Interaction of solar flare X-rays with the atmosphere of Titan

During solar flares an intense flux of X-rays is emitted into space. When it reaches Saturn's orbit, it is still strong enough to significantly disturb Titan's dense atmosphere. The main effect is to ionize the neutral component of the atmosphere and to increase, therefore, the electron and ion density at altitudes of 400-900 km. Especially near a maximum of the solar cycle, when flare activity is high, the average plasma density can, for long intervals, remain at a level of a few tens of particles per cm(3). As a result, the atmospheric photochemistry will be affected, but also an increase of production rate of small haze particles might be expected. Ionized atoms are usually excited; when they relax to the ground level in the process of resonant fluorescence, Titan's albedo at specific wavelengths increases. It is estimated that at Earth orbit the flux of photons emitted from Titan in the 3 KeV argon line during a strong X1-type Rare is equal to 1.6 x 10(-20) J m(-2) s(-1) for 10% Ar abundance in Titan's atmosphere. (C) 1999 Elsevier Science Ltd. All rights reserved.