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We depend on what happens in the Sun and we must learn to predict it

When the Solar Orbiter spacecraft was launched on February 11, 2020 from Cape Canaveral (Florida, USA), the mission scientists They did not imagine that a pandemic would force them to leave the control rooms at such a critical time. Despite this, it survived its first weeks in orbit and the commissioning of the instrumentation. This November, after flying over Earth and successfully passing through the clouds of space debris, the spacecraft completed its cruise phase, giving way to the scientific phase .

His objectives are to study the Sun closely and try to better understand how the heliosphere is generated, the region of space that is affected by the phenomena of our star and in which our entire solar system is included. José Carlos del Toro , researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC), is part of this mission of the European Space Agency, in collaboration with NASA, and that has Spanish participation.

That the Sun is so close to us, is it an advantage or a disadvantage to study our star?

All advantages. The Sun is, today, the only star that we can observe in enough detail to be able to do fundamental physics. In fact, studies and developments in atomic physics and optics are made every day on the Sun, for example, which cannot be done on other stars. It is an excellent laboratory of phenomena that can hardly be controlled in terrestrial laboratories, because it is not easy to have temperatures so high, thousands of Kelvin, and pressures orders of magnitude greater than atmospheric pressure.

All those phenomena that we witness in sufficient detail on the Sun teach us things that are useful for our life on Earth. In addition, our star, being at the distance at which it is, is not only our source of energy.

What other role does it play?

It is part of our environment. We live within the extended atmosphere of the Sun, what we call the heliosphere. That region that represents the set of phenomena and particles whose origin is in the Sun and which extends to the confines of the solar system. It includes us. In it a series of events happens that clearly affect our life on Earth. Today what happens in the heliosphere affects us much more than in the 5,000 million years that the Sun has been working.

We depend on what happens in the Sun and we must learn to predict it

We live within the extended atmosphere of the Sun, what we call the heliosphere and, today, what happens in it affects us much more than in the 5,000 million years that our star has been operating

We depend on what happens in the Sun and we must learn to predict it

Why does it affect us more?

We are increasingly dependent on our spatial environment. To talk every day we use telephones that use, at least, the ionosphere as a reflecting mirror. And they also use communications satellites for almost everything. Watching television, ‘googling’ on the internet, surfing both by boat, by plane or in our own vehicles … Our entire lives are increasingly dependent on technology and our space environment, which is vulnerable to phenomena that originate in the Sun and these can significantly affect our life. Therefore, it is crucial to predict these phenomena.

In the same way that we predict the weather…

Exactly. We depend on what happens on the Sun and we have to learn to predict it, in the same way that we have learned to predict the weather. All these phenomena that have to do with life on Earth and whose origin is the Sun is what we call ‘space time’. The discipline that studies space weather and aspires to predict it is space weather.

We depend on what happens in the Sun and we must learn to predict it

Illustration of the Solar Orbiter mission. / ESA / Medialab

Returning to the influence of the heliosphere, how do the Sun’s particles act and affect our technology?

Well, to begin with, we know that the Sun is emitting, continuously, what is called ‘solar wind’, a cloud of particles, mainly protons and electrons, which are expelled with two types of speed, but without apparent great consequences.

However, from time to time enormous energy conversions occur, in which the energy that was previously stored in the Sun’s magnetic field is converted, on the one hand, into electromagnetic radiation, into very notable flares that they can even emit X-rays; and on the other, in kinetic energy, energy of motion.

This kinetic energy accelerates these solar wind particles, which end up being expelled at speeds close to half the speed of light. When these highly energetic particles reach the Earth, as they are ions (that is, electrically charged particles), they are deflected by the magnetic field lines of the same. Their destination usually ends up being the poles.

And so we end up seeing the auroras …

Exactly. The auroras are a very beautiful and necessary manifestation, but they are the tip of the iceberg. When these particles exceed the energy that the Earth’s geomagnetic shield can support, they impact the ionosphere and alter the physical state of this layer.

In these regions we have satellites whose orbit can be altered. We have the International Space Station (ISS) with people inside! And in this one, in fact, they have a receptacle with a good thickness of lead where, in case of a big solar storm, the astronauts must lock themselves in to protect themselves from the radiation.

Today we do not know when these solar storms will occur, but if we were able to predict them, what measures could we take?

Indeed, we do not know how to predict it yet. We are at the dawn of space weather. In the future we could take precautions and remedy. If we are able to anticipate the phenomenon itself well in advance, then we could evacuate, for example, the International Space Station. Or if we know that there is a solar storm that can catch a plane in mid-flight, we could divert it. Knowing this in advance would help us protect ourselves.

We depend on what happens in the Sun and we must learn to predict it

We are at the dawn of space weather. If in the future we are able to predict solar storms, we could, for example, evacuate the International Space Station or divert a plane in mid-flight

We depend on what happens in the Sun and we must learn to predict it

What do we need to achieve this level of prediction?

With the observations we make from Earth, we can only see half the Sun. Typically, our face changes every two weeks, but we can only observe the one in front of us. If we could know what is happening behind (not the hidden side, because that part behind will become the front part in a matter of days!), Then we would have fifteen days in advance.

In fact, in the past theories were formulated with special techniques of helioseismology – one of the most effective techniques to understand the interior of stars – to try to know what was happening in the other side of the Sun. This is how the solar magnetic activity of the back face of our star was predicted.

And in this way we could know if a solar storm could occur within fifteen days…

Exactly! We began to establish this technique and, with the measurements of the face in front, we began to predict what was happening behind.

We depend on what happens in the Sun and we must learn to predict it

The researcher José Carlos del Toro in his IAA-CSIC office. / Lucia Casas

Now let’s talk about Solar Orbiter. How will you help to learn more about our star to predict its activity?

With Solar Orbiter we have put ourselves on the other side, in opposition to the Earth and, lo and behold, the first measurements that we are making of the magnetic field on the back side of the Sun coincide quite well with theoretical predictions. That’s right: for the first time, we have seen the ‘ass’ of the Sun! [laughs].

What results do you hope will be obtained with this mission?

Many things. To begin with, as I was saying, we have seen the part behind the Sun, and that is already important in itself, since it will help us to study space weather. In addition, with Solar Orbiter we will be able to follow the evolution of the structures with greater reliability than when we do it from Earth, because we will be able to more easily separate what is perspective effect from what is the mere evolution of the different solar structures .

We depend on what happens in the Sun and we must learn to predict it

For the first time we have seen the part behind the Sun, something important for the study of space weather, and we will also be able to follow the evolution of solar structures with greater reliability than from Earth

We depend on what happens in the Sun and we must learn to predict it

Think about this: when a structure, like a sunspot, rises in the east and sets in the west, thirteen days have passed. As the surface of the Sun is curved, we do not see this spot in the same way when it is in one limb, as when it is in the other or even in the center. Ideally, if we could rotate with the Sun, we could study in detail what we are seeing regardless of the moment. That’s what this ship will do.

And what about its orbit?

This is also very important! With Solar Orbiter we are going to separate ourselves from the ecliptic, the plane in which the planets meet. The Ulysses spacecraft (NASA and ESA) had already orbited the Sun outside the ecliptic, but now, for the first time, we are going to put one outside the ecliptic to observe the Sun with remote sounding instruments.

What Ulysses did was take local measurements of the properties of the particles that were around him, as Parker Solar Probe (NASA) is doing at the moment. This mission will get very close to our star but, like Ulysses, the ship is ‘blind’. In this sense Solar Orbiter will help other missions thanks to its remote sounding instruments; we will be the ‘eyes’ of other space missions.

How does Solar Orbiter get off the ecliptic?

With successive gravitational aids from Venus and Earth, our ship tilts with respect to the ecliptic. And you can’t do this with fuel alone, you need a big boost. In fact, in November the Solar Orbiter approached Earth precisely to get that extra boost. It came close to Earth, about 400 km. Like from here (Granada) to Madrid, then little else! [laughs].

As you can imagine, when we get out of this plane of the ecliptic we obtain an unbeatable perspective of the poles of the Sun. From the Earth we cannot observe them in this way, since the poles of our star are almost perpendicular to the plane of the ecliptic.

Why do we want to see the poles of the Sun?

We will be able to better understand the magnetic fields of the star. What happens at the poles is very important for the changes in the solar activity cycle that occur every 11 years and that have as a consequence the exchange of the north pole for the south and vice versa. If we are able to measure the magnetic field at the poles well, we will be able to corroborate our theories about the changes in the Sun’s cycle.

We depend on what happens in the Sun and we must learn to predict it

By leaving the plane of the ecliptic we obtain an unbeatable perspective of the Sun’s poles, and thus we will be able to better understand the star’s magnetic fields

We depend on what happens in the Sun and we must learn to predict it

How will we see this magnetic field?

We do everything any astronomer does with light. We study our star with imaging, spectroscopy and polarimetry techniques. Not content with that, on board the ship we translate the light in terms of the physical parameters of the Sun with a code (inversion of the radiative transport equation) that, to put it simply, translates our light measurements into values ​​of the physical parameters of the Sun.

Although there are many instruments that have been called magnetographs over time, ours is the first. We do not send images of the Sun to the Earth, but magnetic fields and speeds already ‘cooked’. The conversion is done on board.

Is ‘cooking’ on board out of necessity or is it a strategy?

We are so far from Earth most of the time… even sometimes behind the Sun! There are times when we don’t even have communication, so we can’t afford to send all the raw data.

Solar Orbiter not only does the typical minimal data processing that is carried out with any other instrument or in any other space mission: we carry out part of the scientific analysis on board to, as it were, compress from intelligently the data. In this way we achieve high conversion factors with hardly any loss of information. We are very efficient in this because we have no other choice.

How do you assess this progress?

Scientists don’t really like this very much, but the particular characteristics of the orbit and the needs of the Solar Orbiter, which carries practically all kinds of instruments, have forced us to do that. However, thanks to this need, today, our satellite is the only one in the world that has a chip that invests in these equations of radiative transport in half an hour on board the spacecraft what other missions, such as Solar Dynamics Observatory of NASA, do with 50 computers on Earth for an hour. It is certainly impressive.

Solar Orbiter has ten instruments. Some will take measurements of the environment in situ , but others are remote sensing, such as Polarimetric and Heliosismic Imager (PHI), in whose manufacture the Andalusian Institute of Astrophysics has participated. What is your function?

The main objective of the Solar Orbiter mission is to understand how the Sun generates and controls the heliosphere, as we have discussed. This great question is broken down into four more specific ones, all related to the Sun’s magnetic activity. For three of these questions, the SO / PHI work is fundamental.

This instrument is an imager designed to provide us with very high resolution measurements showing the magnetic field of the photosphere (the luminous surface of the star) and mapping its brightness. In addition to this, it is the only one capable of probing the interior of the Sun by making speed maps of the movement of this photosphere.

We depend on what happens in the Sun and we must learn to predict it

The main objective of the Solar Orbiter mission is to understand how the Sun generates and controls the heliosphere, and that of the SO / PHI instrument is to offer images and measurements of the magnetic field of the photosphere (luminous surface of the Sun)

We depend on what happens in the Sun and we must learn to predict it
We depend on what happens in the Sun and we must learn to predict it

SO / PHI instrument (Solar Orbiter’s Polarimeter and Helioseismic Imager). / IAA-CSIC

After many years of SO / PHI development, what plans do you now have in the IAA Solar Physics Group that you lead?

Without a doubt, the first thing is to exploit the data that we obtain with this scientific instrument, but our group develops and manufactures others to continue investigating solar magnetic fields. Our journey began 20 years ago when we began to conceive IMaX, our first (misnamed as I explained before) tape recorder, for the Sunrise mission.

It is a stratospheric globe that carries a 1 m aperture telescope up to a height of 37 km above the level of evil, above the Arctic Circle, from Sweden to Canada. With this flight, in collaboration with German and American scientists, we have flown in 2009 and 2013, obtaining very interesting results. We are now preparing a third flight, in which Japanese scientists have also joined us, putting the finishing touches to two instruments (TuMag and SCIP).

And we are also developing another magnetograph (PMI) that will fly on ESA’s Lagrange mission, the first for the European space agency designed specifically to study space weather. As you can see, we have guaranteed entertainment and we hope that the high quality of the data obtained will allow us to carry out excellent science, helping us to understand a little more the mysteries and wonders of the Sun.

This interview has been carried out within the CSIC-FBBVA Scientific Communication aid program.

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