M D Dyar
email: mdyar@mtholyoke.edu

J Helbert

T Boucher

A Maturilli

I Walter

T Widemann

Emmanuel Marcq

S Ferrari

N Müller

S Smrekar

M D Dyar

T Wide- Mann

M. D 'amore

Venus Surface Oxidation and Weatehring as Viewed from Orbit with Six-Window VNIR Spectroscopy

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction: Knowledge of Venus mineralogy is key to constraining surface/atmospheric interactions as they contribute to our understanding of weathering reactions [1] and identify sites of recent volcanism [2]. As basalt weathers, first reacting with SO2 and CO 2 and then oxidizing, its emissivity should transition from high to low, culminating in formation of new mineral alteration products. These reactions are likely defined by progressive oxidation of iron from Fe 2+ to Fe 3+ surface minerals as first suggested in 1964 [3]. This project uses laboratory data to assess whether iron oxidation and changes in mineralogy due to surface/atmosphere interactions can be detected from orbit using a six-window orbital spectrometer [4,5].

Samples and Methods: Rocks and minerals examined include six rocks: two basalts, basaltic andesite, granite, rhyolite, and rhyolitic glass; and four minerals: pyrite, pyrrhotite, magnetite, and hematite. Compositions were determined by x-ray fluorescence (XRF) at the University of Massachusetts [6] or by electron microprobe at Brown University. Fe 3+ /Fe 2+ ratios were measured using Mössbauer spectroscopy. Visible nearinfrared (VNIR) data were collected in the Planetary Spectroscopy Laboratory (PSL) at the German Aerospace Center (DLR) in Berlin [7].

Oxidation State Results: Figure 1 (top) shows the relationship between the internsity of the 1.18 µm band and iron oxidation state. Samples that are dominated by Fe 2+ have the highest emissivities, while those containing Fe 3+ , like magnetite (Fe 3+ 2 Fe 2+ O 4 ) and hematite (Fe 3+ 2 O 3 ), have the lowest. Inspection of the entire spectral range shows that magnetite has the largest negative slope of any sample measured between 0.86 to 0.91 µm. All the felsic rocks also have negative slopes in that region, while Fe 2+ -rich basalts are distinguished on the basis of their positive slopes. Results show that metrics can easily be developed to assess oxidation state of Venus surface rocks.

Surface-atmosphere chemical reactions also result in changes in mineralogy that cause both gradual and sudden changes to radar backscatter at higher elevations. No one mineral satisfies all the current observations that could account for these changes [8]. Compounds such as pyrite, pyrrhotite, magnetite, hematite, chlorapatite and others [8,9] have been proposed by various workers to cause these changes (Figure 1 bottom). Our data show that at least four of these minerals have distinctive spectral signatures that should be sufficient to distingui them on Venus highlands. Acquisition of additional spectra data is underway to further constrain this observation. (top) Relationship between the magnitude of emissivity at 1.18 µm versus total iron contents, expressed as the percentage of the total iron that is Fe 3+ . Pyrite and pyrrhotite are not expected to lie on this trend line because their spectra are so affected by the dominantly covalent bonding in their structures. (bottom) Diagnostic emissivity spectra of possible alteration products from surfaceatmosphere interactions at the six observable wavelengths.

Figure 1 .

 1 Figure 1. (top)Relationship between the magnitude of emissivity at 1.18 µm versus total iron contents, expressed as the percentage of the total iron that is Fe 3+ . Pyrite and pyrrhotite are not expected to lie on this trend line because their spectra are so affected by the dominantly covalent bonding in their structures. (bottom) Diagnostic emissivity spectra of possible alteration products from surfaceatmosphere interactions at the six observable wavelengths.

16th VEXAG Meeting 2018 (LPI Contrib. No. 2137)


Clement Delmas
email: delmas.clement@chutoulouse.fr

Hélène Barbosa

Charles-Henri David

Frédéric Bouisset

Pierre-Guillaume Piriou

François Roubille

Juergen Leick

Marin Pavlov

Guillaume Leurent

Evgenij V Potapov

Pierre- Guillaume Piriou

Axel Linke

Johannes Mierke

Pia Lanmüller

Norman Mangner

Impella for the Management of Ventricular Septal Defect Complicating Acute Myocardial Infarction: An European Multicenter Registry

Keywords: mechanical circulatory support, mortality, acute myocardial infarction, mechanical complication

Ventricular septal defect (VSD) is a rare but fatal complication of myocardial infarction (MI). Over the past decades, the VSD occurrence has gradually declined caused by the increased use of rapid revascularization. Nevertheless, VSD is estimated to complicate about 0.3% of ST elevation myocardial infarction (STEMI).1 Clinical presentation ranges from isolated murmur on thoracic auscultation to a severe form of cardiogenic shock (CS). Post-MI VSD is a serious disease with a high early mortality of 40-80% escalating to up to 94% at 30 days in case of medical management. Despite medical advances, this prognosis has remained unchanged for years, particularly in cases of hemodynamic instability and CS.2 Surgical septum repair is the mainstay treatment, mostly by VSD patch closure through a double ventriculotomy technique but remains a high-risk procedure. Percutaneous closure is increasingly undertaken alone or in association with surgical management with promising results in selected patients.3 However, VSD closure is not always technically feasible (necrotic edges) or patients are not operable caused by hemodynamic compromise and severe comorbidities including multiple organ failure associated with CS itself. [START_REF] Chioncel | Epidemiology, pathophysiology and contemporary management of cardiogenic shock-A position statement from the Heart Failure Association of the European Society of Cardiology[END_REF] Observational and retrospective data suggest that early repair (<7 days from MI) appears to be associated with higher mortality, but these results may reflect a patient selection bias in favor of late surgery because only stabilized patients could be operated.5 Clinical stabilization and evolution of the infarcted heart tissue theoretically allow for a better tissue suture substrate and more efficient repair.

Therefore, while awaiting surgery, treatment should focus on lowering left ventricle end diastolic pressure (LVEDP) to decrease the left-to-right shunt and myocardial oxygen consumption, while increasing anterograde cardiac output to maintain organ perfusion and prevent/treat secondary multiple organ failure. Although medical management using catecholamines may be considered, their effect may be limited in patients with CS. Temporary mechanical circulatory support (t-MCS) devices are a promising therapeutic option given their ability to improve hemodynamics and tissue perfusion.6 However, data on the intracardiac and systemic hemodynamic effects of t-MCS in post-MI VSD or based on hemodynamic simulation are scarce.7 Although the catheter-based axialflow pump Impella (Abiomed, Danvers, MA, USA) is not recommended in this clinical setting by the manufacturer, experienced centers used it in post-MI VSD patients. We collected the data through a European multicenter retrospective study to describe characteristics, associated management, and outcomes.

Materials and Methods

Study Design

We conducted a European retrospective multicenter registry that aimed to collect post-MI VSD patients managed with Impella device (2.5, CP or 5.0) during the last 12 years (2010-2021). The registry was proposed by email or phone to experts' European centers recognized for their experience with Impella in CS management.

Population

Patients age of greater than or equal to 18 years who received an Impella for hemodynamic support caused by a post-MI VSD admitted to the critical care unit of the participating center were included. The non-inclusion criteria were patient under measure of justice. Cardiogenic shock was defined by the combination of a systemic hypotension (systolic blood pressure [SBP] ≤ 90 mm Hg or need for vasopressors/inotropes) with presence of at least one sign of systemic hypoperfusion (eg, confusion, oliguria, marbles, or lactate elevation) and signs of pulmonary congestion (crackles or left ventricular filling pressures elevation based on noninvasive or invasive evaluation). The choice of the t-MCS, its timing but also any t-MCS combination was made locally by the team treating the patient in accordance with the contemporary local protocols of the VSD management.

Data Collection

Data were abstracted from the medical record to a standardized electronic case report form by the sites study coordinators. Information on the patient's demographic characteristics, medical history, clinical presentation, hemodynamic, echocardiographic, and angiographic characteristics, treatment received during hospitalization, hospital discharge status, and follow-up status were collected.

Follow-Up

At 24 hours, simplified acute physiology score (SAPS) II score, noninvasive and invasive hemodynamic, biology (lactate, creatinine, bilirubin, lactate deshydrogenase [LDH], hemoglobin, platelets), medication, and organ support were also collected.

In-hospital complications were collected based on medical file of the patients (ischemic and hemorrhagic stroke, acute renal failure requiring dialysis, major bleeding; Bleeding Academic Research Consortium classification [BARC] ≥ 3 or needing surgery), acute limb ischemia requiring interventional or surgical management, Impella device dysfunction needing its drop off, infection (insertion sites, septicemia, pneumonia), clinical hemolysis needing medical intervention (vascular filling, reduction of axial flow pump (AFP) flow or device replacement or drop off).

All-cause mortality was assessed at hospital discharge (primary end-point) and at 6 and 12 months by consultation of the patient's medical file, or telephone call of the patient, his attending physician, or relatives.

Ethics and Regulation

The study was consistent with the principles set out in the Helsinki Declaration. After evaluation and validation by the data protection officer and in accordance with the General Data Protection Regulation, this study has met all the criteria and is registered in the retrospective study register of the Toulouse University Hospital (number's register: RnIPH2021-101) and covered by the MR-004 (CNIL number: 2206723 v0). The individual anonymized data sharing were performed according to the permission of the Independant review board (IRB) of each center.

Statistical Analysis

Continuous variables are presented as medians (interquartile range) and categorical variables as counts (percentage). First, we compared patients according to in-hospital survival. Second, we compared patients according to the type of Impella used: surgical (mainly 5.0) versus percutaneous (exclusively 2.5 and CP). Third, patients were compared according to the associated VSD management (surgical versus percutaneous closure versus medical). Comparison between groups was made with Wilcoxon signed rank tests for continuous variable and with χ 2 tests or Fisher exact tests according to their respective conditions of applicability for categorical variables.

All tests were two-sided, and p values of less than 0.05 were considered statistically significant. Missing data were systematically reported as they were removed from the statistical analysis. All statistical analyses were performed with XLSTAT 2022.1 by Addinsoft (Paris, France).

Results

Population

Of 20 centers contacted, 17 (85%) answered, and 7 (41.2%) reported the use of Impella for a post-MI VSD in at least one case. Table S1, Supplemental Digital Content, http://links.lww.com/ASAIO/B131, describes the center that responded and number of VSD cases included. Over the study period (2010-2021), a total of 28 patients were included. Table 1 describes patients' characteristics at admission. Patients were predominantly male (n = 18, 64%) and were 66 (58.5-78.5) years old. Survivors were younger (61 vs. 74 years old, p = 0.02). Cardiovascular risk factors were frequent, especially hypertension (n = 17, 61%). At admission for acute coronary syndrome (ACS) (see Table S2, Supplemental Digital Content, http://links. lww.com/ASAIO/B131), patients were hemodynamically stable (median systolic blood pressure 110 (86-127) mm Hg with a median heart rate of 100 (86-106) beats/min). Nevertheless, 16 (57%) patients presented with left and 13 (46%) patients with right heart failure signs. Trans-thoracic echocardiography showed a left ventricle dysfunction with left ventricular ejection fraction (LVEF) of less than or equal to 40% for 14 (50%) patients and 15 (53%) patients had right ventricle dysfunction (tricuspid annular plane systolic excursion [TAPSE] < 17 mm). The right coronary artery was the main culprit lesion found for 20 patients (71%).

Median time between ACS occurrence (defined as chest pain time) and medical care was 3 days (interquantile range [IQR] = 1-6). Coronary revascularization was performed in 64% of the patients: 57% by percutaneous coronary intervention (n = 16) and 11% by coronary artery bypass graft (CABG) (n = 3).

Presentation at Ventricular Septal Defect Diagnosis

Baseline characteristics of the population at VSD diagnosis are presented in Table 2. Median time from pain onset to VSD diagnosis was 5 days (IQR 3-8). The median systolic blood pressure was 101 mm Hg with a diastolic blood pressure of 62 mm Hg and a heart rate of 106 beats/min. Eighteen (64%) and 17 (61%) patients presented with signs of left and right heart failure, respectively. Oliguria was present in 18 (64%), mottling in 15 (54%), and confusion in 10 (36%) patients. Trans-thoracic echocardiography showed an LVEF of less than or equal to 40% in 16 (57%) patients, and 17 (61%) patients had right ventricle dysfunction (TAPSE < 17 mm). The VSD was apical in 10 (36%) and inferior basal in 17 (61%) patients (localization not available for one patient).

Management

Table 3 describes the in-hospital management. Dobutamine support was used for 17 (55%) patients with a median duration of 3 days (IQR 1-7). Norepinephrine support was required for 27 (96%) patients with a median duration of 3 days (IQR 2-8). Twenty-five (89%) patients needed invasive mechanical ventilation and 14 (40%) renal replacement therapy.

The Impella was implanted early (on the day of vasopressor/ inotropes introduction) via a percutaneous or a surgical approach in 21 (75%) and seven (25%) patients, respectively. Five patients received a 5.0 device, 2 a surgical CP device, 18 a percutaneous CP device, and 1 a 2.5 device. The type of Impella device was not known for two patients. The median duration of support was 6 days (IQR 2-11). Additional t-MCS was used in 14 (50%) patients, mainly as an extracorporeal life support (ECLS) (n = 9, 32%) (Figure 1).

A surgical or a percutaneous VSD closure was attempted in 10 (36%) and six (21%) patients, respectively. Among these patients, 12 (75%) were supported by Impella before the VSD closure and four (25%) patients were implanted the same day. No combination of surgical and percutaneous closure was reported. Finally, an isolated medical management was selected for 12 (43%) patients.

In-Hospital Complications

The most common Impella-associated complication was a major bleeding (BARC ≥ 3) in 14 (50%) patients followed by a clinical hemolysis (n = 3, 11%) (Table 4). No significant difference between survivors and nonsurvivors was found. Figure S1, Supplemental Digital Content, http://links.lww.com/ASAIO/ B131, shows differences in Impella-associated complications according to the pump type (percutaneous versus surgical).

Outcomes and Associate Correlates

We observed no significant difference between survivors and non-survivors in clinical parameters or biomarkers within the first 24 hours from the time of Impella implantation (not shown).

In-hospital and 1 year mortality rates were both 75%. Only seven (25%) patients were discharged alive from hospital. No long-term ventricular assist device or heart transplantation was realized.

We found no difference in survival according to the type of Impella used (percutaneous versus surgical) (see Figure S2, Supplemental Digital Content, http://links.lww.com/ASAIO/ B131) nor according to the different combinations of t-MCS used (Figure 2). On the contrary, we found a significantly higher survival for patients with combined surgical closure and Impella support (Figure 3 and Table 3). There was no difference in terms of delay between VSD diagnosis and closure between survivors and non-survivors.

Survivors were more likely to have undergone CABG revascularization (43% vs. 0%, p = 0.011). Moreover, non-survivors were older (74 vs. 61 years old, p < 0.022) at admission. No other significant difference was found according to medical history, characteristics at admission or at VSD diagnosis, or according to management.

Discussion

We reported the first large multicentric series of patients with post-MI VSD supported by Impella device regardless of the type of implantation (surgical or percutaneous) and the associated VSD management (Figure S1, Supplemental Digital Content, http://links.lww.com/ASAIO/B131). This report shows feasibility of Impella support in compensating the interventricular shunt in post-MI VSD patients. Further, patients without surgical repair do not survive. Elucidating the place of Impella in the management of post-MI VSD will require larger cohorts and standardization of patient/VSD management, to assess whether these serious outcomes are patient-related, secondary to the device itself or timing of the implantation.

In the registry, we reported an excessive mortality of post-MI VSD patients (75% in-hospital and 1 year mortality). The cause of such a high mortality is difficult to pin down unambiguously however, the results must be interpreted considering several points and potential confounders. First, we included exclusively patients in CS (stage C-E from the Society for Cardiovascular Angiography and Interventions (SCAI) classification), whereas recent UK and Japanese nationwide registries reported only 50-60% of patients in CS.3,5 In our cohort, the shock was more profound, inotropes, and vasopressors were used more often (dobutamine 55% and norepinephrine 96% in our cohort vs. 26% of inotropes in the Japanese registry), as well as renal replacement therapy (40% in our population vs. 25% in the Japanese registry).5 In accordance to our hypothesis, CS at presentation was independently associated with in-hospital (adjusted hazard ratio [HR] = 2.17 [1.43-3.29], p < 0.001) and long-term mortality (adjusted HR = 1.97 [1.37-2.84], p < 0.001) in the recent and large UK registry.3 Second, we included patients regardless of whether VSD closure (surgical or percutaneous) was attempted for technical or ethical considerations. Conservative treatment was associated with extremely high early mortality in multiple studies (>90% in-hospital mortality). We aimed to report the Impella device use regardless of the associated treatment contrary to previous series focusing on the mode of closure (surgery or interventional cardiology) which eliminated patients managed medically. This may in part explain high mortality rate in our cohort since, as expected, none of the 12 patients managed medically survived. The higher inhospital survival (70%) was observed for AFP patients with associated surgical closure.

For European Society of Cardiology Guidelines, t-MCS may be used as a bridge-to-recovery or surgery in patients with VSD associated CS with a class IIa recommendation (level of evidence C) without specifying the type and timing of the support.8 To date, mainstay is still intra-aortic balloon pump (IABP) based on the old data suggesting an afterload reduction and a left-to right shunting decrease. Alternatively, the use of Tandem Heart (Cardiac Assist Inc., Pittsburgh, PA) was reported in a small series (11 post-MI VSD patients) with interesting results in case of early implantation before VSD surgical closure with only 25% mortality rate at 6 months.9 Limited availability and the need for high expertise for implantation may explain the low implementation rate. Recent simulated hemodynamic analysis comparing effects of different t-MCS in VSD model showed more efficient hemodynamic effect with Impella.7 Indeed, despite attractive and potentially advantageous hemodynamic effects of Impella over other devices, the data on its use alone or in combination with ECLS in the context of post-MI VSD are scarce.10-12

The potential positive effect of the Impella is based on a direct pumping of the blood from the left ventricule (LV) to the aorta, increase in total flow to the body (+1.1 to +1.6 L/ min of cardiac output according to its size (Impella CP vs. 5.0) versus +0. 5 L/min for IABP), and significant decrease in the left to right shunt through the VSD (decrease of the Qp: Qs from 3.0 to 2.3 and 2.1, respectively for Impella CP and 5.0).7

Consequently, direct LV unloading decreases LVEDP and increases coronary perfusion, suggesting higher potential LV recovery and preventing worsening of the right ventricule (RV) function. Small and retrospective design of our case series with a lack of hemodynamic data, and the absence of control group preclude the confirmation or rejection of our conclusions.

Potential benefit of direct LV unloading could be counterbalanced by the adverse effects associated with the device itself (hemolysis, bleedings, infection), the risk of producing rightto left shunting and the risk of increased VSD and systemic embolization because of its intraarterial/intraventricular position.13,14 In our population, the three most relevant inhospital complications were significant bleeding (50%), acute renal failure (46%), and pneumonia (36%). Bleeding is a well-known complication of t-MCS regardless of the type, a fact confirmed in studies with Impella support in 8-71% of cases according to the definition used and context of implantation and support.15 Indeed access site-related bleeding and associated transfusion are reported in up to 25% and 67% of Impella cases respectively with higher rate in case of CS and t-MCS combination.13,15,16 Numerous factors depending on 1) the patient: initial presentation (hemodynamic instability and multiorgan failure), comorbidities (peripheral artery disease), associated treatment (anticoagulation and antiplatelets regimens); 2) the device: implantation, management, and explanation (echo or fluoroscopic guidance, device fixation, fluids and inotropes management, hemostatic compression device); and 3) the possible development of acquired von Willebrand syndrome,17 could promote bleeding occurrence and may be preventable to a degree. [START_REF] Lüsebrink | Percutaneous transvalvular microaxial flow pump support in cardiology[END_REF] No deoxygenation caused by inversion of the shunt from right to left side was described contrary to previous case report. [START_REF] Sato | Right-to-left shunt depending on the support level of Impella for post-infarction ventricular septal defect[END_REF] Despite particular attention given to the risk of VSD size increase, systemic embolism, and stroke, we found no signal of harm in our small series. The risk of direct aspiration of VSD's debris by the impeller seems low and may probably be prevented by initial adequate positioning and close monitoring of the AFP. Moreover, the LV unloading may decrease shear forces delivered at the necrotic edges, thus lowering the risk of VSD enlargement and debris. Future dedicated and larger studies should pay particular attention to these issues.

Extracorporeal life support is possibly the most effective circulatory support and the best way to perfuse and oxygenate peripheral organs but several preclinical and clinical studies have shown the association with an increase LV afterload, increase in LVEDP and pulmonary capillary wedge pressure (PCWP).7, 19 LV overload correlated with the intensity of flow and associated with worst prognosis including mortality, especially in case of LV-failure.20, 21 In case of VSD, these effects potentially lead to a worsening of the left-to-right shunt with an increased risk of RV dysfunction and death.7 The combination of ECLS and Impella (association of ECLS and Impella device [ECMELLA]) could improve peripheral organ perfusion while unloading the LV and RV, however, it is associated with an increase in adverse event rates.22,23 The viable alternative is a single arterial access ECMELLA. [START_REF] Eulert-Grehn | ECMELLA 2.0: Single arterial access technique for a staged approach in cardiogenic shock[END_REF] In the absence of clear recommendation, the strategy should be chosen in a case-by-case discussion. The choice should depend on the available t-MCS, but also on the multidisciplinary expertise and practice of the center. Two important points seem to emerge from the literature: the early implantation of t-MCS aimed at preventing multiorgan failure,25 and the early LV unloading to preserve RV and LV functions. [START_REF] Schrage | Timing of active left ventricular unloading in patients on venoarterial extracorporeal membrane oxygenation therapy[END_REF] This justifies a multidisciplinary approach in expert medical surgical centers allowing an evolving personalized approach to each patient, whether in terms of medical management, type of device, and timing of implantation, but also in VSD closure strategy.

Limitations

First, and most importantly, the retrospective nonconsecutive study design precluded definitive conclusion with a possible selection bias despite the data coming from multiple centers especially as most patients came from one center. But as Impella use in post-MI VSD is scarce because of device availability, local protocols, and beliefs, this study reflects real-life practice and collection of all available cases was our main objective. We assume that our report is only an exploratory analysis to be used as a first description/step before performing larger studies. Second, no multivariate analysis was performed because of patient's heterogeneity and small number of patients. In particular, immortal time bias was not accounted for preventing any clear conclusion on the role of surgical VSD closure. Third, the international multicenter retrospective design necessitated a simplified data collection form with a limited number of variables to avoid missing data limiting analyses. Thus, the invasive hemodynamic variables before implantation or under support were available for only few patients-a fact that does not allow to present consistent hemodynamic effect of the Impella device in this context. Fourth, no consensual medical management protocol and indications for type of device and timing of implantation are known even though recommendations suggest urgent/emergent surgical repair under inotrope/vasopressor and t-MCS support.8 This is supported by data as ours, which showed that mortality associated with a conservative approach reaches 100%.

Conclusion

Impella use in patients with post-MI VSD seems feasible in this first exploratory analysis. Larger prospective registries with predefined variables and hemodynamic parameters are necessary to further elucidate potential benefits of LV unloading with this device in the setting of post-MI VSD.

Acknowledgment

Investigators: Bonello L (Hôpital Nord, AP-HM, Marseille, France), Schurtz G (Lille University Hospital, France), Gaudard P (CHU de Montpellier, Montpellier, France), Genet T (CHU de Tours, France), Lebreton G (La Pitié Salpétrière, AP-HP, Paris, France), Pappalardo F (Milan University Hospital, Italy), Hassager C (Copenhagen University Hospital, Danemark), Kindo M (Nouvel Hôpital Civil, Strasbourg, France), Pernot M (Hôpital Cardiologique, CHU Bordeaux, Pessac, France), Pozzi M, (Department of Cardiac Surgery, "Louis Pradel" Cardiologic Hospital, Lyon, France), Schibilsky D (Department of Cardiac Surgery, Freiburg University Hospital, Germany), Letocart V (Department of Cardiology, Nantes University Hospital, France), and Charbonneau E (Rennes University Hospital, France).

Conflict of interest statement

Disclosure:

C.D. has received personal fees from Abott and Abiomed outside the submitted work. G.L. has received proctor, orator and consulting fees from Abbott SA. E.V.P. has received institutional fees from Abott, Medtronic, and Abiomed outside the submitted work. J.L. has received research funds that were paid to the institution from Shockwave Medical Inc. and from Abiomed, and payment or honoraria from AstraZeneca and Boston Scientific, outside the submitted work. J.M. has received personal fees from Abiomed outside the submitted work. P.L. has received personal fees from Abiomed outside the submitted work. N.M. has received personal fees from Edwards Lifesciences, Medtronic, Biotronik, Novartis, Sanofi Genzyme, AstraZeneca, Pfizer, Bayer, Abbott, Abiomed, and Boston Scientific outside the submitted work. The other authors have no conflicts of interest to report.


Markus Benedikt

Manuel Scherf

Helmut Lammer

Emmanuel Marcq

Petra Odert

Martin Leitzinger

Escape and fractionation of elements from planetary embryos

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Escape and fractionation of elements from planetary embryos

Markus Benedikt (1), Manuel Scherf (1), Helmut Lammer (1), Emmanuel Marcq (2), Petra Odert (1), Martin Leitzinger (3)

(1) Space Research Institute, Austrian Academy of Sciences, Graz, Austria, (2) LATMOS, Université de Versailles Saint-Quentin-en-Yvelines, Guyancourt, France, (3) Institute of Physics/IGAM, University of Graz, Austria

Abstract

In the early evolution of planetary systems, protoplanets originate from the coagulation of dust and ice and initially reside embedded in the gas of the circumstellar disks. From isotope studies, it is expected that the Earth (and terrestrial planets) formed from pre-fractionated differentiated planetary embryos and a few percent carbonaceous chondrites. Large planetesimals and planetary embryos are differentiated bodies with sizes of several hundred to a few thousand kilometers. Planetary embryos form protoplanets via mutual collisions, which can lead to the development of magma oceans. During their solidification, significant amounts of the mantles' volatile contents may be outgassed. We show that the resulting steam atmospheres can be lost efficiently via hydrodynamic escape that drag heavier elements like noble gases, K, Na, Mn, Mg, P, etc. into space so that they are also lost. Planetary embryos that are later involved in terrestrial planet formation can be drier than previously expected. We model the outgassing and subsequent hydrodynamic escape of steam atmospheres from such embryos, including the efficient outflow of H that drags along heavier species like O, CO2, CO, K, Na, Mn, Mg, P, etc., and noble gases (Ar, Ne, Xe, Kr) and their isotopes. The full range of possible EUV evolution tracks of a young solar-mass star is taken into account. We investigate the atmospheric/elemental escape from Moon, 0.5Mars-, Mars-and 1.5Mars-sized planetary embryos at different orbital distances. Finally, we discuss the implications of our findings in relation to elemental composition of the bulk silicate Earth composition.

Acknowledgements

We acknowledge support by the Austrian Fonds zur Förderung der Wissenschaftlichen Forschung, Nationales Forschungs Netzwerk (FWF NFN) project S116-N16 and the subprojects, S11606-N16, and S11607-N16. H.L, M.L. and P.O. acknowledge also support of the FWF project P27256-N27.