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)

Cosmic Rays enhance Prebiotic Chemistry on Sunless Worlds

In the International Journal of Astrobiology, Camille Bilger, Christiane Helling and Paul Rimmer (2014) presented a proof-of-concept on the potential effect of cosmic rays in the upper atmospheres of exoplanets (atmospheric pressures between 0.000001 bar and 0.000000001 bar, where 1 bar is the pressure of Earth’s atmosphere at sea level). We model the cosmic ray transport through the atmosphere of a planet with elemental composition and surface gravity similar to (but not the same as) Jupiter, if Jupiter were much farther away from the sun. This model atmosphere was produced using the Drift-Phoenix code (an upcoming post will be available soon on the Drift-Phoenix code).

Cosmic rays are charged particles (electrons, protons, bare nuclei) hurled through our galaxy at relativistic speeds by supernovae. When they strike the upper atmosphere of a planet, found to change its chemistry.

Cosmic Ray air shower

Figure 1. Cosmic Ray air shower

The combination of ultraviolet light from a star and cosmic ray ionization involves a delicate interplay between physics and chemistry, and is a hard problem to solve. It is simpler to consider cosmic ray chemistry on planets without daylight. These planets are often gas giants far from their host star, or rogue planets without a host star at all. These gas giants, like Jupiter, have an atmosphere made up not of mostly oxygen and nitrogen, but of mostly hydrogen, with a significant amount of nacient atomic hydrogen.

This is therefore a reducing atmosphere, and provides an ideal environment for making molecules believed to be important for the origin of life. Cosmic rays would ionize the molecular hydrogen, and this would make the atmosphere even more reducing.

Artistic impression of cosmic rays entering Earth's atmosphere. (Credit: Asimmetrie/Infn via CERN).

Figure 2. Artistic impression of cosmic rays entering Earth’s atmosphere. (Credit: Asimmetrie/Infn via CERN).

A reducing atmosphere is the standard initial chemical environment used in “origin-of-life” experiments, such as the Urey-Miller experiment. In the Urey-Miller experiment, an ionizing source in the form of an electrical discharge is initiated in a molecular gas, and so long as the atmosphere is reducing, prebiotic molecules are formed, including the twenty common amino acids found in living systems. If a reducing atmosphere, such as one dominated by oxygen and nitrogen, is used, the experiment produces no organic compounds.

The ion-neutral reactions made possible by cosmic ray ionization allow more of the hydrogen to be liberated from its molecular form, and increases the rate of reducing reactions. These reactions are found to be responsible for much of the prebiotic chemistry. Specifically, cosmic rays help to make biologically important molecules such as ammonia and acetylene. How much do cosmic rays help? They increase the abundance of some of these species by 10x or 100x in some cases.

Figure 3. Volume fraction of various species as a function of the gas pressure, p [bar] for the model atmosphere of a free-floating giant gas planet. The results assuming chemical quenching of C2H2 and C2H4 at height at ∼10−3 (dashed), and the results with cosmic ray ionization (solid) are all presented in this plot. A thick black horizontal line indicates the pressure above which termolecular (??) reactions may dominate.

Figure 3. Volume fraction of various species as a function of the gas pressure, p [bar] for the model atmosphere of a free-floating giant gas planet. The results assuming chemical quenching of C2H2 and C2H4 at height at ∼10−3 (dashed), and the results with cosmic ray ionization (solid) are all presented in this plot. A thick black horizontal line indicates the pressure above which termolecular reactions may dominate. (Rimmer et al. 2014, Fig. 4.)

The third picture in this article is from our paper, showing how much various molecules are enhanced or reduced because of cosmic rays. Some of the molecules that are enhanced, like ammonia, are key ingredients in the formation of the amino acid Glycine. These ingredients often must overcome a reactive barrier in order to form the amino acid, and overcoming this barrier may be made possible by electrostatic activation of ammonia (see our previous post here).

An image of the HR8799 planetary system from the December 2010 press release.

Figure 4. An image of the HR8799 planetary system from the December 2010 press release. (Credit: NRC-HIA, C. Marois, and Keck Observatory)

Our work may be relevant for directly imaged exoplanets orbiting HR 8799. Since these planets are ten times farther from their host star than Jupiter is from the sun, they are forever shrouded in the dark of night. It will be good to see how a star would change the chemistry, but this is a difficult problem. In order to find out what a star does in the upper atmosphere, it will be necessary to consider how the starlight passes through the atmosphere, and how that will affect thetemperature. The temperature will change the chemistry, and the chemistry will in turn affect how the starlight passes through theatmosphere. Much work still needs to be done to solve the problem for planets closer to their sun.

For more details check out the original paper on arXiv:

P. B. Rimmer, Ch. Helling and C. Bilger 2014, IntJAstrobio, 13, 173

And don’t forget to like us on Facebook:

https://www.facebook.com/leap2010