NASA’s ERAST program is developing unmanned aerial vehicles (UAV) to fly high altitude, long endurance missions. This paper studies the performances of these aircraft in low Martian atmosphere, an environment very similar to Earth stratosphere. Since no oxygen is available in Martian atmosphere, a solar powered aircraft (i.e. an UAV with solar panels which power electric motors and charge the batteries needed to fly at night) is analyzed. Results show that with current technology, it is possible to develop an UAV capable of continuous flight in low Martian atmosphere. Pathfinder and Centurion aircraft, developed by AeroVironment Inc., could meet that goal without major modifications. Centurion is found to be the best suited to latitude range. Pathfinder, being smaller, could carry less payload and for shorter periods. Flight latitude and season play significant roles in determining payload mass. Such an aircraft could help the first astronauts on Mars to deploy planet-wide weather station and microrover networks, while providing a very detailed picture of soil chemistry and terrain morphology.