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A truly ambitious and unique scientific mission: what is happening on the Sun and what will be studied by the Solar Orbiter

The unique solar probe should significantly illuminate the surface of the Sun and help solve important puzzles.

The sun is one of the most important elements of our lives since ancient times, both as one of the most important deities of early religions, as well as the most important source of light and heat. However, knowledge about the Sun is small. The sun also affects our lives in a subtle way that we do not fully understand, for example, electromagnetic storms that can disrupt our communication and even our health.


The sun is also a unique laboratory. Its surface itself has a temperature of about 5800 K, comparable to the heat wave of an atomic bomb, which causes much more destruction than other explosion effects, such as the explosive wave itself or prolonged radiation. Extreme densities and temperatures occur in the depths of the Sun that allow fusion processes to take place, the consequences of which can also be observed.

At the same time, the Sun is the star closest to us, but the second star closest to us, Century Proxima, can not even be seen with the naked eye (mainly because its light is still 500 times smaller than the Sun). The brightest star without the sun is Syria, the eleventh star closest to us, 25 times brighter than the Sun, but 7 billion times brighter because of the great distance from Earth. So, to understand other stars, it is much easier to use the sun as a reference point, because we can observe them in more detail.

Solar Orbiter is the sixth space observatory in Europe to study the Sun. The European Space Agency (ESA) plans to launch it as early as 2020 in February. One of the main motivations to create this mission was to extend the solar minimum. The primary goal of the Solar Orbiter mission is to understand how the Sun creates and controls the heliosphere. Mission Objectives:

  • and how does solar wind plasma and magnetic field form in the Sun's crown (the highest part of the Sun's atmosphere)?

  • how do episodic solar phenomena affect the oscillation of the heliosphere (heliosphere – part of the cosmos affecting the sun reaching Earth)?

  • How do solar eruptions form particles that fill the heliosphere?

  • how does the solar dynamo work (a phenomenon that creates and maintains the magnetic field of the sun) and how does it relate to the heliosphere?

This is what the Solar Orbiter Observatory is about: the significant orbit of the observatory will be up to 25 degrees wide. This means that the observatory will be able to observe the polar regions of the Sun, which we cannot effectively do with Earth.

What connects these goals? It is already clear that the heliosphere is created by the sun. The particles are blown into the heliosphere by solar wind, which is caused by high-energy local phenomena in the solar crown associated with the magnetic field. The magnetic field is characterized by characteristic lines that impede the circulation of matter. That is why there are sunspots – cooler parts of the Sun's surface in which magnetic field lines stop convection and, as a consequence, interfere with convection energy transfer.

Due to the differential rotation of the Sun (different rotational speeds depending on depth), magnetic lines wrap around the crown and eventually burst, throwing plasma into the heliosphere. This is the essence of heliophysics. Because the Sun is not exclusive to stars of this kind (dwarves), these studies have a broader astrophysical significance, but they can only be done during the study of the Sun – it is relatively close.

Although it appears that the heliosphere can be explored from Earth, it is already very scattered over more than 150 million kilometers, one astronomical unit, AU, so that its phenomena cannot be effectively associated with solar phenomena. The solar orbiter will fly much closer to 0.28 AU, and will be able to observe solar phenomena in the heliosphere much more effectively. This leads us to the first goal of the mission. It is known that supersonic corona winds are constantly expanding and interacting with planets in the heliosphere up to the heliopause beyond Pluto's orbit.

For example, on Earth, these winds cause most of the magnetic phenomena in our atmosphere, such as the northern glow, to significantly affect the evolution of Venus and Mars, destroying the upper layers of their atmosphere. Solar wind is divided into two types: fast (~ 700 km / s) and slow (~ 400 km / s). The balance of these winds is associated with the 11-year cycle of the Sun's magnetic activity. The fast wind comes from the holes in the crown, but it is not known where the slow wind comes from. They are not the same crown holes, because these winds have different mass flow and composition. From Earth (1 AU), we simply cannot distinguish where a slow wind comes from, and thanks to Solar Orbiter you will be able to see the dynamic properties of the wind itself, which will determine its origin.

Crown mass emissions are a separate class of phenomena occurring in the crown. coronary ejection – CME) – The biggest episodic phenomena on the Sun. They arise when the magnetic field lines are missing and both the material and its magnetic field, large structures, are ejected at speeds up to 3000 km / s. These phenomena have astrophysical significance because they are the main way stars get rid of the magnetic field produced by their dynamic process.

Interplanetary corona mass discharges are the main cause of geomagnetic storms, but they are very difficult to study from the plane in which they are spreading. It's not so much easier to observe CME on the Sun from Earth. Because of the much shorter distance and much above the ecliptic plane (where the planets rotate), Solar Orbiter will help you understand how phenomena such as CMEs occur and spread in the heliosphere.

Particularly noteworthy is the role of the Sun as an efficient particle accelerator. Like many astrophysical objects, solar processes (such as crown mass emissions) accelerate particles to relativistic velocities. After reaching Earth, such particles are called cosmic rays and can be much more energetic than we can achieve in our particle accelerators. The sun produces many such particles, for example, mass emissions of the crown can transfer up to 10% of their kinetic energy to accelerated particles, and acceleration can also occur in magnetic loops. However, observing these phenomena and their accelerated particles from Earth is complicated by the interplanetary distortion of their trajectories, which requires registration much closer to the solar orbit.

Finally, the very dynamics of the Sun should be understood. This global solar magnetic field is created in the convection area of ​​the three-dimensional solar current and transfers energy to the solar atmosphere, to the chromosphere, to the crown, and finally to the heliosphere containing Earth. This dynamic phenomenon occurs in a quasi-stationary cycle lasting 11 years. Despite previous research by Ulysses, SOHO and Hinode space observatories, advances in theoretical models and digital simulation of magnetic phenomena are still far from sufficient to understand dynamics and their effects. Here, Solar Orbiter makes a unique contribution – the observatory will monitor polar regions, which we cannot do from the ecliptic plane. It should be remembered that observing the sun's poles from the ecliptic plane, we look at the atmosphere and properly cover more material than the equator.

In these parts of the Sun there is a wealth of unique information not only about the dynamics that create patches of the Sun, but also about the so-called "magnetically silent" layers. These are so-called because the main dynamics should not have a significant effect on such latitudes, but lower dynamics can work, because such areas also have a magnetic field. Even in convection star atmospheres, where due to their low rotational speed, solar-like dynamics are not affected, magnetic fields are observed. Here too, Solar Orbiter should be a significant source of new knowledge.

The Solar Orbiter Observatory itself will be a 21-sensor, triaxial, constantly stabilized solar satellite that performs remote observations of the Sun and collects data on the surrounding material. It will be protected by heat shields and the photovoltaic batteries will be rotated perpendicular to the direction of the sun to prevent overheating. The planned data transfer rate is 150 kb / s (1 AU from Earth). The planned duration of the mission is 7 years, with the possibility of extension for another 3 years and another 2 years for data processing.

In total, the observatory detectors weigh 180 kg and consist of:

  • environmental monitoring detectors:

    • The energy particle detector will examine the composition, temporal and spatial distribution of energy particles;
    • The magnetometer examines the magnetic field of the environment with high accuracy;
    • The radio and plasma detector system will scan electric and magnetic fields both from the environment and remotely, in high time resolution;
  • The solar plasma wind testing system will examine the properties (density, speed, temperature, etc.) and the chemical composition of solar wind ions and electrons from 0.28 to 1.4 AU
  • remote sensing instruments:
    • the extreme ultraviolet camera will monitor the higher atmospheric layers (due to the high opacity in the UV part, the radiation arises above) and will first display photos of the Sun in the UV region outside the ecliptic plane;
    • the high temporal and spatial resolution of the coronograph will simultaneously record visual, ultraviolet and extreme ultraviolet radiation in the 1.4-1.7 to 3.0-4.1 sun rays from the center;
    • a polarimetric and helioscopic camera will monitor the solar disk in the field of view in high resolution and measure radiation intensity, magnetic field vectors and velocities in the direction of observation primarily to obtain information about dynamic convective layers;
    • helioscopic camera for detecting crown mass emission based on observation of high spatial resolution of scattered light scattered by electrons;
    • Extreme ultraviolet spectrograph for observing the crown on the Sun disk, allowing to link the phenomena of the crown with the solar wind recorded in the environment of the observatory – X-ray spectrometer.

Solar Orbiter is a truly ambitious and unique scientific mission aimed at understanding phenomena that directly affect the Earth, its environment and the Sun, the Sun itself, and phenomena of astrophysical importance in other stars. This mission should start as early as February 2020 and bring many new discoveries!

Based on: Solar Orbiter. Study of the Sun-Heliosphere connection

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