Search

The census of known exoplanets exhibits a variety of physical parameters, including densities that are measured to span the range from less dense than styrofoam to more dense than iron. These densities represent a large diversity of interior structures. Despite this staggering diversity, recent analyses have shown that the densities of planets that orbit a common star exhibit remarkable uniformity. A fascinating exception to this is the system HIP 41378 (also known as K2-93), which contains a super-puff planet, HIP 41378 f, as well as several planets with more typical bulk densities. The range of densities in this system begs the question of what physical processes are responsible for the disparate planetary structures in this system. In this paper, we consider how the densities of the planets in the HIP 41378 system would have changed over time as the host star evolved and the planets' atmospheres were subsequently affected by the evolving insolation level. We also present a range of allowable core masses for HIP 41378 f based on the measured planet parameters, and comment on the feasibility of the proposed existence of planetary rings around HIP 41378 f as an explanation for its current low density., Comment: Accepted to The Astronomical Journal

GJ 229B was the first T-dwarf to be discovered in 1995, and its spectrum has been more thoroughly observed than most other brown dwarfs. Yet a full spectroscopic analysis of its atmosphere has not been done with modern techniques. This spectrum has several peculiar features, and recent dynamical estimates of GJ 229B's mass and orbit have disagreed widely, both of which warrant closer investigation. With a separation of tens of AU from its host star, GJ 229B falls near the border of the planet and stellar population formation regimes, so its atmosphere could provide clues to formation processes for intermediate objects of this type. In an effort to resolve these questions, we performed retrievals on published spectra of GJ 229B over a wide range of wavelengths (0.5-5.1 ${\rm \mu m}$) using the open-source APOLLO code. Based on these retrievals, we present a more precise mass estimate of $41.6\pm3.3\, M_J$ and an effective temperature estimate of $869_{-7}^{+5}$ K, which are more consistent with evolutionary models for brown dwarfs and suggest an older age for the system of $>$1.0 Gyr. We also present retrieved molecular abundances for the atmosphere, including replicating the previously-observed high CO abundance, and discuss their implications for the formation and evolution of this object. This retrieval effort will give us insight into how to study other brown dwarfs and directly-imaged planets, including those observed with JWST and other next-generation telescopes., Comment: 32 pages, 11 figures, 5 tables, accepted for publication in ApJ

The similarity of Venus and Earth in bulk properties make Venus an appealing target for future colonization. Several proposals have been put forward for colonizing and even terraforming Venus despite the extreme conditions on the planet's surface. Such a terraforming project would face large challenges centered around removing Venus's massive carbon dioxide atmosphere and replacing it with a habitable environment. I review past proposals and propose a new method for terraforming Venus by building an artificial surface in the much more hospitable upper atmosphere where the temperature and pressure are both Earth-like. Such a surface could be built with locally produced materials and would float above the bulk of the atmosphere using nitrogen as a lifting gas. This would allow the engineering of a breathable atmosphere above the surface and would remove the need to import or export extreme amounts of mass, except for comparatively modest quantities of water. The engineering, logistical, and energy requirements of this method are surveyed. I find that such a terraforming project could be completed in a minimum of 200 years in a best-case scenario, comparable to other proposals, with significantly lower resource costs., Comment: 15 pages, 1 figure, 5 pages

We report an improved measurement of the degree-scale cosmic microwave background $B$-mode angular-power spectrum over 670 square-degree sky area at 150 GHz with POLARBEAR. In the original analysis of the data, errors in the angle measurement of the continuously rotating half-wave plate, a polarization modulator, caused significant data loss. By introducing an angle-correction algorithm, the data volume is increased by a factor of 1.8. We report a new analysis using the larger data set. We find the measured $B$-mode spectrum is consistent with the $\Lambda$CDM model with Galactic dust foregrounds. We estimate the contamination of the foreground by cross-correlating our data and Planck 143, 217, and 353 GHz measurements, where its spectrum is modeled as a power law in angular scale and a modified blackbody in frequency. We place an upper limit on the tensor-to-scalar ratio $r$ < 0.33 at 95% confidence level after marginalizing over the foreground parameters., Comment: 16 pages, 9 figures, 8 tables, Published in ApJ

One clear aspect of behaviour in the COVID-19 pandemic has been people's focus on, and response to, reported or observed infection numbers in their community. We describe a simple model of infectious disease spread in a pandemic situation where people's behaviour is influenced by the current risk of infection and where this behavioural response acts homeostatically to return infection risk to a certain preferred level. This model predicts that the reproduction rate $R$ will be centered around a median value of 1, and that a related measure of relative change in the number of new infections will follow the standard Cauchy distribution. Analysis of worldwide COVID-19 data shows that the estimated reproduction rate has a median of 1, and that this measure of relative change calculated from reported numbers of new infections closely follows the standard Cauchy distribution at both an overall and an individual country level., Comment: 9 pages, submitted

We present Myriad, a testbed written in JAX for learning and planning in real-world continuous environments. The primary contributions of Myriad are threefold. First, Myriad provides machine learning practitioners access to trajectory optimization techniques for application within a typical automatic differentiation workflow. Second, Myriad presents many real-world optimal control problems, ranging from biology to medicine to engineering, for use by the machine learning community. Formulated in continuous space and time, these environments retain some of the complexity of real-world systems often abstracted away by standard benchmarks. As such, Myriad strives to serve as a stepping stone towards application of modern machine learning techniques for impactful real-world tasks. Finally, we use the Myriad repository to showcase a novel approach for learning and control tasks. Trained in a fully end-to-end fashion, our model leverages an implicit planning module over neural ordinary differential equations, enabling simultaneous learning and planning with complex environment dynamics., Comment: Updated to match version accepted at NeurIPS 2022

We present the first measurements of asteroids in millimeter wavelength (mm) data from the South Pole Telescope (SPT), which is used primarily to study the cosmic microwave background (CMB). We analyze maps of two $\sim270$ deg$^2$ sky regions near the ecliptic plane, each observed with the SPTpol camera $\sim100$ times over one month. We subtract the mean of all maps of a given field, removing static sky signal, and then average the mean-subtracted maps at known asteroid locations. We detect three asteroids$\text{ -- }$(324) Bamberga, (13) Egeria, and (22) Kalliope$\text{ -- }$with signal-to-noise ratios (S/N) of 11.2, 10.4, and 6.1, respectively, at 2.0 mm (150 GHz); we also detect (324) Bamberga with S/N of 4.1 at 3.2 mm (95 GHz). We place constraints on these asteroids' effective emissivities, brightness temperatures, and light curve modulation amplitude. Our flux density measurements of (324) Bamberga and (13) Egeria roughly agree with predictions, while our measurements of (22) Kalliope suggest lower flux, corresponding to effective emissivities of $0.66 \pm 0.11$ at 2.0 mm and $<0.47$ at 3.2mm. We predict the asteroids detectable in other SPT datasets and find good agreement with detections of (772) Tanete and (1093) Freda in recent data from the SPT-3G camera, which has $\sim10 \times$ the mapping speed of SPTpol. This work is the first focused analysis of asteroids in data from CMB surveys, and it demonstrates we can repurpose historic and future datasets for asteroid studies. Future SPT measurements can help constrain the distribution of surface properties over a larger asteroid population., Comment: 21 pages, 9 figures

Photosystems II and I (PSII and PSI) are the reaction centre complexes that drive the light reactions of photosynthesis. PSII performs light-driven water oxidation (quantum efficiencies and catalysis rates of up to 80% and 1000 $e^{-}\text{s}^{-1}$, respectively) and PSI further photo-energises the harvested electrons (quantum efficiencies of ~100%). The impressive performance of the light harvesting components of photosynthesis has motivated extensive biological, artificial and biohybrid approaches to re-wire photosynthesis to enable higher efficiencies and new reaction pathways, such as H2 evolution or alternative CO2 fixation. To date these approaches have focussed on charge extraction at the terminal electron quinones of PSII and terminal iron-sulfur clusters of PSI. Ideally electron extraction would be possible immediately from the photoexcited reaction centres to enable the greatest thermodynamic gains. However, this was believed to be impossible because the reaction centres are buried around 4 nm within PSII and 5 nm within PSI from the cytoplasmic face. Here, we demonstrate using in vivo ultrafast transient absorption (TA) spectroscopy that it is possible to extract electrons directly from photoexcited PSI and PSII, using both live cyanobacterial cells and isolated photosystems, with the exogenous electron mediator 2,6-dichloro1,4-benzoquinone (DCBQ). We postulate that DCBQ can oxidise peripheral chlorophyll pigments participating in highly delocalised charge transfer (CT) states after initial photoexcitation. Our results open new avenues to study and re-wire photosynthesis for bioenergy and semi-artificial photosynthesis.