The Weak Equivalence Principle is the founding pillar of General Relativityand as such it should be verified as precisely as possible. The Microscopeexperiment tested it in low Earth orbit, finding that Pt and Ti test massesfall toward Earth with the same acceleration to about 1e-15, an improvement ofabout two orders of magnitude over ground tests. Space missions, even if small,are expensive and hard to replicate; yet, the essence of physics isrepeatability. This work is an assessment of the Microscope results based onthe laws of physics and knowledge from previous experiments, focusing on thelimiting thermal noise and the treatment of acceleration outliers. Thermalnoise reveals anomalies that we explain by stray sub-microVolt potentialscaused by patch charges, giving rise to an unstable zero. The measurements wereaffected by numerous acceleration spikes occurring at the synodic frequenciesrelative to the Earth (the signal frequency) and the Sun, which we interpret asevidence of a thermal origin. In Microscope authors' analysis, the spikes wereremoved and the resulting gaps replaced with artificial data (up to 35, 40 percent of the sessions data), which retain memory of the gaps and may simulate orcancel an effect (signal or systematic). An alternative approach basedexclusively on real measured data would avoid any ambiguity. The lessons ofMicroscope are crucial to any futures improved mission.
ExoSim 2 is the next generation of the Exoplanet Observation Simulator(ExoSim) tailored for spectro-photometric observations of transiting exoplanetsfrom space, ground, and sub-orbital platforms. This software is a completerewrite implemented in Python 3, embracing object-oriented design principles,which allow users to replace each component with their functions when required.ExoSim 2 is publicly available on GitHub, serving as a valuable resource forthe scientific community. ExoSim 2 employs a modular architecture using Taskclasses, encapsulating simulation algorithms and functions. This flexibledesign facilitates the extensibility and adaptability of ExoSim 2 to diverseinstrument configurations to address the evolving needs of the scientificcommunity. Data management within ExoSim 2 is handled by the Signal class,which represents a structured data cube incorporating time, space, and spectraldimensions. The code execution in ExoSim 2 follows a three-step workflow: thecreation of focal planes, the production of Sub-Exposure blocks, and thegeneration of non-destructive reads (NDRs). Each step can be executedindependently, optimizing time and computational resources. ExoSim 2 has beenextensively validated against other tools like ArielRad and has demonstratedconsistency in estimating photon conversion efficiency, saturation time, andsignal generation. The simulator has also been validated independently forinstantaneous read-out and jitter simulation, and for astronomical signalrepresentation. In conclusion, ExoSim 2 offers a robust and flexible tool forexoplanet observation simulation, capable of adapting to diverse instrumentconfigurations and evolving scientific needs. Its design principles andvalidation results underscore its potential as a valuable resource in the fieldof exoplanet research.
Since the Voyager mission flybys in 1979, we have known the moon Io to beboth volcanically active and the main source of plasma in the vastmagnetosphere of Jupiter. Material lost from Io forms neutral clouds, the Ioplasma torus and ultimately the extended plasma sheet. This material issupplied from Io's upper atmosphere and atmospheric loss is likely driven byplasma-interaction effects with possible contributions from thermal escape andphotochemistry-driven escape. Direct volcanic escape is negligible. The supplyof material to maintain the plasma torus has been estimated from variousmethods at roughly one ton per second. Most of the time the magnetosphericplasma environment of Io is stable on timescales from days to months.Similarly, Io's atmosphere was found to have a stable average density on thedayside, although it exhibits lateral and temporal variations. There ispotential positive feedback in the Io torus supply: collisions of torus plasmawith atmospheric neutrals are probably a significant loss process, whichincreases with torus density. The stability of the torus environment may bemaintained by limiting mechanisms of either torus supply from Io or the lossfrom the torus by centrifugal interchange in the middle magnetosphere. Variousobservations suggest that occasionally the plasma torus undergoes majortransient changes over a period of several weeks, apparently overcomingpossible stabilizing mechanisms. Such events are commonly explained by somekind of change in volcanic activity that triggers a chain of reactions whichmodify the plasma torus state via a net change in supply of new mass. However,it remains unknown what kind of volcanic event (if any) can trigger events intorus and magnetosphere, whether Io's atmosphere undergoes a general changebefore or during such events, and what processes could enable such a change inthe otherwise stable torus.