The Astrophysics of Planetary Habitability, Days 4 and 5

The Astrophysics of Planetary Habitability has ended yesterday, and during its 5-day run, it has brought forward many interesting questions along with approches to find their answers. Can M dwarfs host Earth-like habitable planets? How severely do various stellar properties impact the prospects of habitability? How do orbital dynamics in different kinds of system constrain what worlds could stably exist there? What role do radioisotope abundances play in the evolution of potentially habitable planetary environments? What processes shape planetary atmospheres and how do they interact? How does interior structure of a planet influence its habitability? Although we don’t and perhaps for a very long time won’t know exact answers to most of them, research presented here can at least point us to some directions to explore observationally when we can, give us some notions about what to expect, and provide testable hypotheses that will help us assess which models approximate the reality better and how do they connect to other measured evidence.

The fourth day of the conference hosted two main topics: interiors of planets, and search for exoplanets. The former started with an invited talk by Paul Tackley, who spoke about long-term evolution of planetary interiors and factors that can affect it, such as large impacts, viscosity of the mantle, internal heating or water content. His simulations resulted in plate tectonics on super-Earths equally or more likely than on Earth-mass planets. That is a very interesting result and a compelling one when considering the habitability of super-Earths. However, the model assumed apriori differentiation into core and mantle and then just calculated with the mantle. But would super-Earths undergo differentiation comparably to Earth-like planets? When I asked him during the coffee break, Dr. Tackley said that most likely yes, as differentiation would go quickly enough in the molten material. Sufficiently large impacts may induce enough melting. Zeng and Sasselov (2013) previously argued that differantiation would depend on the redox state and not all terrestrial-composition planets may undergo it. I had also seen David Stevenson’s lecture about how super-Earths may not be Earth-like ( It’s an interesting topic and one of which we’ll hopefully know more with more models such as these and most importantly much more precise measurements in the future.

Lena Noack, whose previous work I had seen at last year’s EPSC, set to answer the question whether terrestrial planets ranging from Mars-sized to super-Earths can outgas enough CO2 to be able to support liquid water at the outer edge of the classically defined HZ. She estimated the mantle depletion by partial melting of the mantle, and found that bigger radii and also relatively larger cores than Earth’s would lead to lower outgassing rates. Earth-sized or slightly smaller planets with a bit smaller cores may outgas their CO2 more efficiently. Plate tectonics, if present, also help outgassing a lot.

Constraining planetary composition from existing crude measurements was the topic of Caroline Dorn’s talk. She used observational evidence of Fe/Si and Mg/Si ratios of the host stars to estimate the relative sizes of core and mantle for planets whose size and mass had been measured. Although all of the used values have huge uncertainties at this time, it’s a very promising and potentially highly useful work for future study of exoplanets. Dorn’s and Noack’s talks also had somewhat pessimistic conclusions about the habitability of currently known planets – both concluded that known HZ-located planets seem unlikely to host conditions similar to Earth’s. If they’re right – and both studies seemed very thorough, although laden with similar limitations as all of them – our search is still to yield the results some people wish to see so badly. They certainly provide useful tools how to conservatively estimate a planet’s habitability.

The latter topic, search for extrasolar planets, was summed up very nicely in two invited talks, one by Heike Rauer about space-based telescopes and the other by Stephane Udry about Earth-based search. Telescopes such as CHEOPS, TESS or PLATO should provide us with far more (quantitatively as well as with respect to completeness and precision) measurements in the near future, and Earth-based projects such as HARPS, ESPRESSO, CARMENES or MEarth cannot be neglected. All of them have or will have an important place in the search for exoplanets. We missed the talk by Eike Günther about the Graz-Tautenburger-Imager (GTI), as we went to visit Ruth-Sophie Taubner’s workplace in a different part of the University of Vienna. She cultivates methanogens under different gas and nutrient mixtures resembling those we could possibly find on Enceladus. She had a great poster here at the Astrophysics of Planetary Habitability, as well as last year’s EPSC. I’m very much looking forward to the papers that are going to stem from this research. Last year, Ruth-Sophie also had a review about ecophysiology of methanogens with respect to astrobiology in the Life journal. The whole ExoLife project group at the University of Vienna seems very promising.

The final day of the conference was focused on orbital dynamics and their role in habitability. The role of Kozai-Lidov mechanism, scattering (especially by different number, orbital properties and mass distribution of giant planets in a system), dynamical stability, use of dynamical simulations to constrain the possible presence of other massive planets in currently known systems and the possibility of eccentric planets with life-supporting climates were discussed by the speakers.

The whole conference tied the diverse topics – host stars, planet formation, HZ concept, atmospheres, planetary interiors, search for exoplanets, and architecture and dynamics of planetary systems – together very nicely and made it apparent that none of these variables are totally independent of the other ones and scientist studying them with respect to habitability should speak to their colleagues from different habitability-related fields.

The Astrophysics of Planetary Habitability was a great conference full of interesting talks and posters. I want to thank the organizers for making it happen, and I hope that there will be another similarly-focused conference in 2018, as they had mentioned this possibility yesterday. As to discussions during coffee breaks, the “mixing ratio of people” seemed lower to me than on EPSC, but it was always possible to find the people I wanted to ask something, and we’ve also met many new interesting people during the breaks and social events. And I also thank the Department of Geophysics (MFF UK) for enabling me and my colleague to come here. The conference was certainly worth it and I’m looking forward to seeing advances in the research presented here!

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Tomas Petrasek, I and Michaela Kanova from the Department of Geophysics, standing above the stairs leading to the conference room. Photo taken by Dr. Jeff Linsky.

The Astrophysics of Planetary Habitability, Day 3

Principles of Habitability session opened today’s Astrophysics of Planetary Habitability. In the first talk, Ravi Kopparapu reviewed the concept of habitable zone, or rather surface liquid water zone, as he emphasized – it’s a very helpful concept for assessing the likelihood that a given planet may be habitable, but the actual habitability depends on many factors, as already stressed in previous talks. The number of HZ studies has rocketed up in the last three years, providing different estimates based on the used models and input parameters. Kopparapu himself favors the conservative HZ limits, which provide a useful framework for choosing targets for transmission spectroscopy and other methods. He was quite pessimistic about hydrogen greenhouse HZ extension – not that it wouldn’t work, but it would be extremely hard to detect more distant terrestrial planets and explore their properties.

However, I hope that they may be of interest, and framework for their exploration exists: Sara Seager et al. provide two excellent papers (both from 2013 in The Astrophysical Journal) related to the possibility of biosignature gases in H2 atmospheres of super-Earths (for the case of a Sun-like star and an M5V dwarf). Nevertheless, the semi-major axes of the planets considered in the detection model are still near the stars and the atmospheric pressure is 1 bar. Detecting and observing much more distant planets with thicker atmospheres would certainly remain difficult for some time.

Seager et al. (2013b) say: “Is there any hope that the next space telescope, JWST could be the first to provide evidence of biosignature gases? Yes, if–and only if–every single factor is in our favor. First, we need to discover a pool of transiting planets orbiting nearby (i.e., bright) M dwarf stars. Second, the planet atmosphere should preferably have an atmosphere rich in molecular hydrogen to increase the planetary atmosphere scale height. Third, the M dwarf star needs to be a UV-quiet M dwarf star with little EUV radiation. Fourth, the planet must have life that produces biosignature gases that are spectroscopically active.”

These articles are certainly worth reading, and especially 2013a is fascinating in exploring the possible biosignature gases and biomasses of putative life on planets with hydrogen-dominated atmospheres. I must admit I hope we detect a Haber World some day.

Two talks about binary system habitable zones were the highlights of today’s program. More than half the stars in our neighbourhood are multiple systems, so we need to understand the stability and habitability of their planets. We know from observational data that they can have planets around one component (S-type orbit) as well as around both stars in other cases (P-type). Siegfried Eggl from the University of Paris stressed the importance of orbital evolution on habitability, because if it’s accounted for, the permanent HZ shrinks to barely half the usual estimates without this parameter. However, the extended and average HZ still remain quite large. It seems a nice framework for estimating the likelihood of habitable planets in binary systems.

Manfred Cuntz of the University of Texas, Arlington, presented a new approach to habitability of binary systems. His model did not assume an S-type or P-type HZ up front – its results showed that. Nearly circular orbits and high luminosities seem favorable for both, the resulting type of course depends on the separation. In the follow-up work, he’d also like to explore HZs for different solvents than water. It seems a demanding work; some proposed alternative solvents, such as formamide and hydrazine, would need basically water-free environments, which makes me very skeptical about their existence as solvents for life. However, this isn’t a problem for solvents liquid under different conditions or forming a solution with water. Climate models assuming the abundance of different solvents would also be interesting, but that is a completely different future work someone will hopefully try to do.

There was also a highly interesting poster by Mason et al., taking into account the rotational evolution of the binary system and its effect on habitability. Under some range of separation of the components, the tidal effects dampen the stars’ rotation rates and thus decrease the XUV and stellar winds, making the surrounding environment more friendly to planetary atmosphere and possibly life. It works for similar-mass as well as different-mass components. They have a calculator at

Feng Tian from the University of Beijing began the Planetary Atmospheres session with his great review of processes in work in the evolution of atmospheres. He discussed many factors influencing it, both from the host star and the planet itself, and one of his final remarks really hit the spot: “We’ve talked about liquid water habitable zones, but maybe it’s time to talk about more kinds of habitable zones.” The UV environment, stellar winds and activity… all could produce its kind of HZ, although the definitions would not be as nice and simple as the surface liquid water HZ. Special HZs may be a hyperbole, but after finding a planet in the classical HZ, these are the factors we certainly cannot neglect.

A potentially very important lecture was delivered by Andrew Lincowski who researched the effects of CO2 clouds on the planetary climate and found that current outer HZ limits, based on CO2-derived warming even with CO2 clouds, may be too optimistic.

Giada Arnay talked about “pale orange dots”, late archean Earth analogs with prominent organic hazes. Around stars with too high UV flux, hazes would likely not form because of the oxygen radicals from photolysis in the upper atmosphere, but otherwise, with the CH4/CO2 ratio above approx. 0.1, hazes seem likely and could serve as biomarkers for worlds with Earth-like CO2 levels, because abiotic methane would not be sufficient for haze formation – life would need to produce it. Organic haze would also act as an UV shield – by far not as efficient as ozone layer, but nevertheless very helpful for the prospects of surface life.

That wraps up today’s highlights. Although all the talks were interesting, it would be impossible to mention all of them. I’m coming down with a cold and in addition, there is the conference dinner tomorrow, so I may clump days four and five together and post another mini-summary on Friday. We shall see.

I’m also curious how many times we’ll see the HZ diagram by Chester Harman (below). It has been shown five times so far. I’m counting.


Many thanks to the Department of Geophysics (Charles University) which enabled me and my colleague Tomas to attend the conference!

The Astrophysics of Planetary Habitability, Day 2

The first whole day of the Astrophysics of Planetary Habitability conference has been quite fruitful. The first session, The Host Star, was concerned mainly with the stellar environment of potentially planet-hosting stars. The talks especially explored the relationship between stellar age, rotation period, magnetic fields and activity. Several of them addressed the question whether M dwarfs could host habitable planets. The answer is by no means clear yet, as the question is very complex, our observational knowledge can constrain only some parameters and M dwarfs come in many flavors. Rotation rate, through the related intensity of the stellar wind, can have a big impact on whether a planet loses or retains its atmosphere. Slow rotators seem far more habitability-friendly – but what’s their actual abundance?

Stellar flares and coronal mass ejections are another potential problem for the atmosphere and any putative life on the planet’s surface. Modeling the effect of flares on the ozone layer has had mixed results so far. We haven’t observed any CMEs directly so far, but the radio observation Starburst Program, presented by Jackie Villadsen, could change that quite soon. Also, properties of the planet – particularly its magnetic field – are important in whether it keeps its atmosphere, how much stellar activity-related heating it undergoes and what radiation doses the surface receives.

We also talked to Jeffrey Linsky from the MUSCLES survey, providing complex stellar flux data for several M and K dwarfs based on the data from Hubble and Chandra. Using the coupled data enabled to reconstruct the flux across the spectrum, and Lyman alpha and EUV could be calculated. No UV inactive M dwarfs have been observed in the survey. The data may be instrumental in assessing the impact of M and K stars’ environment on planetary atmospheres.

The Planetary Formation session began with Yan Alibert, who reviewed planetary formation and habitability. Among other parts of the topic, he talked about the water content of planets, and stated that worlds with high-pressure ice at the bottom of the ocean would not be habitable due to the loss of the geochemical carbon cycle working on Earth. On ocean planets, no weathering would be depleting the atmosphere of CO2 and the CO2 released by volcanism would warm the planet and lead it into a moist greenhouse state (and acidify the ocean). However, that is presuming the convection in the HP ice – if present – would not enable sufficient removal of CO2. Weathering in deep sea vents does occur. And if conduction is not sufficient for releasing the planet’s inner heat, convection in HP ice should occur, although its frequency and intensity are difficult to estimate. Alibert also seems to have presumed rates of volcanism comparable to a planet whose rocky mantle is not covered with HP ice. Some models have already shown that it could inhibit volcanic activity. (And the degree of activity should be logically connected to heat release and therefore convection, which could provide some weathering… it’s certainly not as simple as Alibert had put it, although it’s hard not to simplify in the time frame of a conference presentation.) Later in the afternoon, Nader Haghighipour also pointed out that omitting collisions in a model of planetary development could lead to big overestimations of the usual water content. If included, impacts lead to water loss and produce far less water-rich worlds than Alibert’s model. Ocean planets may not be highly common after all.

Maria Lugaro had a fascinating talk about radioactive elements distribution in solar systems. Thorium seems to be more abundant in most solar analogs than the Sun. Why? It likely comes from neutron star mergers, rare events, so we can expect the distribution to be inhomogenous. The implications for more thorium-rich systems I can think of are thought-provoking: more long-lived radiogenic heating could lead to widening of the habitable region around a star, higher abundance and lifetime of subsurface oceans… For other elements and their izotopes, such as aluminum 26, we don’t know the distribution well. This much shorter-lived izotope has been abundant in the solar system and the related heating could possibly lead to more water loss in small building blocks of our system’s objects. The source increasing the solar system’s metallicity is not certain; it could have been a stellar death nearby and recently before the Sun’s formation, but possibly also self-pollution of the original giant molecular cloud.

Eduard Vorobyov had a very interesting lecture on planetary formation by disk fragmentation. A few dozens of planets (or likely brown dwarfs in some cases) several tens to thousands AU from their stars had been detected, but their origin is unclear. Were they scattered into those regions, captured by the star, or formed in situ? Vorobyov modeled gas clumps in the disk surrounding a young star. In his model (including just one forming star), clumps up to 100 Jupiter masses up to hundreds AU from the star formed, but most of them quickly migrated inwards and fell onto the star. However, especially in the later stage of clump formation during the star’s T Tauri phase, some clumps from about 3 to 43 Jupiter masses remained from 178 to 415 AU away from the star. The masses reproduce the observed ones very well, however, the range of semi-major axes is much broader in the observations. The model raises some interesting questions: If the clumps lose material during their inward migration, could their presence lead to smaller, even terrestrial, planet formation? Such a planet would probably accrete a primordial atmosphere (whether it would actually retain it depends mostly on its mass and distance from the star). Distant hydrogen greenhouse worlds, anyone? Also, in a few cases the fall had stopped in the model, but other migrating clumps would either push it onto the star or kick it outward. I wonder what orbits the potential resulting bodies might end up on.

To sum it up, today’s program has been interesting and raised many questions, some of which I hope to pursue further in some future popular science articles. Unfortunately, two lecturers did not arrive. Hans Zinnecker should have talked about the possibility of Earth-mass planets and life around metal-poor stars, Eric Gaidos about the ZEIT project. I was looking forward to meeting Gaidos; I wanted to ask some questions about degassed atmospheres vs. atmospheric collapse on young planets with low insolation, Tomas wanted to ask him about hydrogen atmosphere planets and their significance in astrobiology. Gaidos has contributed to papers on topics related to these, and many more.

Well, there’s e-mail. Even though it’s always more pleasant to just have a short chat during a coffee break.

And to give you some notion of how conferences are done Viennese-style, here’s a glimpse of yesterday’s reception on the university’s observatory, including a string quartet.

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We thank the Department of Geophysics of the Mathematical-Physical Faculty of the Charles University in Prague for enabling us to attend the conference.

The Astrophysics of Planetary Habitability, Day 1

The Astrophysics of Planetary Habitability conference has started this afternoon with two invited lectures: one by Victoria Meadows from the University of Washington about factors influencing planetary habitability, the other by Christian Köberl from the University of Vienna about the bombardment history of early Earth.

Doctor Meadows summed up the complexity of habitability very nicely. Too often – mostly in popular science texts, rarely in words of scientists working on the topic – we encounter a highly simplified notion of a habitable zone determined by the stellar flux and enveloped in sharp borders, where a planet either is or is not habitable. Many people don’t realize that this is far from the case. Habitable zone is a useful concept in assessing the probability that a given planet hosts liquid water on its surface and therefore may be habitable for life similar to ours. But even if we set aside possibilities such as distant or even rogue planets with dense hydrogen atmospheres, which could retain conditions optimal for liquid water, or life in the subsurface, habitability is a complex question.

Composition, size, mass and interior of the planet in question play a role we cannot neglect, as well as the planetary architecture (which can influence everything from the stability and eccentricity of the orbit to the early water delivery), stellar parameters, distance from the star, number of stars in the system, atmosphere (dependent largely on the planetary composition and stellar activity), tectonics (dependent on the interior…) etc. A terrestrial planet orbiting inside the habitable zone is not necessarily habitable and can turn out many different ways, which is something we unfortunately don’t see in most press releases informing of new HZ planets. Victoria Meadows and her colleagues had proposed a habitability index instead of the HZ (see the HITE – habitability index for transiting exoplanets – in Barnes et al., 2015). I’m not sure whether the approach provides more reliable estimates of likelihood than the HZ – it’s nice that it’s a continuum of values instead of a binary variable, but no one in clear mind takes HZ as strictly binary and we lack constraints on many values featuring in the index for many worlds. But I’ll need to read this paper and others carefully before pursuing this deeper.

Dr. Meadows mostly focused on HZ around M dwarfs in her talk. Habitability of worlds orbiting M dwarfs, the most common stars, is an interesting and complex question that has been tackled from various approaches for decades. The impact of the UV and proton flux from the star on a planet’s atmosphere has been studied in multiple works with varying results (more about that later, I hope). Another of the many intriguing topics surrounding this question is the role of tides.

Tidally locked planets, especially their interior convection dynamics and climate, have been modeled for quite a while. The role of tidal heating, well-known from some solar system bodies such as Io, is not as often brought up but could have several effects. To some extent, it could warm a planet which would otherwise be too cold to retain surface liquid water. It could also potentially play havoc with a planet’s magnetic field by influencing the interior convection. Last but not least, it could possibly heat a planet sufficiently to lead it to a Venus-like greenhouse state.

That possibility was explored by Barnes et al. (2013) who provide an exhaustive account of the related characteristics and also a nice appendix with the model. Though I don’t understand the models myself, I look forward to discussing them with my geophysicist colleagues who could hopefully point out new directions stemming from them.

The early atmosphere loss, possible O4 collisional features in the spectra and the notion that planets orbiting cooler stars could exhibit enhanced biosignature signs are also interesting, but I’d be summing up Dr. Meadows’ lecture if I were to venture into all topics she had mentioned. It was a great opening lecture for a conference where several of the talks and posters will be focused on M dwarfs and their impact on habitability, so I hope to provide a short account of news after the conference ends.

The other lecture by Dr. Köberl mostly summarized what we don’t know about the Late Heavy Bombardment. Hopefully more Moon geology missions would improve our knowledge. If I manage to catch him later for a word, I’ll ask about the possibility of dating impact record on icy bodies such as Ganymede or Callisto. Ganymede lander is still a long shot now and wouldn’t provide much data to this question, but in more distant future, data from more solar system objects such as the gas and ice giants’ moons could improve our understanding of the history of our system (and certainly not just in questions related to impacts).

I’ll be much more brief tomorrow, as there will be seventeen talks… Some articles other than these very quick blogposts will follow (likely mostly in Czech, though).

I’d love to give you some eye candy but I didn’t want to disturb the lectures by taking pictures. However, the conference has some nice and witty custom water bottles, which you can see below.

More about happyability coming soon!

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Looking forward to the rest of the conference! I also thank the Department of Geophysics of the Mathematical-Physical Faculty of the Charles University in Prague for enabling me and my colleague Tomas Petrasek to come here.

Did you say NaNoWriMo? (Plus a new story!)

I’ve never been into stuff like NaNoWriMo much. But there is always a first time for everything… My challenge is different. Behold, my November writing schedule:

  • Finish my next novel (already very much behind). Presumably some 60,000 words left. Oh dear.
  • Write a grant proposal. Deadline fast approaching. Maybe some 4,000 words.
  • Write several popular science articles, columns and reviews of various length. Maybe some 12,000 w. in total.
  • Write some newsletters or posts for my employer. That should not be too long; let’s say 6,000 words?
  • Polish a paper, submit it, start a new one. Mostly editing work and drafting.
  • Possibly translate a couple of articles.

That leaves me with over 80,000 words for the month. While doing my usual part-time jobs, attending a conference, preparing my lectures and going to classes. Well, you know what they say about challenges?

(Guess I must be nuts.)


And because I don’t want it to look like I basically haven’t written anything lately (’cause that would be a totally wrong picture!), kindly gaze at the anthology of Professor Moriarty stories that was published some two weeks ago and contains over thirty stories from many talented authors, yours humblest included.


Planetary Science Hot News, Part 2

This year’s European Planetary Science Congress is over. It’s been exciting, full of news and interesting people and really well-organized. What were some of the highlights from Thursday and Friday?

The Ceres section has been wonderful. C. T. Russel first summarized the Dawn mission, its current status and future prospects, and the first results from the Survey orbit. The possibility of a locally or temporarily magnetized surface (assumed as one possible explanation for the spikes in recorded spectra) is certainly worth a thought and further investigation, although Dawn itself doesn’t have a magnetometer, so it would have to be tested indirectly or by another craft. Maria Cristina De Sanctis presented the results of VIR observations and ammonia seems to be the best fit for the surface composition. As ammonia otherwise seems quite rare in the inner solar system and its frostline should lie around Neptune’s orbit, it could suggest that Ceres either formed in its present orbit from smaller bodies having drifted there from the Kuiper Belt, or that it’s originally a Kuiper Belt object too (see McKinnon 2008 for this hypothesis). And if ammonia proves more abundant in these regions (for example if more KBOs drifted there early in the solar system’s evolution), could it have some implications for brines on Mars?

Ralf Jaumann from DLR proposed brine upwelling as a possible explanation for the geologic features seen on Ceres, especially flows, mountains and possible salt domes. He also analyzed spectra of reddish and bluish regions and tentatively came up with perchlorates as a good fit for them. Perchlorates and ammonia…? That’s a highly combustible combination. As Tomas reminded me, spectra of salts tend to be complicated to distinguish, so it could well be a different compound. The results are still preliminary and a more detailed analysis will tell us more. In any way, the brine upwelling hypothesis is certainly very interesting. Tomas Petrasek has written a detailed article about Ceres (in Czech), which should be published very soon. I’ll be sure to tweet it when it’s out. By the way, the shown topographic and color/albedo maps of Ceres seemed to me to show similar patterns. We’ll see later if it really is so and what it might mean in that case.

Klára Kalousová presented her model of shallow subsurface water under Europa’s strike-slip faults. Its implications for astrobiology and crustal processes are large and I’ll be certain to follow her subsequent work closely; she’ll be adding more variables into the model, including varying the ice’s composition, and working on other complex models with the people from Nantes University. The following talks about JUICE and Europa Mission, respectively, nicely summarized the missions’ planned equipment, trajectories, time scales and objectives.

Petr Brož presented evidence for features of possible volcanic origin on Mars, dating back just into the mid to late Amazonian epoch. The cone clusters, often with associated flows, are morphologically similar to such volcanic features on Earth. Could Mars have been so active even is such relatively recent past? We’ll do a Mars-themed feature article with Tomas (in Czech, possibly English too), so stay tuned for more than just this brief mention. Mars has certainly been one of the hottest topics of this year’s EPSC.

The planetary habitability section was very interesting as well, covering a wide range of topics from dynamical perturbations of eccentric orbits, across C/O ratio’s influence on habitability, to conditions in high-pressure layers in ocean world. Especially the latter talk by Lena Noack has been amazing. It would be great to combine her approach with Baptiste Journaux’s models of convection in HP ice layers, and as it is, that is actually a real plan. Works by Noack, Journaux, Tobie, Choblet and others may tell us much more about the possible habitability boundaries for water-rich worlds, be they exoplanets or large icy moons within our own system. Certainly one of the greatest conference highlights! We’ll also cover this topic more extensively in upcoming articles.

The outer planets section on Friday was centered mostly on Titan, with some talks also about Enceladus. In short: Serpentinization highly likely on Enceladus, overall composition and conditions favorable for life as we know it. Will we see LIFE or ELF chosen as a mission to implement anytime soon? As for Titan, could a large cometary impact account for its present atmosphere? Melting at the bottom of the high-pressure ice layer seems likely. Is there a thick layer of ethane clathrates, also explaining the overall abundance of methane in Titan’s lakes? Those are just hints of what has been there today; we’ll cover it later.

Both I and Tomas would like to thank the Geophysics Department of the Charles University for enabling us to attend. It has been a wonderful event full of many interesting answers and even more questions to follow up on in the future. As for you, dear readers, you may look forward to a series of articles about topics discussed in the conference talks. Czech readers are likely to see them in Vesmir (both print magazine and website), website and elsewhere. English-speaking readers can be sure to find anything in English published or linked here. It’s going to be a busy time ahead of us. We hope that then you can enjoy the news from the conference as much as us.

P.S.: Tomas’s popular science article on rogue planets has been published in Clarkesworld!

P.P.S.: The outreach section of EPSC in the lobby of the congress centre was great as well, attracting a lot of attention from the visitors, schools etc. We couldn’t miss the VR simulation of Rosetta and Philae!




Planetary Science Hot News, Part 1

As some of you already know, I and my colleague Tomas Petrasek are currently at the European Planetary Science Congress in Nantes, thanks to the Department of Geophysics of the Charles University in Prague, which enabled us to attend. It’s been a busy few days so far, so I barely had time to even tweet anything about it, but I decided to at least quickly summarize a few of the highlights so far. I apologize for only providing this short summary in English but Czech readers can look forward to a whole series of articles by me and Tomas, some of which may not be fully available in English, so the wait should be worth it!

Colin Johnstone had a really interesting talk about stellar winds and high-energetic radiation environment in the vicinity of fast and slow rotating young stars. His team is also looking into possible evidence of whether the Sun was a fast or slow rotator pre-main sequence, which would have influenced the system’s evolution – planetary atmospheres (which highly depends on whether the planets were formed already in this short phase) and the development of the protoplanetary disk itself. His colleague Kristina Kislyakova is also starting a research into the properties of habitable zones around different types of stars, including those out of main sequence like white dwarfs. They’re both from the University of Vienna. In February 2016, the Pathways to Habitability conference is going to be held there.

You certainly all heard the interesting news about the recurring slope lineae on Mars, which was presented on the congress and in the NASA press release on Monday. We’ve briefly talked with Alfred McEwen today about the history of Martian water, role of perchlorates and other salts and the possible origins of Martian gullies, which are not to be mistaken with RSLs but could have a similar origin with water condensing from the atmosphere. Tjalling de Haas has studied the gullies and concluded that such source is most likely to explain their properties, which raises the question of past Martian environment dependent on the axial tilt – if it was higher recently, the CO2 polar caps may have sublimated more, resulting in a denser and slightly warmer atmosphere and allowing for more water vapor in the atmosphere. His talk comes on Thursday, we’ve just briefly discussed it so far. Another process contributing to the gullies, based on cracking of CO2 condensed ice and escape of trapped gases, was proposed here on Monday by Pilorget and his team. This is just a tiny snapshot (and I’m not even going into the history of the difference between the hemispheres) – more articles to follow!

We have shortly talked with Matt Taylor and Patrick Martin about the Rosetta mission. To very briefly summarize the recent news, the activity around perihelion was even higher than expected, including the very large diamagnetic cavity after one of the big jets, and the surface changes seem to be quite large – but we’ll know more about them as Rosetta goes into a closer orbit again. That also means that during the next few months, it will come into the cone of communication with Philae and will be sufficiently close. If Philae is still active, we may hear more roughly until the end of this year, hardly later.

Lots of interesting talks about the icy moons of the solar system. Baptiste Journaux presented a model of convection in high pressure ices (based also on experimental data on their saturation with salts), which may have big relevance especially for Ganymede and Titan. I’ve only had time for one question about dissolved gases but may catch him for a few more questions later – there will certainly be articles about the icy moons, especially as we discussed them with Gabriel Tobie. Tobie’s and Choblet’s team is also presenting their own model of high pressure ices and the chemical exchange between them and the rocky mantle on Friday. Klára Kalousová is presenting her model of water accumulation below Europa’s strike-slip faults tomorrow. And the talks about Titan were really frequent here. Impossible to completely summarize now, it’s after midnight here and I’m exhausted. More articles to come!

A few isolated remarks: The possibility of lightning features in Saturn’s ring and interesting approaches to their dynamics (our talk with Larry Esposito). Tribocharging as a mechanism possibly playing a role in ring processes. Could it play a role in clouds and hazes? I asked the author, Scott Waitukaitis, about it, and he thinks it’s entirely possible but we’re lacking data. Will try to look into this in more detail. We’ve by now got hours of interviews about Mars, Venus, icy moons, planetary rings and more exciting topics, building upon the news presented here. (Also some anecdotes about citing Darwin, big scientists as Star Wars fans and the benefits of free food!) It may take a while before we can process it all. Another brief highlights article will follow during the weekend, the rest gradually in the following weeks. Stay tuned! Yours truly, tired and excited faithful observer.

P.S.: Tomas will have a popular science article about rogue planets in the upcoming issue of Clarkesworld. Check it out!


Matt Taylor and Patrick Martin in front of a Rosetta poster. Photo by Tomas Petrasek.

Surpassing borders: more translations

When I first started writing in English just over two years ago, I did not imagine publishing in any more languages than Czech and English anytime soon. Yet earlier this year, I’ve had a story (The Symphony of Ice and Dust) translated into Romanian, along with other Czech authors, thanks to the magazine’s editor Cristian Tamas. Now I’m stepping a bit further from home with a translation into Chinese.

ZUI-FoundThe story has first appeared recently in my “Terra nullius” anthology in Czech under the title Zaříkávač lodí. The English title is The Ship Whisperer – and you will see it in Asimov’s next March! It was also chosen for translation into Chinese by Geng Hui, whose translations include works by C. C. Finlay, Ted Chiang and many other authors I greatly admire. Under the title 船语者 (Chuan Yu Zhe), it’s going to be published in a few days in the September issue of ZUI Found. I’m looking forward to it and I’m very grateful to Geng for contacting me and choosing to translate the story! I hope you like it as well, whether you read it in Czech, Chinese or English.

I’ve also translated a few Czech works by other authors into English; they’re currently under consideration. I’ll keep you updated!

Pluto: a world more fascinating than we’d hoped for

Pluto and its largest moon Charon proved to be extremely interesting objects during the recent New Horizons flyby. While the spacecraft is on its way further into the Kuiper belt (hopefully to fly by another fascinating object in the foreseeable future), it keeps sending the flyby data home. What can it tell us about Pluto so far?

I have interviewed Dr. Hauke Hussmann, planetary geophysics scientist from the German Aerospace Center (DLR), about Pluto and other objects of our solar system. Dr. Hussmann has published lots of studies especially on the icy moons of our system, including a 2006 model of the possibilities of subsurface water reservoirs. He is also the principal investigator for GALA, the laser altimeter aboard the planned JUICE spacecraft bound to map the three icy Galilean moons: Europa, Callisto, and especially Ganymede.


The composite image of Pluto captured by New Horizons on July 14. Credit: NASA/JHUAPL/SwRI.


The world is excited by the New Horizons’ images of Pluto and Charon. The terrain, especially on the so far seen Pluto images, seems very young, geologically active and some features may indicate cryovolcanism. Thoughts about the possibility of a subsurface ocean appear with increasing frequency. Your study from 2006 centers on modeling conditions under which such reservoirs of water could persist. Do you think that further data from New Horizons can put more constraints on the model’s application on Pluto and Charon, e.g. reveal significantly more about their past gravitational interactions, degree of differentiation, amount of ammonia or other characteristics?

Regarding its surface, Pluto is showing a diversity of terrain types that is beyond all expectations. Some of these features require large amounts of energy and heat in Pluto’s interior. Therefore, the surface features, including e.g. flow patterns, mountains and troughs are telltale sign of a very eventful history. From the number of craters the relative ages of these features can be derived and the geological history of Pluto can be revealed. Although we can observe only the surface, the processes are linked to internal heat sources and Pluto’s internal evolution. Through tidal interaction it is even connected to the evolution of the Pluto-Charon system and models will tell us whether liquid water could persist in Pluto’s interior. Our 2006 models are much too simple in that sense. Now, with the data from New Horizons planetary scientists are able to go beyond these very generic models taking into account imaging and compositional data. Unfortunately, the degree of Pluto’s differentiation, an assumption in our 2006 models, cannot be well-constrained from the gravity field data of one flyby, but indirect evidence again might come from the analysis of imaging and compositional data. The latter is extremely important to constrain the melting temperature of the ices involved.


Image of the southern region of the Sputnik Planum, showing some of the most interesting features of Pluto at once. Credit: NASA/JHUAPL/SwRI.


One of the interpretations of the pattern of polygons seen in Pluto’s Sputnik Planum is convection in the icy crust. If this hypothesis is correct, would it mean that based on its extent, there probably is a subsurface ocean beneath, or would there be other as likely options?

Even if we find clear evidence for convection in Pluto’s ice shell or in a specific region it would not directly tell us whether there is liquid water beneath the convecting cells. Convection in the ice shell requires temperature or compositional gradients that control the buoyancy of up- and down-wellings. It does not necessarily require temperatures that reach the melting point of the ices involved. The polygons have typical dimensions of about 20 km which would imply a relatively thin convecting layer, which is unlikely if we consider a global ocean. Due to the low surface temperatures I would expect a global ocean, if it is there, to be located beneath an icy crust of about 200 km thickness. Furthermore, there might be other explanations for the polygons, e.g. contraction of material that is exposed to the surface. In short, I think we should be careful with interpretations regarding liquid water at this stage. Pluto shows unique surface features and a lot of effort will be needed in the next months to reliably interpret the data.


What surprised you most about the so far released data about Pluto? Is there anything you’d like to point out as most deserving a closer look?

I was most surprised by the icy plains region ‘Sputnik Planum’ and by mountains as high as 3.5 km. As an additional aspect I did not expect the surface features to be so young (~100 Mio years). This stands in contrast to most of the icy satellites and puts Pluto into one group with Europa, Enceladus and Triton which all show signs of recent or ongoing activity at their surfaces. Many features deserve a closer look which is unfortunately impossible in the near future with New Horizons receding fast from the Pluto system.


Pluto’s subsurface ocean may remain a highly uncertain possibility for a long time but for several objects of our solar system, the data is very strong, ranging from their surface geology, observed geysers to gravitational measurements or induced magnetic fields. Saturn’s moon Enceladus is one, but the last Cassini flybys are scheduled for this year, and future missions are uncertain. However, the Jovian system may become much better known to us thanks to JUICE, developed by ESA and planned to be launched in 2022. You’re the principal investigator for its laser altimeter GALA, which should be able to map surface topography of the icy Galilean moons in great detail. What are the biggest contributions this mission could bring? Is there anything you hope to find out most of all?

With JUICE, which stands for Jupiter Icy Moons Explorer, we are going into orbit around Ganymede, the largest icy moon in the solar system. Because we are in orbit for several months we will obtain detailed measurements and excellent coverage with global and high-resolution data. For the first time we investigate the icy satellites with subsurface radar and laser altimetry combined with imaging, spectroscopy, magnetometer and gravity field measurements. The combination of instruments will reveal whether Ganymede has a subsurface ocean and at which depth it is located. We want to understand the processes that have shaped Ganymede’s surface (e.g. tectonism, cryo-volcanism) and how these are connected to dynamics in the shallow subsurface and deep interior. Also the question, whether Ganymede is active at present will be answered by this mission. Furthermore, with JUICE we investigate the unique interaction of Ganymede’s intrinsic magnetic field with Jupiter’s magnetosphere.


Jupiter’s moon Callisto is considered something of a mystery due to its incomplete differentiation. What are the current leading hypotheses on its difference from other Galilean moons in this aspect and how would JUICE bring more light into this matter? How does Callisto shape our view of the dynamics of icy moons?

During the Galileo mission Callisto has shown a strong signal of an induced magnetic field which is interpreted as evidence for a subsurface water ocean. On the other hand the gravity field measurements tell us that Callisto has not completely separated the ice from the rock. This is difficult to understand in terms of a complete evolution scenario. With Galileo it was only possible to obtain gravity field data in equatorial flybys. With JUICE we will have the opportunity for several flybys including inclined and polar flybys which will greatly improve the gravity field data which is the basis for refined interior structure models. The process of differentiation on Callisto seems to be very slow. With JUICE we will have the chance to capture different stages of icy satellite evolution comparing Europa, Ganymede and Callisto. Comparing the impact rates on Ganymede and Callisto we can assess whether different energy rates provided by impacts could be the reason for triggering differentiation at Ganymede and not on Callisto. This is one hypothesis. An alternative would be the different orbital evolution and tidal heating of Ganymede.


This year is remarkable in the number of scientific contributions from many parts of our solar system, ranging from Pluto, Saturn or Ceres to Mars or the Churyumov-Gerasimenko comet. Can we even as early as now deduce any new insights on the evolution of our system (e.g. the distribution of elements and their isotopes in the primordial accretion disc, planet migrations…) from their overview? In what ways could we reliably combine the knowledge from these sources to gain a greater understanding of the solar system as a whole? What planned observations are you awaiting most?

Comets, asteroids and Trans-Neptunian Objects tell us a lot about the early stages of solar system evolution. Isotopic abundances and composition of ices and other materials in general provide insight in the distribution and mixing of compounds at the beginning of the solar system. Here, I am looking forward to detailed analyses of the surface composition of Pluto and also Charon. From the volatile ices incorporated in Pluto and Charon the conditions (temperature and pressure) during formation of the Pluto-Charon system can be constrained. It will be interesting to see the differences between Pluto and Charon to better understand the local environment in which they have formed, but also to compare the Pluto-Charon system to the icy satellites and to compare the region of the giant planets to the more distant Trans-Neptunian region in terms of volatile abundancies.
Regarding ongoing mission and measurements I am most curious whether Philae, the Rosetta lander, will become fully operational again while the comet is approaching the sun. Taking further in-situ measurements at the cometary surface would be huge success, technically and scientifically.
On larger scales it will be interesting to see what New Horizons has in store when it is approaching another Kuiper-Belt Object in the coming years.


Is there any object in our system you’d like to see studied in more detail, or any proposed mission concept you would want most to see realized? What should be our objectives regarding planetary science for the next few decades, in your opinion?

I would rather like to skip this question because with lots of really important science questions and future mission proposals in the area of planetary exploration a ranking would be difficult. Furthermore, many scientifically important missions suffer from technical difficulties or from higher costs as compared to others. The search for conditions which might have been conducive for extra-terrestrial life to evolve still is a main driver for planetary exploration. Whether we will have Pluto on this list remains to be seen…


The interview had been conducted in late July and the Czech translation was published on the popular science portal on July 31.

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