Exploring the Nu2 Lupi system with CHEOPS

<p>***Results under embargo. Paper accepted for publication at Nature Astronomy, to be published in June.***</p> <p>Multi-transiting planetary systems around bright stars offer unique windows to comparative exoplanetology. Nu2 Lupi (HD 136352) is a naked-eye (V=5.8) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6, and 107.6 days via radial velocity monitoring with the HARPS spectrograph. The two inner planets (b and c) were recently found to transit by the TESS mission, prompting us to follow up the system with ESA's brand-new CHaracterizing ExOPlanets Satellite (CHEOPS). This led to the exciting discovery that the outer planet d is also transiting. With its bright Sun-like star, long period, and mild irradiation (∼5.7 times the irradiation of Earth), Nu2 Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. By combining all available space and ground-based data, we measured its radius and mass to be 2.56±0.09 R<sub>Earth</sub> and 8.82±0.94 M<sub>Earth</sub>, respectively, and refined the properties of all three planets: planet b likely has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the Nu2 Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.</p>

Atmospheric Entry Probes in the Outer Solar System: Developing a Software Tool to Assess Trajectory Options

<p>The composition of outer planet atmospheres holds fundamental clues to understanding the formation and evolution of the solar system. Measurements of noble gas abundances and key isotope ratios help constrain formation models, and along with measurements of atmospheric structure and dynamics they reveal formation and evolutionary processes [1], [2]. These enable conclusions about giant planet formation and possible migration during the epoch of solar system formation. With the Galileo Probe laying the foundation of in situ atmospheric measurements of the outer planets by exploring Jupiter, entry probe missions to Saturn, Uranus and Neptune are essential to complete the picture of how our solar system evolved to its present state.</p> <p> </p> <p>During the development of entry probe missions, the interplanetary and probe approach trajectory, as well as the selection of the entry interface zone, are critical elements to mission success. Both elements are driven by considerations such as spacecraft safety (e.g. avoiding rings), while balancing science and engineering requirements at the same time (e.g. highly interesting science and entry zone vs. optimal communication geometry between probe and relay spacecraft). Due to the complexity of the problem, there is no analytical solution for finding the ‘best’ trajectory. Instead, one relies on the experience and intuition of mission designers to select a few possible interplanetary trajectories, which are then explored in detail to see how they meet science and engineering requirements. This approach leaves a huge trade space unexplored and may find a local, rather than a global optimum trajectory for the mission.</p> <p> </p> <p>We are addressing this gap by developing a software tool called <em>VAPRE</em> (<strong>V</strong>isualization of <strong>A</strong>tmospheric <strong>PR</strong>obe <strong>E</strong>ntry Conditions for different bodies and trajectories)<em> </em>[3], [4] that allows us to explore those previously unexplored trade spaces. <em>VAPRE</em> can process thousands of trajectories, significantly more than in the currently common mission design processes. Due to its flexible architecture, <em>VAPRE</em> can be adapted and extended to accommodate new science and engineering constraints for different or similar mission scenarios. In our talk, we will present an example of how the tool can be used to design a flyby mission to a giant planet that delivers an atmospheric probe considering opportunities between 2028 and 2042.</p>

A comprehensive investigation of the Galilean moon, Io, by tracing mass and energy flows

Io is the most volcanically-active object in the solar system. The moon ejects a tonne per second of sulphur-rich gases that fill the vast magnetosphere of Jupiter and drives million-amp electrical currents that excite strong auroral emissions. We present the case for including a detailed study of Io within Voyage 2050 either as a standalone mission or as a contribution to a NASA New Frontiers mission, possibly within a Solar System theme centred around current evolutionary or dynamical processes. A comprehensive investigation will provide answers to many outstanding questions and will simultaneously provide information on processes that have formed the landscapes of several other objects in the past. A mission investigating Io will also study processes that have shaped the Earth, Moon, terrestrial planets, outer planet moons, and potentially extrasolar planets. The aim would be simple – tracing the mass and energy flows in the Io-Jupiter system.

Toward constraining Saturn's rotation rate by interior modeling

<p>The rotation rate of the outer planet Saturn is not well constrained by classical measurements of periodic signals [1]. Recent and diverse approaches using a broad spectrum of Cassini and other observational data related to shape, winds, and oscillations are converging toward a value about 6 to 7 minutes faster than the Voyager rotation period.<br>Here we present our method of using zonal wind data and the even harmonics J<sub>2</sub> to J<sub>10</sub> measured during the Cassini Grand Finale tour [2] to infer the deep rotation rate of Saturn. We assume differential rotation on cylinders and generate adiabatic density profiles that match the low-order J<sub>2</sub> and J<sub>4</sub><br>values. Theory of Figures to 7th order is applied to estimate the differences in the high-order moments J<sub>6 </sub>to J<sub>10</sub> that may result from the winds and the assumed reference rotation rate. Presented results are preliminary as the method is under construction [3].</p><p>[1] Fortney, Helled, Nettelmann et al, in: 'Saturn in the 21st century', Cambridge U Press (2018)<br>[2] Iess, Militzer, Kaspi, Science 364:2965 (2019)<br>[3] Nettelmann, AGU Fall Meeting, P066-0007 (2020)</p><p> </p>

Elastic Electron Scattering from Methane Molecule in the Energy Range from 50–300 eV

Electron interaction with methane molecule and accurate determination of its elastic cross-section is a demanding task for both experimental and theoretical standpoints and relevant for our better understanding of the processes in Earth’s and Solar outer planet atmospheres, the greenhouse effect or in plasma physics applications like vapor deposition, complex plasma-wall interactions and edge plasma regions of Tokamak. Methane can serve as a test molecule for advancing novel electron-molecule collision theories. We present a combined experimental and theoretical study of the elastic electron differential cross-section from methane molecule, as well as integral and momentum transfer cross-sections in the intermediate energy range (50–300 eV). The experimental setup, based on a crossed beam technique, comprising of an electron gun, a single capillary gas needle and detection system with a channeltron is used in the measurements. The absolute values for cross-sections are obtained by relative-flow method, using argon as a reference. Theoretical results are acquired using two approximations: simple sum of individual atomic cross-sections and the other with molecular effect taken into the account.