Atmospheric mass loss due to giant impacts: the importance of the thermal component for hydrogen-helium envelopes

Systems of close-in super-Earths display striking diversity in planetary bulk density and composition. Giant impacts are expected to play a role in the formation of many of these worlds. Previous works, focused on the mechanical shock caused by a giant impact, have shown that these impacts can eject large fractions of the planetary envelope, offering a partial explanation for the observed spread in exoplanet compositions. Here, we examine the thermal consequences of giant impacts, and show that the atmospheric loss caused by these effects can significantly exceed that caused by mechanical shocks for hydrogen-helium (H/He) envelopes. When a giant impact occurs, part of the impact energy is converted into thermal energy, heating the rocky core and the envelope. We find that the ensuing thermal expansion of the envelope can lead to a period of sustained, rapid mass loss through a Parker wind, resulting in the partial or complete erosion of the H/He envelope. The fraction of the envelope lost depends on the planet's orbital distance from its host star and its initial thermal state, and hence age. Planets closer to their host stars are more susceptible to thermal atmospheric loss triggered by impacts than ones on wider orbits. Similarly, younger planets, with rocky cores which are still hot and molten from formation, suffer greater atmospheric loss. This is especially interesting because giant impacts are expected to occur $10{-}100~\mathrm{Myr}$ after formation. For planets where the thermal energy of the core is much greater than the envelope energy, the impactor mass required for significant atmospheric removal is $M_\mathrm{imp} / M_p \sim \mu / \mu_c \sim 0.1$, approximately the ratio of the heat capacities of the envelope and core. When the envelope energy dominates the total energy budget, complete loss can occur when the impactor mass is comparable to the envelope mass.Comment: 10 pages, 9 figure

A computer integrated manufacturing system for small scale production of electronic units : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Production Technology at Massey University

This research project concerns the design of a rapid response, computer integrated Printed Circuit Board (PCB) Component Assembly System (CAS). The CAS system forms an integral part of a commercially viable Manufacturing Pilot Plant (MPP) for the design, production, and assembly of high quality special purpose PCBs in low volumes. The design of the CAS system begins with the identification of the characteristics and deficiencies of conventional low volume, high variety PCB manufacturing systems. Next, a vision for the MPP as a whole is presented, with particular emphasis on the CAS system. A Generic Manufacturing System Design Methodology (GDM) is then derived, and is applied to the design of the CAS system. Through the GDM a working CAS system is constructed, based around a central CAS Master and 3 assembly workstations. The working CAS system is then analysed through a comparison with a typical conventional low volume manual assembly system. The results support the expectation of superior performance from the envisioned system. Finally, areas requiring further work are identified

Early childhood education in differing contexts:The impact of the COVID-19 global health pandemic within four countries

The recent Covid‐19 global health pandemic has negatively affected the political and economic development of communities around the world. This article shares the lessons from our multi‐country project Safe, Inclusive Participative Pedagogy: Improving Early Childhood Education in Fragile Contexts (UKRI GCRF) on how children in communities in Brazil, Eswatini, South Africa, and Scotland have experienced the effects of the pandemic. This article benefits from having co‐authors from various countries, bringing their own located knowledge to considerations of children’s rights and early childhood education in the wake of the pandemic. The authors discuss different perspectives on children’s human rights within historical, social, and cultural contexts and, by doing so, will discuss how the global pandemic has placed a spotlight on the previous inequalities within early years education and how the disparity of those with capital (economic and social) have led to an even greater disproportion of children needing health and educational support

Integrating Machine Learning for Planetary Science: Perspectives for the Next Decade

Machine learning (ML) methods can expand our ability to construct, and draw insight from large datasets. Despite the increasing volume of planetary observations, our field has seen few applications of ML in comparison to other sciences. To support these methods, we propose ten recommendations for bolstering a data-rich future in planetary science.Comment: 10 pages (expanded citations compared to 8 page submitted version for decadal survey), 3 figures, white paper submitted to the Planetary Science and Astrobiology Decadal Survey 2023-203

A tale of two cognitions: The Evolution of Social Constructivism in International Relations

Abstract Constructivism in International Relations (IR) is popular, but constructivists seem disappointed. Allegedly something has been lost. Such criticisms are misplaced. There was never a uniform Constructivism. Since constructivism is socially constructed, to argue that constructivism has evolved “wrongly” is odd. This paper explains the dissatisfaction with constructivism followed by a second reading of its evolution as a tale of two cognitions. These two cognitions distinguish genera in the constructivist “family”. A criticism against one genus based on the cognition of the other is unfair. A focus on cognitions and the use of genera helps in perceiving constructivism’s future evolution

Planet formation and evolution in our Solar System and beyond

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 185-212).The discovery of thousands of exoplanets in recent decades has revealed a remarkable diversity of planetary system architectures, including entire classes of planets for which there is no solar system analog. In particular, the Kepler mission has shown that planets intermediate in size between Earth and Neptune with orbital periods less than 100 days are abundant in our galaxy. Concurrently, spacecraft missions to small primitive bodies in our solar system have yielded valuable insights into conditions in the early solar system. This thesis addresses questions in planet formation theory arising from both sets of observations. We begin with an investigation into the observed diversity of super-Earth bulk densities, which range from being consistent with a terrestrial composition to requiring an extended hydrogen-helium (H/He) envelope comprising several percent of the planet's mass. Giant impacts are expected to play a role in the formation of these worlds.We examine the thermal consequences of such an impact, and find that atmospheric loss from these effects can significantly exceed that caused by the previously considered process of mechanical shocks for H/He atmospheres. Specifically, the energy released can produce a period of sustained, rapid mass loss through a Parker wind, partly or completely eroding the envelope. The degree of loss depends on planetary properties and the stochastic details of the impact, making giant impacts an attractive explanation for the observed diversity of super-Earth compositions. The final assembly of the terrestrial planets in our solar system likely also concluded with a period of giant impacts. We explore the significance of post-impact thermal losses for terrestrial planet atmospheres in different evolutionary states, finding that H/He envelopes are unlikely to survive the giant impact phase, but that secondary, outgassed envelopes with higher mean molecular weights may be retained.Atmospheric constituents with high mean molecular weights may be lost, however, if they are mixed into a predominantly H/He envelope. Next, this thesis examines magnetic measurements of comet 67P/Churyumov- Gerasimenko (67P) and their implications for the early solar system environment. Specifically, the remanent magnetization of solar system bodies reflects their accretion mechanism, the space environment in which they formed, and their subsequent geological evolution. We show that the Rosetta magnetometry requires very low bulk magnetizations of cometary material on spatial scales >/=10 cm. If 67P formed during the lifetime of the solar nebula and has not undergone significant subsequent alteration, this low magnetization is inconsistent with its formation from the gentle gravitational collapse of a cloud of millimeter-sized pebbles in a background magnetic field >/~3 [mu]T. This constraint is compatible with theories of magnetically driven evolution of protoplanetary disks.Lastly, this thesis presents the first attempt to determine an exoplanet's oblateness and obliquity through the use of changes in the transit depth caused by the spin precession of an oblate planet. Determination of these quantities would provide insights into a planet's internal structure and formation history. Using Kepler photometry, we examine the brown dwarf Kepler-39b and the warm Saturn Kepler-427b. We do not usefully constrain the oblateness of Kepler-39b, but we find transit depth variations for Kepler-427b at 90% significance consistent with a precession period of 5.5 years and an oblateness comparable to solar system gas giants.by John Brooks Biersteker.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Science