Solar energetic particles (SEP), formerly known as solar cosmic rays, are
high-energy,
charged particle
In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary pa ...
s originating in the
solar atmosphere and
solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
. They consist of
protons
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron m ...
,
electrons
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have n ...
and heavy ions with energies ranging from a few tens of
keV Kev can refer to:
Given name
* Kev Adams, French comedian, actor, screenwriter and film producer born Kevin Smadja in 1991
* Kevin Kev Carmody (born 1946), Indigenous Australian singer-songwriter
* Kev Coghlan (born 1988), Scottish Grand Prix moto ...
to many
GeV. The exact processes involved in transferring energy to SEPs is a subject of ongoing study.
SEPs are relevant to the field of
space weather
Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the ...
, as they are responsible for
SEP event
In solar physics, a solar particle event (SPE), also known as a solar energetic particle (SEP) event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in t ...
s and
ground level enhancements.
History
SEPs were first detected in February and March 1942 by
Scott Forbush indirectly as ground level enhancements.
Solar particle events
SEPs are accelerated during
solar particle events. These can originate either from a
solar flare
A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other sol ...
site or by
shock waves
In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...
associated with
coronal mass ejection
A coronal mass ejection (CME) is a significant release of plasma and accompanying magnetic field from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accept ...
s (CMEs). However, only about 1% of CMEs produce strong SEP events.
Two main mechanisms of acceleration are possible: diffusive shock acceleration (DSA, an example of second-order
Fermi acceleration) or the shock-drift mechanism. SEPs can be accelerated to energies of several tens of MeV within 5–10 solar radii (5% of the Sun–Earth distance) and can reach Earth in a few minutes in extreme cases. This makes prediction and warning of SEP events quite challenging.
In March 2021, NASA reported that scientists had located the source of several SEP events, potentially leading to improved predictions in the future.
Research
SEPs are of interest to scientists because they provide a good sample of
solar material. Despite the
nuclear fusion
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manife ...
occurring in the
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
, the majority of solar material is representative of the material that formed the solar system. By studying SEP's
isotopic composition, scientists can indirectly measure the material that formed the solar system.
See also
*
Solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...
References
*
* Reames D.V., Solar Energetic Particles, Springer, Berlin, (2017a) {{ISBN, 978-3-319-50870-2, doi: 10.1007/978-3-319-50871-9.
External links
Solar Energetic Particles (Rainer Schwenn) The Isotopic Composition of Solar Energetic Particles
Solar phenomena