Europa Plume Project

Yi-Ching Chen, NTU

Adviser: Wei-Ling Tseng, NTNU

Project Outline

◆ We theorize the existence of Europa surface plumes, and study their mechanics

◆ We use DSMC simulation results as the H2O background of plumes

◆ We simulate the plume structure of both “parent” and “daughter” particles under a variety of background conditions

◆ The results we gather would hopefully help us process data from JUICE and Europa Clipper in about 4 years

Europa

◆ Moon of Jupiter (Jupiter II)

◆ Icy moon

◆ Possible surface plumes

▲ Artist illustration (NASA Conceptual Image Lab)

Enceladus

◆ Moon of Saturn (Saturn II)

◆ Icy moon

◆ Surface plumes found near south pole

▲ Cassini space probe

Plume Composition (Assumption)

We assume Europa plumes have the same composition and initial states as Enceladus plumes.

▲ Enceladus plume composition

(ref: Waite et al. 2017)

DSMC Model

3D Direct Simulation Monte Carlo

(ref: Wei-Ling Tseng et al. 2022)

Used as simulation background

Regriding Method

Irregular grids → Regular grids

◆ Take mean value of all data points in the same bin

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◆ Use linear interpolation on bins without raw data points

Regriding Method

Irregular grids → Regular grids

◆ Take mean value of all data points in the same bin

​

◆ Use linear interpolation on bins without raw data points

▲ H2O number density (first octant)

Runge-Kutta Method (RK4)

Simulation Outline

Generate Particles

Process Collision (Yes/No, New velocities)

Calculate Weighting (Chemical lifetime)

Plot Results (Column density)

Collision Probability

◆ Mean Free Path (λ):

Thermal velocity (H2O)

Relative velocity

(between minor species and H2O)

Collision cross-section (between minor species and H2O)

Number density (H2O)

H2O bulk velocity

H2O number density

H2O Translational Temperature

(ref: Ian-Lin Lai et al. 2016)

Collision Probability

◆ Collision Probability (Pcoll):

Where d is the distance traveled by the target particle in a timestep dt.

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(d = dt * particle velocity)

T = 0 → Grid is empty → Pcoll is 0

(ref: Ian-Lin Lai et al. 2016)

Post Collision Velocities

Isotropic in COM frame

COM Velocity

Particle velocity in COM frame

Scattering Angle

Reaction Lifetime

◆ Photodissociation (Use the 4 parent species reactions as example):

Quiet Sun: 1/𝞃 = 1.46*10^-7

Active Sun: 1/𝞃 = 3.34*10^-7

(ref: Huebner et al. 1992)

H2:

CH4:

NH3:

CO2:

Quiet Sun: 1/𝞃 = 7.01*10^-6

Active Sun: 1/𝞃 = 7.90*10^-6

Quiet Sun: 1/𝞃 = 8.02*10^-8

Active Sun: 1/𝞃 = 1.93*10^-7

Quiet Sun: 1/𝞃 = 3.03*10^-7

Active Sun: 1/𝞃 = 7.54*10^-7

Reaction Lifetime

◆ Plasma induced reactions:

(ref: Smith et al. 2019)

Induced by Jupiter’s neutral torus

(ref: Southwest Research Institute)

However, we currently do not have these reaction rates for certain parent species (CH4, NH3, CO2).

Reaction Lifetime

◆ Plasma induced reactions (Use H2 reactions as example):

(ref: Smith et al. 2019)

Rate Coefficient

Low Plasma: 1/𝞃 = 2.17*10^-6

Average Plasma: 1/𝞃 = 6.67*10^-6

High Plasma: 1/𝞃 = 7.69*10^-6

Particle Weighting System

For the n-th step:

Total Lifetime:

We collect all weightings produced in each bin to visualize distribution of the target species

For each step:

Parent Particles

◆ Initial Radial Velocity - Set to the same value of the plume background

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◆ Initial Thermal Velocity - Taken at random under Maxwell distribution (180 K)

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◆ Launch Points - Taken at random in a disk of 5 km radius

Simulations run under backgrounds:

1E28_350；1E28_500；1E28_750；1E28_1000

Parent H2 Simulations (vin = 350 m/s)

Log Scale

Linear

Parent H2 Simulations (vin = 500 m/s)

Linear

Log Scale

Parent H2 Simulations (vin = 750 m/s)

Linear

Log Scale

Parent H2 Simulations (vin = 1000 m/s)

Linear

Log Scale

Kinetic Model Simulation (all minor species)

H2

CO2

Kinetic Model Simulation (all minor species)

CH4

NH3

Daughter Particles

◆ H2O can go through reactions mid-flight to produce “daughter” particles

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◆ Daughter particles include: H2, H, OH, O

Daughter Particles

OH

H

O

H2

◆ We choose a set number of bins with non-zero H2O number density to generate daughter particles, initial weighting = production rate * H2O number density

◆ Upon generation, the daughter particle may receive a “velocity kick” from the reaction excess energy in addition to the bulk velocity inherited from the H2O parent

Daughter H2

Reaction rates:

Quiet Sun: 1/𝞃 = 2.32*10^-10

Active Sun: 1/𝞃 = 8.77*10^-10

Excess energy velocity “kick” = 0

Daughter H2 Simulations

1e28 350 m/s

1e28 500 m/s

Daughter H2 Simulations

1e28 750 m/s

1e28 1000 m/s

Daughter H

Reaction rates:

Quiet Sun: 1/𝞃 = 2.20*10^-9

Active Sun: 1/𝞃 = 6.00*10^-9

Excess energy velocity “kick” = 0

Daughter H Simulations

1e28 350 m/s

1e28 500 m/s

Daughter H Simulations

1e28 750 m/s

1e28 1000 m/s

Daughter OH

Reaction rates:

Quiet Sun: 1/𝞃 = 4.09*10^-7

Active Sun: 1/𝞃 = 6.98*10^-7

Excess energy velocity “kick” =

1468.50 m/s (quiet sun)

1596.07 m/s (active sun)

Daughter OH Simulations

1e28 350 m/s

1e28 500 m/s

Daughter OH Simulations

1e28 750 m/s

1e28 1000 m/s

Daughter O

Reaction rates:

Quiet Sun: 1/𝞃 = 3.00*10^-8

Active Sun: 1/𝞃 = 7.58*10^-8

Excess energy velocity “kick” =

684.82 m/s (quiet sun)

684.82 m/s (active sun)

Daughter O Simulations

1e28 350 m/s

1e28 500 m/s

Daughter O Simulations

1e28 750 m/s

1e28 1000 m/s

Conclusions

◆ Molecular mass has the most significant impact on the plume structures of parent particles

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◆ Velocity “kick” from the reaction excess energy has the most significant impact on the plume structures of daughter particles

Plans for the Future

◆ Acquire the parameters needed to conduct simulations for parent CH4, NH3, and CO2

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◆ Convert weighting from the simulations to actual number density

Thank You For Listening!