  In January 2003, the Chandra Orion Ultradeep Project (COUP) detected about
1400 young stars during a 13.2 day observation of the Orion Nebula Cluster
(ONC). This paper studies a well-defined sample of 28 solar-mass COUP sources
to characterize the magnetic activity of analogs of the young Sun and thereby
to improve understanding of the effects of solar X-rays on the solar nebula
during the era of planet formation.
  We find that active young Suns spend 70% of their time in a characteristic
state with relatively constant flux and magnetically confined plasma with
temperatures kT_2 = 2.1 * kT_1. During characteristic periods, the 0.5-8 keV
X-ray luminosity is about 0.03% of the bolometric luminosity. One or two
powerful flares per week with peak luminosities logL_x ~ 30-32 erg/s are
typically superposed on this characteristic emission accompanied by heating of
the hot plasma component from ~2.4 keV to ~7 keV at the flare peak. The energy
distribution of flares superposed on the characteristic emission level follows
the relationship dN/dE ~ E^-1.7. The flare rates are consistent with the
production of sufficiently energetic protons to spawn a spallogenic origin of
some important short-lived radionuclides found in ancient meteorites. The
X-rays can ionize gas in the circumstellar disk at a rate of 6 10^-9
ionizations per second at 1 AU from the central star, orders of magnitude above
cosmic ray ionization rates. The estimated energetic particle fluences are
sufficient to a account for many isotopic anomalies observed in meteoritic
inclusions.
