With the Solar Orbiter, the Esa Wants to (Re)discover the Sun.

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Artist’s view of Solar Orbiter in front of its subject of study

For the first time, a mission takes off to observe the high latitudes of the sun and its poles. The ambitious European probe will approach the Sun with ten new instruments.

3, 2, 1, and liftoff!

The launch is scheduled for Monday, February 10 at 5:03 a.m. from Florida. NASA, which is a partner in the Solar Orbiter mission, is contributing to the project by ensuring takeoff from Cape Canaveral. Everything will therefore be played out under the hood of an Atlas V launcher, which will have the heavy responsibility of sending the probe out of the Earth’s attraction … All in 53 minutes! A long period of stress for the teams, some of which have been preparing for Solar Orbiter (also known as SolO) since its genesis in 2001.

Such a mission takes time to be formulated, prepared, and to have its precise objectives well defined. In 2009, ESA selected the ten instruments that will fly with the mission, before signing the contract for the design of the probe itself in 2012. A true jewel of engineering and research, Solar Orbiter can finally begin its mission.

Fundamental Questions

This marks the beginning of a long journey for the 1.8-tonne probe, which is carrying more than 200 kg of scientific instruments to study the Sun from a new angle. The mission must provide answers to four fundamental questions.

First, the solar wind. What phenomenon is at its origin and how do the particles of the solar wind accelerate? Next, the high latitude areas. Solar Orbiter will be able to observe the Sun’s poles, and in particular its magnetic field, thanks to its inclination of orbit. How is it generated, and how does it pass through the “surface” of the Sun and its corona? What happens in the polar regions when the polarity of the solar magnetic field reverses about every eleven years?

Finally, the probe will attempt to observe solar flares and coronal mass ejections to answer questions about these extreme events: how do they impact the Solar System and how can they generate energetic particles?

Solar Orbiter vehicle

The Solar Orbiter

A strange journey

These questions, which led to the design of the probe, are the result of several decades of observation of the Sun. ESA is at the forefront in this field, having initiated and participated in at least five space missions including a heliophysical study: Ulysses (1990), SOHO (1995), Cluster (2000), Double Star (2002) and Proba-2 (2009), in addition to major advances in ground observation and research.

In fact, the very profile of Solar Orbiter’s mission is special. After lift-off, the probe will pass as close to the Sun as possible about once every five months, and will use overflights of the Earth (2021) and especially Venus (2020, 2021, 2022, 2025, 2026, 2028, 2029, 2030…) to modify its orbit thanks to a gravitational slingshot effect. This will allow SolO to save as much fuel as possible and extend its mission over more than a decade. From 2027 onwards, its orbit will be inclined by more than 24° to the solar equator: it will then be able to observe the Sun’s North and South Poles at length during each revolution. Teams are hoping for 22 full orbits and a possible extension into the 2030s…

Shield wall!

Since Solar Orbiter will be approaching the Sun from less than 42 million kilometres away, the probe will have to operate for long periods behind an impressive shield. Designed to withstand temperatures in excess of 500°C, it has been developed using a combination of high-strength materials: titanium, carbon fibre and aluminium. The shield will absorb up to 13 times the solar radiation that satellites around the Earth have to withstand. And he’s equipped… Small windows. Indeed, some instruments are designed to observe the Sun directly at regular intervals. To make them work, the shield is equipped with tiny little sliding flaps and dedicated sensor portholes.

All the equipment has been specially prepared for a mission close to the Sun, including the Solar panels which will be piloted to show only a minimum of their cells as they approach our star: a single misorientation and the components would be irreparably damaged.

The instruments are divided into two categories: those that will observe the Sun from a distance and those that will measure the in situ characteristics of the environment through which the probe passes. The ten on-board instruments include imagers with different frequency bands to highlight certain characteristics, an X-ray spectrometer, a coronograph (an instrument that hides the Sun to better observe its corona), a magnetometer, a radio and plasma wave analyzer, a solar wind sensor and an energetic particle detector.

A very international group with teams spread throughout Europe and in Washington. France is fortunate to manage two instruments, the radio wave and plasma analyser RPW from the LESIA laboratory (Paris Observatory) and the coronal environment spectral imager SPICE from the IAS in Orsay.

Solar Orbiter instruments

Solar Orbiter instruments

Family photos

The latest feature of Solar Orbiter? His cousin! Indeed, another exceptional mission is taking place at the same time, that of the Parker solar probe (PSP). The latter is specialized with a suite of five instruments for in situ observations . And with good reason: it plunges at regular intervals until it touches the solar corona, less than 20 million kilometres from our star (and by 2025 it will be as close to it as 6.5 million kilometres)!

Parker is much smaller than Solar Orbiter, and while she also hides behind a big shield, her instruments are not quite the same. On the other hand, when both probes are active, they will produce complementary results: each one will be able to give context to the measurements of the other . And we already know that this data will be crucial for future publications.

Heliophysics is a field that is experiencing a golden age with these two missions and the appearance of new ground-based telescopes such as the Daniek K. Inouye, 4 metres in diameter. Together, they will make it possible to unravel some of the mysteries of our star, which is much more than a thermonuclear fusion reaction: the energetic, magnetic and physical phenomena are so extreme in its different layers that they are sometimes beyond comprehension.

And after all, without the Sun, we wouldn’t be here…

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