1. Motion of Charged Particles through Titan’s Atmosphere
Austin Windsor, Matthew Richard
Presented By: Austin Windsor
nasa.gov

2. Motion of Charged Particles through Titan’s Atmosphere
Previous Titan Research
• Discovery Day 2014
• Ion Production Rates in
Titan’s Ionosphere
• Electron Precipitation
• Became co-author of
peer-evaluated
publication

3. Motion of Charged Particles through Titan’s Atmosphere
Goal for Discovery Day 2015
• Build a Monte Carlo computer code
• Produce simulated results of charged particles
entering Titan’s atmosphere
• Show the relationship of ion production with respect
to the altitude
nasa.gov

4. Motion of Charged Particles through Titan’s Atmosphere
What is Titan and Why?
• Saturn’s Largest Moon
• Titan’s atmosphere
resembles an early Earth
atmosphere in a deep
freeze (-190 C).
• Titan is the only other
planetesimal in the solar
system with sustainable
liquid on the surface
(methane)nasa.gov
Howell [2014]

5. Motion of Charged Particles through Titan’s Atmosphere
Cassini Solstice Mission
• Launched in 1997 to reach
orbit in 2004
• The Magnetospheric Imaging
Instrument (MIMI)
• The Cassini Plasma
Spectrometer (CAPS)
• Huygens, first atmospheric
entry probe to reach the
surface
European Space Agency [2003]

6. Motion of Charged Particles through Titan’s Atmosphere
Titan’s Haze
• Thick, dense layer of
Hydrocarbons
• Goal: Understand how the
haze is produced
• Starts around 500 km in
altitude
• Instruments could not see
through haze to view the
surface of Titan
nasa.gov

7. Motion of Charged Particles through Titan’s Atmosphere
Particle Interaction in Titan’s Atmosphere
• Photoionization, Electron Impact Ionization, and Ion Precipitation
• O+ , H2
+ , H+
Waite et al. [2004]

8. Motion of Charged Particles through Titan’s Atmosphere
Theoretical Background
• Motion in Magnetic Field, B
• Motion in Electric Field, E
• Approximation of particle’s next
position
• Probability of Collision with
Atmosphere

9. Motion of Charged Particles through Titan’s Atmosphere
Motion in Magnetic Field, B
• The path of the charged particle is circular.
• The force is always perpendicular to the path of motion.
BYU Physics

10. Motion of Charged Particles through Titan’s Atmosphere
Motion in Magnetic Field, B

11. Motion of Charged Particles through Titan’s Atmosphere
Motion in Magnetic Field, B

12. Motion of Charged Particles through Titan’s Atmosphere
Motion in Electric Field, E
• Generalized Ohm’s Law
• Strength of E is dependent of Plasma Flow Rates and B
• Motion of charged particles create an Electric Field
NPTEL

13. Motion of Charged Particles through Titan’s Atmosphere
Combining E and B Equations
Split Vectors into Components

14. Motion of Charged Particles through Titan’s Atmosphere
Split Vectors into Components

15. Motion of Charged Particles through Titan’s Atmosphere
Approximating Particle’s Next Position
• Initial Conditions: Position and Velocity
• Calculate Acceleration from Initial Conditions
• Use Newton’s motion equations for new position, velocity, and accelera
Small Time Step, dt, later
zi vz,i az,i
xi vx,i ax,i yi vy,i ay,i
yf vy,f ay,fxf vx,f ax,f
zf vz,f az,f

16. Motion of Charged Particles through Titan’s Atmosphere
Adding an Atmosphere
• Primarily made up of N2 (about 95%) and CH4 (about 5%)
• Probability of charged particles colliding with neutral species in the
atmosphere potentially causing ionization to occur
• Obtain data from Cassini Spacecraft to integrate a realistic
atmosphere

17. Motion of Charged Particles through Titan’s Atmosphere
Adding an Atmosphere
• σ = 2.27 x 10-5 cm-3
• no = 1.096 x 1010 prts/cm3
• z = altitude
• H = scale height
• kB = 1.3806 x 10-23 J/K
• T = 150 K
• m = 4.65 x 10-26 kg
• g = force of gravity
• G = 6.673 x 10-11 m3kg-1s-2
• mT = 1.345 x 1023 kg
• r = distance from center of Titan
space.com

18. Motion of Charged Particles through Titan’s Atmosphere
Building the Code
• Monte Carlo Simulation: problem solving technique used to
approximate the probability of certain outcomes by running
multiple trial runs using random numbers
• Random Number Generator Produced

19. Motion of Charged Particles through Titan’s Atmosphere
Building the Code
1. Track Particle’s motion with induced Magnetic Field
2. Add Electric Field Vector
3. Define Electric Field in terms of Plasma Flow Rates
4. Track multiple particles with random initial conditions generated
5. Shoot particles at Titan, do they hit the surface?
6. Add atmosphere with collision probability
7. Produce random number to compare with probability
8. Count the number of collision for given altitude bin

20. Motion of Charged Particles through Titan’s Atmosphere
Final Results

21. Motion of Charged Particles through Titan’s Atmosphere
Final Results
• Total of 100,000 Protons, 30% Collided with Atmosphere

22. Motion of Charged Particles through Titan’s Atmosphere
Future Plans
• Continue to build and develop code
• Integrate more better cross sections
• Incorporate plasma flow rates received from Cassini
• Add more neutral species to the atmosphere
• Run larger quantity of particles for better results