An elementary particle that is a constituentof all atomic nuclei, that carries a positive charge numerically equal tothe charge of an electron, and that has a mass of 1.673 x 10^(-24) gram.
The measurement of proton flux reaching and sustaining ~ 10 p.f.u. (1 p.f.u. = 1 particle cm-2 s-l sr-1) for at least 15 min. at energies > 10 MeV by the primary NOAA geosynchronous satellite. The sta
rt time of the event is defined as the earliest time at which event thresholds have been reached. The end time is the last time 10 p.f.u. was observed. This definition allows multiple injections from flares and interplanetary shocks to be encompassed by a single event.
A Solar proton event occurs when protons emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated wi
th coronal mass ejections.
A Solar proton event occurs when protons emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated wi
th coronal mass ejections.
A circumstellar disk of gas and dust surrounding a pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of accretion disks which bring forth stars. Typically, th
eir sizes are ~100-500 AU, masses ~10^-2 solar masses, lifetimes ~10^6 - 10^7 years, and accretion rates ~10^-7 - 10^-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of dust grains which stick together and produce ever larger bodies, known as planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a debris disk around the central object that has become a main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by gravitational instabilities. The validity of these two theories is presently debated.
A circumstellar disk of gas and dust surrounding a pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of accretion disks which bring forth stars. Typically, th
eir sizes are ~100-500 AU, masses ~10^-2 solar masses, lifetimes ~10^6 - 10^7 years, and accretion rates ~10^-7 - 10^-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of dust grains which stick together and produce ever larger bodies, known as planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a debris disk around the central object that has become a main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by gravitational instabilities. The validity of these two theories is presently debated.
A circumstellar disk of gas and dust surrounding a pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of accretion disks which bring forth stars. Typically, th
eir sizes are ~100-500 AU, masses ~10^-2 solar masses, lifetimes ~10^6 - 10^7 years, and accretion rates ~10^-7 - 10^-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of dust grains which stick together and produce ever larger bodies, known as planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a debris disk around the central object that has become a main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by gravitational instabilities. The validity of these two theories is presently debated.
A circumstellar disk of gas and dust surrounding a pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of accretion disks which bring forth stars. Typically, th
eir sizes are ~100-500 AU, masses ~10^-2 solar masses, lifetimes ~10^6 - 10^7 years, and accretion rates ~10^-7 - 10^-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of dust grains which stick together and produce ever larger bodies, known as planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a debris disk around the central object that has become a main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by gravitational instabilities. The validity of these two theories is presently debated.
A circumstellar disk of gas and dust surrounding a pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of accretion disks which bring forth stars. Typically, th
eir sizes are ~100-500 AU, masses ~10^-2 solar masses, lifetimes ~10^6 - 10^7 years, and accretion rates ~10^-7 - 10^-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of dust grains which stick together and produce ever larger bodies, known as planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a debris disk around the central object that has become a main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by gravitational instabilities. The validity of these two theories is presently debated.
A stage in the process of star formation, after the gravitational collapse of the dense pre-stellar core and before the initiation of nuclear fusion in the central object which will eventually become
a star. Protostars are classified into four groups: Class 0, Class I, Class II, and Class III.
A stage in the process of star formation, after the gravitational collapse of the dense pre-stellar core and before the initiation of nuclear fusion in the central object which will eventually become
a star. Protostars are classified into four groups: Class 0, Class I, Class II, and Class III.
A typical thing generalized from a particular set of entities, characterized by a subset of the attributes of the real world entity(ies), and/or idealizations of those attributes. Attribute values are
assigned, not measured, and are normally specified as a possible range of values [Angus and Dziulka, 1998].