The solar wind was dismissed as nonsense until Soviet probes flew through it
In 1958 a reviewer told Eugene Parker to go to the library before writing about a subject he clearly misunderstood. Parker's claim was that the Sun's corona is so hot it streams outward as a supersonic gale of charged particles. A year later, Luna 1 measured that wind directly.
The corona, the Sun's outer atmosphere, sits at around a million degrees Celsius, hot enough that its particles can escape the Sun's gravity. What pours out is a plasma of electrons, protons and alpha particles, with traces of heavier nuclei such as carbon, oxygen and iron, dragging the Sun's magnetic field with it. A few solar radii out, it travels at 250 to 750 kilometres per second. It shapes the auroras, triggers geomagnetic storms and explains why comet tails always point away from the Sun.
The clues piled up for a century. In 1859 Richard Carrington and Richard Hodgson each spotted what we now call a solar flare, and a powerful magnetic storm struck Earth the next day. Kristian Birkeland, noticing that auroras almost never stopped, proposed in 1916 that the Sun fires out both negative and positive particles. In the 1950s Ludwig Biermann argued that a steady solar outflow must be pushing comet tails, while Sydney Chapman calculated that the corona should reach past Earth's orbit.
Parker put these together at the University of Chicago, reportedly needing just four lines of algebra. He treated the corona as a gas that, as gravity weakens with distance, speeds up past the speed of sound, much like the flow in a rocket nozzle. He chose the word wind because it was an ordinary flow of gas rather than a spray of separate bullets. He also predicted that the Sun's rotation twists its outflowing magnetic field into what is now called the Parker spiral. The journal editor, Subrahmanyan Chandrasekhar, overruled both hostile reviewers and published it, despite not agreeing with it himself.
Proof came fast. Luna 1 measured the wind in January 1959, and Mariner 2 later found fast and slow streams. The SOHO spacecraft showed that the fast wind accelerates closer to the Sun than Parker expected, a puzzle still unsolved. In December 2010, Voyager 1, 17.4 billion kilometres from Earth, found the outward flow had slowed to zero.
Source: Solar wind
