The Solar Extreme Ultraviolet Monitor for MAVEN

Abstract

The Extreme Ultraviolet (EUV) monitor is an instrument on the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, designed to measure the variability of the solar soft x-rays and EUV irradiance at Mars. The solar output in this wavelength range is a primary energy input to the Mars atmosphere and a driver for the processes leading to atmospheric escape. The MAVEN EUV monitor consists of three broadband radiometers. The radiometers consist of silicon photodiodes with different bandpass-limiting filters for each channel. The filters for the radiometers are: Channel A: thin foil C/Al/Nb/C for 0.1–3 nm and 17–22 nm, Channel B: thin foil C/Al/Ti/C for 0.1–7 nm, and Channel C: interference filter for 121–122 nm. A fourth, covered photodiode is used to monitor variations in dark signal due to temperature and radiation background changes. The three science channels will monitor emissions from the highly variable corona and transition region of the solar atmosphere. The EUV monitor is mounted on the top deck of the MAVEN spacecraft and is pointed at the Sun for most of its orbit around Mars. The measurement cadence is 1-second. The broadband irradiances can be used to monitor the most rapid changes in solar irradiance due to flares. In combination with time-interpolated observations at Earth of slower varying solar spectral emissions, the broadband MAVEN EUV monitor measurements will also be used in a spectral irradiance model to generate the full EUV spectrum at Mars from 0 to 190 nm in 1-nm bins on a time cadence of 1-minute and daily averages.