On the possibility of sprites on other planets

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On the possibility of sprites on other planets

• Yoav Yair and Roy Yaniv

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Lightning Activity in our solar system

• Earth, Jupiter, Saturn - definite
• Venus probable, debatable
• Uranus, Neptune probable, partly confirmed
• Mars, Titan - theoretically possible
• Moon, Mercury, Pluto - impossible

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If there are planetary lightning flashes, should
there also be planetary TLEs?
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Computing conventional breakdown thresholds for
various atmospheric compositions

• Ek is the critical electric field, where
  ionization
• exactly balances attachment.
• Ionization
• Attachment
• E/p is the electric field normalized to pressure,
  and Ek (the critical electric field) been
  expressed in normalized form of E/p. To find Ek
  at other pressures, we multiplied by the pressure
  (in torr units).

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Parameters (Sentman, 2004)
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Determination of Electrical Fields

• we assumed 3 different Electrical charges that a
  Lightning can produce.
• For Earth and Venus we assumed 100 Coulomb, 500
  Coulomb and 1000 Coulomb values produced by
  Lightning discharge.
• For the Gas Giants we assumed 100 Coulomb, 1000
  Coulomb and 10000 Coulomb values produced by
  Lightning discharge.

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Verification Earth Electrical Fields (10km cloud)
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Calculations for Venus

Clouds heights 48, 55, 70 km Ionospheric height
is 300 km
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Venus Electrical Fields (48km cloud)
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Venus Electrical Fields (55km cloud)
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Venus Electrical Fields (70km cloud)
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Titan Electrical Fields

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The Clouds of Jupiter

• Permanent global coverage organized in belts and
  zones
• Lower cloud - probably water - 5 bar pressure
  level, convective, mixed-phase
• Middle cloud - NH4SH at the 2 bar pressure level,
  stratiform
• Upper cloud - Ammonia Ice, Cirrus-like

• Ionospheric height is 1600 km above the 1-bar
  level
• Clouds H2O 2 bar (-20km), 3 bar (-33 km), 4
  bar (-44km).

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Jupiter Electrical Fields (-20km cloud)

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Jupiter Electrical Fields (-33km cloud)

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Jupiter Electrical Fields (-44km cloud)

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Saturns cloud layers (Atreya, 1986)

• Weaker convection, water clouds deeper and
  warmer probably no ice
• H2O 4 bar (-90km), 6 bar (-120 km), 8 bar
  (-150km).

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Saturn Electrical Fields (-90km cloud)

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Saturn Electrical Fields (-120km cloud)

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Saturn Electrical Fields (-150km cloud)

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Summary

• The huge surface atmospheric pressure on Venus
  (9 MPa) means that no cloud-to-ground discharge
  from the high-level sulfuric acid clouds (Zs 50
  to 70 km) are possible.
• Sprites can be produced by IC discharges (van der
  Velde et al., 2006), so even if all lightning
  activity in Venus is entirely intra-cloud
  discharges, sprites and Elves are still possible.
• Venusian IC discharges would be slow to build-up
  and would exhibit different characteristics
  compared to their terrestrial analogues (Gurnett
  et al., 2001).
• Potential emission bands from CO2 between 290 and
  500 nm, with prominent lines near 288, 410 and
  427 nm (Smyth, 1931). Also OI (777.7 nm).
• In Jupiter and Saturn, the amount of charge
  required to initiate sprites is of the order of
  104 C. Although these may seem highly unrealistic
  values, it has already been shown that lightning
  in these planets are far more energetic than on
  earth.