Oceanic tides for ocean planets

Oceanic tides from Earth-like to ocean planets

ABSTRACT: Oceanic tides are a major source of tidal dissipation. They drive the evolution of planetary systems and the rotational dynamics of planets. However, 2D models commonly used for the Earth cannot be applied to extrasolar telluric planets hosting potentially deep oceans because they ignore the three-dimensional effects related to the ocean vertical structure. Our goal is to investigate in a consistant way the importance of the contribution of internal gravity waves in the oceanic tidal response and to propose a modeling allowing to treat a wide range of cases from shallow to deep oceans. A 3D ab initio model is developed to study the dynamics of a global planetary ocean. This model takes into account compressibility, stratification and sphericity terms, which are usually ignored in 2D approaches. An analytic solution is computed and used to study the dependence of the tidal response on the tidal frequency and on the ocean depth and stratification. In the 2D asymptotic limit, we recover the frequency-resonant behaviour due to surface inertial-gravity waves identified by early studies. As the ocean depth and Brunt-Väisälä frequency increase, the contribution of internal gravity waves grows in importance and the tidal response become three-dimensional. In the case of deep oceans, the stable stratification induces resonances that can increase the tidal dissipation rate by several orders of magnitude. It is thus able to affect significantly the evolution time scale of the planetary rotation.


Self-organization of planetary systems

Stability and self-organization of planetary systems

ABSTRACT: We show that stability of planetary systems is intimately connected with their internal order. An arbitrary initial distribution of planets is susceptible to catastrophic events in which planets either collide or are ejected from the planetary system. These instabilities are a fundamental consequence of chaotic dynamics and of Arnold diffusion characteristic of many body gravitational interactions. To ensure stability over astronomical time scale of a realistic planetary system — in which planets have masses comparable or those of planets in the solar system — the motion must be quasi-periodic. A dynamical mechanism is proposed which naturally evolves a planetary system to a periodic state from an arbitrary initial condition. A planetary self-organization predicted by the theory is similar to the one found in our solar system.


Satellites of large Kuiper belt objects

Medium-sized satellites of large Kuiper belt objects

ABSTRACT: While satellites of mid- to small-Kuiper belt objects tend to be similar in size and brightness to their primaries, the largest Kuiper belt objects preferentially have satellites with small fractional brightness. In the two cases where the sizes and albedos of the small faint satellites have been measured, these satellites are seen to be small icy fragments consistent with collisional formation. Here we examine Dysnomia and Vanth, the satellites of Eris and Orcus, respectively. Using the Atacama Large Millimeter Array (ALMA), we obtain the first spatially resolved observations of these systems at thermal wavelengths. We find a diameter for Dysnomia of 700±115 km and for Vanth of 475±75 km, with albedos of 0.04+0.02-0.01 and 0.08±0.02 respectively. Both Dysnomia and Vanth are indistinguishable from typical Kuiper belt objects of their size. Potential implications for the formation of these types of satellites are discussed.

EPIC 210897587: Three Super-Earths

EPIC 210897587: A Bright Metal-Poor M Dwarf with Three Transiting Super-Earths

ABSTRACT: We report on the discovery of three transiting super-Earths around EPIC 210897587, a relatively bright early M dwarf (V=12.81 mag) observed during Campaign 13 of the NASA K2 mission. To characterize the system and validate the planet candidates, we conducted speckle imaging and high-dispersion optical spectroscopy, including radial velocity measurements. Based on the K2 light curve and the spectroscopic characterization of the host star, the planet sizes and orbital periods are 1.55-0.17+0.20 R and 6.34365±0.00028 days for the inner planet; 1.95-0.22+0.27 R and 13.85402±0.00088 days for the middle planet; and 1.64-0.17+0.18 R and 40.6835±0.0031 days for the outer planet. The outer planet (EPIC 210897587.3) is near the habitable zone, with an insolation 1.67±0.38 times that of the Earth. The planet’s radius falls within the range between that of smaller rocky planets and larger gas-rich planets. To assess the habitability of this planet, we present a series of 3D global climate simulations assuming that EPIC 210897587.3 is tidally locked and has an Earth-like composition and atmosphere. We find that the planet can maintain a moderate surface temperature if the insolation proves to be smaller than ∼ 1.5 × that of the Earth. Doppler mass measurements, transit spectroscopy, and other follow-up observations should be rewarding, since EPIC 210897587 is one of the optically brightest M dwarfs known to harbor transiting planets.

Foo over UDP

Jonathan Corbet on UDP tunneling

Tunneling protocols are increasingly important in modern networking setups. By tying distant networks together, they enable the creation of virtual private networks, access to otherwise-firewalled ports, and more. Tunneling can happen at multiple levels in the networking stack; SSH tunnels are implemented over TCP, while protocols like GRE and IPIP work directly at the IP level. Increasingly, though, there is interest in implementing tunneling inside the UDP protocol. The “foo over UDP” (FOU) patch set from Tom Herbert, which has been pulled into the net-next tree for 3.18, implements UDP-level tunneling in a generic manner.

Why UDP? Just about any network interface out there has hardware support for UDP at this point, handling details like checksumming. UDP adds just enough information (port numbers, in particular) to make the routing of encapsulated packets easy. UDP can also be made to work with protocols like Receive Side Scaling (RSS) and the Equal-cost multipath routing protocol (ECMP) to improve performance in highly connected settings. The advantages of UDP tunneling are enough that some developers think it’s going to become nearly ubiquitous in the coming years.

Packet encapsulation and tunneling over UDP is a relatively straightforward concept to understand. Suppose a simple TCP packet is presented to the tunneling interface:

TCP package

This packet has the usual IP and TCP headers, followed by the data the user wishes to send. The encapsulation process does something like this:

Fou encapsulation

At this point, the packet looks like a UDP packet that happens to have a TCP packet buried within it. The system can now transmit it to the destination as an ordinary UDP packet; at the receiving end, the extra headers will be stripped off and the original packet will be fed into the network stack.


Rings and gaps in Elias 24

Rings and gaps in the disc around Elias 24 revealed by ALMA

ABSTRACT: We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle 2 observations of the 1.3 mm dust continuum emission of the protoplanetary disc surrounding the T Tauri star Elias 24 with an angular resolution of ∼0.2″ (∼28 au). The dust continuum emission map reveals a dark ring at a radial distance of 0.47″ (∼65 au) from the central star, surrounded by a bright ring at 0.58″ (∼81 au). In the outer disc, the radial intensity profile shows two inflection points at 0.71″ and 0.87″ (99 and 121 au respectively). We perform global three-dimensional smoothed particle hydrodynamic gas/dust simulations of discs hosting a migrating and accreting planet. Combining the dust density maps of small and large grains with three dimensional radiative transfer calculations, we produce synthetic ALMA observations of a variety of disc models in order to reproduce the gap- and ring-like features observed in Elias 24. We find that the dust emission across the disc is consistent with the presence of an embedded planet with a mass of ∼0.7 MJ at an orbital radius of ∼60 au. Our model suggests that the two inflection points in the radial intensity profile are due to the inward radial motion of large dust grains from the outer disc. The surface brightness map of our disc model provides a reasonable match to the gap- and ring-like structures observed in Elias 24, with an average discrepancy of ∼ 5% of the observed fluxes around the gap region.

Sub-Jupiter Orbiting an M-dwarf

Spitzer Microlensing Parallax for OGLE-2016-BLG-1067: a sub-Jupiter Orbiting an M-dwarf in the Disk

ABSTRACT: We report the discovery of a sub-Jupiter mass planet orbiting beyond the snow line of an M-dwarf most likely in the Galactic disk as part of the joint Spitzer and ground-based monitoring of microlensing planetary anomalies toward the Galactic bulge. The microlensing parameters are strongly constrained by the light curve modeling and in particular by the Spitzer-based measurement of the microlens parallax, πE. However, in contrast to many planetary microlensing events, there are no caustic crossings, so the angular Einstein radius, θE has only an upper limit based on the light curve modeling alone. Additionally, the analysis leads us to identify 8 degenerate configurations: the four-fold microlensing parallax degeneracy being doubled by a degeneracy in the caustic structure present at the level of the ground-based solutions. To pinpoint the physical parameters, and at the same time to break the parallax degeneracy, we make use of a series of arguments: the χ2 hierarchy, the Rich argument, and a prior Galactic model. The preferred configuration is for a host at DL=3.73-0.67+0.66 kpc with mass ML=0.30-0.12+0.15 M, orbited by a Saturn-like planet with Mplanet=0.43-0.17+0.21 MJup at projected separation a=1.70-0.39+0.38 au, about 2.1 times beyond the system snow line. Therefore, it adds to the growing population of sub-Jupiter planets orbiting near or beyond the snow line of M-dwarfs discovered by microlensing. Based on the rules of the real-time protocol for the selection of events to be followed up with Spitzer, this planet will not enter the sample for measuring the Galactic distribution of planets.

Normal Science in a Multiverse

Beyond Falsifiability: Normal Science in a Multiverse

Sean M. Carroll

Cosmological models that invoke a multiverse – a collection of unobservable regions of space where conditions are very different from the region around us – are controversial, on the grounds that unobservable phenomena shouldn’t play a crucial role in legitimate scientific theories. I argue that the way we evaluate multiverse models is precisely the same as the way we evaluate any other models, on the basis of abduction, Bayesian inference, and empirical success. There is no scientifically respectable way to do cosmology without taking into account different possibilities for what the universe might be like outside our horizon. Multiverse theories are utterly conventionally scientific, even if evaluating them can be difficult in practice.


Atmospheric Beacons of Life

Atmospheric Beacons of Life from Exoplanets Around G and K Stars

ABSTRACT: The current explosion in detection and characterization of thousands of extrasolar planets from the Kepler mission, the Hubble Space Telescope, and large ground-based telescopes opens a new era in searches for Earth-analog exoplanets with conditions suitable for sustaining life. As more Earth-sized exoplanets are detected in the near future, we will soon have an opportunity to identify habitable worlds. Which atmospheric biosignature gases from habitable planets can be detected with our current capabilities? The detection of the common biosignatures from nitrogen-oxygen rich terrestrial-type exoplanets including molecular oxygen (O2), ozone (O3), water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) requires days of integration time with largest space telescopes, and thus are very challenging for current instruments. In this paper we propose to use the powerful emission from rotational-vibrational bands of nitric oxide, hydroxyl and molecular oxygen as signatures of nitrogen, oxygen, and water rich atmospheres of terrestrial type exoplanets highlighted by the magnetic activity from young G and K main-sequence stars. The signals from these fundamental chemical prerequisites of life we call atmospheric beacons of life create a unique opportunity to perform direct imaging observations of Earth-sized exoplanets with high signal-to-noise and low spectral resolution with the upcoming NASA missions.


Gravitational Microlensing Event

OGLE-2014-BLG-0289: Precise Characterization of a Quintuple-Peak Gravitational Microlensing Event

ABSTRACT: We present the analysis of the binary-microlensing event OGLE-2014-BLG-0289. The event light curve exhibits very unusual five peaks where four peaks were produced by caustic crossings and the other peak was produced by a cusp approach. It is found that the quintuple-peak features of the light curve provide tight constraints on the source trajectory, enabling us to precisely and accurately measure the microlensing parallax πE. Furthermore, the three resolved caustics allow us to measure the angular Einstein radius θE. From the combination of πE and θE, the physical lens parameters are uniquely determined. It is found that the lens is a binary composed of two M dwarfs with masses M1 = 0.52±0.04 M and M2=0.42±0.03 M separated in projection by a = 6.4±0.5 au. The lens is located in the disk with a distance of DL = 3.3±0.3 kpc. It turns out that the reason for the absence of a lensing signal in the Spitzer data is that the time of observation corresponds to the flat region of the light curve.