All planets and stars rotate. All gas planets in our solar system, the Sun, and many stars show a pattern of east- or westward mean flows. This phenomenon is known as differential rotation in the stellar and as zonal jets in the planetary context. Observations, laboratory experiments and simulations show that the zonal flow kinetic energy scales like $\ell^{-5}$, where $\ell$ is the spherical harmonic degree (which is effectively a latitudinal wave number). Here, we analyze observation of the Sun, as well as simulations of the dynamics in Saturn and in the outer atmosphere of an ultra-hot Jupiter. While these systems are very different, they all develop strong zonal winds that obey the $\ell^{-5}$ scaling. Our results strongly suggest that there is a simple common mechanism that shapes zonal mean flows in planets and stars independent of the flow driving.
Kolja Joeris, Matthias Keulen, Jonathan E. Kollmer
We detail a platform for partial g environment and an experiment for simulated impacts on asteroid surfaces based on it. The partial g environment is created by a two stage approach: First, create microgravity using the ZARM drop tower. Second, convert microgravity to partial gravity by steady acceleration of experiment volume on linear drive inside microgravity environment. The experiment we conducted on this platform simulates low-velocity impacts into a simulated asteroid surface. To recreate the asteroid environment, in addition to the partial gravity, a vacuum chamber is used. We explain requirements, setup and operation of partial gravity platform and experiment and discuss its performance. Finally, we are open for requests for external experiments which might benefit from our platform with $9.3\,$s of controlled partial gravity down to the mm/s$^2$ range with low g-jitter.
In preceding papers, Project Lyra has covered many possible trajectory options available to a spacecraft bound for 1I/Oumuamua, including Solar Oberth manoeuvres, Passive Jupiter encounters, Jupiter Oberths, Double Jupiter Gravitational Assists, etc. Because feasibility was the key driver for this analysis, the important question of which launcher to exploit was largely skirted in favour of adopting the most powerful options as being sufficient, though these launchers are clearly not necessary, there being alternative less capable candidates which could be utilised instead. In this paper the various launch options available to Project Lyra are addressed to allow a general overview of their capabilities. It is found that the SpaceX Super-Heavy Starship would be a game-changer for Project Lyra, especially in the context of refuelling in LEO, and furthermore a SpaceX Falcon Heavy Expendable could also be utilised. Other launchers are considered, including Ariane 6 and the future Chinese Long March 9. The importance of the V infinity Leveraging Manoeuvre (VILM) in permitting less capable launchers to nevertheless deliver a payload to Oumuamua is elaborated
Este artigo de revisão apresenta uma introdução à Cosmologia Quântica, incluindo os métodos matemáticos fundamentais para a abordagem canônica, alguns dos problemas conceituais existentes e a conexão dos modelos com possíveis observáveis.
Cyclic activity on the Sun and stars is primarily explained by generation of the magnetic field by a dynamo mechanism, which converts the energy of the poloidal field into the energy of the toroidal component due to differential rotation. There is, however, an alternative point of view, which explains the field generation by gravitational influence of the planetary system and, first of all, Jupiter. This hypothesis can be verified by comparing the characteristics of exoplanets with the activity variations on their associated stars. We have performed such a comparison and have drawn a negative conclusion. No relationship between the gravitational influence of the exoplanets and cycle of the host star could be found in any of the cases considered. Moreover, there are reasons to believe that a strong gravitational influence may completely eliminate cyclic variation in stellar activity.
Uma nova geração de telescópios está prestes a elevar nosso conhecimento astrofísico e cosmológico a outro patamar, e neste contexto se insere a colaboração J-PAS. Este artigo apresenta as características desta colaboração, com particular foco nos equipamentos que compõem o Observatório Astrofísico de Javalambre e nas suas peculiaridades. Os objetivos e alguns projetos-chave, envolvendo dezenas de instituições de diferentes nacionalidades, são brevemente apresentados. Apesar de inicialmente concebido como observatório dedicado à observação de oscilações acústicas bariônicas e estudos de propriedades da energia escura, a astronomia se beneficiará dos futuros catálogos de dados do J-PAS em diversas escalas.
Buracos negros podem ser estudados de diferentes maneiras. A partir das equações da relatividade geral geral, passando por observações em raios X e ondas gravitacionais, podemos tentar entender diferentes aspectos destes objetos astrofísicos. Também é possível que existam objetos ainda mais exóticos disfarçados de buracos negros no universo.
Although habitability, defined as the general possibility of hosting life, is expected to occur under a broad range of conditions, the standard scenario to allow for habitable environments is often described through habitable zones (HZs). Previous work indicates that stellar binary systems typically possess S-type or P-type HZs, with the S-type HZs forming ring-type structures around the individual stars and P-type HZs forming similar structures around both stars, if considered a pair. However, depending on the stellar and orbital parameters of the system, typically, there are also regions within the systems outside of the HZs, referred to as dead zones (DZs). In this study, we will convey quantitative information on the width and location of DZs for various systems. The results will also depend on the definition of the stellar HZs as those are informed by the planetary climate models.
A monomodal model for stellar and planetary convection is derived for the magnitude of the rms velocity, degree of superadiabaticity, and characteristic length scale as a function of rotation rate as well as with thermal and viscous diffusivities. The convection model is used as a boundary condition for a linearization of the equations of motion in the transition region between convectively unstable and stably-stratified regions, yielding the depth to which convection penetrates into the stable region and establishing a relationship between that depth and the local convective Rossby number, diffusivity, and pressure scale height of those flows. Upward and downward penetrative convection have a similar scaling with rotation rate and diffusivities, but they depend differently upon the pressure scale height due to the differing energetic processes occurring in convective cores of early-type stars versus convective envelopes of late-type stars.
There is a long history of radio telescopes being used to augment the radio antennas regularly used to conduct telemetry, tracking, and command of deep space spacecraft. Radio telescopes are particularly valuable during short-duration mission critical events, such as planetary landings, or when a mission lifetime itself is short, such as a probe into a giant planet's atmosphere. By virtue of its high sensitivity and frequency coverage, the next-generation Very Large Array would be a powerful addition to regular spacecraft ground systems. Further, the science focus of many of these deep-space missions provides a "ground truth" in the solar system that complements other aspects of the ngVLA's science case, such as the formation of planets in proto-planetary disks.
Benjamin J. Fulton, Erik A. Petigura, Sarah Blunt
et al.
RadVel is an open source Python package for modeling Keplerian orbits in radial velocity (RV) time series. RadVel provides a convenient framework to fit RVs using maximum a posteriori optimization and to compute robust confidence intervals by sampling the posterior probability density via Markov Chain Monte Carlo (MCMC). RadVel allows users to float or fix parameters, impose priors, and perform Bayesian model comparison. We have implemented realtime MCMC convergence tests to ensure adequate sampling of the posterior. RadVel can output a number of publication-quality plots and tables. Users may interface with RadVel through a convenient command-line interface or directly from Python. The code is object-oriented and thus naturally extensible. We encourage contributions from the community. Documentation is available at http://radvel.readthedocs.io.
In this article we review the methods used to determine the gas and dust masses of protoplanetary disks, with an emphasis on the lesser characterized total gas mass. Our review encompasses all the indirect tracers and the methodology that is be used to isolate the hidden H2 via dust, CO, and HD emission. We discuss the overall calibration of gaseous tracers which is based on decades of study of the dense phases of the interstellar medium. At present, disk gas masses determined via CO and HD are (in a few instances) different by orders of magnitude, hinting at either significant evolution in total disk mass or in the CO abundance . Either of these would represent a fundamental physical or chemical process that appears to dominate the system on ~million year timescales. Efforts to reconcile these differences using existing and future facilities are discussed.
Eclipsing binary stars have long served as benchmark systems to measure fundamental stellar properties. In the past few decades, asteroseismology - the study of stellar pulsations - has emerged as a new powerful tool to study the structure and evolution of stars across the HR diagram. Pulsating stars in eclipsing binary systems are particularly valuable since fundamental properties (such as radii and masses) can determined using two independent techniques. Furthermore, independently measured properties from binary orbits can be used to improve asteroseismic modeling for pulsating stars in which mode identifications are not straightforward. This contribution provides a review of asteroseismic detections in eclipsing binary stars, with a focus on space-based missions such as CoRoT and Kepler, and empirical tests of asteroseismic scaling relations for stochastic ("solar-like") oscillations.
Stellar activity can produce large amounts of high-energy radiation, which is absorbed by the planetary atmosphere leading to irradiation-driven mass-loss. We present the detection and an investigation of high-energy emission in a transiting super-Earth host system, GJ 1214, based on an XMM-Newton observation. We derive an X-ray luminosity LX=7.4E25 erg/s and a corresponding activity level of log(LX/Lbol)~ -5.3. Further, we determine a coronal temperature of about -3.5 MK, which is typical for coronal emission of moderately active low-mass stars. We estimate that GJ 1214 b evaporates at a rate of 1.3E10 g/s and has lost a total of ~2-5.6 MEarth.
Siegfried Eggl, Anatoliy Ivantsov, Daniel Hestroffer
et al.
Among the currently known Near Earth Objects (NEOs), roughly 1400 are classified as being potentially hazardous asteroids. The recent Chelyabinsk event has shown that these objects can pose a real threat to mankind. We illustrate that high precision asteroid astrometry plays a vital role in determining potential impact risks, selecting targets for deflection demonstration missions and evaluating mitigation mission success. After a brief introduction to the NEOShield project, an international effort initiated by the European Commission to investigate aspects of NEO mitigation in a comprehensive fashion, we discuss current astrometric performances, requirements and possible issues with NEO risk assessment and deflection demonstration missions.