EXO-LIGHTNING Part I: what can we learn from the Solar System?

Is lightning a phenomenon only occurring on Earth? Or is it universal? How can the knowledge we learnt from Solar System lightning help with discovering lightning on exoplanets and to understand these very different worlds? The next two entries will be devoted to the work on extraterrestrial lightning carried out by Gabriella Hodosán, LEAP PhD student, under the supervision of LEAP PI Dr Christiane Helling, in collaboration with various LEAP group members. In Part I we apply results of lightning surveys of several Solar System planets, including Earth, to different groups of extrasolar planets. Part II will be about a specific planet, HAT-P-11b and the possibility of lightning detection in its atmosphere.

Lightning is one of the most spectacular phenomena on Earth. It has interested not just scientists but the general public for thousands of years. However, it is not a unique phenomenon to Earth. It has been observed before on several Solar System planets, such as Jupiter, Saturn, or Uranus and Neptune. Spacecraft like Cassini, Galileo, New Horizons or the Voyagers provided us with breath-taking images of the outer Solar System, including images and measurements of lightning occurring on the gas giant planets (Fig. 1).

Lightning on Jupier (right top and bottom) and Saturn (left bottom). (Credit: NASA/JPL-Caltech/SSI, NASA/Galileo)

Figure 1. Lightning on Jupiter (right top and bottom) and Saturn (left bottom). (Credit: NASA/JPL-Caltech/SSI, NASA/Galileo)

Since the late 90s, thousands of exoplanets have been discovered. These exoplanets show a large diversity (Fig. 2) in sizes, masses, even distances to the host star, much different to our Solar System planets: Jupiter-size planets orbiting other stars at the distance of Mercury; planetary systems with several planets inside the orbit of Mercury; terrestrial planets several times bigger than Earth, but still rocky and not made of gas. Could these planets host lightning in their atmospheres? Let’s look at Earth and Saturn. They have different composition, different sizes, masses, different atmospheres. And still, they both show lightning activity. So why couldn’t it occur on exoplanets?

Diversity of exoplanets and brown dwarfs on a mass-radius and distance-density plot (Hodosán et al. 2016).

Figure 2. Diversity of exoplanets and brown dwarfs on a mass-radius and distance-density plot. The lines on the top plot indicate the potential chemical composition of the bodies based on their obtained mass and radius  (Hodosán et al. 2016).

In our work, we were focusing on the statistical side of lightning occurrence on Solar System planets, then extrapolated to extrasolar objects. Lightning climatology explores the spacial and temporal distribution of lightning. It uses the quantity of flash rate [flashes/unit time, e.g. flashes/hour] or flash density [flashes/unit time/unit surface area, e.g. flashes/hour/km2] to quantify this distribution. It is a tool to estimate the lightning activity on the surface of an object. This is important in order to estimate the total energy released of lightning flashes, and to determine whether the signatures produced by lightning would be observable from Earth.

Earth

Lightning observing networks net the whole surface of the Earth and satellites continuously look for lightning flashes from near Earth orbits. Lightning monitoring is important because of the hazards (e.g. forest fires, large scale power outage, fatalities) it causes. Measurements from Earth provide the largest data sets we can work with. In our study we analyzed data from the Lightning Imaging Sensor (LIS)/Optical Transient Detector (OTD), which are optical instruments on board of satellites, and from two ground based radio networks, the Sferics Timing and Ranging Network (STARNET) and World Wide Lightning Location Network (WWLLN). Figure 3 shows an example of lightning climatology maps produced from LIS/OTD data. It shows an average of lightning occurrence over the period of 1995-2013. It shows clear trends of more lightning over continents than over oceans, and more lightning over lower latitude regions than higher latitude regions.

Figure 3. LIS/OTD lightning climatology map averaged from 1995-2013 (Hodosán et al. 2016).

Figure 3. LIS/OTD lightning climatology map averaged from 1995-2013 (Hodosán et al. 2016).

Lightning occurs not only in thunderclouds but in volcano plumes as well (e.g. see work by our group, and the eruption of Eyjafjallajökull). Based on literature research we collected flash densities from two volcano eruptions: Mt Redoubt in 2009 and Eyjafjallajökull in 2010. Some interesting fact: both eruptions show orders of magnitude larger flash densities than what thunderclouds produce. On average the LIS/OTD data showed a 2×10-4 flashes/km2/h flash density while Eyjafjallajökull showed 0.1 – 0.32 flashes/km2/h and Mt Redoubt produced up to 2000 flashes in an hour over a square kilometer.

Venus, Jupiter and Saturn

Is there lightning on Venus? The long debated question has not yet been fully answered, however, more and more clue indicate the existence of such phenomenon on Earth’s sister planet. If lightning does exist on Venus, it is probably not very energetic and it appears deep within the atmosphere, since no optical observation of it has been made to date. Radio data from the Venus Express mission, however, shows a possible ~10-11 flashes/km2/hour flash density.

Figure 4. Lightning distribution on Jupiter. Triangles: Galileo data from 1997. Circles: New Horizons data from 2007.

Figure 4. Lightning distribution on Jupiter. Triangles: Galileo data from 1997. Circles: New Horizons data from 2007.

Jupiter and Saturn are more interesting, since, apart from Earth, these are the only planets in the Solar System where lightning has been observed directly. We used published data from the Galileo (1997, Jupiter), New Horizons (2007, Jupiter) and Cassini (2009, 2011, Saturn, e.g.) spacecraft. Figure 4 shows and example lightning distribution map for Jupiter. It shows and increased lightning activity around the +- 50-degree latitude regions, most probably due to the increased affect of internal heating on convection and cloud formation. Until 2009, only radio signals of lightning were observed on Saturn. The so-called SEDs (Saturnian Electrostatic Discharges) are short and strong radio bursts from lightning, detected by e.g. the Voyagers and Cassini spacecraft. The two giant gas planet, on average, shows a flash density of 10-6 – 10-7 flashes/km2/hour.

Exoplanets

Now the most exciting part: How does this all relate to exoplanetary research? The idea behind our paper is to use the statistics from Solar System planets to estimate a possible lightning occurrence on exoplanets with similar environments to those described in the previous sections. E.g. let’s take possible ocean planet: Kepler-62f. Then apply the flash density derived for Earth for above oceans: ~5 x 10-5/km2/hour. Combining this, we estimate the flash density on Kepler-62f, throughout its whole surface, to be the same: ~5 x 10-5/km2/hour. Another example is to apply the flash densities in order to estimate the total lightning occurrence during the transit of a planet. 55 Cancri e is a close-in rocky planet, most probably cover by lava. How much lightning could occur during its transit on the projected disk of the planet, if we assume continuous flashing from volcano activity? Depending on which eruptions we consider as the template, 55 Cnc e could produce as many as 108-1012 flashes on its whole disk during its 1.5-hour transit. This enormous amount of lightning would produce radio emission that might be observable during the transit.

In Part II we introduce our original idea of estimating whether a weak and tentative radio signal observed on the mini-Neptune, HAT-P-11b, could have been caused by lightning or not.

If you have an opinion, please leave a comment below.

For more details check out the original paper on ADS:

 Hodosán, G.; Helling, Ch; Asensio-Torres, R.; Vorgul, I.; Rimmer, P. B., MNRAS, 461, 3927, 2016

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Interdisciplinary thinking: Atmospheric electrification in the Solar System and beyond

According to Wikipedia, interdisciplinarity involves the contribution of two or more academic disciplines to allow progress through recognition of different ways of thinking. Driven by curiosity, a group of researchers from the disciplines of plasma physics, meteorology, volcanology and astrophysics (observations and modelling of brown dwarfs, exoplanets, protoplanetary disks) met in the Scottish Highlands in Pitlochry in 2014 to discuss their research on ‘Electrification in dusty atmospheres inside and outside the solar system’. This workshop was the inspiration for a review articles ‘Atmospheric electrification in dusty, reactive gases in the solar system and beyond’ accepted for publication in ‘Surveys of Geophysics’, which aims to stimulate a closer interaction between the communities involved. A short summery of aim and content is given here.

The last few decades have taken us from a Universe with only a single planetary system known, to one with thousands, and maybe millions, of such systems. We are now entering the time when we explore theories and results derived for the Solar System and for Earth in application to unknown worlds. As such, it is more and more important for the different science communities, in this case earth sciences and astronomy and astrophysics, to share the knowledge they have gathered, in order to combine their approaches to explore new worlds.

“Planets are the coldest and smallest objects in the universe known to possess a cloud-forming and potential life protecting atmosphere”. In Figure 1 we see Jupiter in the astrophysical context. It is compared to the coolest stellar objects, M-dwarfs and brown dwarfs, while these are compared to the Sun representing a regular star. Brown dwarfs bridge the stellar and the planetary regime as their atmospheres can be as cold as those of planets but they form like stars. The Sun, including its corona, the hot plasma surrounding it, is well studied by satellites like SOHO and HINODE. However, such high-resolution monitoring is not yet possible for Solar System planets, moons, comets and for extrasolar objects. In case we want to learn about their cold cloud-forming atmospheres, which may host electrical phenomena, we need to combine experimental work on Earth, Earth observations, modelling and comparative studies for the Solar System and extrasolar objects.

Figure1. M-dwarfs, brown dwarfs and giant gas planets in comparison. Teide 1 is an example for a late M-dwarf, GD 165B for a cloud-forming brown dwarf of spectral type L, Gliese 229B is a cooler cloud-forming brown dwarf of spectral class T, and Jupiter is the example for a giant gas plane.

Figure 1. M-dwarfs, brown dwarfs and giant gas planets in comparison. Teide 1 is an example for a late M-dwarf, GD 165B for a cloud-forming brown dwarf of spectral type L, Gliese 229B is a cooler cloud-forming brown dwarf of spectral class T, and Jupiter is the example for a giant gas plane (Helling et al. 2016).

Plasma and discharge experiments are essential in providing a controlled environment in contrast to observation of atmospheric phenomena. An atmospheric environment that is only partially ionized may show plasma character on only local scales compared to the global scale of a comet, moon, planet, brown dwarf or protoplanetary disk. Volcanic eruptions on Earth have been shown to produce significant electrostatic charging and subsequent lightning. It is also possible that similar charging mechanisms occur on Jupiter’s moon Io, for example. Understanding dust-charging processes is important for space exploration because the local ionization changes on the surface of a moon or an asteroid as a result of the variability of the solar wind hitting these objects. When a spacecraft, like the Rosetta lander Philae, lands on the surface of such objects, it creates a very similar effect. The ionization of the local environment influences the spacecraft’s operation on the object and the landing itself.

In situ measurements of the chemically active Earth-atmosphere offer insight in charge and discharge processes, their local properties, and their global changes. These measurements in the natural atmospheric environment lead to an understanding of the role of electrons, ions and dust involved in the ionization of the atmosphere. Such observations allow an understanding of atmospheric processes on Earth that can only be gained for Solar System and extrasolar bodies from intensive modelling efforts in combination with observations and experiments.

Ionization processes also have implications for industry. One example of plasma technology development is included in our review to demonstrate the impact of the theme of this paper beyond academic research. The paper gives an overview of electrification processes inside and outside the Solar System. It moves from small-scale to large-scale charge processes in different types of environments, such as the terrestrial atmosphere, the Moon and asteroids, and also extrasolar planetary and brown dwarf atmospheres and protoplanetary disks.

Interdisciplinary thinking: Meteorological balloon experiment launch (Credit: Giles Harrison); laboratory volcanic lightning experiment (Cimarelli et al. 2014); temperature variations between the day and night side of the exoplanet HD 189733b (Credit: Graham Lee)

Interdisciplinary thinking:
Meteorological balloon experiment launch (Credit: Giles Harrison); laboratory volcanic lightning experiment (Cimarelli et al. 2014); temperature variations between the day and night side of the exoplanet HD 189733b (Credit: Graham Lee)

The paper first sets the stage for the interdisciplinary exchange: it introduces the fundamental physics of charging processes, defines general terms, and shows the field of experimental dust-charging works to the reader. The next chapter explains the electrification and discharging of planetary atmospheres. Explains the role of the Wilson Global Circuit (continuous movement of electric current between the ionosphere and the surface of a planetary object), the production of thundercloud lightning and its subsequent phenomena, the transient luminous events and how the electrification of volcano plumes lead to volcanic lightning. We get an insight on the chemical changes in Solar System planetary atmospheres caused by lightning discharges. Those who are interested in the Moon or asteroids in the Solar System can learn about charging processes in the environments on these objects from the next big section. The paper finishes with the very new topic of charging in extrasolar environments, such as exoplanetary and brown dwarf atmospheres and protoplanetary disks. Each of these topics could be the core of individual blog entries. This blog can, therefore, only provide a very minimalistic introduction to the whole paper with which we hope to inspire further interdisciplinary communications.

This paper was born as collaboration between scientists from various fields of earth sciences and astrophysics. It intends to show the importance of such multi-disciplinary works. To help the readers of different background, it includes a glossary at the end.

 

For more details check out the original paper on ADS:

 Ch. Helling, R. G. Harrison, F. Honary, D. A. Diver, K. Aplin, I. Dobbs-Dixon, U. Ebert, S. Inutsuka, F. J. Gordillo-Vazquez, S. Littlefair, 2016, Surveys in Geophysics, 37, 705

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Electrification in dusty atmospheres inside and outside the solar system, Pitlochry, 8-11 Sep. 2014

The workshop ‘Electrification of dusty atmospheres inside and outside the solar system’ hosted by the LEAP Group took place in Pitlochry, Scotland. The cross-disciplinary nature of the workshop attracted scientists from fields of plasma physics, volcanology, meteorology, and astrophysics from all over the world.

The meeting started with a welcome barbeque on Sunday evening: people were talking in small groups, catching up with old friends and meeting new colleagues.

The welcome barbeque in the garden of the hotel

_DSC1519 The welcome barbeque in the garden of the hotel (Credit: Rubén Asensio Torres)

On Monday morning Christiane Helling summarized the scientific idea that lead to the organization of this workshop: she talked about the benefits of the meeting for both astrophysicists and scientists from other fields. She also introduced a new proceeding idea, which is planned to be published in Surveys of Geophysics.

The first talk was given by Alan Phelps who discussed laboratory studies of crystalline-like ordered structure in dense dusty plasmas, with the potential to investigate similar behaviour in substellar atmospheres. In this context, the exciting possibility exists of identifying a unique observable signature associated with plasma crystals that could be used to diagnose the charged environment.

The difficulties of the inter-disciplinary nature of the workshop appeared right after the first talk when it turned out that the definition of ‘dust’ is not the same in every field. However, after discussing the issue, the speakers and participants quickly got used to the fact that most of the people are from a different field than they are and explained their fields in a way, which was understandable for everyone.

Keri Nicoll and Corrado Cimarelli gave exciting talks on volcanic lightning. Nicoll gave an overview on the different charging mechanisms in volcanic plumes and reported that broad particle size distributions of volcanic ash clouds are more susceptible to triboelectric charging, which give an analogy to substellar clouds with atmospheric regions with the appropriate particle size distribution. Cimarelli described a laboratory experiment where they reproduced volcanic lightning strikes, and explained how the particle size and distribution affects the charge separations on plumes.

Euan Bennet’s talk on isolating different sized bacteria using electrostatic disruption of water droplets was an interesting part of the conference. It showed some of the unexpected applications that can arise from the study of aerosol electrification.

During the afternoon session Ute Ebert introduced us into the mechanism of lightning development and gave an overview of streamer propagation. The following talks were about Transient Luminous Events (TLEs) such as sprite modelling and the possibility of TLE initiation on gas giant planets like Jupiter.

The afternoon ended with the poster pop-up, where each poster presenter was given one minute to advertise his or her work, which was followed by the poster session itself. Delicious pretzels and Guinness accompanied the session.

_DSC1609

_DSC1623 Poster session (Credit: Rubén Asensio Torres)

On Tuesday we started with a very interesting talk by Farideh Honary on Lunar dust charging and how this can affect future (and past) landing missions. Karen Aplin introduced us a similar approach but with asteroids. She raised the question of what would happen if a, possibly, oppositely charged landing spacecraft (negatively charged) and the surface of an asteroid (positively charged) interact with each other and showed a model of how the electrostatic effects can be best measured in situ.

The afternoon session started with Ian Dobbs-Dixon’s presentation on dynamical modelling of the atmospheres of tidally locked hot Jupiters. Michael Rycroft introduced the audience to the conditions a planet would need in order to host a global electric circuit.

In the evening we had the workshop dinner in the hotel. In a short dinner speech, Christiane Helling also thanked all the participants for their exciting contributions to the workshop. Towards the end of the dinner Craig Stark announced the winners of the poster contest, Graham Lee and Karen Aplin. Congratulations!

Wednesday was the day of brown dwarfs (BDs) and ionization processes. Sara Caswell talked about two White Dwarf–Brown Dwarf systems and showed how different the spectra of the day and night side of an irradiated BD can be. Irena Vorgul gave a talk on how flash ionization processes (such as lightning) could be detected through cyclotron maser emission going through the affected atmospheric volume. Craig Stark summarized the concept of the LEAP Project, then talked about the basics of Alfvén ionization, a process where a low density magnetized plasma is hit by a high speed flow of neutral gas. He then talked about the possibility of creating prebiotic molecules (like glycen) on the surface of dust particles in plasmas. An impressive talk was given by Takayuki Muranushi, how proposed to use ion lines width for detection lightning occurring within protoplanetary disks.

On the last day of the workshop we learnt a lot about cosmic ray (CR) air showers and their ionizing effects. However, due to a change in the schedule, the first talk was about multi-wavelength observations of BDs given by Stuart Littlefair. He showed that consistent cyclotron emission detection shows very good correlation with optical observations, suggesting an aurora-like mechanism for the radio emission. There is though some variation in radiated power for different periods of rotation, which might also be attributed to undergoing transient processes in the atmosphere (like lightning).

Alan Watson talked about the work at the Pierre Auger Observatory, an ultra-high-energy CR detector in Argentina. He showed us an unusual phenomenon observed by multiple detectors and asked the opinion of the audience on the topic. Large variety of ideas came including possible lightning events, and military missile activity as well. Although the question has not been answered unequivocally, the response from the audience showed how beneficial such a multi-disciplinary meeting can be for the different scientific fields. Paul Rimmer went into the details of CR ionization in BD atmospheres and proposed the possibility of using Jupiter as a giant gamma-ray detector through the extensive CR air showers occurring in its atmosphere.

The last talk of the day and the workshop was given by Scott Gregory who showed us how stellar magnetic fields can affect the habitability of a planet orbiting that star. He also pointed out that the magnetic field structures differ for different stars.

The afternoon was rounded off with a whiskey tour and tasting in the Blair Atholl Destillery where we learnt a lot on how whiskey is made, what are the main ingredients, how is the alcohol content regulated and how much time the infusion spends in the barrels.

A few of the participants had the opportunity to tour the Blair Castle and its extensive grounds on Friday. The fresh apples and pears from the trees in the Hercules garden were especially enjoyable.

On the whole the workshop was a great experience for all of us, the talks were very diverse still related to our work in the LEAP Group. All speakers made great efforts to allow the audience to appreciate their contribution to the workshop’s theme. We had a great opportunity to meet scientists from other fields and discuss our projects, concerns, works with them.

We would like to thank all of the participants for their contribution to the success of the workshop. The high quality of the talks and posters gave an insight for the audience into the different disciplines.

 

Participants of the workshop (Credit: Rubén Asensio Torres)

Participants of the workshop (Credit: Rubén Asensio Torres)

Lightning on exoplanets and brown dwarfs: How extended and energetic could these events be?

Lightning events are very spectacular phenomena on Earth. They are one of those beautiful plays of nature, which interest both scientists and non-scientists equally. But can lightning occur on objects outside our Solar System? The St Andrews student Rachel Bailey studies the scales that large-scale gas discharges can develop, what atmospheric volume might be affected, and what amount of energy may be deposited into the atmospheres of brown dwarfs and planets under the supervision of Dr Christiane Helling. This study was performed in collaboration with Gabriella Hodosán, Camile Bilger and Craig Stark.

Lightning strike above the Arabian Peninsula captured from aboard the ISS. (Credit: NASA)

Fig. 1. Lightning strike above the Arabian Peninsula captured from aboard the ISS. (Credit: NASA)

Atmospheric electrical discharges (like lightning) are observed not only on Earth. Lightning on Jupiter was observed both in optical and radio wavelengths of the electromagnetic spectrum. In the late ‘70s early ‘80s the Voyager 1 spacecraft recorded impulsive events in the radio band which were called SEDs or Saturnian Electrostatic Discharges. These events were identified as lightning discharges, although the optical confirmation did not come until 2009. Electromagnetic signatures associated with lightning activity were also detected on Uranus and Neptune by Voyager 2.

Lightning activity on Saturn captured by NASA’s Cassini Spacecraft. For the animated version check out Space.com  (Credit: NASA/ JPL-Caltech/ SSI/ University of Iowa)

Fig. 2. Lightning activity on Saturn captured by NASA’s Cassini Spacecraft. For the animated version check out Space.com (Credit: NASA/ JPL-Caltech/ SSI/ University of Iowa)

Not all processes involved in lightning are known in detail. The simplest idea is the following: first, a strong electric field needs to be present for long enough. This electric field, or potential difference, builds up by various ionisation processes. Processes like particle encounters with cosmic rays would make the electrons break away from their ‘parent’ atom or molecule, which leads to the formation of negative and positive ions and the atmospheric gas becomes conductive. Second, a large-scale separation of these charges over large enough distances is needed. One process causing large-scale charge separation is gravitational settling (also known as‘rain’). If the distance between the charged cloud layers is large enough, the electric field can grow so strong that it exceeds a threshold, which results in the acceleration of electrons to very high energies. These energetic electrons will ionise their surroundings by freeing more electrons resulting in an avalanche of high-energy electrons and, as a final step, a lightning discharge. This process is called runaway breakdown.

Charge separation and different types of lightning discharges (inter- and intra-cloud, and cloud-to-ground discharges) (thunder.msfc.nasa.gov/primer)

Fig. 3. Charge separation and different types of lightning discharges (inter- and intra-cloud, and cloud-to-ground discharges) (thunder.msfc.nasa.gov/primer)

Other interesting phenomena related to lightning activity are Sprites. Sprites appear above thunderclouds as extended red discharges, right after a lightning strike. These luminous events on Earth can be observed from space.

It is very likely that lightning also occurs outside the Solar System. Both exoplanets and brown dwarfs host clouds, which are made of minerals or gemstones. Why is it important to know how extended and energetic lightning events are on extrasolar bodies of interest? First, lightning affects the local chemistry of the atmosphere creating molecules that otherwise would not appear, such as prebiotic molecules responsible for the origin of life on the young Earth. On the other hand it is of interest to know whether the discharge energy is large enough to be detectable from Earth.

Atmospheres of cool objects (brown dwarfs and gas giant planets with global temperatures between 500 and 2700 K) are cold and dense enough for mineral clouds to condense. In this paper we adopt the idea that a large-scale discharge is initiated by an electron avalanche that develops into a streamer (electrically conducting channel). We apply our discharge-propagation model to one-dimensional Drift-Phoenix atmosphere models, which provide information about the local gas temperature, pressure and chemical composition.

Streamer properties in laboratory experiments as used in this paper: the segment length, L, is the length of a single segment of the streamer. The minimum diameter, dmin, is the minimal segment diameter as streamer can reach. The energy per length is the amount of dissipated energy per length of single segment. (Briels, T. M. P. et al. 2008, JPhD, 41, 234008; ©IOP Publishing. Reproduced with permission. All rights reserved.)

Fig. 4. Streamer properties in laboratory experiments as used in this paper: the segment length, L, is the length of a single segment of the streamer. The minimum diameter, d_min, is the minimal segment diameter as streamer can reach. The energy per length is the amount of dissipated energy per length of single segment. (Briels, T. M. P. et al. 2008, JPhD, 41, 234008; ©IOP Publishing. Reproduced with permission. All rights reserved.)

 Our analysis shows that the electrical breakdown can occur inside the cloud layer (lightning) and/or above the cloud layer (sprite). From these locations the discharge propagates through the atmosphere while subsequent branches appear until it reaches a minimum diameter and the discharge terminates.

Our results show that a lightning strike reaches longer distances in a brown dwarf than in an exoplanet, which means it affects larger atmospheric volumes in the former than in the latter. The total energy that dissipates from one such event is less then 1012 J. (For comparison, on Jupiter and Saturn this value is around 1012-1013 J while on Earth it is ~108-109 J.) This energy causes an increase in the local gas temperature, which results in changes in the local chemistry as well. In the paper we showed the increase of small carbohydrate molecules such as CH and CH2.

Total lengths, L_discharge, that a large-scale discharge can reach in different atmospheres (left), and total dissipated energy for different model atmospheres (right) (top panels – giant gas planet, bottom panels – brown dwarf). Solid lines indicate solar metallicity, dashed lines show sub-solar metallicity. Left: results for two different value of a constant number of charges (Q). (Bailey et al. 2014, Fig. 9, Fig 11.)

Fig. 5. Total lengths, L_discharge, that a large-scale discharge can reach in different atmospheres (left), and total dissipated energy for different model atmospheres (right) (top panels – giant gas planet, bottom panels – brown dwarf). Solid lines indicate solar metallicity, dashed lines show sub-solar metallicity. Left: results for two different value of a constant number of charges (Q). (Bailey et al. 2014, Fig. 9, Fig 11.)

Considering mineral clouds, the closest alternatives on Earth we can investigate are volcano plumes, which are composed of small silicate ash particles. After explosive eruptions, volcano plumes host lightning activity that is orders of magnitudes larger than in a common thundercloud on Earth. Taking these arguments into account it is suggested that we provided a lower limit of the dissipation energy and that, in reality lightning can be stronger and more frequent on fast rotating extrasolar objects.

Volcanic lightning captured over the Puyehue-Cordon Caulle volcanic chain in southern Chile on 4 June, 2011. (Credit: Francisco Negroni/Agenciauno /EPA)

Fig. 6. Volcano lightning captured over the Puyehue-Cordon Caulle volcanic chain in southern Chile on 4 June, 2011. (Credit: Francisco Negroni/Agenciauno /EPA)

For more details check out the original paper on ADS:

R. L. Bailey, Ch. Helling, G. Hodosán, C. Bilger & C. R. Stark 2014, ApJ, 784, 43.

Also look at the University press release of the paper:

http://www.st-andrews.ac.uk/news/archive/2014/title,242028,en.php

Christiane Helling gives a press conferenc on 30 April, 2014 (9 am):

 http://client.cntv.at/EGU2014/?play=31

The LEAP Group can be found here:

http://leap2010.wp.st-andrews.ac.uk/

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