coronagraph is an open-source Python package for generalized telescope noise modeling for extrasolar planet (exoplanet) science. This package is based on Interactive Data Language (IDL) code originally developed by T. Robinson (Robinson, 2018), and described in detail with science applications in (Robinson, Stapelfeldt, & Marley, 2016).
New research from VPL Team members Jacob Lustig-Yaeger, Andrew Lincowski, and their faculty advisor Dr. Victoria Meadows, recently published in…
Context. The Kepler Object of Interest Network (KOINet) is a multi-site network of telescopes around the globe organised for follow-up observations of transiting planet candidate Kepler objects of interest with large transit timing variations (TTVs). The main goal of KOINet is the completion of their TTV curves as the Kepler telescope stopped observing the original Kepler field in 2013.
Aims. We ensure a comprehensive characterisation of the investigated systems by analysing Kepler data combined with new ground-based transit data using a photodynamical model. This method is applied to the Kepler-82 system leading to its first dynamic analysis.
Methods. In order to provide a coherent description of all observations simultaneously, we combine the numerical integration of the gravitational dynamics of a system over the time span of observations with a transit light curve model. To explore the model parameter space, this photodynamical model is coupled with a Markov chain Monte Carlo algorithm.
Results. The Kepler-82b/c system shows sinusoidal TTVs due to their near 2:1 resonance dynamical interaction. An additional chopping effect in the TTVs of Kepler-82c hints to a further planet near the 3:2 or 3:1 resonance. We photodynamically analysed Kepler long- and short-cadence data and three new transit observations obtained by KOINet between 2014 and 2018. Our result reveals a non-transiting outer planet with a mass of mf = 20.9 ± 1.0 M? near the 3:2 resonance to the outermost known planet, Kepler-82c. Furthermore, we determined the densities of planets b and c to the significantly more precise values ?b = 0.98?0.14+0.10 g cm?3 and ?c = 0.494?0.077+0.066 g cm?3.
Terrestrial planets orbiting M dwarfs may soon be observed with the James Webb Space Telescope (JWST) to characterize their atmospheric composition and search for signs of habitability or life. These planets may undergo significant atmospheric and ocean loss due to the superluminous pre-main-sequence phase of their host stars, which may leave behind abiotically generated oxygen, a false positive for the detection of life. Determining if ocean loss has occurred will help assess potential habitability and whether or not any O2 detected is biogenic. In the solar system, differences in isotopic abundances have been used to infer the history of ocean loss and atmospheric escape (e.g., Venus, Mars). We find that isotopologue measurements using transit transmission spectra of terrestrial planets around late-type M dwarfs like TRAPPIST-1 may be possible with JWST, if the escape mechanisms and resulting isotopic fractionation were similar to Venus. We present analyses of post-ocean-loss O2- and CO2-dominated atmospheres containing a range of trace gas abundances. Isotopologue bands are likely detectable throughout the near-infrared (18 ?m), especially 34 ?m, although not in CO2-dominated atmospheres. For Venus-like D/H ratios 100 times that of Earth, TRAPPIST-1b transit signals of up to 79 ppm are possible by observing HDO. Similarly, 18O/16O ratios 100 times that of Earth produce signals at up to 94 ppm. Detection at signal-to-noise ratio = 5 may be attained on these bands with as few as four to 11 transits, with optimal use of JWST’s NIRSpec Prism. Consequently, H2O and CO2 isotopologues could be considered as indicators of past ocean loss and atmospheric escape for JWST observations of terrestrial planets around M dwarfs.
The James Webb Space Telescope (JWST) will offer the first opportunity to characterize terrestrial exoplanets with sufficient precision to identify high mean molecular weight atmospheres, and TRAPPIST-1’s seven known transiting Earth-sized planets are particularly favorable targets. To assist community preparations for JWST observations, we use simulations of plausible post-ocean-loss and habitable environments for the TRAPPIST-1 exoplanets, and test simulations of all bright object time-series spectroscopy modes and all Mid-Infrared Instrument photometry filters to determine optimal observing strategies for atmospheric detection and characterization using both transmission and emission observations. We find that transmission spectroscopy with the Near-Infrared Spectrograph Prism is optimal for detecting terrestrial, CO2-containing atmospheres, potentially in fewer than 10 transits for all seven TRAPPIST-1 planets, if they lack high-altitude aerosols. If the TRAPPIST-1 planets possess Venus-like H2SO4 aerosols, up to 12 times more transits may be required to detect an atmosphere. We present optimal instruments and observing modes for the detection of individual molecular species in a given terrestrial atmosphere and an observational strategy for discriminating between evolutionary states. We find that water may be prohibitively difficult to detect in both Venus-like and habitable atmospheres, due to its presence lower in the atmosphere where transmission spectra are less sensitive. Although the presence of biogenic O2 and O3 will be extremely challenging to detect, abiotically produced oxygen from past ocean loss may be detectable for all seven TRAPPIST-1 planets via O2O2 collisionally induced absorption at 1.06 and 1.27 ?m, or via NIR O3 features for the outer three planets. Our results constitute a suite of hypotheses on the nature and detectability of highly evolved terrestrial exoplanet atmospheres that may be tested with JWST.
Kepler-62f is the first exoplanet small enough to plausibly have a rocky composition orbiting within the habitable zone (HZ) discovered by the Kepler Mission. The planet is 1.4 times the size of the Earth and has an orbital period of 267 days. At the time of its discovery, it had the longest period of any small planet in the habitable zone of a multi-planet system. Because of its long period, only four transits were observed during Kepler’s interval of observations. It was initially missed by the Kepler pipeline, but the first three transits were identified by an independent search by Eric Agol, and it was identified as a planet candidate in subsequent Kepler catalogs. However in the latest catalog of exoplanets (Thompson et al., 2018), it is labeled as a false positive. Recent exoplanet catalogues have evolved from subjective classification to automatic classifications of planet candidates by algorithms (such as Robovetter). While exceptionally useful for producing a uniform catalogue, these algorithms sometimes misclassify planet candidates as a false positive, as is the case of Kepler-62f. In particularly valuable cases, i.e., when a small planet has been found orbiting in the habitable zone (HZ), it is important to conduct comprehensive analyses of the data and classification protocols to provide the best estimate of the true status of the detection. In this paper we conduct such analyses and show that Kepler-62f is a true planet and not a false positive. The table of stellar and planet properties has been updated based on GAIA results.
We describe the circumstances that led to the discovery of Kepler-36b, and the subsequent characterization of its host planetary system. The Kepler-36 system is remarkable for its physical properties: the close separation of the planets, the contrasting densities of the planets despite their proximity, and the short chaotic timescale. Its discovery and characterization was also remarkable for the novelty of the detection technique and for the precise characterization due to the large transit-timing variations caused by the close proximity of the planets, as well as the precise stellar parameters due to asteroseismology. This was the first multi-planet system whose transit data was processed using a fully consistent photometric-dynamical model, using population Markov Chain Monte Carlo techniques to precisely constrain system parameters. Amongst those parameters, the stellar density was found to be consistent with a complementary, concurrent asteroseismic analysis. In a first, the 3D orientation of the planets was constrained from the lack of transit-duration variations. The system yielded insights into the composition and evolution of short-period planet systems. The denser planet appears to have an Earth-like composition, with uncertainties comparable to the highest precision rocky exoplanet measurements, and the planet densities foreshadowed the rocky/gaseous boundary. The formation of this system remains a mystery, but should yield insights into the migration and evolution of compact exoplanet systems.
One-dimensional (vertical) models of planetary atmospheres typically balance the net solar and internal energy fluxes against the net thermal radiative and convective heat fluxes to determine an equilibrium thermal structure. Thus, simple models of shortwave and longwave (optical and infrared) radiative transport can provide insight into key processes operating within planetary atmospheres. Here, we develop a simple, analytic expression for both the downwelling thermal and net thermal radiative fluxes in a planetary troposphere. For thermal wavelengths, we assume that the atmosphere is non-scattering and that opacities are grey (i.e., wavelength-independent). Additionally, we adopt an atmospheric thermal structure that follows a modified dry adiabat as well as a physically-motivated power-law relationship between grey thermal optical depth and atmospheric pressure. To verify aspects of our analytic treatment, we compare our model to more sophisticated full physics tools as applied to Venus, Earth, and a cloudfree Jupiter, thereby exploring a diversity of atmospheric conditions. Next, we seek to better understand our analytic model by exploring how thermal radiative flux profiles respond to variations in key physical parameters, such as the total grey thermal optical depth of the atmosphere. Using energy balance arguments, we derive convective flux profiles for the tropospheres of all Solar System worlds with thick atmospheres, and propose a scaling that enables inter-comparison of these profiles. Lastly, we use our analytic treatment to discuss the validity of other simple models of convective fluxes in planetary atmospheres. Our new expressions build on decades of analytic modeling exercises in planetary atmospheres, and further prove the utility of simple, generalized tools in comparative planetology studies.
Oxygen and methane are considered to be the canonical biosignatures of modern Earth, and the simultaneous detection of these gases in a planetary atmosphere is an especially strong biosignature. However, these gases may be challenging to detect together in the planetary atmospheres because photochemical oxygen radicals destroy methane. Previous work has shown that the photochemical lifetime of methane in oxygenated atmospheres is longer around M dwarfs, but M dwarf planet habitability may be hindered by extreme stellar activity and evolution. Here, we use a 1D photochemical-climate model to show that K dwarf stars also offer a longer photochemical lifetime of methane in the presence of oxygen compared to G dwarfs. For example, we show that a planet orbiting a K6V star can support about an order of magnitude more methane in its atmosphere compared to an equivalent planet orbiting a G2V star. In the reflected-light spectra of worlds orbiting K dwarf stars, strong oxygen and methane features could be observed at visible and near-infrared wavelengths. Because K dwarfs are dimmer than G dwarfs, they offer a better planet-star contrast ratio, enhancing the signal-to-noise ratio (S/N) possible in a given observation. For instance, a 50 hr observation of a planet at 7 pc with a 15 m telescope yields S/N = 9.2 near 1 ?m for a planet orbiting a solar-type G2V star, and S/N = 20 for the same planet orbiting a K6V star. In particular, nearby mid-late K dwarfs such as 61 Cyg A/B, Epsilon Indi, Groombridge 1618, and HD 156026 may be excellent targets for future biosignature searches.
We derive analytic, closed form, numerically stable solutions for the total flux received from a spherical planet, moon, or star during an occultation if the specific intensity map of the body is expressed as a sum of spherical harmonics. Our expressions are valid to arbitrary degree and may be computed recursively for speed. The formalism we develop here applies to the computation of stellar transit light curves, planetary secondary eclipse light curves, and planetplanet/planetmoon occultation light curves, as well as thermal (rotational) phase curves. In this paper, we also introduce starry, an open-source package written in C++ and wrapped in Python that computes these light curves. The algorithm in starry is six orders of magnitude faster than direct numerical integration and several orders of magnitude more precise. starry also computes analytic derivatives of the light curves with respect to all input parameters for use in gradient-based optimization and inference, such as Hamiltonian Monte Carlo (HMC), allowing users to quickly and efficiently fit observed light curves to infer properties of a celestial body’s surface map. (Please see https://github.com/rodluger/starry, https://rodluger.github.io/starry/, and https://doi.org/10.5281/zenodo.1312286).
This tutorial is an introduction to techniques used to characterize the atmospheres of transiting exoplanets. We intend it to be a useful guide for the undergraduate, graduate student, or postdoctoral scholar who wants to begin research in this field, but who has no prior experience with transiting exoplanets. We begin with a discussion of the properties of exoplanetary systems that allow us to measure exoplanetary spectra, and the principles that underlie transit techniques. Subsequently, we discuss the most favorable wavelengths for observing, and explain the specific techniques of secondary eclipses and eclipse mapping, phase curves, transit spectroscopy, and convolution with spectral templates. Our discussion includes factors that affect the data acquisition, and also a separate discussion of how the results are interpreted. Other important topics that we cover include statistical methods to characterize atmospheres such as stacking, and the effects of stellar activity. We conclude by projecting the future utility of large-aperture observatories such as the James Webb Space Telescope and the forthcoming generation of extremely large ground-based telescopes.
We have observed the active star ? Boo A (HD 131156A) with high precision broadband linear polarimetry contemporaneously with circular spectropolarimetry. We find both signals are modulated by the 6.43 d rotation period of ? Boo A. The signals from the two techniques are 0.25 out of phase, consistent with the broadband linear polarization resulting from differential saturation of spectral lines in the global transverse magnetic field. The mean magnitude of the linear polarization signal is ?4 ppm?G1 but its structure is complex and the amplitude of the variations suppressed relative to the longitudinal magnetic field. The result has important implications for current attempts to detect polarized light from hot Jupiters orbiting active stars in the combined light of the star and planet. In such work stellar activity will manifest as noise, both on the time-scale of stellar rotation, and on longer time-scales where changes in activity level will manifest as a baseline shift between observing runs.
The TRAPPIST-1 planetary system provides an unprecedented opportunity to study terrestrial exoplanet evolution with the James Webb Space Telescope (JWST) and ground-based observatories. Since M dwarf planets likely experience extreme volatile loss, the TRAPPIST-1 planets may have highly evolved, possibly uninhabitable atmospheres. We used a versatile, 1D terrestrial planet climate model with line-by-line radiative transfer and mixing length convection (VPL Climate) coupled to a terrestrial photochemistry model to simulate environmental states for the TRAPPIST-1 planets. We present equilibrium climates with self-consistent atmospheric compositions and observational discriminants of postrunaway, desiccated, 10–100 bar O2- and CO2-dominated atmospheres, including interior outgassing, as well as for water-rich compositions
(The Astrophysical Journal, 2018)
Refraction can lead to a brightening just before ingress and just after egress of a transit, as light passes through the exoplanet’s atmosphere and is refracted into our line of sight (Sidis & Sari 2010; Misra & Meadows 2014; Misra et al. 2014; Dalba 2017; Alp & Demory 2018). Refraction just outside of transit has been seen and modeled in our own solar system during transits of Venus (Pasachoff et al. 2011; García Muñoz & Mills 2012; Tanga et al. 2012). For short-period planets, the model of (Sidis & Sari 2010, hereafter S&S) implies refraction peaks typically under 100 parts per million (ppm) and comparable in duration to ingress and egress. Kepler photometry (Borucki et al. 2010) currently provides the best opportunity for detecting refraction. We search for the signature of refraction just outside of transit in Kepler photometry of 45 gas giants and firmly rule out the S&S model for four candidates.
We select Kepler Objects of Interest (KOIs) with radii at least twice that of Earth for which the S&S Equation (30) implies a peak effect greater than 10 parts per million (ppm), adjusted for Rayleigh scattering using their Equations (40)(45). We eliminate KOIs with grazing transits as well as those identified in Ford et al. (2012), Mazeh et al. (2013), and Holczer et al. (2016) as having significant transit timing variations. We also eliminate a few KOIs identified by Holczer et al. (2016) as likely planetary false positives based on the behavior of the light curves, leaving 45 planet candidates. To calculate the expected effect, we adopt the masses predicted in Chen & Kipping (2018).
Recent work by Virtual Planetary Laboratory researcher, Eric Agol (University of Washington), has been highlighted in a UW News Article…
Proxima Centauri b provides an unprecedented opportunity to understand the evolution and nature of terrestrial planets orbiting M dwarfs. Although Proxima Cen b orbits within its star’s habitable zone, multiple plausible evolutionary paths could have generated different environments that may or may not be habitable. Here, we use 1-D coupled climate-photochemical models to generate self-consistent atmospheres for several evolutionary scenarios, including high-O2, high-CO2, and more Earth-like atmospheres, with both oxic and anoxic compositions. We show that these modeled environments can be habitable or uninhabitable at Proxima Cen b’s position in the habitable zone. We use radiative transfer models to generate synthetic spectra and thermal phase curves for these simulated environments, and use instrument models to explore our ability to discriminate between possible planetary states.
We explore the occurrence and detectability of planet-planet occultations (PPOs) in exoplanet systems. These are events during which a planet occults the disk of another planet in the same system, imparting a small photometric signal as its thermal or reflected light is blocked. We focus on the planets in TRAPPIST-1, whose orbital planes we show are aligned to < 0\buildrel{\circ}\over{.} 3 at 90% confidence. We present a photodynamical model for predicting and computing PPOs in TRAPPIST-1 and other systems for various assumptions of the planets’ atmospheric states. When marginalizing over the uncertainties on all orbital parameters, we find that the rate of PPOs in TRAPPIST-1 is about 1.4 per day. We investigate the prospects for detection of these events with the James Webb Space Telescope, finding that ∼10-20 occultations per year of b and c should be above the noise level at 12-15 μm. Joint modeling of several of these PPOs could lead to a robust detection. Alternatively, observations with the proposed Origins Space Telescope should be able to detect individual PPOs at high signal-to-noise ratios. We show how PPOs can be used to break transit timing variation degeneracies, imposing strong constraints on the eccentricities and masses of the planets, as well as to constrain the longitudes of nodes and thus the complete three-dimensional structure of the system. We further show how modeling of these events can be used to reveal a planet’s day/night temperature contrast and construct crude surface maps. We make our photodynamical code available on github (https://github.com/rodluger/planetplanet).
On August 11, Rodrigo Luger successfully defended his dissertation to earn his Astronomy and Astrobiology Dual-Title PhD. He discussed his…
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