Planet Size Research Articles

창의적 사고 계발을 위한 고등학교 학습 프로그램 개발: 태양계 축소 모형을 중심으로

The purpose of this study was to develop instructional programs for 10th graders to facilitate their creative thinking abilities and understanding concerning the scale of the Solar System. The programs were based on four major themes and composed of eight lessons which dealt with the relative scale of the Solar System. The programs were applied to 155 students at G high school in Gumi City. The results showed that the programs were helpful to students in that they facilitated easier understanding of the relative sizes of planets within the solar system as well as creative thinking abilities including divergent thinking and convergent thinking.

Transits against Fainter Stars: The Power of Image Deconvolution

AbstractCompared to bright star searches, surveys for transiting planets against fainter (V = 12–18) stars have the advantage of much higher sky densities of dwarf star primaries, which afford easier detection of small transiting bodies. Furthermore, deep searches are capable of probing a wider range of stellar environments. On the other hand, for a given spatial resolution and transit depth, deep searches are more prone to confusion from blended eclipsing binaries. We present a powerful mitigation strategy for the blending problem that includes the use of image deconvolution and high-resolution imaging. The techniques are illustrated with Lupus-TR-3 and very recent IR imaging with PANIC on Magellan. The results are likely to have implications for the CoRoT and KEPLER missions designed to detect transiting planets of terrestrial size.

Hydrothermal Systems in Small Ocean Planets

We examine means for driving hydrothermal activity in extraterrestrial oceans on planets and satellites of less than one Earth mass, with implications for sustaining a low level of biological activity over geological timescales. Assuming ocean planets have olivine-dominated lithospheres, a model for cooling-induced thermal cracking shows how variation in planet size and internal thermal energy may drive variation in the dominant type of hydrothermal system-for example, high or low temperature system or chemically driven system. As radiogenic heating diminishes over time, progressive exposure of new rock continues to the current epoch. Where fluid-rock interactions propagate slowly into a deep brittle layer, thermal energy from serpentinization may be the primary cause of hydrothermal activity in small ocean planets. We show that the time-varying hydrostatic head of a tidally forced ice shell may drive hydrothermal fluid flow through the seafloor, which can generate moderate but potentially important heat through viscous interaction with the matrix of porous seafloor rock. Considering all presently known potential ocean planets-Mars, a number of icy satellites, Pluto, and other trans-neptunian objects-and applying Earth-like material properties and cooling rates, we find depths of circulation are more than an order of magnitude greater than in Earth. In Europa and Enceladus, tidal flexing may drive hydrothermal circulation and, in Europa, may generate heat on the same order as present-day radiogenic heat flux at Earth's surface. In all objects, progressive serpentinization generates heat on a globally averaged basis at a fraction of a percent of present-day radiogenic heating and hydrogen is produced at rates between 10(9) and 10(10) molecules cm(2) s(1).

Thermo‐mechanical adjustment after impacts during planetary growth

The thermal evolution of planets during their growth is strongly influenced by impact heating. The temperature increase after a collision is mostly located next to the shock. For Moon to Mars size planets where impact melting is limited, the long term thermo‐mechanical readjustment is driven by spreading and cooling of the heated zone. To determine the time and length scales of the adjustment, we developed a numerical model in axisymmetric cylindrical geometry with variable viscosity. We show that if the impactor is larger than a critical size, the spherical heated zone isothermally flattens until its thickness reaches a value for which motionless thermal diffusion becomes more effective. The thickness at the end of advection depends only on the physical properties of the impacted body. The obtained timescales for the adjustment are comparable to the duration of planetary accretion and depend mostly on the physical properties of the impacted body.

Mass‐Radius Relationships for Solid Exoplanets

We use new interior models of cold planets to investigate the mass-radius relationships of solid exoplanets, considering planets made primarily of iron, silicates, water, and carbon compounds. We find that the mass-radius relationships for cold terrestrial mass planets of all compositions we considered follow a generic functional form that is not a simple power law: log10 Rs = k1 + log10(Ms) - k2M for up to Mp ≈ 20 M⊕, where Ms and Rs are scaled mass and radius values. This functional form arises because the common building blocks of solid planets all have equations of state that are well approximated by a modified polytrope of the form ρ = ρ0 + cPn. We find that highly detailed planet interior models, including temperature structure and phase changes, are not necessary to derive solid exoplanet bulk composition from mass and radius measurements. For solid exoplanets with no substantial atmosphere we have also found the following: with 5% fractional uncertainty in planet mass and radius it is possible to distinguish among planets composed predominantly of iron or silicates or water ice but not more detailed compositions; with ~5% uncertainty water ice planets with 25% water by mass may be identified; the minimum plausible planet size for a given mass is that of a pure iron planet; and carbon planet mass-radius relationships overlap with those of silicate and water planets due to similar zero-pressure densities and equations of state. We propose a definition of super-Earths based on the clear distinction in radii between planets with significant gas envelopes and those without.

Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006

Every three years the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report introduces improved values for the pole and rotation rate of Pluto, Charon, and Phoebe, the pole of Jupiter, the sizes and shapes of Saturn satellites and Charon, and the poles, rotation rates, and sizes of some minor planets and comets. A high precision realization for the pole and rotation rate of the Moon is provided. The expression for the Sun’s rotation has been changed to be consistent with the planets and to account for light travel time

Detection of transits of the nearby hot Neptune GJ 436 b

This Letter reports on the photometric detection of transits of the Neptune-mass planet orbiting the nearby M-dwarf star GJ 436. It is by far the closest, smallest and least massive transiting planet detected so far. Its mass is slightly larger than Neptune's at M = 22.6 +- 1.9 M_earth. The shape and depth of the transit lightcurves show that it is crossing the host star disc near its limb (impact parameter 0.84 +- 0.03) and that the planet size is comparable to that of Uranus and Neptune, R = 25200 +- 2200 km = 3.95 +- 0.35 R_earth. Its main constituant is therefore very likely to be water ice. If the current planet structure models are correct, an outer layer of H/He constituting up to ten percent in mass is probably needed on top of the ice to account for the observed radius.

Subduction origin on early Earth: A hypothesis

I propose a hypothesis for the origin of subduction on early Earth that is directly coupled with mantle upwelling and the formation of mafi c crust. The hypothesis invokes spatial and temporal overlap of both endogenic and exogenic processes, broad quasi-cylindrical mantle upwelling and large bolide impact, respectively, leading to subduction and spreading, two signature processes of modern plate tectonics. The spatial and temporal intersection of these processes could have occurred variably across early Earth, and thus subduction could have begun at different locations and times globally. The hypothesis postulates that the ability of a terrestrial planet to evolve plate tectonics results from a balance between the strength of its lithosphere and the size bolide it can attract and survive; both factors, to a fi rst order, are a function of planet size.

Characterizing extrasolar terrestrial planets with reflected, emitted and transmitted spectra.

NASA and ESA are planning missions to directly detect and characterize terrestrial planets outside our solar system (nominally NASA-Terrestrial Planet Finder and ESA-DARWIN missions). These missions will provide our first opportunity to spectroscopically study the global characteristics of those planets, and search for signs of habitability and life. We have used spatially and spectrally-resolved models to explore the observational sensitivity to changes in atmospheric and surface properties, and the detectability of surface biosignatures, in the globally averaged spectra and light-curves of the Earth. Atmospheric signatures of Earth-size exoplanets might be detected, in a near future, by stellar occultation as well. Detectability depends on planet's size, atmospheric composition, cloud cover and stellar type. According to our simulations, Earth's land vegetation signature (red-edge) is potentially visible in the disk-averaged spectra, even with cloud cover, and when the signal is averaged over the daily time scale. Marine vegetation is far more difficult to detect. We explored also the detectability of an exo-vegetation responsible for producing a signature that is red-shifted with respect to the Earth vegetation's one.

An Extrasolar Planet Transit Search with Subaru Suprime-Cam

Abstract We report the results of a prototype photometric search for transiting extrasolar planets using Subaru Suprime-Cam. Out of about 100000 stars monitored around the Galactic plane ($l=90^{\circ}, b=0^{\circ}$), we find that 7700 show photometric precision better than 1% for 60s exposures, which is required to detect extrasolar planets by the transit method. Thus, Suprime-Cam has the photometric stability and accuracy necessary for a transiting planet survey. During this observing run, we detected three objects (around 18.5 mag for $i'$-band) that exhibit a single full transit-like light curve with a fractional depth of $< 5\%$. While a spectroscopic follow-up remains to be done using future telescopes in the 20–30 m class, the estimated parameters for the three systems are consistent with the planetary size companions around main-sequence stars. We also found two eclipsing binary candidates and eleven variable stars exhibiting W UMa-like light curves.

High-Resolution Spectroscopy in Tr 37: Gas Accretion Evolution in Evolved Dusty Disks

Using the Hectochelle multifiber spectrograph, we have obtained high-resolution (R ~ 34,000) spectra in the Hα region for a large number of stars in the 4 Myr old cluster Tr 37, containing 146 previously known members and 26 newly identified ones. We present the Hα line profiles of all members, compare them to our IR observations of dusty disks (Two Micron All Sky Survey JHK + IRAC + MIPS 24 μm), use the radial velocities as a membership criterion, and calculate the rotational velocities. We find a good correlation between the accretion-broadened profiles and the presence of protoplanetary disks, noting that a small fraction of the accreting stars presents broad profiles with Hα equivalent widths smaller than the canonical limit separating classical T Tauri stars (CTTSs) and weak-lined T Tauri stars (WTTSs). The number of strong accretors appears to be lower than in younger regions, and a large number of CTTSs have very small accretion rates ( ≤ 10-9 M⊙ yr-1). Taking into account that the spectral energy distributions are consistent with dust evolution (grain growth/settling) in the innermost disk, this suggests a parallel evolution of the dusty and gaseous components. We also observe that about half of the transition objects (stars with no IR excesses at λ ≤ 6 μm) do not show any signs of active accretion, whereas the other half is accreting with accretion rates ≤10-9 M⊙ yr-1. These zero or very low accretion rates reveal important gas evolution and/or gas depletion in the innermost disk, which could be related to grain growth up to planetesimal or even planet sizes. Finally, we examine the rotational velocities of accreting and nonaccreting stars, finding no significant differences that could indicate disk locking at these ages.

Looking towards the detection of exoearths with SuperWASP

The WASP consortium is conducting an ultra-wide field survey of stars between 8–15 mag from both hemispheres. Our primary science goal is to detect extra-solar ‘hot-Jupiter’-type planets that eclipse (or transit) bright host stars and for which further detailed investigation will be possible. We summarize the design of the SuperWASP instruments and describe the first results from our northern station SW-N, sited in La Palma, Canary Islands. Our second station, which began operations this year, is located at the South African Astronomical Observatory. Between April and September, 2004, SW-N continuously observed ~6.7 million stars. The consortium's custom-written, fully automated data reduction pipeline has been used to process these data, and the information is now stored in the project archive, held by the Leicester database and archive service (LEDAS). We have applied a sophisticated, automated algorithm to identify the low-amplitude (~0.01 mag), brief (~few hours) signatures of transiting exoplanets. In addition, we have assessed each candidate in the light of all available catalogue information in order to reject data artefacts and astrophysical false positive detections. The highest priority candidates are currently being subjected to further observations in order to select the true planets. Once the exoplanets are confirmed, a host of exciting opportunities are open to us. In this paper, we describe two techniques that exploit the transits in order to detect other objects within the same system. The first involves determining precise epochs for a sequence of transit events in order to detect the small timing variations caused by the gravitational pull of other planets in the same system. The second method employs ultra-high precision photometry of the transits to detect the deviations caused by the presence of exoplanetary moons. Both of these techniques are capable of detecting objects the size of terrestrial planets.

Exoplanet detection from Dome C, Antarctica: opportunities and challenges

Many methods have been proposed for the detection of exoplanets. The minimum detectable planetary size and mass, and the maximum distance from us at which exoplanets are observable, are determined by both technological and environmental constraints. The unique atmospheric conditions found at Dome C offer significant advantages. Using what is now known about the turbulence profile of the atmosphere above Antarctic plateau sites, we explore the potential these sites offer for detecting exoplanets around nearby stars using various methods.

Baroclinic Multiple Zonal Jets on the Sphere

Abstract Multiple zonal jets are investigated with a two-level primitive equation model on the sphere in which both baroclinicity and planetary radius are varied. As in the case for a two-layer quasigeostrophic model on a β-plane channel, it is found both that the Rhines scale successfully predicts the meridional scale of the multiple zonal jets, and that these jets are maintained in part by an eddy momentum flux divergence associated with slow baroclinic waves at the interjet minimum. A scaling analysis suggests that njets∝ (a/θm)1/2, with the constraints ζe ≡ 8 sin2f (θm/▵θ ) > 1 and njets ≥ 1, where njets is the number of the jets, a the planetary radius, θm one-half of the pole-to-equator potential temperature difference, ξe the supercriticality of the two-layer Phillips model, Δθ the potential temperature difference between the two levels, and ϕ the latitude. The number of jets simulated by the model agrees with this scaling, provided that Ljet ≤ a, where Ljet is the jet scale. In model runs with a large planet where multiple zonal jets exist, the time–mean eddy heat flux is found to be consistent with the diffusive picture of Held and Larichev. In contrast, for the model runs with the planetary size equal to that of Earth, baroclinic adjustment is found to be more relevant. These results are consistent with the finding that in the large-planet (Earth-like) model runs, the jet/eddy scale is smaller than (comparable to) the corresponding planetary radius.

From Hot Jupiters to Hot Neptunes ... and Below

Since the discovery of the first Hot Jupiter around 51 Pegasi in 1995, the field of exoplanet detection has been driven by the improvements in the precision of radial velocity measurements. Reaching accuracies lower than 10 m s -1 on Doppler measurements has allowed to explore the domain of gas giants like Jupiter and Saturn. Now, the domain of 1 m s -1 accuracy has been reached, opening the realm of Neptune-mass planets and lower. In parallel, the transit method has come of age. with six detections in the past two years. Transiting planets offer a direct view into planet structure and composition. Planetary size, density, and even the composition of their atmosphere can be measured during the transit. Several elements have already been detected in the transiting planet HD209458, which seems to be slowly evaporating. In the coming few years, the combination of space-based transit surveys and dedicated radial-velocity spectrograph will open the domain of terrestrial exoplanets.

On the Surface Heating of Synchronously Spinning Short‐Period Jovian Planets

We consider the atmospheric flow on short-period extra-solar planets through two-dimensional numerical simulations of hydrodynamics with radiation transfer. One side is always exposed to the irradiation from the host star. The other is always in shadow. The temperature of the day side is determined by the equilibrium which the planetary atmosphere establishes with stellar radiation. Part of the thermal energy deposited on the day side is advected to the night side by a current. The radiation transfer, the night-side temperature distribution and by this the spectroscopic signature of the planet are sensitive functions of the atmospheric opacity. If the atmosphere contains grains with an abundanceand size distribution comparable to that of the interstellar medium, shallow heating occurs on the day side and the night side cools well below the day side. The temperature difference decreases as the abundance of grains is reduced. A simple analytic model of the dissipation of the circulation flow and associated kinetic heating is considered. This heating effect occurs mostly near the photosphere, not deep enough to significantly affect the size of planets. We show that the surface irradiation suppresses convection near the photospheric region on the day side. In some cases convection zones appear near the surface on the night side. This structural modification may influence the response and dissipation of tidal disturbances and alter the circularization and synchronization time scales.

XRD Line Broadening Analysis with Ball Milled Palladium

Palladium powder was deformed by ball milling under an argon atmosphere in two types of mills for different milling times. Two methods for X-ray diffraction line profile analysis, the Williamson-Hall method and the Warren-Averbach method, yielded similar trends, but different quantitative results for crystallite sizes (column lengths) and microstrains. With both methods, from the anisotropic line broadening for planetary milled Pd smaller crystallite sizes and larger microstrains were obtained along the <100> direction than along <111>. Milling in a shaker mill causes microstrain higher by a factor of about two than milling in a planetary mill. The evolution of the crystallite size upon milling was discussed in terms of bimodal size distributions.

A Model for Estimating the Number of Stars for which Terrestrial Planets can be Detected Using Transits

Borucki & Summers (1984) have suggested that extrasolar terrestrial planets can be detected by looking for transits. A discussion is presented of a model used to estimate the number and distance of stars for which planets can be detected as a function of spectral type and luminosity class, apparent brightness, planetary size and orbit, and realistic noise sources that must be considered. A choice for an optimum location of the field to search is described given the realistic constraints of a space mission and maximizing the number of available stars.

The bow shocks and upstream waves of Venus and Mars

Because they both lack measurable magnetic fields, Venus and Mars are often compared to each other in terms of their solar wind interaction. Upstream from each planet the most distant signs of this interaction occur at the bow shock, and in regions upstream from the shock where plasma waves are observed. In many respects the collisionless shocks at Venus and Mars are quite different. The Martian shock is located slightly farther from the planet (with respect to planetary size) and is more variable than the Venus shock. In addition, the position of the Martian shock is not observed to correlate strongly with solar cycle, unlike at Venus. These differences indicate that the solar wind obstacles at the two planets are somehow quite different. However, the characteristics of observed upstream waves at the two planets (and at other solar system bodies) suggest that similar processes are at work at both shocks, and that the size and shape of the shock do not play significant roles in wave generation or damping. This review compares the observations of the bow shocks and upstream waves at Venus and Mars, with reference to model predictions and observations at Mercury and Earth.

Pulsating white dwarfs as astrophysical tools

AbstractThe study of pulsating white dwarfs is a scientifically productive exercise as their measured pulsation characteristics yield both unique data on their interiors and also shed light on more general astrophysical questions. The modelling process is simplified due to their assumed chemically homogeneous and layered structures. As well as being archaeological remnants of their nuclear burning progenitors, white dwarfs are cosmic laboratories that can provide some observational constraints on theories of matter in regions of phase space that are unattainable in laboratories on Earth. The hotter white dwarfs should feature neutrino production by several unusual weak interaction processes, while their cooler cousins should exhibit core crystallization. White dwarf pulsators are very stable in period (if not always in amplitude) and suitable objects can be used as sensitive orbiting clocks in a search for stellar companions, including those of planetary size. Finally, the ensemble of cooling white dwarfs can be used as an independent cosmic chronometer over very long timescales if the cooling curve is properly calibrated. The pulsators make important contributions in this regard.