Pub Date : 2020-09-01DOI: 10.1051/0004-6361/202038350
K. Chubb, M. Rocchetto, S. Yurchenko, M. Min, I. Waldmann, J. Barstow, P. Mollière, A. Al-Refaie, M. Phillips, J. Tennyson
A publicly available database of opacities for molecules of astrophysical interest, ExoMolOP, has been compiled for over 80 species, based on the latest line list data from the ExoMol, HITEMP and MoLLIST databases. These data are generally suitable for characterising high temperature exoplanet or cool stellar/substellar atmospheres, and have been computed at a variety of pressures and temperatures, with a few molecules included at room-temperature only from the HITRAN database. The data are formatted in different ways for four different exoplanet atmosphere retrieval codes; ARCiS, TauREx, NEMESIS and petitRADTRANS, and include both cross-sections (at R~=~$frac{lambda}{Delta lambda}$~=~15,000) and k-tables (at R~=~$frac{lambda}{Delta lambda}$~=~1000) for the 0.3~-~50$mu$m wavelength region. Opacity files can be downloaded and used directly for these codes. Atomic data for alkali metals Na and K are also included, using data from the NIST database and the latest line shapes for the resonance lines. Broadening parameters have been taken from the literature where available, or from those for a known molecule with similar molecular properties where no broadening data are available. The data are available from this http URL.
{"title":"The ExoMolOP database: Cross sections and k-tables for molecules of interest in high-temperature exoplanet atmospheres","authors":"K. Chubb, M. Rocchetto, S. Yurchenko, M. Min, I. Waldmann, J. Barstow, P. Mollière, A. Al-Refaie, M. Phillips, J. Tennyson","doi":"10.1051/0004-6361/202038350","DOIUrl":"https://doi.org/10.1051/0004-6361/202038350","url":null,"abstract":"A publicly available database of opacities for molecules of astrophysical interest, ExoMolOP, has been compiled for over 80 species, based on the latest line list data from the ExoMol, HITEMP and MoLLIST databases. These data are generally suitable for characterising high temperature exoplanet or cool stellar/substellar atmospheres, and have been computed at a variety of pressures and temperatures, with a few molecules included at room-temperature only from the HITRAN database. The data are formatted in different ways for four different exoplanet atmosphere retrieval codes; ARCiS, TauREx, NEMESIS and petitRADTRANS, and include both cross-sections (at R~=~$frac{lambda}{Delta lambda}$~=~15,000) and k-tables (at R~=~$frac{lambda}{Delta lambda}$~=~1000) for the 0.3~-~50$mu$m wavelength region. Opacity files can be downloaded and used directly for these codes. Atomic data for alkali metals Na and K are also included, using data from the NIST database and the latest line shapes for the resonance lines. Broadening parameters have been taken from the literature where available, or from those for a known molecule with similar molecular properties where no broadening data are available. The data are available from this http URL.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87180623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-09-01DOI: 10.32023/0001-5237/70.3.2
G. Maciejewski
Origins of giant planets on tight orbits, so called hot Jupiters, are a long-lasting question in the planetary formation and evolution theory. The answer seems to be hidden in architectures of those systems that remain only partially understood. Using multi-sector time-series photometry from the Transiting Exoplanet Survey Satellite, we searched for additional planets in the KELT-18, KELT-23, KELT-24, Qatar-8, WASP-62, WASP-100, WASP-119, and WASP-126 planetary systems using both the transit technique and transit timing method. Our homogenous analysis has eliminated the presence of transiting companions down to the terrestrial-size regime in the KELT-23 and WASP-62 systems, and down to mini-Neptunes or Neptunes in the remaining ones. Transit timing analysis has revealed no sign of either long-term trends or periodic perturbations for all the studied hot Jupiters, including the WASP-126 b for which deviations from a Keplerian model were claimed in the literature. The loneliness of the planets of the sample speaks in favour of the high-eccentricity migration mechanism that probably brought them to their tight orbits observed nowadays. As a byproduct of our study, the transit light curve parameters were redetermined with a substantial improvement of the precision for 6 systems. For KELT-24 b, a joint analysis allowed us to place a tighter constraint on its orbital eccentricity.
{"title":"Search for planets in hot Jupiter systems with multi-sector TESS photometry. I. No companions in planetary systems KELT-18, KELT-23, KELT-24, Qatar-8, WASP-62, WASP-100, WASP-119, and WASP-126","authors":"G. Maciejewski","doi":"10.32023/0001-5237/70.3.2","DOIUrl":"https://doi.org/10.32023/0001-5237/70.3.2","url":null,"abstract":"Origins of giant planets on tight orbits, so called hot Jupiters, are a long-lasting question in the planetary formation and evolution theory. The answer seems to be hidden in architectures of those systems that remain only partially understood. Using multi-sector time-series photometry from the Transiting Exoplanet Survey Satellite, we searched for additional planets in the KELT-18, KELT-23, KELT-24, Qatar-8, WASP-62, WASP-100, WASP-119, and WASP-126 planetary systems using both the transit technique and transit timing method. Our homogenous analysis has eliminated the presence of transiting companions down to the terrestrial-size regime in the KELT-23 and WASP-62 systems, and down to mini-Neptunes or Neptunes in the remaining ones. Transit timing analysis has revealed no sign of either long-term trends or periodic perturbations for all the studied hot Jupiters, including the WASP-126 b for which deviations from a Keplerian model were claimed in the literature. The loneliness of the planets of the sample speaks in favour of the high-eccentricity migration mechanism that probably brought them to their tight orbits observed nowadays. As a byproduct of our study, the transit light curve parameters were redetermined with a substantial improvement of the precision for 6 systems. For KELT-24 b, a joint analysis allowed us to place a tighter constraint on its orbital eccentricity.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"119 4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88750576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The analytical theory of satellite orbits in an atmosphere developed by King-Hele remains widely in use for satellite mission design because of its accurate approximation to numerical integration under simplifying assumptions. Over the course of six decades, modifications to the theory have addressed many of its weaknesses. However, in all subsequent modifications of the original theory, the assumption of a constant drag-coefficient has been retained. The drag-coefficient is a dynamic parameter that governs the physical interaction between the atmosphere and the satellite and depends on ambient as well as satellite specific factors. In this work, Fourier series expansion models of the drag-coefficient are incorporated in the original King-Hele theory to capture time-variations of the drag-coefficient in averaging integrals. The modified theory is validated through simulations that demonstrate the attained improvements in approximating numerical results over the original King-Hele formulation.
{"title":"King-Hele orbit theory for periodic orbit and attitude variations","authors":"V. Ray, D. Scheeres","doi":"10.1093/mnras/staa3630","DOIUrl":"https://doi.org/10.1093/mnras/staa3630","url":null,"abstract":"The analytical theory of satellite orbits in an atmosphere developed by King-Hele remains widely in use for satellite mission design because of its accurate approximation to numerical integration under simplifying assumptions. Over the course of six decades, modifications to the theory have addressed many of its weaknesses. However, in all subsequent modifications of the original theory, the assumption of a constant drag-coefficient has been retained. The drag-coefficient is a dynamic parameter that governs the physical interaction between the atmosphere and the satellite and depends on ambient as well as satellite specific factors. In this work, Fourier series expansion models of the drag-coefficient are incorporated in the original King-Hele theory to capture time-variations of the drag-coefficient in averaging integrals. The modified theory is validated through simulations that demonstrate the attained improvements in approximating numerical results over the original King-Hele formulation.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78571080","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-08-18DOI: 10.1051/0004-6361/202037858
T. Löhne
The excess emission seen in spectral energy distributions (SEDs) is commonly used to infer the properties of the emitting circumstellar dust in protoplanetary and debris discs. Most notably, dust size distributions and details of the collision physics are derived from SED slopes at long wavelengths. This paper reviews the approximations that are commonly used and contrasts them with numerical results for the thermal emission. The inferred size distribution indexes are shown to be greater and more sensitive to the observed sub(mm) spectral indexes than previously considered. This effect results from aspects of the transition from small grains with volumetric absorption to bigger grains that absorb and emit near to their surface, controlled by both the real and the imaginary part of the refractive index. The steeper size distributions indicate stronger size-dependence of material strengths or impact velocities or, otherwise, less efficient transport or erosion processes. Strong uncertainties remain because of insufficient knowledge of the material composition, porosity, and optical properties at long wavelengths.
{"title":"Relating grain size distributions in circumstellar discs to the spectral index at millimetre wavelengths","authors":"T. Löhne","doi":"10.1051/0004-6361/202037858","DOIUrl":"https://doi.org/10.1051/0004-6361/202037858","url":null,"abstract":"The excess emission seen in spectral energy distributions (SEDs) is commonly used to infer the properties of the emitting circumstellar dust in protoplanetary and debris discs. Most notably, dust size distributions and details of the collision physics are derived from SED slopes at long wavelengths. This paper reviews the approximations that are commonly used and contrasts them with numerical results for the thermal emission. The inferred size distribution indexes are shown to be greater and more sensitive to the observed sub(mm) spectral indexes than previously considered. This effect results from aspects of the transition from small grains with volumetric absorption to bigger grains that absorb and emit near to their surface, controlled by both the real and the imaginary part of the refractive index. The steeper size distributions indicate stronger size-dependence of material strengths or impact velocities or, otherwise, less efficient transport or erosion processes. Strong uncertainties remain because of insufficient knowledge of the material composition, porosity, and optical properties at long wavelengths.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91157897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jake T. Clark, Mathieu Clerté, N. Hinkel, C. Unterborn, R. Wittenmyer, J. Horner, D. Wright, B. Carter, T. Morton, L. Spina, M. Asplund, S. Buder, J. Bland-Hawthorn, A. Casey, G. D. De Silva, V. D’Orazi, L. Duong, M. Hayden, K. Freeman, J. Kos, G. Lewis, Jane Lin, K. Lind, S. Martell, Sanjib Sharma, J. Simpson, D. Zucker, T. Zwitter, C. Tinney, Yuan-Sen Ting (丁源森), T. Nordlander, A. Amarsi
An unprecedented number of exoplanets are being discovered by the Transiting Exoplanet Survey Satellite (TESS). Determining the orbital parameters of these exoplanets, and especially their mass and radius, will depend heavily upon the measured physical characteristics of their host stars. We have cross-matched spectroscopic, photometric, and astrometric data from GALAH Data Release 2, the TESS Input Catalog and Gaia Data Release 2, to create a curated, self-consistent catalog of physical and chemical properties for 47,285 stars. Using these data we have derived isochrone masses and radii that are precise to within 5%. We have revised the parameters of three confirmed, and twelve candidate, TESS planetary systems. These results cast doubt on whether CTOI-20125677 is indeed a planetary system since the revised planetary radii are now comparable to stellar sizes. Our GALAH-TESS catalog contains abundances for up to 23 elements. We have specifically analysed the molar ratios for C/O, Mg/Si, Fe/Si and Fe/Mg, to assist in determining the composition and structure of planets with $R_p < 4R_oplus$. From these ratios, 36% fall within 2 sigma of the Sun/Earth values, suggesting that these stars may host rocky exoplanets with geological compositions similar to planets found within our own Solar system.
{"title":"The GALAH Survey: using galactic archaeology to refine our knowledge of TESS target stars","authors":"Jake T. Clark, Mathieu Clerté, N. Hinkel, C. Unterborn, R. Wittenmyer, J. Horner, D. Wright, B. Carter, T. Morton, L. Spina, M. Asplund, S. Buder, J. Bland-Hawthorn, A. Casey, G. D. De Silva, V. D’Orazi, L. Duong, M. Hayden, K. Freeman, J. Kos, G. Lewis, Jane Lin, K. Lind, S. Martell, Sanjib Sharma, J. Simpson, D. Zucker, T. Zwitter, C. Tinney, Yuan-Sen Ting (丁源森), T. Nordlander, A. Amarsi","doi":"10.1093/MNRAS/STAB1052","DOIUrl":"https://doi.org/10.1093/MNRAS/STAB1052","url":null,"abstract":"An unprecedented number of exoplanets are being discovered by the Transiting Exoplanet Survey Satellite (TESS). Determining the orbital parameters of these exoplanets, and especially their mass and radius, will depend heavily upon the measured physical characteristics of their host stars. We have cross-matched spectroscopic, photometric, and astrometric data from GALAH Data Release 2, the TESS Input Catalog and Gaia Data Release 2, to create a curated, self-consistent catalog of physical and chemical properties for 47,285 stars. Using these data we have derived isochrone masses and radii that are precise to within 5%. We have revised the parameters of three confirmed, and twelve candidate, TESS planetary systems. These results cast doubt on whether CTOI-20125677 is indeed a planetary system since the revised planetary radii are now comparable to stellar sizes. Our GALAH-TESS catalog contains abundances for up to 23 elements. We have specifically analysed the molar ratios for C/O, Mg/Si, Fe/Si and Fe/Mg, to assist in determining the composition and structure of planets with $R_p < 4R_oplus$. From these ratios, 36% fall within 2 sigma of the Sun/Earth values, suggesting that these stars may host rocky exoplanets with geological compositions similar to planets found within our own Solar system.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"1 4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83837749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Harald Krüger, P. Strub, M. Sommer, N. Altobelli, H. Kimura, Ann-Kathrin Lohse, E. Grün, R. Srama
Cometary meteoroid trails exist in the vicinity of comets, forming fine structure of the interplanetary dust cloud. The trails consist predominantly of cometary particles with sizes of approximately 0.1 mm to 1 cm which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. When re-analysing the Helios dust data measured in the 1970s, Altobelli et al. (2006) recognized a clustering of seven impacts, detected in a very narrow region of space at a true anomaly angle of 135 deg, which the authors considered as potential cometary trail particles. We re-analyse these candidate cometary trail particles to investigate the possibility that some or all of them indeed originate from cometary trails and we constrain their source comets. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new universal model for cometary meteoroid streams in the inner solar system, developed by Soja et al. (2015). Using IMEX we study cometary trail traverses by Helios. During ten revolutions around the Sun, and in the narrow region of space where Helios detected the candidate dust particles, the spacecraft repeatedly traversed the trails of comets 45P/Honda-Mrkos-Pajduvsakova and 72P/Denning-Fujikawa. Based on the detection times and particle impact directions, four detected particles are compatible with an origin from these two comets. We find a dust spatial density in these trails of about 10^-8 to 10^-7 m^-3. The in-situ detection and analysis of meteoroid trail particles which can be traced back to their source bodies by spacecraft-based dust analysers opens a new window to remote compositional analysis of comets and asteroids without the necessity to fly a spacecraft to or even land on those celestial bodies. This provides new science opportunities for future missions like Destiny+, Europa Clipper and IMAP.
彗星流星体的轨迹存在于彗星附近，形成了精细结构的行星际尘埃云。这些彗尾主要由直径约0.1毫米至1厘米的彗星粒子组成，这些彗星粒子以低速喷射出来，在绕太阳转几圈的时间里，它们离彗星轨道非常近。当重新分析20世纪70年代测得的太阳神尘埃数据时，Altobelli等人(2006)发现在一个非常狭窄的空间区域以135度的真正异常角检测到7次撞击，作者认为这是潜在的彗星痕迹粒子。我们重新分析了这些候选彗星轨迹粒子，以研究它们中的一些或全部确实来自彗星轨迹的可能性，并限制了它们的源彗星。星际流星体环境探索(Interplanetary Meteoroid Environment for eXploration, IMEX)空间尘埃流模型是Soja等人(2015)提出的一种新的太阳系内彗星流星体流通用模型。利用IMEX，我们研究了太阳神彗星的轨迹。在绕太阳十圈的过程中，在太阳神号探测到候选尘埃粒子的狭窄空间内，航天器反复穿越了45P/Honda-Mrkos-Pajduvsakova彗星和72P/Denning-Fujikawa彗星的轨迹。根据探测次数和粒子撞击方向，4个被探测到的粒子与这两颗彗星的一个起源是相容的。我们发现这些尘埃的空间密度约为10^-8到10^-7 m^-3。通过基于航天器的尘埃分析仪对流星体轨迹粒子进行原位检测和分析，可以追溯到它们的源体，这为彗星和小行星的远程成分分析打开了一扇新的窗口，而不需要飞到这些天体上，甚至不需要降落在这些天体上。这为未来的任务提供了新的科学机会，比如命运+、木卫二快船和IMAP。
{"title":"Helios spacecraft data revisited: Detection of cometary meteoroid trails by in-situ dust impacts","authors":"Harald Krüger, P. Strub, M. Sommer, N. Altobelli, H. Kimura, Ann-Kathrin Lohse, E. Grün, R. Srama","doi":"10.5194/epsc2020-320","DOIUrl":"https://doi.org/10.5194/epsc2020-320","url":null,"abstract":"Cometary meteoroid trails exist in the vicinity of comets, forming fine structure of the interplanetary dust cloud. The trails consist predominantly of cometary particles with sizes of approximately 0.1 mm to 1 cm which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. When re-analysing the Helios dust data measured in the 1970s, Altobelli et al. (2006) recognized a clustering of seven impacts, detected in a very narrow region of space at a true anomaly angle of 135 deg, which the authors considered as potential cometary trail particles. We re-analyse these candidate cometary trail particles to investigate the possibility that some or all of them indeed originate from cometary trails and we constrain their source comets. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new universal model for cometary meteoroid streams in the inner solar system, developed by Soja et al. (2015). Using IMEX we study cometary trail traverses by Helios. During ten revolutions around the Sun, and in the narrow region of space where Helios detected the candidate dust particles, the spacecraft repeatedly traversed the trails of comets 45P/Honda-Mrkos-Pajduvsakova and 72P/Denning-Fujikawa. Based on the detection times and particle impact directions, four detected particles are compatible with an origin from these two comets. We find a dust spatial density in these trails of about 10^-8 to 10^-7 m^-3. The in-situ detection and analysis of meteoroid trail particles which can be traced back to their source bodies by spacecraft-based dust analysers opens a new window to remote compositional analysis of comets and asteroids without the necessity to fly a spacecraft to or even land on those celestial bodies. This provides new science opportunities for future missions like Destiny+, Europa Clipper and IMAP.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"29 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74028416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent study suggests that the streaming instability, one of the leading mechanisms for driving the formation of planetesimals, may not be as efficient as previously thought. Under some disc conditions, the linear growth rate of the instability decreases significantly when multiple dust species are considered, and the instability growth timescale can be longer than the disc lifetime. To further explore this finding, we use both linear analysis and direct numerical simulations with gas fluid and dust particles to mutually validate and study the unstable modes of the instability in more detail. We extend the previously studied parameter space by one order of magnitude in both the range of the dust-size distribution $[T_{s,min}, T_{s,max}]$ and the total solid-to-gas mass ratio $varepsilon$ and introduce a third dimension with the slope $q$ of the size distribution. We find that the converged fast-growth regime and the non-converged slow-growth regime are distinctly separated by a sharp boundary in the $varepsilon$-$T_{s,max}$ space, while this boundary is not appreciably sensitive to $q$ or $T_{s,min}$. Moreover, it is not necessary that the largest dust species dominate the growth of the unstable modes, and the smaller dust species can either increase or decrease the growth rate significantly. In any case, we find that the converged fast-growth regime is bounded by $varepsilongtrsim1$ or $T_{s,max}gtrsim1$, which may represent the favourable conditions for planetesimal formation.
{"title":"Streaming instability with multiple dust species – I. Favourable conditions for the linear growth","authors":"Zhaohuan Zhu(朱照寰), Chao-Chin Yang(楊朝钦)","doi":"10.1093/mnras/staa3628","DOIUrl":"https://doi.org/10.1093/mnras/staa3628","url":null,"abstract":"Recent study suggests that the streaming instability, one of the leading mechanisms for driving the formation of planetesimals, may not be as efficient as previously thought. Under some disc conditions, the linear growth rate of the instability decreases significantly when multiple dust species are considered, and the instability growth timescale can be longer than the disc lifetime. To further explore this finding, we use both linear analysis and direct numerical simulations with gas fluid and dust particles to mutually validate and study the unstable modes of the instability in more detail. We extend the previously studied parameter space by one order of magnitude in both the range of the dust-size distribution $[T_{s,min}, T_{s,max}]$ and the total solid-to-gas mass ratio $varepsilon$ and introduce a third dimension with the slope $q$ of the size distribution. We find that the converged fast-growth regime and the non-converged slow-growth regime are distinctly separated by a sharp boundary in the $varepsilon$-$T_{s,max}$ space, while this boundary is not appreciably sensitive to $q$ or $T_{s,min}$. Moreover, it is not necessary that the largest dust species dominate the growth of the unstable modes, and the smaller dust species can either increase or decrease the growth rate significantly. In any case, we find that the converged fast-growth regime is bounded by $varepsilongtrsim1$ or $T_{s,max}gtrsim1$, which may represent the favourable conditions for planetesimal formation.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79561206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-08-03DOI: 10.3847/1538-3881/ABB536
Emily D. Safsten, R. Dawson, A. Wolfgang
Many exoplanets have orbital characteristics quite different from those seen in our own solar system, including planets locked in orbital resonances and planets on orbits that are elliptical or highly inclined from their host star's spin axis. It is debated whether the wide variety in system architecture is primarily due to differences in formation conditions (nature) or due to evolution over time (nurture). Identifying trends between planetary and stellar properties, including stellar age, can help distinguish between these competing theories and offer insights as to how planets form and evolve. However, it can be challenging to determine whether observed trends between planetary properties and stellar age are driven by the age of the system -- pointing to evolution over time being an important factor -- or other parameters to which the age may be related, such as stellar mass or stellar temperature. The situation is complicated further by the possibilities of selection biases, small number statistics, uncertainties in stellar age, and orbital evolution timescales that are typically much shorter than the range of observed ages. Here we develop a Bayesian statistical framework to assess the robustness of such observed correlations and to determine whether they are indeed due to evolutionary processes, are more likely to reflect different formation scenarios, or are merely coincidental. We apply this framework to reported trends between stellar age and 2:1 orbital resonances, spin-orbit misalignments, and hot Jupiters' orbital eccentricities. We find strong support for the nurture hypothesis only in the final case.
{"title":"Nature vs. nurture: a Bayesian framework for assessing apparent correlations between planetary orbital properties and stellar ages","authors":"Emily D. Safsten, R. Dawson, A. Wolfgang","doi":"10.3847/1538-3881/ABB536","DOIUrl":"https://doi.org/10.3847/1538-3881/ABB536","url":null,"abstract":"Many exoplanets have orbital characteristics quite different from those seen in our own solar system, including planets locked in orbital resonances and planets on orbits that are elliptical or highly inclined from their host star's spin axis. It is debated whether the wide variety in system architecture is primarily due to differences in formation conditions (nature) or due to evolution over time (nurture). Identifying trends between planetary and stellar properties, including stellar age, can help distinguish between these competing theories and offer insights as to how planets form and evolve. However, it can be challenging to determine whether observed trends between planetary properties and stellar age are driven by the age of the system -- pointing to evolution over time being an important factor -- or other parameters to which the age may be related, such as stellar mass or stellar temperature. The situation is complicated further by the possibilities of selection biases, small number statistics, uncertainties in stellar age, and orbital evolution timescales that are typically much shorter than the range of observed ages. Here we develop a Bayesian statistical framework to assess the robustness of such observed correlations and to determine whether they are indeed due to evolutionary processes, are more likely to reflect different formation scenarios, or are merely coincidental. We apply this framework to reported trends between stellar age and 2:1 orbital resonances, spin-orbit misalignments, and hot Jupiters' orbital eccentricities. We find strong support for the nurture hypothesis only in the final case.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"152 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79032580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-07-30DOI: 10.1051/0004-6361/202037569
A. Groot, L. Rossi, V. Trees, J. Cheung, D. Stam
Understanding the total flux and polarization signals of Earth-like planets and their spectral and temporal variability is essential for the future characterization of such exoplanets. We provide computed total (F) and linearly (Q and U) and circularly (V) polarized fluxes, and the degree of polarization P of sunlight that is reflected by a model Earth, to be used for instrument designs, optimizing observational strategies, and/or developing retrieval algorithms. We modeled a realistic Earth-like planet using one year of daily Earth-observation data: cloud parameters (distribution, optical thickness, top pressure, and particle effective radius), and surface parameters (distribution, surface type, and albedo). The Stokes vector of the disk-averaged reflected sunlight was computed for phase angles alpha from 0 to 180 degrees, and for wavelengths lambda from 350 to 865 nm. The total flux F is one order of magnitude higher than the polarized flux Q, and Q is two and four orders of magnitude higher than U and V, respectively. Without clouds, the peak-to-peak daily variations due to the planetary rotation increase with increasing lambda for F, Q, and P, while they decrease for U and V. Clouds modify but do not completely suppress the variations that are due to rotating surface features. With clouds, the variation in F increases with increasing lambda, while in Q, it decreases with increasing lambda, except at the largest phase angles. In earlier work, it was shown that with oceans, Q changes color from blue through white to red. The alpha where the color changes increases with increasing cloud coverage. Here, we show that this unique color change in Q also occurs when the oceans are partly replaced by continents, with or without clouds. The degree of polarization P shows a similar color change. Our computed fluxes and degree of polarization will be made publicly available.
{"title":"Colors of an Earth-like exoplanet","authors":"A. Groot, L. Rossi, V. Trees, J. Cheung, D. Stam","doi":"10.1051/0004-6361/202037569","DOIUrl":"https://doi.org/10.1051/0004-6361/202037569","url":null,"abstract":"Understanding the total flux and polarization signals of Earth-like planets and their spectral and temporal variability is essential for the future characterization of such exoplanets. We provide computed total (F) and linearly (Q and U) and circularly (V) polarized fluxes, and the degree of polarization P of sunlight that is reflected by a model Earth, to be used for instrument designs, optimizing observational strategies, and/or developing retrieval algorithms. We modeled a realistic Earth-like planet using one year of daily Earth-observation data: cloud parameters (distribution, optical thickness, top pressure, and particle effective radius), and surface parameters (distribution, surface type, and albedo). The Stokes vector of the disk-averaged reflected sunlight was computed for phase angles alpha from 0 to 180 degrees, and for wavelengths lambda from 350 to 865 nm. The total flux F is one order of magnitude higher than the polarized flux Q, and Q is two and four orders of magnitude higher than U and V, respectively. Without clouds, the peak-to-peak daily variations due to the planetary rotation increase with increasing lambda for F, Q, and P, while they decrease for U and V. Clouds modify but do not completely suppress the variations that are due to rotating surface features. With clouds, the variation in F increases with increasing lambda, while in Q, it decreases with increasing lambda, except at the largest phase angles. In earlier work, it was shown that with oceans, Q changes color from blue through white to red. The alpha where the color changes increases with increasing cloud coverage. Here, we show that this unique color change in Q also occurs when the oceans are partly replaced by continents, with or without clouds. The degree of polarization P shows a similar color change. Our computed fluxes and degree of polarization will be made publicly available.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90639082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-07-24DOI: 10.1002/essoar.10503836.1
E. Cangi, M. Chaffin, J. Deighan
Much of the water that once flowed on the surface of Mars was lost to space long ago, and the total amount lost remains unknown. Clues to the amount lost can be found by studying hydrogen (H) and its isotope deuterium (D), both of which are produced when atmospheric water molecules H$_2$O and HDO dissociate. The freed H and D atoms then escape to space at different rates due to their different masses, leaving an enhanced D/H ratio. The rate of change of D/H is referred to as the fractionation factor $f$. Both the D/H ratio and $f$ are necessary to estimate water loss; thus, if we can constrain the range of $f$, we will be able to estimate water loss more accurately. In this study, we use a 1D photochemical model of the Martian atmosphere to determine how $f$ depends on assumed temperature and water vapor profiles. We find that for most Martian atmospheric conditions, $f$ varies between $10^{-1}$ and $10^{-5}$; for the standard Martian atmosphere, $f=0.002$ for thermal escape processes, and $fapproxeq0.06$ when both thermal and non-thermal escape are considered. Using these results, we estimate that Mars has lost at minimum 66-123 m GEL of water. Our results demonstrate that the value of $f$ is almost completely controlled by the amount of non-thermal escape of D, and that photochemical modeling studies that include fractionation must thus model both neutral and ion processes throughout the atmosphere.
许多曾经在火星表面流动的水很久以前就消失在太空中了，损失的总量仍然未知。通过研究氢(H)和它的同位素氘(D)，我们可以找到损失数量的线索，这两种物质都是在大气中的水分子H$_2$O和HDO解离时产生的。释放的H和D原子由于它们的质量不同，以不同的速率逃逸到太空中，留下一个增强的D/H比。D/H的变化率称为分馏因子f。D/H比和f$都是估算失水的必要条件;因此，如果我们可以限制f的范围，我们将能够更准确地估计失水。在这项研究中，我们使用火星大气的一维光化学模型来确定$f$如何依赖于假设的温度和水蒸气剖面。我们发现，对于大多数火星大气条件，$f$在$10^{-1}$和$10^{-5}$之间变化;对于标准火星大气，f=0.002，当考虑热逸和非热逸时，f约为0.06。根据这些结果，我们估计火星已经损失了至少66-123 m GEL的水。我们的研究结果表明，$f$的值几乎完全由D的非热逸出量控制，因此，包括分馏在内的光化学建模研究必须同时模拟整个大气中的中性和离子过程。
{"title":"Higher Martian atmospheric temperatures at all altitudes lead to enhanced D/H fractionation and water loss","authors":"E. Cangi, M. Chaffin, J. Deighan","doi":"10.1002/essoar.10503836.1","DOIUrl":"https://doi.org/10.1002/essoar.10503836.1","url":null,"abstract":"Much of the water that once flowed on the surface of Mars was lost to space long ago, and the total amount lost remains unknown. Clues to the amount lost can be found by studying hydrogen (H) and its isotope deuterium (D), both of which are produced when atmospheric water molecules H$_2$O and HDO dissociate. The freed H and D atoms then escape to space at different rates due to their different masses, leaving an enhanced D/H ratio. The rate of change of D/H is referred to as the fractionation factor $f$. Both the D/H ratio and $f$ are necessary to estimate water loss; thus, if we can constrain the range of $f$, we will be able to estimate water loss more accurately. In this study, we use a 1D photochemical model of the Martian atmosphere to determine how $f$ depends on assumed temperature and water vapor profiles. We find that for most Martian atmospheric conditions, $f$ varies between $10^{-1}$ and $10^{-5}$; for the standard Martian atmosphere, $f=0.002$ for thermal escape processes, and $fapproxeq0.06$ when both thermal and non-thermal escape are considered. Using these results, we estimate that Mars has lost at minimum 66-123 m GEL of water. Our results demonstrate that the value of $f$ is almost completely controlled by the amount of non-thermal escape of D, and that photochemical modeling studies that include fractionation must thus model both neutral and ion processes throughout the atmosphere.","PeriodicalId":8428,"journal":{"name":"arXiv: Earth and Planetary Astrophysics","volume":"9 3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78264190","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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