EXOA5

Large planetesimals and planetary embryos ranging from several hundred to a few thousand kilometers can develop magma oceans through mutual collisions, gravitational energy, and the heating of short-lived radioactive elements. After the evaporation of the protoplanetary gas disk, one can divide such planetary embryos into two distinct populations. If they grow to a certain mass of about >0.5 M_Earth before the dissipation of the disk, they will start to accrete a substantial primordial hydrogen-dominated atmosphere, while the gravitational potential of the smaller ones (≤0.5 M_Earth) will be too low to support this type of primordial atmosphere. For the smaller planetary embryos, the initial magma ocean will subsequently solidify, and a steam atmosphere will be catastrophically outgassed that, if it does not condense, may be lost efficiently via hydrodynamic escape. The escaping H-atoms will further drag heavier trace elements like noble gases and outgassed moderately volatile elements (MVEs) such as K, Na, Si, and Mg into space. For the larger population of planetary embryos, however, the magma ocean below the primordial atmosphere will not solidify until most of the gaseous envelope will be lost, thereby providing favorable conditions for MVEs to be dissolved within such atmosphere.

In our first study (Benedikt et al. 2020), we applied an upper atmosphere hydrodynamic escape model that includes the dragging of heavier species by escaping H-atoms and investigated atmospheric and elemental escape from planetary embryos between 1 M_Moon and 1.5 M_Mars (that is, the population of small protoplanets that does not accrete a primordial hydrogen-dominated atmosphere) by assuming that the noble gases and MVEs mostly reside within the escaping atmosphere. Our results indicated that the steam atmospheres and the embedded trace elements will be lost efficiently before they condense for masses ≤0.5 M_Mars and orbital distances up to 1 AU. For heavier embryos of up to 1.5 M_Mars the atmosphere together with the trace elements can only be lost completely if a shallow magma ocean remains below the gaseous envelope which might be achieved through frequent impacts onto the planetary embryo. For embryos with masses ≤M_Moon, on the other hand, the gravity is too weak for a dense atmosphere to build up against the high magma ocean related surface temperatures and all outgassed elements will escape immediately into space. The studied planetary embryos will, therefore, be severely depleted in noble gases and MVEs.

In a follow-up study (Erkaev et al. 2022), we are currently focusing on the loss of the heat producing element ⁴⁰K from initially bigger planetary embryos (that is, the population of protoplanets that was able to accrete a substantial primordial atmosphere). Contrary to our first study, we additionally applied equilibrium condensation models with the equilibrium chemistry GG_CHEM code (Woitke et al. 2018) and found that for magma ocean surface temperatures of ≥2500 K no condensates that fix potassium are thermally stable, and ⁴⁰K isotopes indeed populate such a primordial atmosphere to a great extent. By applying a sophisticated multispecies hydrodynamic upper atmosphere evolution model to study the loss of the atmosphere together with ⁴⁰K, we found that depending on the initial size of the protoplanet and the early evolution of the host star, this process can indeed remove substantial amounts of ⁴⁰K from protoplanetary bodies that are ≥0.5 M_Earth. This effect alone can, together with the loss of MVEs from the smaller planetary embryos that serve as building blocks for the bigger ones, result in a wide variety of different potassium abundances at the fully grown planet.

Since different abundances of heat producing elements have a significant influence onto the subsequent thermal and tectonic evolution of a planet, and therewith connected, on its tectonic modes (e.g., O’Neill et al. 2020), the process of early hydrodynamic escape of the heat producing isotope ⁴⁰K can significantly impact the habitability, since not all rocky planets will end up with the "right" amount of heat production in its interior. However, this process cannot be viewed separately; other factors will additionally determine the initial heat budget of a planet such as collisional erosion, the feeding zone of the growing protoplanet or the initial composition of the protoplanetary disk.

References:

Benedikt, M.R., Scherf, M., Lammer, H., Marcq, E., Odert, P., Leitzinger, M., Erkev, N.V., Escape of rock-forming volatile elements and noble gases from planetary embryos, Icarus, 347, 113772, 2020.
Erkaev, N.V., Scherf, M., Herbort, O., Lammer, H., Odert, P., Kubyshkina, D., Leitzinger, M., Woitke, P., O’Neill, C., Modification of the radioactive heat budget of Earth-like exoplanets by the loss of primordial atmospheres, Mon. Not. R. Ast. Soc., under revision, 2022.
O’Neill, C., O’Neill, H.S.C., Jellinek, A.M., On the Distribution and Variation of Radioactive Heat Producing Elements Within Meteorites, the Earth, and Planets, Space Sci. Rev., 216, id.37, 2020.
Woitke, P., C. Helling, Hunter, G.H., Millard, J.D., Turner, G.E., Worters, M., Blecic, J., Stock, J.W., Equilibrium chemistry down to 100 K. Impact of silicates and phyllosilicates on the carbon to oxygen ratio, Astron. Astrophys. 614, id.A1, 2018.

How to cite: Scherf, M., Benedikt, M., Erkaev, N., Lammer, H., Herbort, O., Marcq, E., Woitke, P., Odert, P., O'Neill, C., Kubyshkina, D., and Leitzinger, M.: Escape of moderately volatile elements from protoplanets and its potential effect on habitability, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-999, https://doi.org/10.5194/epsc2022-999, 2022.

In order to form a rocky, potentially habitable planet, like Earth, the planet’s building blocks must loose volatiles. White dwarfs that have accreted planetary material provide the perfect opportunity to study the volatile content of planetary building blocks. The unique behaviour of Mn and Na depending on the conditions under which volatiles are lost means that planetary material in the atmospheres of white dwarfs can tell us how planetary building blocks lost volatiles [1]. This talk will summarise some recent results regarding observations of volatiles in the atmospheres of white dwarfs, models that describe how white dwarfs accrete volatiles and evidence from white dwarfs for volatile loss both early, in the hot, inner regions of a planet-forming disc and late, when large-scale melting is induced following impacts. 

How to cite: Brouwers, M., Bonsor, A., Harrison, J., Shorttle, O., and Malamud, U.: How do planetary bodies lose volatiles?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1223, https://doi.org/10.5194/epsc2022-1223, 2022.

The formation and main element composition of rocky planets can be simulated as equilibrium condensation of the most common species in a protoplanetary disk with parameterized abundance patterns. We have developed an open access python code to perform condensation simulations based on a Gibbs free energy minimisation including thermochemical and stellar abundance databases. Our main objective was to provide a code that is easy to use, adapt, and expand. With our code, we simulated condensation for a representative selection of F, G and K stars. We analysed the influence of stellar abundance patterns and specific element ratios on the equilibrium chemistry in the protoplanetary disk. I will present our results about the connection between stellar elemental abundance patterns, volatility of elements, and planet composition. We found significant variations in condensation temperatures and planetary bulk compositions even for the conservative parameter range of 0.1 < C/O < 0.8, challenging previous assumptions regarding the general consistency of disk chemistry in low to medium C-systems. Our simulations show that the combined differences in various element ratios and overall metallicity of the system have an intricate effect on the condensation behaviour of solid phases. We systematise these effects in an effort to enable cursory estimations of planetary compositions.

How to cite: Timmermann, A., Reiners, A., Pack, A., and Shan, Y.: Connecting Stellar Abundance with Element Volatility & Rocky Planet Composition, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-488, https://doi.org/10.5194/epsc2022-488, 2022.

The volatility of an element is defined by its 50% condensation temperature (T_c⁵⁰) from a nebular gas of Solar composition at 10^-4 bar. However, the variability in compositions of extrasolar systems inferred from the spectroscopic measurements of their parent stars implies that the identity, abundance and sequence of condensing phases should deviate from that of our Solar System. Here we perform Gibbs free energy minimisation with FactSage over temperatures from 1723 K to 473 K and 10^-4 bar total pressure to calculate the condensation sequence of 39 stellar compositions in the system H-C-O-Na-Mg-Al-Si-S-Ca-Ti-Fe-Ni that span the range from -0.4 to +0.4 dex. In accord with previous work, the C/O ratio of the gas plays a profound role in determining the mineralogy and order of condensing phases. Nebulae with 0.3 < C/O < 0.75 display broadly solar condensation sequences. Condensing nebulae with C/O > 0.75 exhibit strongly decreasing T_c⁵⁰ of lithophile elements whose condensation reactions depend upon the availability of oxygen (Ca, Al, Si, Ti, Mg) relative to those whose condensation does not (Fe, Ni). This trend is progressively reversed at very high C/O ratios for elements that form stable carbides, namely, TiC (C/O > 0.9) and SiC (C/O > 0.95), causing a dramatic increase in the T_c⁵⁰ of Ti and Si. The T_c⁵⁰ of S jumps from ~650 K below C/O = 0.75 to ~1100 K above C/O = 0.75 due to the condensation of oldhamite (CaS) and plateaus at higher C/O. The T_c⁵⁰ of Fe and Ni increase monotonically with Fe/H, and are fit to equations T_c⁵⁰(Fe) = 87.3(Fe/H) + 682 (r² = 0.999) and T_c⁵⁰(Ni) = 88.7(Fe/H) + 696 (r² = 0.999) valid for 7.08 < Fe/H < 7.95 and 0.3 < C/O < 0.95. As the C/O and Fe/H ratios are broadly correlated, only high metallicity stars are expected to produce nebula condensates whose compositions diverge drastically from those of our Solar System. Planets formed from these systems should be richer in Fe, Ni and S at the expense of Al and Ca.

How to cite: Sossi, P. and Wang, H.: The effect of stellar composition on nebular condensation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-188, https://doi.org/10.5194/epsc2022-188, 2022.

Rocky planets formed at different heliocentric distances from the Sun are thought to experience different and systematic devolatilization (i.e. depletion of volatile elements) with respect to the solar composition. The canonical empirical model of devolatilization is calibrated based on the bulk compositional difference between the Sun and Earth as a function of 50% condensation temperature of elements (T_C). The quantification of the volatility trends for other solar system rocky bodies, with a goal of formulating a general devolatilization model, has been expected to be useful for estimating the bulk compositions of rocky exoplanets orbiting at different distances to the central star in a planetary system.

To do so, we compiled an enormous set of literature data for the bulk compositions of a wide range of rocky bodies in our Solar System, including the terrestrial planets, asteroids, and chondritic bodies. Following the previous studies on quantifying Earth’s volatility trends, we adopted two relationship forms: one is in the log-log space (log (f) = α log (T_C) + β, where f is the bulk compositional ratio of a rocky body relative to the Sun; α and β are the model coefficients); and the other is in the linear space (f = 1/(1+e^-k(T-T0)), where T is the mid-plane temperature assuming the in-situ formation of these planetary bodies; and k and T0 are the model coefficients). Based on the best literature data that have been compiled, we did not find any statistically robust trend of devolatilization for these rocky bodies, except for Earth and Mars.  If we arbitrarily increase the uncertainties of the coefficients of the poorly quantified volatility trends for Venus and Mercury by a factor of 3, the best possible general trend that we can quantify as a function of heliocentric distance (d) is α = (3.773 ± 0.202)/d^3/4 and β = (-11.832 ± 0.613)/d^3/4. However, Mercury is still statistically deviated (towards a larger slope and thus severer devolatilization) from the general trend. We find the similar behaviour if we adopt the alternative sigmoid function. This may imply a more violent thermal history that Mercury experienced during its formation, beyond what can be constrained with the assumptions of the in-situ formation and stellar-irradiation-relevant-only devolatilization. Furthermore, Vesta and ordinary and carbonaceous chondrites do not follow this nominal general trend, either.

We therefore report here that no universal devolatilization trend has been found (empirically) for the solar system rocky bodies. This null result warrants the future efforts in advancing this field on two fundamental aspects. One is to further improve the measurements of the compositions of the solar system objects through various missions. The other is to launch a comprehensive investigation of nebular condensation, disc evolution, hydrodynamic escape, accretionary dynamics, and impacts towards establishing a sophisticated planet formation model of both dynamics and chemistry.

How to cite: Lin, W.-J., Wang, H., Hunt, A., and Quanz, S.: No universal devolatilization trend has been found for the solar system rocky bodies, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-678, https://doi.org/10.5194/epsc2022-678, 2022.

How to cite: Schwarz, K.: The Evolution of Volatile Carbon During Planet Formation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-316, https://doi.org/10.5194/epsc2022-316, 2022.

Introduction

The inner solar system is significantly depleted in carbon when compared to the interstellar medium, Observations suggest that the meteorites that formed early in the inner solar system are severely carbon deficit ([1]). The reason for the deficit is surprisingly unknown. Delving into why planet forming dust lose their carbon would give us important insights into the puzzle of planet formation. There have been efforts previously to address this puzzle but do not properly consider dust collisional growth ([2], [3]). We use a Monte Carlo dust evolution code that implements the physics of vertical settling, turbulent mixing and dust coagulation to explore how efficiently high energy stellar radiation can deplete carbon when dust collisional growth is considered. 

Methods

We use a Monte Carlo code for dust coagulation that uses a representative particle approach ([4]). We introduce bouncing as one of the collisional outcomes and compare the distributions arrived with and without bouncing. We then track the carbon fraction of the representative particles. Vertical settling and mixing are the major driving mechanisms for the vertical dust grain movement. As these particles get exposed to the Far ultra violet (FUV) photons, they undergo photolysis. Fig. 1 shows the vertical profile of the model and the processes the dust grains undergo. 

Fig 1: The vertical profile of the 1D model we use for investigation of photolysis in protoplanetary disks

Modelling photolysis requires an accurate description of the regions in the disk surface exposed to far-ultraviolet radiation (FUV). We find that the forward scattering nature of the dust grains and resonant scattering effects help the high energy (FUV) photons penetrate deeper into the disk. We devise a simple analytical model that takes into account the scattering of FUV photons and Ly-α photons ([5]).We make use of scattering phase function to find the probabilities of being scattered forward and downward, as these are the important directions that propagate FUV flux through the disk. We benchmark our analytical FUV model with a simulation from the sophisticated astrochemical code DALI ([6]). We find that our model is very much in agreement with the results of the code at lower optical depths, τ < =1. This is where most of the FUV flux resides thereby leading to a major chunk of carbon being lost in this region.

Results

Our results allow better modelling of carbon depletion in protoplanetary disks and stress the importance of collisional redistribution of species that acts as a way to replenish carbon to the exposed layers. This can be seen in the no collisions case in Fig 2.

Fig 2: The time evolution of three runs, (left) a simulation with collisions and mixing, (centre) without mixing and (right) without collisions. The simulations without collisions stresses the importance of collisions as a way to transport and replenish carbon to accelerate carbon depletion.

We present carbon destruction rates and the timescale of carbon depletion in the simulation at 1 AU and compare it with the present calculations. We arrive at depletion timescales ranging from 140-300 Kyr for different α parameter values as seen in Fig 3. When bouncing is included, the depletion is slower than in a no bouncing case. With our results, although we arrive at faster timescales than previous literature, it is not as fast as to deplete carbon before radial mixing of the outer disk species takes place. But recent evidence suggests that in the early solar system, the planet formation histories of the inner and outer disks are bifurcated due to weak radial mixing ([7]). Further work is needed to look into this aspect of radial mixing. We conclude that, although the photolysis alone is not likely to be the solution to the carbon deficit in the inner solar system, it is still an important process to take into account when developing quantitative predictions for the elemental composition of rocky exoplanets.

Fig 3. Carbon depletion time scale vs the α parameter for both the Analytical model and the DALI model.

References

How to cite: Vaikundaraman, V., Drążkowska, J., Binkert, F., Birnstiel, T., and Miotello, A.: Altered Carbon : Destruction of carbon in protoplanetary disks using Monte Carlo simulations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-647, https://doi.org/10.5194/epsc2022-647, 2022.

Sticking properties play an important role in the early phase of planet formation. In the protoplanetary disc, grains drift towards the star, being exposed to increasingly higher temperatures. Tensile strength measurements by means of the Brazilian test along with results from Mössbauer spectroscopy suggest that there is a spacial region that favours planetesimal formation between 900 K and 1300 K [1,2]. 

For the Brazilian test pieces of two meteorites, namely Sayh al Uhaymir 001 and Allende, were milled to micrometer dust, pressed into cylinders, and tempered at increasing temperatures up to 1400 K before the tensile strength measurement. The Sayh al Uhaymir is an L4/5 type chondrite that has undergone a slight thermal metamorphosis. The Allende however is classified as CV3. It is unequilibrated and therefore the closest to a realistic mix of minerals in the protoplanetary disc. Comparing sticking properties in terms of surface energies in relation to the heating temperature of the two different meteorite samples, they show no significant difference for heating under vacuum. Both datasets show a considerable increase in sticking around 1200 K by orders of magnitude. The new Allende data fits the older Sayh al Uhaymir data in this respect. This confirms the former found location in the warm inner disc that supports planetesimal formation best.

The most abundant element in protoplanetary discs is gaseous hydrogen. To see how the presence of hydrogen might influence the results, we followed the same measurement procedure but tempering in a continuous hydrogen atmosphere. The heating chamber is flushed with hydrogen during the entire heating process. This also does not produce any significant change in the results. The relative surface energies still increase monotonously and rise by orders of magnitude around 1200 K. 

We see an influence of composition and atmosphere as well as water content, grain size and morphology on sticking properties. Overall, also our new results not only suggest subtle changes but imply a boost in surface energy for high-temperature dust. This continues to support the idea of a hot spot around 1200 K that favours aggregation and might trigger a high number of planetesimals and subsequently  planets in the inner part of protoplanetary discs [in prep]. 

[1] Bogdan, T., Pillich, C., Landers, J., Wende, H., & Wurm, G. (2020). Drifting inwards in protoplanetary discs I: Sticking of chondritic dust at increasing temperatures. Astronomy & Astrophysics, 638, A151.

[2] Pillich, C., Bogdan, T., Landers, J., Wurm, G. & Wende, H., (2021). Drifting inwards in protoplanetary discs II: The influence of water on sticking properties at increasing temperatures. Astronomy & Astrophysics, 652, A106.

How to cite: Bogdan, T., Pillich, C., Landers, J., Wende, H., and Wurm, G.: Influence of Early Formation Steps on Inner Planetary System Architecture and Composition: High-temperature dust boosts planetesimal formation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-235, https://doi.org/10.5194/epsc2022-235, 2022.

In many ways the architecture of the Trappist-1 system resembles that of the Galilean moons orbiting around Jupiter. With seven confirmed planet, including three terrestrial planets in the habitable zone, it is a unique laboratory to study planetary formation scenarios. Recent results derived from interior modelling show a gradient in the planets’ water mass fractions (WMF). From little to no water to an estimated WMF of 10%, this gradient is puzzling formation models considering that all planets’ orbits are inside the system’s snow line. A mean to bring water inside the snow line is to consider the dihydroxylation of hydrated minerals. Phyllosilicates are good candidates as they can carry up to 10% of water in mass. With a 1+1D proto- stellar nebula toy model (PSN), we study the effect of a water vapor source at the location of the dehydroxylation of particles dominated by phyllosilicates. One major unknown remains however the dehydroxylation temperature of phyllosilicates under PSN thermodynamic conditions. We have then used three plausible devolatilization temperatures, namely 400 K, 600 K and 800 K. We show that the water vapor released from phyllosilicates can increase the water ice abundance located at the snowline. Those enrichments range from 2 to 5 times the initial water abundance in phyllosilicates.

How to cite: Schneeberger, A. and Mousis, O.: Phyllosilicates as a source of water in the Trappist-1 protoplanetary disk, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-421, https://doi.org/10.5194/epsc2022-421, 2022.

Photosynthesis in our planet sustains all life by converting the radiation from our Sun to chemical energy. This metabolic route only requires water and carbon dioxide (Hall & Rao 1999; Blankenship 2021) to be present in any exoplanet retaining an atmosphere (Hu et al. 2012; Trifonov et al. 2021) and transform the light from its host star to a biological source of energy.

We came up with an algorithm that combines the characteristics of an exoplanet and its atmosphere, its host star and some photosynthetic systems for assessing the feasibility of photosynthetic activity in an exoplanetary system.

This algorithm provides a new metric, the total absorption rate, γt, for evaluating the likeliness of detecting biomarkers from the live organisms producing photosynthesis in that system. It can also be figured as an indicator of the evolutionary path of primeval pigments, and can help us understand the steps that led to the highly evolved chlorophylls and analogues existing on the Earth (García de la Concepción et al., subm.).

There are some previous metrics related to this topic like the photosynthetic photon flux density, or the total stellar irradiance, but do not provide with absolute quantitative results.

We compare these metrics that relate the spectral type of the host star, the composition and properties of the atmosphere of the planet, and the different varieties of photopigments that they might host (Kiang et al. 2007; Komatsu et al. 2015; Gale & Wandel 2017; Ritchie et al. 2018; Mullan & Bais 2018; Lehmer et al. 2018, 2021; Lingam & Loeb 2019, 2020; Covone et al. 2021; Lingam et al. 2021) to the total absorption rate.

References:

Blankenship, R. E. 2021, Molecular mechanisms of photosynthesis (John Wiley & Sons)

Covone, G., Ienco, R. M., Cacciapuoti, L., & Inno, L. 2021, Monthly Notices of the Royal Astronomical Society, 505, 3329

Gale, J. & Wandel, A. 2017, International Journal of Astrobiology, 16, 1

Hall, D. O. & Rao, K. 1999, Photosynthesis (Cambridge University Press)

Hu, R., Seager, S., & Bains, W. 2012, Astrophysical Journal, 761 [arXiv:1210.6885]

Kiang, N. Y., Segura, A., Tinetti, G., et al. 2007, Astrobiology, 7, 252, pMID:17407410

Komatsu, Y., Umemura, M., Shoji, M., et al. 2015, International Journal of Astrobiology, 14, 505–510

Lehmer, O. R., Catling, D. C., Parenteau, M. N., & Hoehler, T. M. 2018, The Astrophysical Journal, 859, 171 

Lehmer, O. R., Catling, D. C., Parenteau, M. N., Kiang, N. Y., & Hoehler, T. M. 2021, Frontiers in Astronomy and Space Sciences, 8

Lingam, M., Balbi, A., & Mahajan, S. M. 2021, The Astrophysical Journal Letters, 921, L41

Lingam, M. & Loeb, A. 2019, Monthly Notices of the Royal Astronomical Society, 485, 5924

Lingam, M. & Loeb, A. 2020, The Astrophysical Journal Letters, 889, l15

Mullan, D. J. & Bais, H. P. 2018, The Astrophysical Journal, 865, 101

Ritchie, R. J., Larkum, A. W., & Ribas, I. 2018, International Journal of Astrobiology, 17, 147–176

Trifonov, T., Caballero, J., Morales, J., et al. 2021, Science, 371, 1038

How to cite: Marcos-Arenal, P., Cerdán, L., Burillo-Villalobos, M., Fonseca-Bonilla, N., García de la Concepción, J., Gómez, F., and Caballero, J. A.: ExoPhot: Developing a new metric for measuring the fitness of photosystem activity in an exoplanetary environment., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-870, https://doi.org/10.5194/epsc2022-870, 2022.