Solar energetic particles (SEP) are high-energy particles coming from the Sun which had been first observed in the early 1940s. They consist of protons, electrons, helium ions, and HZE ions with energy ranging from a few tens of keV to GeV (the fastest particles can reach speed up to 80% of the speed of light). They are of particular interest and importance because they can endanger life in outer space (especially particles above 40 MeV). Solar energetic particles can originate from two processes: energetization at a solar-flare site or by shock waves associated with coronal mass ejections (CMEs). However, only about 1% of the CMEs produce strong SEP events.
SEPs are also of interest because they provide a good sample of solar material. Despite the nuclear fusion occurring in the core, the majority of solar material is representative of the material which formed the Solar System. By studying the isotopic composition of SEPs, scientists can obtain an indirect measurement of the material which formed the Solar System, and thus learn about its origins.
Two main mechanisms of acceleration are possible: diffusive shock acceleration (DSA, sometimes referred as first-order Fermi acceleration) or shock-drift mechanism. SEPs can be accelerated to energies of several tens of MeV within 5-10 solar radii (0.05% of the Sun–Earth distance) and can reach Earth in a matter of a few hours after a flare or an ejection. This makes prediction and warning of SEP events quite challenging. The seed population and composition of these SEP events is also an active area of research.
Read more about Solar Energetic Particles: See Also
Famous quotes containing the words solar, energetic and/or particles:
“Senta: These boats, sir, what are they for?
Hamar: They are solar boats for Pharaoh to use after his death. They’re the means by which Pharaoh will journey across the skies with the sun, with the god Horus. Each day they will sail from east to west, and each night Pharaoh will return to the east by the river which runs underneath the earth.”
—William Faulkner (1897–1962)
“I will write, as in the past, simply for the pleasure of writing, for myself alone, with no thought of money or fame. Apollo at least will be grateful to me, and perhaps at last I will produce something beautiful—for all things make way before the unceasing striving of an energetic sentiment.”
—Gustave Flaubert (1821–1880)
“In another’s sentences the thought, though it may be immortal, is as it were embalmed, and does not strike you, but here it is so freshly living, even the body of it not having passed through the ordeal of death, that it stirs in the very extremities, and the smallest particles and pronouns are all alive with it. It is not simply dictionary it, yours or mine, but IT.”
—Henry David Thoreau (1817–1862)