The MAVEN/EUVM solar soft x-ray (SXR) and Lyman-α measurements are
compared with analogous measurements made from Earth to characterize the
typical error introduced when phase-shifting solar EUV irradiance
measurements made from Earth to other points in the solar system
according to the 27.27 day synodic solar rotation period. The
phase-shifting error, ε, measured at SXR and Lyman-α are extrapolated to
the full EUV spectrum by assuming it is proportional to the variability
that occurs over the 27-day timescale of solar rotation. Values for ε as
a function of wavelength are reported and used to find the typical error
for estimates of photoionization frequencies of some major species found
in planetary upper atmospheres derived by phase-shifted EUV irradiance.
This study finds that the typical extrapolation error for the CO
photoionization frequency is 5.7% of the solar cycle mean value, and
87% of the typical 27-day variability.