Symposium 345 - Abstracts
Early life on Earth – tracing the physical/chemical process from non-living to living
Pross, Addy
The origin of life on Earth remains one of the most tantalizing scientific questions of all time. In this talk I will describe recent developments in the field that suggest that the chemical process by which inanimate matter was transformed into simplest life and Darwinian evolution are actually one single continuous process. Much of the basis for that unification comes from a new area of chemistry, termed systems chemistry. Studies in that area point to the existence of a previously unrecognized stability kind in nature, dynamic kinetic stability (DKS), applicable only to replicating systems, whether chemical or biological. Consideration of this ‘other’ stability kind allows the driving force for both chemical and biological evolution to be revealed, throwing new light on central biological questions, including what is life, how did it emerge, and how would one make it [1].Reference[1] A. Pross, What is life? How chemistry becomes biology, Oxford University Press, 2nd Ed., Oxford, 2016.
Star Formation in the solar neighborhood - surveys, generalities, simulations
Juvela, Mika
Star formation is a major cosmic process that started soon after the big bang and still continues, albeit at a decreasing rate. It is the formation of dense interstellar clouds, their fragmentation, andeventual collapse that gives birth to new stars. These steps are best studied using high-resolution observations of nearby regions in the Milky Way. The progress is following the improvement of infrared and radio wavelength instruments that are able to probe the inner cloud regions and thus directly the initial phases of the star-formation process. On the other hand, numerical simulations are already able to take into account most of the relevant physics and they provide another, sometimes more clear view into the general principles behind the star formation. The comparison of observations and simulations is particularly fruitful, to validate the models and to separate universal trends from the complexity of individual sources. I will review recent star-formation studies, touching on both observations and simulations and seeking connections between the two.
Constraining the early evolution of terrestrial planets by reproducing elemental ratios
Lammer, Helmut
Compositional variations between the solar nebula, chondrites and the chemical abundances of the terrestrial planets provide evidence that some sort of elemental and isotopic fractionation should have taken place early in the history of the solar system. During the disk-embedded phase, early in the evolutionary history of the solar system, protoplanetary cores are believed to accumulate hydrogen gas and to form thin planetary H2-envelopes. According to the “Grant-Tack” scenario, those protoplanetary cores (proto-Earth and proto-Venus) should have accumulated a size of 0.5-0.75 Earth- and Venus-masses, respectively, until the solar nebular evaporated. Afterwards, EUV-driven hydrodynamic escape started to slowly erode the accumulated hydrogen-envelopes of the proto-planets. In addition, constant bombardment of impacting material, delivered further material to growing proto-Earth and -Venus. Lighter elements, such as potassium (K) compared to uranium (U), as well as isotopes, as for example 36Ar compared to 38Ar, or 20Ne compared to 22Ne can escape easier from proto-Earth and proto-Venus due to H-drag from a nebula-captures hydrogen-envelope compared to a magma ocean related outgassed steam atmosphere, whereas heavier elements and isotopes cannot be dragged away that easily. Simulations of the hydrodynamic escape of the accumulated hydrogen envelope around proto-Earth and proto-Venus show that this effect can explain initial compositional variations between the terrestrial planets and the solar nebula. It is also shown that in the case of the Earth delivery of chondritic material is necessary to reproduce the observed fractionations. These model results are also supporting the Grant-Tack scenario, and are in agreement with 182Hf-182W chronometric fast accretion scenarios of the Earth with a late Moon-forming giant impact.
Formation and evolution of protoplanetary disks - observations and modeling of jets, disks, and disk substructures
Perez, Laura
Planet formation takes place in the gaseous and dusty disks that surround young stars, known as protoplanetary disks. With the advent of sensitive observations and together with developments in theory, our field is making rapid progress in understanding how the evolution of protoplanetary disks takes place, from its inception to the end result of a fully-formed planetary system. In this review, I will discuss how observations that trace both the dust and gas components of these systems inform us about their evolution, mass budget, and chemistry. Particularly, the process of disk evolution and planet formation will leave an imprint on the distribution of solid particles at different locations in a protoplanetary disk, and I will focus on recent observational results at high angular resolution in the sub-millimeter regime, which have revealed a variety of substructures present in these objects.
The Characterization and Properties of Earth-like Planets
Apai, Daniel
In this talk, I will review the observational challenges to characterize earth-sized (and possibly earth-like) planets. I will summarize our current knowledge on the properties of the small exoplanet population. I will also discuss how observations with future facilities will be able to further characterize the habitable zone rocky planet population and what observational strategies we may follow in identifying and confirming habitable planet candidates.
Early planetary atmospheres and surfaces, origin of the Earth's water, crust and atmosphere
Breuer, Doris
The origin of early planetary atmospheres is controversially discussed. There are two competing models, i.e. the atmosphere is either formed by outgassing from the interior or by a late delivery from comets or volatiles-rich asteroids after most of the planet has been formed. Of these models, the former is currently preferred. Meteorite compositions as well as radial mixing during accretion derived from planetary formation models suggest that the building blocks of the terrestrial planets contained some volatiles. Processes like dehydration by hydrous melting, oxidation, impact devolatilization, and in particular degassing during magma ocean solidification lead to a significant volatile loss of the interior and to the formation of a dense atmosphere during the early stages of planetary evolution. These processes also influenced the oxidation state of this early atmosphere, i.e. whether it was more strongly reduced or oxidized.Despite the efficient volatile loss, some water likely remained in the interior and was redistributed between silicate mantle, crust and atmosphere in the subsequent evolution. Under favourable temperature and pressure conditions, which depend on atmospheric pressure, composition and solar radiation, atmospheric water vapour condenses and precipitates on the surface. The main processes responsible for the redistribution of water are volcanic outgassing by partial melting of the silicate mantle and associated formation of the crust and recycling of water-rich crustal material. An important difference between the terrestrial planets is the predominant tectonic style on the planet. For the Earth with its plate tectonics, recycling of water is very efficient and can even balance the outgassing. For terrestrial planets in the stagnant lid regime of mantle convection such as Mars, the exchange of water between the interior and the surface/atmosphere is mainly in one direction and results in a continuous depletion of the interior.
Cosmic Pathways to Life: From Interstellar Molecules to the First Traces of Life (Plenary Talk)
Güdel, Manuel & IAU S345 SOC
Life on a planet like Earth has its roots in processes starting with the formation of interstellar clouds and first complex molecules. What follows is a sequence of events that are decisive for the success of eventual life formation: - the collapse of clouds to protostars in a cluster environment, - the onset of "chemical factories" inside protostellar disks, - the formation of a planetary system that remains dynamically stable with the right type of planet in the habitable zone, - the transport of sufficient amounts of water to such a planet, - the generation of a solid surface and an habitable atmosphere, - a clement interaction with the young host star, - the favorable formation of biomolecules on the planetary surface, - and eventually the steps to metabolism and reproduction of initial life forms.Many of these steps are still poorly understood and some of them appear unlikely, but recent research in this widely interdisciplinary field has provided surprising insights into the complex conditions for life. We present research highlights from a tale of several 100 million years of cosmic evolution from the interstellar medium to first life forms on a planet, emphasizing the sequence of critical events that must all succeed for life to emerge.
Physical and Chemical Properties of Planet Forming Disks
Kamp, Inga
VLT instruments and ALMA have revolutionized in the past five years our view and understanding of how disks turn into planetary systems. They provide exquisite insights into non-axisymmetric structures likely closely related to ongoing planet formation processes. This talk will review our current understanding of the physical properties (e.g. solid and gas mass content, snow and ice lines) and chemical composition of planet forming disks at ages of 1-few Myr, especially in the context of the planetary systems that are forming inside them. It will highlight recent advances achieved by means of consistent multi-wavelength studies of gas AND dust in protoplanetary disks.
Formation of Terrestrial Planets
Kokubo, Eiichiro
In the standard formation scenario of planetary systems, planets form from a protoplanetary disk that consists of gas and dust. The scenario can be divided into three stages: (1) formation of planetesimals from dust, (2) formation of protoplanets from planetesimals, and (3) formation of planets from protoplanets. In stage (1), planetesimals form from dust through some instability of a dust layer or coagulation of dust grains. Planetesimals are small building blocks of solid planets. Planetesimals grow by mutual collisions to protoplanets or planetary embryos through runaway and oligarchic growth in stage (2). The final stage (3) depends on a type of planets. The final stage of terrestrial planet formation is giant impacts among protoplanets while sweeping residual planetesimals. In the present talk, I review the elementary processes of terrestrial planet formation and also discuss the origin of the diversity of terrestrial planets.
The birth environment of the solar system constrained by the relative abundances of the radionuclides
Young, Edward
The relative abundances of the radionuclides in the solar system at the time of its birth are crucial arbiters for competing hypotheses regarding the birth environment of the sun. The presence of short-lived radionuclides, as evidenced by their decay products in meteorites, has been used to suggest that particular, sometimes exotic, stellar sources were proximal to the sun's birth environment. The recent confirmation of neutron star - neutron star (NS-NS) mergers and associated kilonovae as potentially dominant sources of r-process nuclides can be tested in the case of the solar birth environment using the relative abundances of the longer-lived nuclides. Critical analysis of the 15 radionuclides and their stable partners for which abundances and production ratios are well known suggests that the sun formed in a typical massive star-forming region (SFR). The apparent overabundances of short-lived radionuclides (e.g., 26Al, 41CA, 36Cl) in the early solar system appears to be an artifact of a heretofore under-appreciation for the important influences of enrichment by Wolf-Rayet winds in SFRs. The long-lived nuclides (e.g., 238U, 244Pu, 247Cr, 129I) are consistent with an average time interval between production events of 108 years, seemingly too short to be the products of NS-NS mergers alone. The relative abundances of all of these nuclides can be explained by their mean decay lifetimes and an average residence time in the ISM of ~ 200 Myr. This residence time evidenced by the radionuclides is consistent with the average lifetime of dust in the ISM and the timescale for converting molecular cloud mass to stars.
Star formation in cloud cores – simulations and observations of dense molecular cores and the formation of solar mass stars
Federrath, Christoph
I will present an invited review on star formation in molecular cloud cores. The focus will be on the roles of gravity, turbulence, magnetic fields and feedback (jets and radiation) for the star formation rate and the initial mass function of stars.
Kinematics of OB-associations in the 3-kpc solar neighborhood
Melnik, Anna
We use Gaia stellar proper motions to study the kinematics of OB-associations. The average one-dimensional velocity dispersion inside 18 OB-associations with more than 10 Gaia stars is sigmav=3.9 km s-1. The median virial and stellar masses of OB-associations equal 7.1 105 and 9.0 103 solar masses, respectively. Thus OB-associations must be unbound objects provided they do not include a lot of dense gas. The median star-formation efficiency is epsilon=2.1%. Nearly one third of stars of OB-associations must lie outside their tidal radius. We found that the Per OB1 and Car OB1 associations are expanding with the expansion started in a small region of 11--27 pc 7--10 Myr ago. The average expansion velocity is 6.3 km s-1. The location of the Sun near the OLR of the bar creates conditions which stimulate formation of giant molecular clouds.
Unveiling the whole from its parts. Or to see the forest from its parts
Pacheco, Eduardo
If DNA molecules were present in the interstellar medium, their observed spectral signatures would be rather complicated. Even the molecular array of a unique dinucleotide will generate a tangled signature. On the other hand, a part of it, e.g. bands of the simpler group of HNCO (isocianic acid) may be detected as a part from the whole, but being confused as coming from an isolated HNCO molecule. We selected 5 key transitions of parts of purines and pyrimidines that have been observed in the ISM as isolated molecules and propose to look for them in molecular clouds. If the ensemble of the 5 transitions are observed together in the same target, it may be that we are detecting the whole from its part.
ALMA observations of the Orion Integral Filament: evidence for fibers in a massive cloud
Hacar, Alvaro
We have investigated the dense gas substructure of the Integral Shape Filament (ISF) in Orion combining ALMA and single-dish observations down to resolutions of 0.009pc. Our analysis of the gas kinematics demonstrates that this massive filaments is actually a collection of 55 dense fibers forming a complex bundle with multiple hub-like associations. The ISF fibers show transonic internal motions respect their local sound speed, lengths of ~0.15 pc, and a mass distribution consistent with hydrostatic equilibrium. Within this complex network, the ISF fibers show a compact radial emission profile with a median FWHM of 0.035 pc systematically narrower than the previously proposed universal 0.1 pc filament width. Our new ALMA observations suggest strong similarities between the internal substructure of this massive filament and previously studied lower-mass objects. The fibers show identical dynamic properties in both low- and high-mass regions, and their widespread detection in nearby clouds suggests a preferred organizational mechanism of gas in which the physical fiber dimensions (width and length) are self-regulated depending on their intrinsic gas density. Combining these results with previous works in Musca, Taurus, and Perseus, we identify a systematic increase of the surface density of fibers as a function of the total mass per-unit-length in filamentary clouds. Based on this empirical correlation, during my talk I will discuss a possible unified star-formation scenario where the observed differences between low- and high-mass clouds, and the origin of clusters, emerge naturally from the initial concentration of fibers. Referenece: Hacar et al 2018, arXiv:1801.01500v1 See also: ORION-4D project website
The implications of clustered star formation for (proto)planetary systems and habitability
Kruijssen, Diederik
Star formation is spatially clustered, such that radiative or dynamical interactions with neighbouring stars may disrupt (proto)planetary systems, leaving a lasting impact on their potential habitability. For decades, the commonly-adopted picture has been that all stars and planetary systems form in compact clusters that subsequently disperse, with important implications for the early evolution of (proto)planetary systems. I will present our group's recent theoretical and observational work showing that the classical picture is inaccurate. Our work reveals a broad range of formation environments, from dense stellar clusters to associations spanning tens of pc that formed in-situ. In the solar neighbourhood, we find that the vast majority of stars form in unbound associations, in which the interaction of (proto)planetary systems with neighbouring stars is extremely limited. However, the fraction of star formation occurring in compact clusters was considerably higher in the past, peaking at >50% in the young Milky Way. Focusing on those (proto)planetary systems that do form in clusters, I will proceed to show how their stability and potential habitability are affected by the host cluster. Both observations and theory show that the protoplanetary disc mass function is largely unchanged, but the disc radii are strongly truncated. This is driven by the single closest encounter with a neighbouring star, rather than the combined effect of many distant encounters. Together, these results demonstrate that the large-scale star formation environment is critical in determining the occupation probability of the habitable zone.
Water inventory from beyond the Jupiter orbit to the terrestrial planets and the Moon
Marov, Mikhail
?omputer simulations of migration of planetesimals from beyond the Jupiter’s orbit to the forming terrestrial planets are discussed. Probabilities of collisions of planetesimals with planets, the Moon, and their embryos based on orbital elements of planets and planetesimals during their dynamical lifetimes were evaluated. The results of modeling argue that provided the total mass of planetesimals amounted to ~ 200 Earth’s masses, the mass of water delivered to Earth from beyond the Jupiter orbit could be about the mass of terrestrial oceans. The water received by the Earth’s embryo of a half of its present mass from the same regions was estimated ~ 30% of the total water mass delivery. We assume that both exogenic and endogenic sources were responsible for the Earth water resources. While bodies similar to C-asteroids appeared to deliver a considerable fraction of water, endogenic water exiled from the Earth interior could balance the high D/H ratio pertinent to comets. The water inventory to the terrestrial planets from beyond the Jupiter orbit was assessed when normalizing water mass to that of a planet. For Venus and Mercury it turned out nearly the same as for Earth while for Mars it was by the factor of about 2-3 more implying that absolute value of water was 3 to 5 times smaller. The mass of water delivered from beyond the Jupiter orbit to the Moon per unit its mass was estimated to be about 20 times smaller than for Earth or in absolute values up to 3·1023 kg. The work was supported by the grant of Russian Science Foundation N 17-17-01279 (planetesimals migration to the Moon) and by the Program of Fundamental Studies of the Presidium of RAS ? 17 as a part of Russian state program for GEOKHI N 00137-2018-0030 (migration of planetesimals to the terrestrial planets and influence of initial orbits of the giant planets on migration of planetesimals and planets).
Formation of the Earth-Moon system
Ipatov, Sergei
Computer simulations showed [1-2] that trans-Neptunian satellite systems and embryos of the Earth and the Moon could be formed as a result of contraction of rarefied condensations. The angular momenta of condensations needed for formation of trans-Neptunian satellite systems could be acquired at collisions of condensations [3-4]. The same conclusion is true for the Earth-Moon system. The angular momentum of the present Earth-Moon system could be acquired at a collision of two rarefied condensations with a total mass not smaller than 0.1ME, where ME is the mass of the Earth. The mass of the condensation that was a parent for the embryos of the Earth and the Moon could be about 0.01ME, if we take into account the growth of the angular momentum of the embryos at the time when they accumulated solid planetesimals. In order to explain small fraction of iron in the Moon, it is needed that the mass of the Moon embryo increased by no more than 1.3 times. For such Moon growth, the mass of the Earth embryo that accumulated planetesimals would increase by no more than a factor of 3. The initial masses of embryos of the Earth and the Moon could be small if the Moon embryo accumulated mainly iron depleted bodies ejected from the Earth embryo in numerous collisions of planetesimals with the Earth embryo. The work was supported by the grant of Russian Science Foundation N 17-17-01279 (formation and growth of the embryos of the Earth and the Moon) and by the Program of Fundamental Studies of the Presidium of RAS ? 28 as a part of state program for GEOKHI N 00137-2018-0033 (studies of the angular momenta of colliding celestial objects). [1] Nesvorny D., et al. Astron. J. 2010. 140. 785-793. [2] Galimov E.M., Krivtsov A.M. Origin of the Moon. New concept / De Gruyter. Berlin, 2012, 168 p. [3] Ipatov S.I. Solar System Research, 2017. 51. 321-343. https://arxiv.org/abs/1801.05217. [4] Ipatov S.I. Solar System Research, 2017. 51. 409–416. https://arxiv.org/abs/1801.05254.
Bio-habitability and life on planets of M- to G-type stars
Wandel, Amri
The recent detection of Earth-sized planets in the habitable zone of Proxima Centauri, Trappist-1, and many other nearby M-type stars (which consist some 75% of the stars) has led to speculations, whether liquid water and life actually exist on these planets. Defining the bio-habitable zone, where liquid water and complex organic molecules can survive on at least part of the planetary surface, we suggest that planets orbiting M-type stars may have life-supporting conditions for a wide range of atmospheric properties (Wandel 2018, ApJ in press). We extend this analyses to locked planets of K- and G-type stars and discuss the implications for the evolution and sustaining of life, in particular, oxygenic photosynthesis, in analogy to early Earth, as well as to present Earth extreme environments.
Triggered Star Formation inside the Shell of a Wolf–Rayet Bubble as the Origin of the Solar System
DWARKADAS, VIKRAM
A critical constraint on solar system formation is the high 26Al/27Al abundance ratio of 5 x 10-5 at the time of formation, which was about 17 times higher than the average Galactic ratio, while the 60Fe/56Fe value was about 2 x 10-8, lower than the Galactic value of 3 x 10-7. This challenges the assumption that a nearby supernova was responsible for the injection of these short-lived radionuclides into the early solar system. We show that this conundrum can be resolved if the Solar System was formed by triggered star formation at the edge of a Wolf-Rayet (W-R) bubble. Aluminium-26 is produced during the evolution of the massive star, released in the wind during the W-R phase, and condenses into dust grains (that have been observed around W-R stars in IR observations). The dust grains survive passage through the reverse shock and the low density shocked wind, reach the dense shell swept-up by the bubble, detach from the decelerated wind and are injected into the shell. The dust grains will be destroyed by grain evaporation or non-thermal sputtering, releasing the 26Al into the shell. Some portions of this shell subsequently collapses to form the dense cores that give rise to solar-type systems. The star will either collapse directly to a black hole, as in some models, or give rise to a supernova explosion. Even if the latter, the aspherical supernova does not inject appreciable amounts of 60Fe into the proto-solar-system, thus accounting for the observed low abundance of 60Fe. We discuss the details of various processes within the model using numerical simulations, as well as nucleosynthesis modelling, and analytic and semi-analytic calculations. We conclude that it is a viable model that can explain the initial abundances of 26Al and 60Fe. We estimate that 1%–16% of all Sun-like stars could have formed in such a setting of triggered star formation in the shell of a W–R bubble.
Exoplanet host-star properties: the active environment of exoplanets
Pye, John
Seven institutes in Europe have combined their expertise in the field of exoplanetary research to develop the European Horizon-2020 ExoplANETS_A project (Grant Agreement no. 776403; started January 2018) under the coordination of CEA Saclay. In the framework of the project, novel data calibration and spectral extraction tools, as well as novel retrieval tools, based on 3D models of exoplanet atmospheres, will be developed to exploit archival data from space- and ground-based observatories, and produce a homogeneous and reliable characterization of the atmospheres of transiting exoplanets. Additionally, to model successfully the exoplanet atmosphere, it is necessary to have a sound knowledge of the host star. To this end, we will collect a coherent and uniform database of the relevant properties of host stars from online archives (e.g. XMM-Newton, GAIA) and publications. These exoplanet and host-star catalogues will be accompanied by computer models to assess the importance of star – planet interactions, for example the ‘space weather’ effects of the star on its planetary system. The knowledge gained from this project will be published through peer-reviewed scientific journals and modelling tools will be publicly released. In this paper, we present early results from the host-star investigations, including the basic observational and physical properties of the systems, and indications of future observations needed to maximize the coverage of the target list (of ~50 – 100 systems).
Towards Realistic Understandings of Gas Dynamics in Protoplanetary Disks
Bai, Xuening
The gas dynamics and long-term evolution of protoplanetary disks (PPDs) play a crucial role in almost all stages of planet formation, yet they are far from being well understood largely due to the complex interplay among various microphysical processes. Primarily, PPD gas dynamics is likely governed by magnetic field, and its coupling with the weakly ionized gas is described by non-ideal magnetohydrodynamic (MHD) effects. Incorporating these effects, I will present the first fully global simulations of PPDs aiming to incorporate most realistic disk microphysics. Accretion and disk evolution is primarily driven by magnetized disk winds with significant mass loss comparable to accretion rate. The overall disk gas dynamics strongly depends on the polarity of large-scale poloidal magnetic field threading the disk owing to the Hall effect. The flow structure in the disk is highly unconventional with major implications on planet formation.
Short-lived radioisotopes in meteorites from Galactic-scale correlated star formation
Fujimoto, Yusuke
Meteoritic evidence shows that the Solar system at birth contained significant quantities of short-lived radioisotopes (SLRs) such as 60Fe (with a half-life of 2.6 Myr) and 26Al (with a half-life of 0.7 Myr) produced in supernova explosions and in the Wolf-Rayet winds that precede them. Proposed explanations for the high SLR abundance include formation of the Sun in a supernova-triggered collapse or in a giant molecular cloud (GMC) that was massive enough to survive multiple supernovae (SNe) and confine their ejecta. However, the former scenario is possible only if the Sun is a rare outlier among massive stars, while the latter appears to be inconsistent with the observation that 26Al is distributed with a scale height significantly larger than GMCs. We present a high-resolution chemo-hydrodynamical simulation of the entire Milky Way Galaxy, including stochastic star formation, HII regions, SNe, and element injection, that allows us to measure for the distribution of 60Fe/56Fe and 26Al/27Al ratios over all stars in the Galaxy. We show that the Solar System's abundance ratios are well within the normal range, but that SLRs originate neither from triggering nor from confinement in long-lived clouds as previously conjectured. Instead, we find that SLRs are abundant in newborn stars because star formation is correlated on galactic scales, so that ejecta preferentially enrich atomic gas that will subsequently be accreted onto existing GMCs or will form new ones. Thus new generations of stars preferentially form in patches of the Galaxy contaminated by previous generations of stellar winds and supernovae.
New insights into the complex chemistry of young stars from the ALMA PILS survey
Jorgensen, Jes Kristian
One of the most important problems of astrochemistry is to understand how, when and where complex organic and potentially prebiotic molecules are formed - and the link between the rich chemistry observed toward some star-forming regions and the emerging Solar System. From an observational point of view, ALMA is revolutionizing the field with its high sensitivity for faint lines, high spectral resolution limiting line confusion, and high angular resolution making it possible to study the structure of young protostars down to scales of their emerging protoplanetary disks.In this talk, I will present an overview of some of the results from a large ALMA survey of the low-mass protostellar binary and astrochemical template source, IRAS 16293-2422. The program, "Protostellar Interferometric Line Survey (PILS)", is more than an order of magnitude more sensitive than previous surveys of chemical complexity and provide images of the inner 25 AU of the gas around each of the young stars. The high sensitivity and spectral resolution of ALMA has allowed us to detect a wealth of previously undetected species in this object and the ISM in general - for example, molecules of importance for prebiotic chemistry such as peptide-bond containing molecules (Ligterink et al. 2017) and simple sugars (Jørgensen et al. 2012), as well as species that can be used to link protostars in the earliest stages of their evolution to our own Solar System such as measurements of methyl chloride and sulfur-molecules toward Comet 67P and IRAS 16293-2422 (Fayolle et al. 2017; Drozdovskaya et al. 2018). Also, the data show the presence of numerous rare isotopologues of complex organic molecules and other species (e.g., Coutens et al. 2016, 2018; Jørgensen et al. 2016; Persson et al. 2018): the exact measurements of the abundances of these isotopologues shed new light onto the formation of the complex molecules and provide a chemical link between the embedded protostellar stages and the early Solar System.
Resolving star and planet formation with ALMA
Bjerkeli, Per
Disks around young stars are the sites of planet formation. As such, the physical and chemical structure of disks have direct impact on the formation of planetary bodies. The innermost disk regions are particularly interesting, due to the potential for planet formation. These are also the regions where winds, capable of affecting the disk build-up itself, are launched magnetically. Until very recently, we have lacked the facilities to provide the necessary observational constraints and insights into what is actually going on the smallest scales during the earliest stages of solar system formation, meaning it is completely uncharted territory.Within the framework of the "Resolving star formation with ALMA" program (PI: P. Bjerkeli), we are targeting young disks and outflows with ALMA in its largest possible configuration (16 km baselines, yielding a resolution of 2-6 au) to zoom in on early disk evolution, outflow launching, and star- and planet-formation. We will here present an overview of the program, focusing on the first/initial results. The first resolved images of outflow launching from a disk were recently reported towards the Class I source TMC1A (P. Bjerkeli, et al., 2016, Nature, 540, 406). Since then, we have continued our observations towards TMC1A and in addition included a younger system in the study. The observations allow us to constrain the detailed kinematics and structure of the disks (D. Harsono et al., in prep.), but also to constrain the launching mechanism and the physical properties of outflows on the smallest scales (e.g. mass and momentum; M. H. D. van der Wiel, et al., in prep.).
A mid-infrared interferometric survey of the planet-forming region around young Sun-like stars
Varga, Jozsef
The 0.5-10 au region of the dense circumstellar disks around the few million years old T Tauri stars is the cradle where planets similar to the Earth and her rocky planet sisters were formed. The small size of the region makes it challenging to obtain spatially resolved information about the physical, chemical and mineralogical conditions in the inner disk area. Mid-infrared interferometry is the only tool to do that, thus star formation was one of the main driving science case behind the 13-years mission of the MIDI interferometer at ESO's Paranal Observatory. When dismounted in 2015, MIDI left behind a rich archive of young stellar object observations. Motivated by the opportunity, our group recently carried out a homogeneous data processing and analysis of 82 low- and intermediate-mass young stellar objects. From a simple geometric disk modeling we typically found continuous disk geometries, but in a few objects a model with an inner gap with radii ranging from 0.5 to 10 au gave a better match. The mid-infrared size of the disks scales with the stellar luminosity, although the correlation is much weaker than in the near-infrared. This suggests that the 1-10 au disk region has more diverse structure than the inner 1 au region. Once we account for differences in stellar luminosity, the disks around Sun-like stars are generally colder and more extended, than disks around intermediate-mass stars. The interferometric measurements on the profile and amplitude of the 10 micrometer silicate spectral feature revealed that the dust in the inner disk is more processed (coagulated, crystallized). T Tauri stars typically show weaker silicate emission than Herbig Ae stars, which may indicate that the disk flaring is less pronounced. Our atlas made possible the so-far most complete spatially resolved statistical study of the terrestrial planet forming zone around young Sun-like stars, and the results will provide valuable input for future instruments like VLTI/MATISSE or JWST.
The First 200 kyr of the Solar System
Pignatale, Francesco
Chondrites are the most puzzling objects in the Solar System as they are made of minerals that experienced different thermal histories. Carbonaceous chondrites, that are thought to have assembled in the outer cooler region of the Solar System, are, paradoxically, the richest in high refractory material that should have formed close to the Sun. The mechanisms that led to the formation and accretion of chondrites are still unconstrained.The age of their oldest components (Ca-Al-rich inclusions, CAIs) shows that their building blocks could have formed concurrently with the Sun, during the collapse of the parent cloud that formed our Solar System. Here we investigate, for the first time, the dynamical and chemical evolution of different solids from the collapsing cloud to their transport in the forming protoplanetary disk. Our 1D disk model includes several processes such as gas and dust condensation/evaporation, dust growth/fragmentation, radiative and viscous heating, dead zone and a cloud infall in the form of a source term.We find that the interplay among (1) the location in which material is injected in the disk from the cloud, (2) the physical and thermal properties of the considered material, (3) the disc dynamics and (4) several flash-heating events, naturally produces aggregates where components with different thermal histories can coexist.Moreover, the disk expansion causes an efficient advection of refractory material towards large radii. The dead zone plays a crucial role in creating and keeping an heterogeneous mixture of dust. Our results also reconciles with the CAIs production timescales and their distribution in chondrites without including any other mechanism of outward transport of material in the disk. The observed strong flash-heating events can then be responsible for CAIs re-heating and chondrule formation.
Outbursts of young Sun-like stars may change how terrestrial planets form
Abraham, Peter
While the Sun is nowadays a quiet and well-balanced star, in its first few million years it might have been often out of temper, like those young low-mass stars which episodically undergo unpredictable outbursts. The prototype of one of the two classes of young erupting stars, EX Lupi, had its historically largest outburst in 2008. It brightened by a factor of 30 for six months, due to elevated accretion from the circumstellar disk on to the star. Our group observed the system during the outburst, and discovered the crystallisation of amorphous silicate grains in the inner disk by the heat of the outburst (Ábrahám et al., Nature, 2009). Our mid-infrared monitoring of the freshly produced crystals revealed that their emission in the inner disk quickly dropped already within a year after the outburst (Juhász et al. 2012). Here we report on new observations of the 10 micrometer silicate feature, obtained with the MIDI and VISIR instruments at Paranal Observatory, which demonstrate that within four years practically all forsterite disappeared from the inner disk. We attempt to model this process by a stellar wind that transports the crystals from the terrestrial zone to outer disk regions where comets are supposed to assemble. We also performed ALMA observations of a set of key molecular lines, whose intensity - according to our chemical evolutionary models - should reflect how chemistry changed in the disk due to the extra irradiation provided by the outburst. Since the eruptions of EX Lup seem to be recurrent, we speculate that the early Sun also experienced similar brightenings, and the forming planetary system might have incorporated some of the mineralogical and chemical yields provided by the outbursts. EX Lup, as a proxy for the proto-Sun, may be a telltale object to help to understand the origin of molecules and minerals we routinely encounter on planet Earth.
Characterizing the youngest protostellar disks with the IRAM-PdBI and ALMA: large Class 0 disks are rare
Maury, Anaëlle
While large circumstellar disks are observed around young stars, only a handful of large (r>100 au) candidate protostellar disks have been detected around the youngest (Class 0) protostars so far. However, the pristine properties of circumstellar disks during the main accretion phase could be key in understanding their later evolution, and the way they ultimately form planets. Only the recent advent of powerful interferometric facilities probing km baselines at (sub-)mm wavelengths has allowed the inner envelopes of Class 0 protostars to be explored at resolutions and sensitivities sufficient to disentangle envelope from resolved disk emission at relevant scales (20--200 au).We will present our results with the IRAM-PdBI CALYPSO survey, establishing the paucity of young large disks: in this sample >75% of the 16 Class 0 protostars have no resolved disks at radii r>60 au. We will also present new follow-up observations obtained with the ALMA interferometer. We will discuss how these observations challenge the classical paradigm of disk formation as a natural result of angular momentum conservation, and argue in favor of magnetized protostellar collapse scenario.Finally, we will present our analysis of both the chemical complexity and multi-frequency dust continuum emission at scales ~100 au, suggesting that significant grain growth, maybe precursor to the formation of planetesimals, has already occured at these scales during the Class 0 stage.
Dynamics of protoplanets embedded in gas/pebble disks and its complex dependence on parameters
Broz, Miroslav
Several-Earth-mass protoplanets interact with the gaseous and pebble disk in a complex way. The hot-trail effect arises as a consequence of accretion heating, it raises planetary eccentricities, and may prevent resonant captures of migrating planets (see Chrenko et al. 2017, or Eklund & Masset 2017). Here we study the dependence of this effect and subsequent evolution on parameters such as the surface density, viscosity, pebble flux, mass, or the number of protoplanets. For modelling we use Fargo-Thorin 2D hydrocode which incorporates all necessary terms.In particular, for a disk with high surface density (3x MMSN) there are numerous "unsuccessful" two-body encounters which do not lead to a merger or a coorbital. Only later, when the 3rd embryo arrives to the convergence zone, three-body encounters lead to mergers. For a low-viscosity disk (10-6 in code units) there is a massive coorbital (two times 8 ME) as a possible outcome, for which a pebble isolation develops and the coorbital is further stabilised.Interestingly, for many low-mass protoplanets (120 times 0.1 ME) the dynamics is totally different, mostly because the spiral arms overlap with each other and affect not only a single protoplanet but many in the surroundings. The evolution of semimajor axes and eccentricities is no longer smooth, but rather random-walk. The latter task is computationally very expensive, because we need to resolve the Hill sphere, both in radial and tangential directions, fulfil the Courant condition, and compute disk->planet interactions for all of them, so it essentially scales as N4.
Unified Picture of Chemical Differentiation in Disk-Forming Regions of Low-Mass Protostellar Sources
Oya, Yoko
Young (Class 0-I) low-mass protostars are known to show significant chemical diversity in their envelopes at a few 1000 au scale: specifically, hot corino (HC) chemistry and warm carbon-chain chemistry (WCCC). HC sources are rich in saturated complex organic molecules (COMs: e.g. HCOOCH3), while WCCC sources in unsaturated carbon-chain molecules (e.g. C4H). It is of great interest how the chemical diversity is inherited to chemistry of disk-forming regions.We investigated distributions and kinematics of various molecules in the disk/envelope system for the 6 young low-mass protostar at a spatial resolution of a few 10 au with ALMA. We found that the chemical diversity at a few 1000 au scale is indeed delivered into the disk-forming regions at a 100 au scale. Moreover, the chemical composition was found to change drastically from envelopes to disks.Such chemical diversity in disk-forming regions was totally unexpected before the ALMA observations. Most interestingly, we found composite sources (L483 and B335) where both the WCCC and HC chemistry are occurring in a single source. In these sources, carbon-chains are abundant in the envelope as in the case of WCCC sources, while COMs are abundant in the disk as in the case of HC sources. This result is consistent with the chemical model of collapsing cores: HC chemistry emerges with the evaporation of COMs from dust grains in a hot (>100 K) region near the protostar, while WCCC is triggered by evaporation of CH4 in a warm (>30 K) region a bit apart from the protostar. Thus, the composite case harbors both rich COMs and rich CH4 on dust grains at the onset of star formation, and may be a common occurrence. In contrast, the HC and WCCC sources are regarded as distinct cases, where either COMs or CH4 are particularly abundant, respectively. This unified view of chemistry in disk-forming regions will be an important clue to tracing the chemical evolution from protostellar cores to protoplanetary disks.
Episodic accretion in focus: revealing the circumstellar environment of FU Orionis-type stars with millimeter interferometry
Fehér, Orsolya
The earliest phases of star formation are characterised by intense mass accretion from the circumstellar disk to the central star. FU Orionis-type stars (FUors) also exhibit accretion rate peaks accompanied by bright eruptions. These recurring outbursts might represent an important evolutionary period that may solve the luminosity problem of young stellar objects (YSOs), play a key role in accumulating the final star mass, and can have a significant effect on the parameters of the envelope and the disk, and consequently the processes of planet formation. In the framework of the Structured Accretion Disks ERC project at Konkoly Observatory we are conducting a systematic investigation of FUors to examine whether these outbursting objects represent normal embedded young stars in exceptional times (implying that all low-mass young stars undergo eruptive phases) or they are unusual objects.Using IRAM and PdBI/NOEMA millimeter wavelength single-dish and interferometric measurements we mapped the 12CO, 13CO, C18O and 2.7 mm continuum emission towards 12 northern FUors, reaching spatial resolutions of 2-4” (~1000 AU). We also surveyed the 108-116 GHz frequency range, searching for molecular transitions characteristic to young stellar systems. We revealed a diverse sample of circumstellar morphologies and identified internally heated, circular envelopes, outflows, envelope rotation, neighbouring sources and large-scale shock fronts. The detection of several molecular species (e.g. C17O, HC3N, SO, CN) can be used for chemical modeling of the circumstellar environments. Comparison of the envelope parameters among the FUors and to the parameters of quiescent YSOs show that some FUors are similar to embedded Class I stars, while others have only small envelopes, resembling Class II sources. This reinforces the theory that FUors are in a special evolutionary phase between the two classes and their infall-driven episodic eruptions are the main driving force of the transition.
Neutral atmospheric escape in the Solar and extrasolar planetary systems
Shematovich, Valery
New data obtained by space missions to various objects in the Solar system and observations of the outer Solar system and exoplanets by space and ground-based telescopes allowed us to conclude that the atmospheric escape plays an important role in the evolution of the terrestrial planets in the Solar system (Marov et al., 1996). Observations and theoretical models of the exoplanet atmospheres exposed to the extreme fluxes of X-ray and UV radiation of the parent star provide a remarkable opportunity to test theoretical understanding of the key processes - thermal and non-thermal escape. Such improved models of the neutral escape will lead to a better understanding of the paleoclimate and the evolution of the of primary and secondary atmospheres of terrestrial planets (Massol et al., 2016). It is known, that a prediction of escape rates due to thermal and nonthermal processes defines the long-term evolution of planetary atmospheres, therefore atmospheric escape has long been a subject of interest in the comparative planetology, and in recent years especially in understanding of the evolution of exoplanet atmospheres. A critical feature is that escape occurs in the rarefied atmosphere, which is usually called the exosphere, where the state of the gas is significantly nonequilibrium. Accordingly, continuum models are no longer applicable, so that only kinetic modeling at the molecular level of the description allows us to accurately predict the structure of the atmospheric gas flow and escape rate. The report presents the kinetic approach to the problem of neutral escape from planetary atmospheres. As an example, the recent measurements by Mars Express and MAVEN spacecraft are compared with the calculations of neutral escape with the aim to understand the atmospheric loss at Mars. Also the recent calculations (Ionov et al., 2018) of the mass-loss rates of the exoplanet atmospheres leading to the formation of hot Neptune desert will be presented.
The role of automated methods for filament finding in understanding the complex relationship between filaments, magnetic fields and star formtion
Cunningham, Maria
The discovery of the ubiquity of filaments in the interstellar medium in the last two decades has begged the question: "What role do filaments play in star formation?"Here we describe how our automated filament finding algorithms are combined with both magnetic field measurements, and high-resolution observations of dense cores in these filaments to provide a statistically large sample to investigate the effect of filaments on star formation.We find that filaments are likely actively accreting mass from the interstellar medium, explaining why some 60% of stars, and all massive stars form "on-filament".
Earth's paleo-magnetosphere and its implications on the evolution of the terrestrial atmosphere
Scherf, Manuel
The present-day terrestrial atmosphere is providing a habitable environment for a diverse range of life forms. However, simulations of the terrestrial paleo-magnetosphere as well as of the solar wind induced atmospheric ion-pickup escape ~4 Gyr ago are indicating that during the Hadean eon a nitrogen dominated atmosphere would not have been able to survive, but would have been eroded within a few Myr due to the strong EUV flux and solar wind of the early Sun. In addition, these results are suggesting that the present-day nitrogen-dominated atmosphere has its origin during later stages of the geological history, whereas for the late Hadean and early Archean, CO2 can be considered as the dominating atmospheric constituent. However, the 14N/15N disequilibrium between internal and surface reservoirs at the Earth is indicating that some atmospheric escape of nitrogen should have taken place in the past.Atmospheric escape is strongly coupled to the shape of the paleo-magnetosphere and to its interplay with the varying solar activity factors. Thus, we will present simulations of the terrestrial paleo-magnetosphere during the late Hadean and Archean eons and its influence on the evolution of the nitrogen atmosphere, including an estimation of N2 lost to space. Our results support the idea that the nitrogen dominated atmosphere started to build up during the Archean and evolved from a low-pressure atmosphere via outgassing of N2 into the present-day habitable environment. Important environmental conditions for this evolution will be discussed within this presentation. This also includes a potential solution for the before mentioned 14N/15N disequilibrium.Acknowledgement. The authors acknowledge the support of the FWF NFN project Pathways to “Habitability: From Disks to Active Stars, Planets and Life”, in particular its related sub-projects S11604-N16, S11606-N16 and S11607-N16. This is supported by the Austrian Science Fund (FWF) and the 550 US NSF (EAR1015269 to JAT).
Simulating putative Enceladus-like conditions: The possibility of biological methane production on Saturn's icy moon
Taubner, Ruth-Sophie
Enceladus is one of the most remarkable objects in the Solar System. Besides its spectacular plume located near its south pole, it is the origin of the plume particles which makes Enceladus to one of the hot spots in Astrobiology nowadays: a subsurface liquid water ocean (e.g., Cadek et al., 2016). The molecules detected in the plume (Waite et al., 2009) including water (H2O), carbon dioxide (CO2), and methane (CH4), in combination with the possibility of hydrothermal vents at the ocean floor (Hsu et al., 2015), lead to the assumption that this icy moon might be habitable for life as we know it. The final evidence for molecular hydrogen (H2) in the plume, produced most likely by serpentinization of olivine in the chondritic core (Waite et al., 2017), made this assumption even more likely.Possible life forms on Enceladus could be chemotrophic, i.e. independent of products of photosynthesis, and would need to be anaerobic, i.e. independent of molecular oxygen. Hydrogenotrophic methanogens, i.e. archaea that metabolize H2 and CO2 to produce CH4 and H2O, are among the organisms that meet these characteristics. In this study we raise the question, if some of the CH4 detected in the plume could in principle originate from biological activity.We tested three different methanogenic archaea (Methanothermococcus okinawensis, Methanothermobacter marburgensis, and Methanococcus villosus) under putative Enceladus-like conditions, i.e. high pressure experiments including tests on the tolerance towards potential gaseous and liquid inhibitors detected in Enceladus’ plume. In particular, M. okinawensis, an isolate from a deep marine trench (Takai et al., 2002), showed tolerance towards all of the added inhibitors and continue performing methanogenese also for experimental pressure comprised between 3 and 50 bar (Taubner et al., 2018). The experiments indicate that conditions on Enceladus are not so different from some localities on Earth and could perhaps sustain methanogenic life.
The dense galactic environments of the Milky Way
Nguyen-Luong, Quang
The dense galactic environments of the Milky WayStar formation takes place in the dense gas phase, therefore a simple dense gas and star formation rate relation has been proposed. With the advent of multi-beam receivers, new observations show that the deviation from linear relations is possible. In addition, different dense gas tracers might also change significantly the measurement of dense gas mass and subsequently the relation between star formation rate and dense gas mass. In the talk, we report a multi-year and multi-tracers wide-field survey that trace the dense gas toward a suit of well-characterized massive star forming regions in the Milky Way. Using the new observations of HCO+ 1–0, HCN 1–0, CS 2–1 and C34S 2–1, we discuss the current understanding of the dense gas phase where star formation takes place.
MASSES: An SMA Large Project Surveying Protostars to Reveal How Stars Gain their Mass
Stephens, Ian
Low-mass stars form from the gravitational collapse of dense molecular cloud cores. While a general consensus picture of this collapse process has emerged, many details on how mass is transferred from cores to stars remain poorly understood. MASSES (Mass Assembly of Stellar Systems and their Evolution with the SMA), an SMA large project, has just finished surveying all 75 Class 0 and Class I protostars in the nearby Perseus Molecular Cloud in order to reveal the interplay between fragmentation, angular momentum, and outflows in regulating accretion and setting the final masses of stars. In this presentation I will give an overview of the survey and highlight key science results.
TOWARDS ASTROBIOLOGICAL EXPERIMENTAL APPROACHES TO STUDY UV SURFACE ENVIRONMENTS: FROM THE EARLY SOLAR SYSTEM TO EXOPLANETS
Abrevaya, Ximena C.
To determine the conditions about the existence and emergence of life in the universe, it is essential to study stellar radiation which itself can be a constraint for life development. Particularly, UV radiation wavelengths (200-400 nm) can reach the surface of the planets. Even though several studies have analyzed the UV surface environments on planetary bodies considering UV radiation as a limiting factor, this has only been approached partially from a theoretical point of view and experimental approaches are missing so far, e.g.: biological effects are based on theoretical calculations. All these points can be addressed more accurately through an interdisciplinary approach. To this end we carry out two international collaborations by combining a team of experts in astrophysics, microbiology, photobiology and cosmochemistry: The BioSun project and the EXO-UV project whose aim is to analyze the influence of stellar UV radiation on life in a comprehensive way. Our approach includes: (i) astrophysical studies focused on the characterization of the radiation environments by using observational data and considering potential atmospheric compositions; (ii) 1-D radiative transfer modeling of the planetary atmosphere; (iii) simulation of these UV environments in laboratory experiments to study the effects of radiation on life. Within these projects we aim to to study the conditions for the origin, evolution and habitability of life on the early Solar System as well as in other planetary bodies. During this talk I will show the first advances of this collaboration and the first results of the experimental simulations of these UV radiation environments in laboratory experiments by using radioresistant microorganisms.
Stellar activity and winds shaping the atmospheres of Earth-like planets
Lüftinger, Theresa
Planets orbiting young, active stars are embedded in an environment that is far from being as calm as the present solar neighbourhood. They experience the extreme environments of their host stars, which cannot have been without consequences for young stellar systems and the evolution of Earth-like planets to habitable worlds. Stellar magnetism and the related stellar activity are crucial drivers of ionization, photodissociation, and chemistry. Stellar winds can compress planetary magnetospheres and even strip away the outer layers of their atmospheres, thus having an enormous impact on the atmospheres and the magnetospheres of surrounding exoplanets. Modelling of stellar magnetic fields and their winds is extremely challenging, both from the observational and the theoretical points of view, and only ground breaking advances in observational instrumentation and a deeper theoretical understanding of magnetohydrodynamic processes in stars enable us to model stellar magnetic fields and their winds – and the resulting influence on the atmospheres of surrounding exoplanets – in more and more detail. We have initiated a national and international research network (NFN): 'Pathways to Habitability - From Disks to Active Stars, Planets to Life', to address questions on the formation and habitability of environments in young, active stellar/planetary systems. In this presentation, we will discuss the work we are carrying out within this project and focus on how stellar evolutionary aspects in relation to activity, magnetic fields and winds influence the erosion of planetary atmospheres in the habitable zone. We will present recent results of our theoretical and observational studies based on Zeeman Doppler Imaging (ZDI), field extrapolation methods, wind simulations, and the modeling of planetary upper atmospheres.
Critical and ordinary hydrodynamic and magnetism of planetary interiors
Starchenko, Sergey
Own magnetic field of a planet protects atmosphere against star wind making possible for any live to exist. The value, structure and evolution of the planetary magnetic field are linked to the properties of the planetary interiors those are also important for habitual planet. Correspondent critical and ordinary hydrodynamic and magnetic events are examined using the available knowledge about the Solar system planets. The first critical event is convection onset that is well-described numerically, asymptotically and even analytically for the typical planetary conditions. For the ordinary convection, I present new results related to the optimal similarity factors allowing the solution of the convection problem with real planetary parameters. The next critical event is magnetic field onset via convection that is determined by the properties and evolution of the planetary interiors. Ones established the ordinary magnetic field is mainly determined by the planetary heat/composition power flows and rotation. Here previously two-decade promising numerical planetary MHD dynamo-like first principal modeling has troubles nowadays in its’ parameter space. It is been very far from realistic also gives doubtful access to the true physical scales and values via the known scaling laws. I have analytically reintroduced/supplemented those laws and suggested hopefully correct and new ones.
Transitional disk archaeology from exoplanet population synthesis
Chaparro, Germán
Increasingly better observations of resolved protoplanetary disks show a wide range of conditions in which planets can be formed. Many transitional disks show gaps in their radial density structure, which are usually interpreted as signatures of planets. It has also been suggested that observed inhomogeneities in transitional disks are indicative of dust traps which may help the process of planet formation. However, it is yet to be seen if the configuration of fully evolved exoplanetary systems can yield information about the later stages of their primordial disks. We propose to use supervised learning algorithms to probabilistically predict whether the progenitor disk of an exoplanetary system was originally density perturbed. We use synthetic exoplanet population data from Monte Carlo simulations of systems forming under different density perturbation conditions, which are based on current observations of transitional disks. The simulations use a core instability, oligarchic growth, dust trap analytical model that has been benchmarked against exoplanetary populations. We can thus infer some properties of progenitor disks, and probabilities of finding planets in the habitable zone of stars based on general properties of observed exoplanetary systems.
A Planetary Mass Companion in an Edge-on Protoplanetary Disk System
Stapelfeldt, Karl
A small number of candidate planetary mass companions (PMCs) have been detected to young stars, at least one showing evidence of ongoing accretion. While ALMA has the sensitivity to detect circumplanetary disks around these objects, none have been detected around a bona-fide PMC. We report ALMA's detection of unresolved millimeter continuum emission from the planetary mass companion SSTc2dJ162221.0-230402 b. Discovered in HST optical images, this companion appears projected at the outer radius of an edge-on protoplanetary disk and aligned in the disk plane. Keck AO photometry shows that the companion has a comparable temperature to the brown dwarf GQ Lupi B but with 10x less luminosity - consistent with a planetary mass object. Keck AO spectroscopy detects weak 2.12 micron H2 emission from the companion. We will report on the full ALMA dataset, plus deep HST imaging and HST grism spectroscopy that are expected to be taken this spring. SSTc2dJ162221.0-230402 appears to be an accreting protoplanet and circumplanetary disk seen at 110 AU projected separation, and thus offers support to models of planet formation by gravitational instability.
3D radiation MHD simulations of gas and dust in protoplanetary disks
Flock, Mario
I will present recent results from 3D global radiation MHD simulations of gas and dust in protoplanetary disks. From our recent simulation results (Flock et al. 2015 and Flock et al. 2017) we are able to compare for the first time detailed observational constraints from high-resolution observations by ALMA with the gas and dust dynamics obtain in 3D state-of-art simulations of protoplanetary disks. For this talk I will focus on measurements of the dust scale height obtain from the disk around the young system HL Tau. We compared best fit Monte Carlo radiation transfer models of the dusty disk to our results of the dust scale height in 3D radiation MHD and HD simulations. Our findings are that magnetized models fit perfectly the observational constraints, both showing a strongly settled disk, while hydrodynamical turbulence leads to a dust uplifting which is much stronger than expected.This works opens a new window to compare future multi-wavelength observations to simulations.
Resolved Maps of Star Formation Rate and Efficiency for the GMC Orion A
Großschedl, Josefa Elisabeth
The giant molecular cloud OrionA is the closest massive star forming region to earth and therefore a prime location to study the laws of star formation. In our work we construct resolved maps of star formation rate (SFR) and efficiency (SFE) across the entire GMC OrionA using a Planck/Herschel dust column-density map and a sample of ~3000 YSOs. To this end, we refine previously existing YSO catalogues using a deep NIR ESO-VISTA survey that allows us to rule out false positives from previous samples (e.g. galaxies, cloud edges). Additionally we add ~200 new candidates in the surroundings to get a complete census of the spatial distribution of YSOs in this cloud as compared to the previously analysed region. We find that the spatial distribution of flat-spectrum sources shows a stronger connection to regions of high dust column-density compared to ClassIIs. This suggests that flat-spectrum sources may not be an observational artifact, as often suggested in the literature (e.g. disk inclination effects), and should be considered as a younger evolutionary phase, likely closer to the protostellar phase (Class I). From the resolved SFR and SFE maps of the cloud we find that the SFR varies by a factor of ~10 across the cloud while the instantaneous SFE is about constant (within a factor of two). The increased SFR at the head of the cloud, including the ONC region, could be explained by cloud compression due to external feedback mechanisms (e.g. SNe, local massive stars). Remarkably, the efficiency of converting dense gas into stars seems to be largely independent of external processes and might be an intrinsic property of the star forming gas.
The biological impact of superflares on a planet in the Habitable Zone
Valio, Adriana
Kepler-96 is a very active star, with many superflares seen on its lightcurve. This star harbours a Super-Earth planet orbiting very close to the star. With an age of 2.4 Gyr, this star is at the same stage of the Sun when the first multicelular organisms appeared on Earth. Here we analyse the four years of continuous short cadence observation of the star by the Kepler telescope. The model used simulates a planetary transit in front of a star with a disk flare of different size, amplitude, and position. By fitting the observational data with this model, it is possible to infer the physical properties of the flares, such as duration (few minutes) and energy released by each flare. The biggest flare observed was found to have an energy of 1.8 10^{35} ergs, that corresponds to the energy range of the superflares found in literature. In addition, we analyze the biological impact of these superflares on a hypothetical Earth with various atmospheres scenarios: an Archean atmosphere and Present-day atmospheres with and without oxygen. The presence of an ocean was also included in our study. We estimated the UV flux produced by the superflare and concluded that life would only survive on the surface of Kepler-96b if there were already an ozone layer present on the planet atmosphere, or in an ocean of a few meters deep.
Biohaze as an atmospheric biosignature of an early Earth
Berdyugina, Svetlana
On the current Earth, the surface biosphere emits a substantial amount of bioaerosols to the atmosphere, where they comprise up to 25% of total airborne particle mass. SImilarly, on the Earth with early life, bioaerols could be continuousy emitted into the atmosphere and create biohazes and cloud droplets containing biopigments and other partially decomposed biomass. Here, we employ our spectro-polarimetric laboratory measurements of various photosynthetic bacteria for modeling planetary atmospheres polluted by bioaerosols, such as living and partially degraded bacteria and biopigments. Using our model for stellar light scattered by a planetary atmosphere, we compute polarized light-curves and spectra from planets with biohazes and cloud droplets containing bacteria and photosynthetic pigments. We estimate the minimum concentration of biomass in the atmosphere necessary for remote detection on distant exoplanets similar to the early and present Earth.
Exploring the Origins of the Earth's Nitrogen
Rice, Thomas
It has long been a goal of astrochemistry to connect measurements of interstellar molecules to the formation of planetary systems such as our own. Observations of cometary ices and interstellar volatiles have allowed for some progress, but understanding the origins of volatiles on terrestrial planets remains a difficult task. It is the goal of this work to outline the connection of interstellar nitrogen molecules to the nitrogen content of terrestrial bodies in our Solar System. What form is nitrogen in when it gets locked into meteoritic planetesimals? While the vast majority of a disk's nitrogen is thought to be found in atomic N and N2 (Schwarz & Bergin 2014), these species do not freeze as readily into solids, and therefore cannot be the progenitor of Earth's nitrogen. Based on an analysis of Herschel spectra toward the star-forming regions Orion KL and IRAS 16293, we have investigated whether N-bearing organic molecular ices can trace the nitrogen that ultimately becomes incorporated into terrestrial worlds. We suggest that refractory dust, not molecular ices, was the bulk carrier of nitrogen to comets. But, importantly, the high 15N enrichment in both nitrogen-bearing ices and in meteoritic nitrogen, not shared by ISM dust, indicates that these 15N-enriched N-bearing ices were an important contributor to the nitrogen in planetesimals and likely to the Earth.
Accounting for the protosolar environment
Küffmeier, Michael
Stars like the Sun predominantly occur clustered among other stars embedded in Giant Molecular Clouds. Contrary to models of individual stars forming due to the collapse of one isolated core, we account for the molecular cloud environment during the epoch of star and protoplanetary disk formation. Using state-of-the art zoom-simulations with the magnetohydrodynamical codes ramses, we investigate the accretion process of young stars that are embedded in such different environments during their first ~100 kyr after formation. Starting initially from a turbulent (40 pc)^3 Giant Molecular Cloud, efficient use of the Adaptive Mesh Refinement technique allows us to resolve the processes inside of protoplanetary disks with a resolution down to 0.06 AU, thus covering a range of spatial scales of more than eight orders of magnitude. We find that the accretionprocess of stars is heterogeneous in space, time and among different protostars with a tendency of more violent accretion for deeply embedded objects. As a follow-up, we evolve the embedded star-disk systems further in time with the new code framework dispatch to constrain the effect of infalling material before and during the onset of planet formation. Infalling material can trigger accretion bursts that are likely to be responsible for the large spread in luminosities observed for young stars. If the Sun underwent such violent accretion bursts in the past, the star might have heated the inner parts of the disk significantly during that time -- potentially leaving some trace in the meteoritic record. Finally, recent observations show stars hosting an inner and an outer disk misaligned with respect to each other. We study whether infall with different angular momentum can be responsible for the misalignment, and by analyzing the stability of misaligned systems in independent models, we speculate whether the Protosun could have hosted two misaligned disks at some point in its past.
Modelling the atmosphere of habitable planets
Iro, Nicolas
The list of planets discovered in the habitable zone of its star is continuously growing. We will present a hierarchy of models (from 1D radiative transfer to 3D climate models) in order to better infer on the habitability of such systems.Particular focus will be on Proxima Centauri b (Anglada-Escudé et al. 2016, Nature, 536, 437) as well as the TRAPPIST-1 planets (Gillon et al. 2017, Nature, 542, 456). In the case of Proxima Centauri b, the two possible planetary rotation regimes (1:1 and 3:2 spin-orbit resonances, as inferred by Ribas, A&A 596, A111, 2016) will be investigated. As far as the TRAPPIST-1 system is concerned, we will focus on planets c, d and e.