations. That is highly important, especially when we're trying to advance our prediction capabilities. So we have observations that I'm going to talk about from a different variety of missions and different types. These inform our models and our models are getting more and more sophisticated, but we still have lots of challenges. We have models that are looking at what's happening on the Sun, what's happening in the solar wind, what's happening at the Earth, how is the Earth responding to these things. Now, in order to understand this coupled system of the Sun and the Earth, we have to basically couple the code and create a modeling framework that encompasses the entire system. So again, it's very complicated and complex. And since we are looking at the Earth I just wanted to mention that the macro scale structure and the dynamics of the Earth's magnetosphere, that's strongly influenced by both the solar wind and solar storms directly impacts the ionosphere thermosphere system below. And so there again, this is another coupled system in this larger system. Alex is going to be discussing energy transfer in these types of wind-planet interactions and the implications of enhancements in close-in exoplanets. So I've already mentioned, the Sun is super dynamic. It offers really a laboratory for us to study a variety of fundamental physical processes, the Earth upper atmosphere, and magnetosphere also offer such a laboratory. Another key challenge we've already mentioned is this system science aspect of the entire system. But another related key challenge is the vast range of scale that heliophysics science covers. We study from plasma physics to the kinetic scales. We do magneto-hydrodynamic modeling. It really depends on what kinds of processes we are studying, but we really have to look at the entire range of scales from the solar wind interacting with comets. We look at the interstate interstellar medium interacting with the heliosphere. Again, this requires an understanding of system dynamics and energy transport across all scales. How do we do this? How do we approach this very complex system? We have a lot of, of data. We have a lot of observations and this is necessary. So here's showing the 20 operating missions that we have in what we call the Heliophysics System Observatory. In order to understand heliophysics, we need to have measurements and observations of the Sun in between, especially here at Earth, at other planets. And so all of these missions are working together really to help us understand the mysteries of heliophysics as a whole and how it impacts us. So the amount of data we gather is quite significant, especially relative to, to astronomy and astrophysics. We have remote-sensing and in-situ data, which is a wonderful combination for really understanding some of the physics here. In fact, I would say we, we actually probably have like a three-dimensional context where your exoplanetary science may not. So I just want to touch on a couple of recent, very exciting mission. This is Parker Solar Probe, an animation showing that it's going very, very, very close to the Sun. It launched in 2018. And it is going closer to the Sun than any other objects in history. So that closest approach will happen in 2025. It's going within 3.8 million miles of the solar surface. It's the fastest spacecraft in history. And why do we need to go to close? Well, first of all, I wanted to mention the, the very innovative technology that went into being able to do this. We, in order to really understand, especially some of the activity and the dynamic behavior going on in the Sun, we need to get into the region where that, the action is taking place, and that is fairly close to the Sun. By the time we measure stuff out of the Earth, things have changed. So getting really getting into that, that inner area of the atmosphere is hugely important. I would note that these very extreme conditions that are close to the Sun are similar conditions to some of the extra planetary systems. And Alex will be talking about this as well, but a very cool mission. I have to say. Another mission that is fairly recent. Solar Orbiter is a European Space Agency and NASA collaboration. It's truly an international collaboration. Do you see all of the different countries involved? But what I wanted to really point out here is the amount of instrumentation. So we have about four in-situ instruments and six remote-sensing instruments. And with all of these instrumentation, we can get data on the plasma, energetic particle, magnetic fields, electric fields, wave... UV imaging, x-ray imaging. Again, this is really allowing a full picture, of heliophysics. And just to really show you briefly the orbit, the, the connections that we're able to make with the in-situ and the remote-sensing that the spacecraft is observing the Sun and then measuring the plasma, coming out from the Sun, being able to make that connection is, is incredibly useful. But the orbit is also really unique in that in its period of time, you're going to see that it starts getting kicked out of the ecliptic using Venus and Earth gravity assists. So this is for the first time allowing us to see the polar regions of the Sun, which is important for global modeling of magnetic field. So very exciting missions. And with that, I just want to close by saying, you know, this, the solar system, our solar system is not unique. Other systems look like this. And with that I'm going to pass it to Alex. So he can talk about more about that.

- [Alex] All right. Thank you.

- There we go. There you go. So thank you very much. So my name's Alex Glocer, I'm at NASA Goddard Space Flight Center for about 10 years now. And, I'm going to build on, on Holly's presentation and talk about some of the applications of heliophysics to exoplanet research and give you some, some examples of how that can be done and how it's, and how it's actually being done. And so by way of an outline, I'm gonna talk about some of the extreme space weather conditions that these exoplanets encounter, and in particular, talk about the implications of some of the extreme energy inputs to the atmosphere of a exoplanet from its host star. In particular, the type of a particle radiation in terms of like stellar energetic particles, stellar, strong stellar winds, and enhanced a photon radiation in the form of a EUV and XUV stellar flux. And for each of these extreme energy inputs, I'm going to show you some examples of how, you know, data constrained heliophysics models that were originally developed for our solar system can contribute to these exoplanetary problems. So as no one, as everyone in this audience already knows, there's been this explosion of detection and characterization of exoplanets around different stars. In particular, a number of Earth-like exoplanets in habitable zones located very close to their, to their host star. And by virtue of them being so close to their host star, they can encounter some very strong inputs kind of like in Holly's presentation, Parker Solar Probe is encountering. So each of these different energy inputs I mentioned before, we're going to walk through now, and we're going to start with the enhanced stellar energetic particle input. In example of this, that was published recently by Ben Lynch and company in 2019 is looking at... strong CMEs and associated stellar energetic particles and flares at Kappa1 Ceti. So Kappa1 Ceti is a young, you know, solar type star, which is an analog for our young Sun. And it's very magnetically active with a lot of observed or with observed super flares. And so what Ben Lynch and his co-authors did is they took a model of the stellar corona, the ARMS code, which is developed at Goddard by Rick DeVore, and use this to simulate a magnetic eruption from the star. And this is a movie of that looking down on the star and you see a very large magnetic eruption that occurs on the star. And associated with that eruption is the large release of flare energy, as well as a, a very large shockwave that accelerates particles to high energies. And that type of event would be on par with some of the strongest events that we've observed from our Sun, like the Carrington event. So of course, those large SEP fluxes can impact planetary atmospheres, You know, as they precipitate into the atmospheres of these planets, they can have some effects. And one example is shown in the right from this paper, from Airapetian et al. in 2016, where enhanced precipitation of energetic particles can dissociate on two molecules and drive a whole chain of nitrogen chemistry in the upper atmosphere. So this can affect potentially greenhouse gas production, as well as HCN production, which is a key ingredient for biochemistry. So now I want to turn to the enhanced stellar wind and, you know, to understand how, you know, very strong stellar winds can impact a planetary atmosphere. It's interesting to consider two cases. So the case of whether you have a magnetic field and whether you don't, and, you know, there's this open question that asks, you know, does a magnetic field help or hinder a planet's ability to hold onto an atmosphere and how is this different for different systems? So as an example of interaction of a planet without a strong magnetic field, you can think of Mars where you have the solar wind directly impinging on the atmosphere of the planet and sputtering that atmosphere off or stripping that atmosphere off directly. Now, if you have an internal magnetic field, you prevent this direct interaction with the atmosphere, but instead what you get is a much larger cross-section presented to the field. So you can interact with the stellar winds over a very large area defined by the magnetic field. And so this is an example of a magnetized planet interacting with the, with a wind in this case, it's Earth interacting with the solar wind. And this is from an MHD simulation. And you can see that you have very strong, that the winds can create a very large interaction region with the field and that the field responds very dynamically to changes in the wind. So the next question is, well, how does that energy get transmitted down to the atmosphere from this large collection area? And there's sort of two ways that that happens. So one is through particle precipitation. So different plasma physics processes out in the magnetosphere can drive energetic, particle precipitation down into the atmosphere where it forms the Aurora, like you see on the left. But also all of that jiggling of the magnetic field can drive electrical currents, which then close in the atmosphere and the conducting regions of the ionosphere. And as they close through the atmosphere, there is a certain amounts of resistive heating. You know, this so-called Joule heating, which is going to heat up the upper part of the atmospheres and for Earth under our more tame space weather conditions. This can lead to effects like satellite drag, which can cause low Earth orbiting satellites to tumble, but for an extreme exoplanet, it can also have other effects, which I'll talk about in, in a minute. So one of the consequences of this interaction is when you have a strong particle precipitation from the Aurora you also get radio emission. And so there's this paper from Zarca 1998, looking at radiated radio power from the Aurora, looking at... how does that correspond to the solar wind power that's collected by the planet. And so this is for all of the different Solar System planets, Neptune, Uranus, or Saturn and Jupiter, and you can draw a line and extrapolate this to what this would imply for close and exoplanets. And you can see that, you know, it's a rather extreme regime that you're looking at. And so this is something that they're exploring with the, with the LOFAR observations, trying to see if they can detect this, but heliophysics models of the Aurora can really help us understand this scaling better. You know, we develop models of the Aurora and of the energy that drives the Aurora. And, you know, this scale may not continue linearly as you're extrapolating, and they saturate at some point. Some of the points on here don't really correspond ideally with how the scaling happened. So heliophysics models can help us understand this scaling better. There's another approach to detecting magnetic fields of exoplanets. So this is from Arthur Cohen's recent paper showing how, if you have a planet with a magnetic field, that's passing in front of a star, you can modulate the background, coronal radio emission, and that background signal is, can be significant. And so this is showing you the perturbation on the background signal caused by the planetary magnetosphere traversing the, the disc of the star. Just another example of a heliophysics stellar coronal model and planetary magnetic field reaction that can be useful here. So going back to the current, the field align currents and the Joule heating, you know, when you're, when the exoplanet is very close to its host star. Its encountering very strong stellar winds, and those very strong stellar winds can drive a lot of Joule heating. And this is an example of showing the amount of Joule heating that you can, that a close in planet could could feel, and then comparing that to Earth during a typical solar wind conditions and Earth during a CME. And what you can see is that these close in conditions in very strong stellar wind drivers, you know, just the background, stellar wind, not even with a coronal mass ejection, or anything extreme going on, is already as strong or stronger than what Earth would feeling... more Joule heating than Earth would be during a CME. Of course, that enhanced heating can have effects on ion escape and atmospheric loss. When you add that much energy to the upper atmosphere, you can cook off that parts of the atmosphere and drive fluxes out into space. And so this is from a simulation. I did illustrate the point showing how as you increase the amount of heating, you're going to get more outflow flux, once you pass a certain threshold. So finally, I am going to talk about the enhanced, interstellar EUV and XUV photon flux, and the implications of that. And so just to show you what I mean when I say that the photon flux is very extreme, this is a comparison of what Earth sees and what Proxima sees. So this is the photon flux and the EUV and XUV range. That's impinging on the upper atmosphere of Earth in blue, and then the same flux that we expect Proxima... Cen b... to feeling green. And so, you know, Proxima feels this because it's very close in, but also it's a very actively flaring star with many flares every, every day. So it's providing a lot of this energy input. So the implications of this for one thing is you get a lot of ion escape in situations like this. So this is from a paper that Vladimir and I did together looking at the ion escape for different levels of XUV input and showing that you get lots of iron escape when you have more XUV input, but also this ion escape happens along open magnetic fields that are connected to the stellar magnetic field. And that... field opens up under these very strong driving conditions. So you can get a lot of atmospheric loss from this. And so Katherine Garcia-Sage in her "ApJ Letters" paper also looked at this for Proxima and looked at the same thing. You know, the mass loss rate and how much the open, the magnetic boundary opens up and use that to estimate a mass loss time for different assumptions about the neutral atmosphere. And found that the ion escape could be so extreme under these conditions that if you look at the age of Proxima Cen b, and look at these loss times, it's possible to evacuate the entire atmosphere under some conditions. So it's not just true-

- [Host] Alex

- Yes.

- [Host] Excuse me for interrupting. Just five more minutes remaining, including questions.

- No problem. I'm this is my second to last slide. It's not just ion escape. It's also a hydrodynamic escape. When you have more EUV and XUV input, you can drive escape of primary atmospheres. And so this is an example for a primary atmosphere for an Earth-like planet, using a model that I developed. For, you know, Earth-like solar input, and then, you know, a hundred times Earth-like stellar input that close-in Earth would see. And what you see first of all, is that you get increased energy absorption, which you would expect. The density increases at high altitudes. And so does the velocities, which gives you larger escape times for these primary atmospheres and the heating of course also goes up. So this is just a sort of summary, you know, the exoplanets experienced very extreme space weather conditions in the form of strong pro... particle, energetic particles, strong winds, strong, photon radiation input to the atmospheres. And so that extreme space weather then has consequences for the atmosphere and also for potential exoplanet observations, like whether or not a planet could have a magnetic field, for example. And so finally, I just make a point that, you know, heliophysics models have been developed for the relatively data rich environment of our solar system, where we're often comparing with in-situ and remote-sensing observations. And I think really have a lot to contribute here. And with that, I'll just say, thank you. And I guess we have some time for questions for myself or for Holly.

- [Host] Yes. Thank you for two great talks. We have a couple minutes for questions. Let me check. I don't see any in the, on the website yet, but I'll, I'll kick off one question actually, I guess, for you Alex. So if folks are interested in incorporating information from these heliophysics models, like you're saying, I guess, where can they access them or can they just reach out to you and Holly folks like that?

- You're certainly welcome to reach out to people like Holly and myself, but also in heliophysics there's a community coordinated modeling center at Goddard, which makes a lot of models available to the community. And you don't have to be an expert to run those models through the community coordinated modeling center. You can put in a request through their webpage and they provide the super computing resources, the expertise to run those models and the visualization tools to interpret. So for many things you might want to do, you can work with that. And for very more specialized cases, you can talk to, you know, people like myself or Holly, or other, we're all very friendly, you know, we like to help.

- Okay. I do see Michael has his hand raised, but there is a question in the, on the website. So I'll ask that first. So I think for either one of you, what would Earth's atmosphere look like today if it had experienced Proxima's sun levels of EUV flux?

- Well, maybe I'll, I'll take that one, Holly So that's basically what we were looking at with, in Katherine Garcia-Sage's paper. And the expectation that we have is that much of the atmosphere could have been evaporated actually from that level of flux. So it might not have been able to maintain an atmosphere. So could look very different. Of course there's limits to what we, what we can know, but that's certainly one possibility.