American Scientist

The European Space Agency’s Solar Orbiter will explore the ways that the Sun influences the Earth and other planets. It will also study how our star creates and controls the heliosphere, the enormous bubble of plasma surrounding the Solar System. Key questions it will address:

• What drives the solar wind, the stream of charged particles blowing from the Sun? And how is the solar wind heated and energized by powerful magnetic fields in the corona, the Sun’s million-degree atmosphere?
• How do eruptions on the Sun accelerate charged particles nearly to the speed of light, giving rise to solar energetic particle events? These events can harm satellites, disrupt radio communications, and force airlines to avoid polar routes.
• How do different forms of solar activity—flares, eruptions, shock waves, and coronal mass ejections—influence space weather, changing the speed, density, and magnetism of the solar wind throughout the heliosphere?
• What is the nature of the solar dynamo that generates the Sun’s magnetic field and drives the 11-year solar activity cycle? Solar Orbiter will provide the best look ever at the little-understood flows that transport magnetic fields near the solar poles.

Close-up views

When the Orbiter reaches its planned orbit in 2023, it will swoop inside Mercury's orbit every five months, coming within 26 million miles of the Sun. At its closest point, its movements will be synchronized with the Sun’s rotation, allowing it to study a single region up close for several days. During these “hover” periods, the probe will monitor the magnetic phenomena that trigger flares and eruptions.

Instrumentation

The Orbiter carries six instruments that will measure conditions in the local environment (in situ), and four that will study the Sun remotely. The in situ instruments will operate continuously, whereas remote sensing will be confined to times when the probe is closest to the Sun and when it is at its highest points above or below the solar equator.

• Remote sensing instruments will measure seismic vibrations of the photosphere (the visible surface of the Sun), the layers above the photosphere, the structure and dynamics of the corona, ultraviolet emissions from the corona, x-ray emissions from flares, and the flow of the solar wind.
• In situ instruments will measure energetic particles, the movement of the solar magnetic field into space, and electromagnetic waves in the solar wind, along with the properties of the solar wind itself (including its density, temperature, and velocity).

A unique perspective

Over seven years, Solar Orbiter will swing repeatedly past Venus and use the planet’s gravity to change the tilt of its orbit. Eventually, it will be inclined 25 degrees to the solar equator, allowing it to see the Sun’s polar regions in ways that are impossible from Earth or from probes that orbit in the same plane as the planets.

Probe partners

NASA’s Parker Solar Probe will complement the Solar Orbiter, coming even closer to the Sun but lacking Solar Orbiter’s high-latitude perspective.

Infographic by Gary Schroeder.