From the June 2019 issue

Whenever I read articles about solar storms, they talk about billions of tons of charged particles that are ejected. How are these amounts calculated?

Ralph Heide El Segundo, California
By | Published: June 19, 2019
On August 31, 2012, NASA’s Solar Dynamics Observatory captured this filament erupting from our Sun. Such events send radiation in the form of fast-moving charged particles out into the solar system.
A: The solar wind is composed of a plasma of positively and negatively charged particles (protons and electrons) with temperatures up to 2.7 million degrees Fahrenheit (1.5 million degrees Celsius). Such high temperatures mean that these particles are moving so fast that they can escape the gravitational attraction of the Sun and are ejected from the Sun’s outer layer, the corona, at speeds between 150 and 500 miles (250 and 800 kilometers) per second. The winds trace the solar magnetic field as it forms a complex structure of closed loops, with some field lines staying close to the Sun and others extending far past Earth.

Since these charged particles were first hypothesized in 1918 by Sydney Chapman, a multitude of studies and hundreds of spacecraft have focused on learning more about their physical properties. One of the most famous spacecraft is the Solar and Heliospheric Observatory (SOHO), launched in December 1995 and still in use today. One of SOHO’s instruments can detect the number of charged particles of different energies hitting its sensor. Particles with smaller energies (1–2 keV; 1,000 to 2,000 electron volts) come from the solar wind, while large energies (>10 MeV; 10 million electron volts) come from large solar eruptions. By determining the number of these particles hitting the sensor over a fixed period of time and knowing the mass of these protons and electrons, it is possible to extrapolate the mass of the particles being ejected from the Sun during a solar storm.

Kathryn Neugent

Ph.D. Candidate and Research Associate,
Department of Astronomy, University of Washington,

and Lowell Observatory, Flagstaff, Arizona