A new spacecraft will examine the sun close up

Feb 13, 2020

THE SUN is one of the most-studied objects in the sky, but plenty of mysteries remain. On February 10th a rocket blasted off from Florida carrying Solar Orbiter, a European space probe designed to solve some of them. This craft will spend the next two years performing fly-bys of Venus and Earth, using the gravity of both planets to kick itself into an unusual orbit that will take it well above the ecliptic, the plane in which all of the sun’s planets orbit.

From that vantage Solar Orbiter will peer at the sun’s poles, something no spacecraft has managed before, and do so from close up. At its nearest, it will be just 42m km from the sun—closer than Mercury, the innermost planet, gets. One of its features is, therefore, a heat shield coated with charcoal made from cooked animal bone and designed to endure temperatures up to 500°C. Tiny windows within this will illuminate the probe’s various instruments.

Those instruments are designed to shed light, as it were, on several questions. One concerns the solar wind, a flow of charged particles that streams from the sun at a rate of more than 1m tonnes a second. The solar wind blows at an average speed of 400km a second, but physicists do not know exactly what accelerates those particles to such a velocity. Another mystery is the...

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