Solar Orbiter: what you need to know about the European mission to the Sun.

Europe returns to the Sun with the Solar Orbiter mission, starting on February 5: it will study the heliosphere for more than 7 years from a whole new perspective

Solar Orbiter di fronte al Sole
Illustration: Esa

In 1998 it was held at Tenerife a congress of heliophysics, the branch of physics that studies our star, in which a plan was outlined of action for the future of the European Space Agency on the Sun . One of the ideas that emerged was that of a mission that would continue the work started by the other European solar probes, Ulysses , Soho and Cluster . We wanted a mission that could observe the Sun in the visible and ultraviolet, like Soho, but that could also do it from different planes from the one on which the Earth orbits, like Ulysses. We wanted a mission that came closer to the Sun than any other, equipped with telescopes capable of obtaining the most detailed images ever. From 1999 work began on this project, which today has a name, Solar Orbiter , a launch date, between 9 and the 10 February 2020, it's a Atlas V launcher ready on the ramp of the Kennedy Space Center in Cape Canaveral .

Solar Orbiter will employ a year and ten months to fit into its final orbit, the one with which it will finally become operational around our star. During this period he will make a series of passages close to the Earth and the planet Venus : a small dynamic magic known as gravitational slingshot which will provide the probe the energy needed to quickly reach the Sun. The final orbit will last five months and will be an extremely flattened ellipse, with the point closest to the Sun at less than a third of the distance that separates the Earth from its star.

A series of further passages around Venus ”, explains Marco Romoli , professor at the University of Florence and responsible of Metis , the coroner of Solar Orbiter, “ will serve to tilt the orbit up to 33 ° with respect to the solar equator. This maneuver will allow to observe in detail the polar regions of the Sun, a goal that other probes in the past had already achieved, but never with the level of detail that will be possible to obtain from Solar Orbiter data. A peculiarity of the probe's orbit is that when it reaches the perihelion [il punto più vicino al Sole, ndr] , its speed will be almost equal to that with which the Sun rotates around its axis, allowing you to observe a single detail of the surface for much longer than you would otherwise . “

The main objective of Solar Orbiter is that of studying the heliosphere , the environment that surrounds our star and which is influenced by its activity and solar winds. The heliosphere has always been a challenge for researchers, because through the many solar probes that have traveled in the past or that are still around the Sun (such as Soho or Parker Solar Probe) we have learned to know it, but there are still many questions which remain without a fully satisfactory answer. What drives the solar winds and how the is formed) magnetic field in the solar corona? How do phenomena such as flares, solar protuberances and mass ejections of the crown interact with the heliosphere? How are the solar dynamo, that process by which the Sun's magnetic field is formed, and the heliosphere connected?

All the instruments on board the mission “, Romoli continues,” are designed precisely with a view to answering these questions, and more generally for the study of phenomena and the heliospheric environment and its interactions with the magnetic field produced by our star “.

On Solar Orbiter there are ten instruments for a total of 200 kilograms : some will deal with measurements in situ , related to the environment that surrounds the probe , such as data collection on the solar wind, high energy particles and the magnetic field in the heliosphere. The other tools will instead be used for the study of the surface and atmosphere of our star, especially using the ultraviolet frequencies, where it is possible to observe the greatest amount of detail. To observe the crown in the visible and ultraviolet it will be necessary to use a coronograph , a telescope equipped with a concealer covering the solar disk showing only the external gas region.

All the instruments will be active at the point closest to the Sun and during the passage to the higher and lower latitudes with respect to the solar equator, while in the rest of the time only the instruments will be active in situ .

As with all solar missions, one of the biggest challenges is that of protection from the Sun itself: in moments of greatest proximity, the probe will be exposed to radiation equal to 13 times the one we receive on Earth . Furthermore, in those parts it is not uncommon to be hit by sudden waves of charged particles . Solar Orbiter must therefore be well prepared to face these challenges: the face of the probe that faces the Sun will be protected by a heat shield that can reach temperatures of 600 ° C and a complex radiator system will disperse excess heat into space.

The mission will last for nominally for 7 years from launch (until 2027) to then be able to be extended for another 3 years if everything goes well. In the nominal phase the inclination of the orbit with respect to the solar equator will be about 24 ° while in the extended one this value will increase up to 33 ° , thus allowing to observe the Sun from a still different perspective.

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