The habitability of the surface of any planet is determined by a complex evolution of its interior, surface, and atmosphere. The electromagnetic and particle radiation of stars drive thermal, chemical and physical alteration of planetary atmospheres, including escape. Many known extrasolar planets experience vastly different stellar environments than those in our Solar system: it is crucial to understand the broad range of processes that lead to atmospheric escape and evolution under a wide range of conditions if we are to assess the habitability of worlds around other stars. One problem encountered between the planetary and the astrophysics communities is a lack of common language for describing escape processes. Each community has customary approximations that may be questioned by the other, such as the hypothesis of H-dominated thermosphere for astrophysicists, or the Sun-like nature of the stars for planetary scientists. Since exoplanets are becoming one of the main targets for the detection of life, a common set of definitions and hypotheses are required. We review the different escape mechanisms proposed for the evolution of planetary and exoplanetary atmospheres. We propose a common definition for the different escape mechanisms, and we show the important parameters to take into account when evaluating the escape at a planet in time. We show that the paradigm of the magnetic field as an atmospheric shield should be changed and that recent work on the history of Xenon in Earth’s atmosphere gives an elegant explanation to its enrichment in heavier isotopes: the so-called Xenon paradox.

Relative sea-level rise is a major coastal hazard affecting about half the population of the United States. The Chesapeake Bay is characterized by the fastest rate of sea-level rise along the Atlantic coast of North America, in part because of land subsidence. Previous studies have quantified a range of land subsidence rates in the Chesapeake Bay (~1-4 mm/yr) from various measurement techniques that contribute to high rates of relative sea-level rise. In this study, we present progress towards developing a new vertical land motion map for the Chesapeake Bay region to provide more robust constraints on estimates of relative sea-level rise. We are using a combination of GNSS observations and InSAR interferograms. Available continuous GNSS data in the region that span November 2014 - September 2020 are processed with GAMIT-GLOBK to align temporally with available Sentinel-1 InSAR satellite data. We are using an approach that combines the two geodetic observations to provide a new solution of vertical land motions for the Chesapeake Bay. Additionally, this project is collecting new campaign GNSS observations across the Chesapeake Bay each fall for 5 years, beginning in 2019. We will also present about the 2020 and planned 2021 campaign GNSS observations, which will ultimately be incorporated into our new map of vertical land motions for the region. The impacts of this work will be improved flooding and inundation hazard maps, as well as updated projections for municipal flood mitigation planning that will be created using the new dataset.

Mantle convection is driven by the transport of heat from a planetary interior. This heat may come from the internal energy of the mantle or may come from the core beneath and in general there will be contributions from both. Past investigations of mixed-mode heating have revealed unusual behavior that confounds our intuition based on boundary layer theory applied to end-member cases. In particular, increased internal heating can cause a decrease in convective velocity despite an increase in surface heat flow. We investigate this behavior using numerical experiments and develop a scaling for velocity in the mixed-heating case. We identify a planform transition that impacts both heat flux and convective velocities. More significantly, we demonstrate that increased internal heating leads not only to a decrease in internal velocities but also a decrease in the velocity of the upper thermal boundary layer (a model analog of the Earth’s lithosphere). This behavior is connected to boundary layer interactions and is independent of any partic- ular rheological assumptions. In simulations with a temperature-dependent viscosity and a finite yield stress, increased internal heating does not cause an absolute decrease in surface velocity but does cause a decrease in sur- face velocity relative to the purely bottom or internally heated cases as well as a transition to rigid-lid behavior at high heating rates. The differences between a mixed system and end-member cases have implications for under- standing the connection between plate tectonics and mantle convection and for planetary thermal history modeling.