Observations Of Planets Research Articles

Secondary eclipse of the hot Jupiter WASP-121b at 2 μm

Ground-based observations of the secondary eclipse in the 2MASS K band are presented for the hot Jupiter WASP-121b. These are the first occultation observations of an extrasolar planet that were carried out with an instrument attached to a 1 m class telescope (the SMARTS 1.3 m). We find a highly significant eclipse depth of (0.228 ± 0.023)%. Together with other planet atmosphere measurements, including the Hubble Space Telescope near-infrared emission spectrum, current data support more involved atmosphere models with species producing emission and absorption features, rather than simple smooth blackbody emission. Analysis of the time difference between the primary and secondary eclipses and the durations of these events yields an eccentricity of e = 0.0207 ± 0.0153, which is consistent with the earlier estimates of low or zero eccentricity, but with a smaller error. Comparing the observed occultation depth in the K band with the one derived under the assumption of zero Bond albedo and full heat redistribution, we find that WASP-121b has a deeper observed occultation depth than predicted. Together with the sample of 31 systems with K-band occultation data, this observation lends further support to the idea of inefficient heat transport between the day and night sides for most of the hot Jupiters.

An Early Compilation of Saturn Observations from Babylon

In this paper, I publish and analyse a compilation of observations of the synodic phenomena of Saturn from Babylon, which can be dated to the early sixth century b.c. By comparing these observations with records found in other early compilations of planetary observations it is possible to trace the development of observational practice in Babylonia. The compilation contains references to several stars that are previously unattested in cuneiform texts. An attempt is made to identify these stars.

Constraining Yukawa gravity from planetary motion in the solar system

In this work we used the observed additional perihelion precession in the Solar System, obtained from the observations of planets and spacecrafts, to study the possible existence of Yukawa correction term to the Newtonian gravitational potential. Our study was motivated by previous analyses which indicated the possible discrepancies from Newtonian gravity in this form and at wide range of astrophysical scales. Yukawa gravity was introduced to cure some shortcomings of General Relativity (GR) at galactic and extragalactic scales. We demonstrated that this form of gravity can give the values for orbital precession which are comparable or even in better agreement with observations than the corresponding predictions of GR. The obtained results can be used for setting stronger constraints on variation of the gravitational constant G, as well as on the fundamental constant δ of Yukawa gravity. Moreover, Yukawa gravity could be used to improve the results for the motion of planets, other Solar System bodies, as well as spacecrafts, and as a consequence, it can help us to get more reliable predictions for natural hazards in the Solar System, such as potential impacts by near-Earth objects.

Astrology—Emblematics—Heraldry: On Comets, Moons and Stars in the Book of Arms by Szymon Okolski

The paper examines the presence of astrology in the heraldic work Orbis Polonus by Szymon Okolski dating from the mid-1600s. While due to a growing fascination with Neoplatonism and hermetic writings, astrology had enjoyed popularity since the Renaissance, in Okolski’s case its influence came mostly through early-modern books of emblems and compendia of symbols. It is, therefore, important not only to track down astrological motifs in the works of Alciatus, Cesare Ripa, Giulio Cesare Capaccio, Julius Wilhelm Zincgref, and Diego de Saavedra to compare them with those found in Orbis Polonus, but also to recognise the fact that emblematics had a great impact on how Okolski perceived the import of his heraldic work as such. The novelty of Okolski’s project consisted in treating armorial bearings as universal symbols and interpreting them not only in accordance with the rules of heraldry, but also through a wide range of cultural sources, trends, and traditions. In order to make the symbolic significance hidden in coats of arms more apparent, the author tried to organise the heraldic entries in a new way. Apart from the usual parts describing the coat of arms (delineatio), its origins (origo) and the family that used it (linea familiae), he introduced subchapters dealing with its symbolic meaning. He called them “considerations”, “precautions”, or “omens” depending on which aspect of the symbolic explanation he wanted to emphasise. Especially the third of these dovetails with astrology because the symbolism of the coat of arms, including motifs derived from, or related to, astrology, is presented as the best path that should be taken by a family bearing a particular coat of arms. All the while, however, these auguries are made based on symbols as such and not on careful observation of stars, planets or comets, and Okolski was not concerned with the destiny of individual people but with more general tendencies that affected the virtue of noble families, and virtue is for Okolski the foundation of nobility.

Analysis of gaseous ammonia (NH3) absorption in the visible spectrum of Jupiter - Update

An analysis of currently available ammonia (NH3) visible-to-near-infrared gas absorption data was recently undertaken by Irwin et al. (2018) to help interpret Very Large Telescope (VLT) MUSE observations of Jupiter from 0.48–0.93 µm, made in support of the NASA/Juno mission. Since this analysis a newly revised set of ammonia line data, covering the previously poorly constrained range 0.5–0.833 µm, has been released by the ExoMol project, “C2018” (Coles et al., 2018), which demonstrates significant advantages over previously available data sets, and provides for the first time complete line data for the previously poorly constrained 5520- and 6475-Å bands of NH3. In this paper we compare spectra calculated using the ExoMol–C2018 data set (Coles et al., 2018) with spectra calculated from previous sources to demonstrate its advantages. We conclude that at the present time the ExoMol–C2018 dataset provides the most reliable ammonia absorption source for analysing low- to medium-resolution spectra of Jupiter in the visible/near-IR spectral range, but note that the data are less able to model high-resolution spectra owing to small, but significant inaccuracies in the line wavenumber estimates. This work is of significance not only for solar system planetary physics, but for future proposed observations of Jupiter-like planets orbiting other stars, such as with NASA’s planned Wide-Field Infrared Survey Telescope (WFIRST).

Arecibo Radar Observations of Dwarf Planet 1 Ceres During the 2018 Apparition

Arecibo Radar Observations of Dwarf Planet 1 Ceres During the 2018 Apparition

The IAU and hazardous Near Earth Objects – a clear and present danger

AbstractThe Minor Planet Center, established in 1947 by the IAU, is the international repository and clearinghouse for the world’s minor planet observations. Since 1989, CCD surveys of Near Earth Objects at ground-based astronomical observatories are operational, mainly in the USA. As of 23 August, 2018, a total of 18,545 Near Earth Asteroids (NEAs) and 107 Near Earth Comets (NECs) have been registered and daily updates are made publicly available on the internet by the MPC, NASA-JPL-CNEOS and ESA-SSA-NEOCC.Concern about the possibility of NEO impacts has been picked up by the United Nations Committee on the Peaceful Uses of Outer Space (UN-COPUOS), where the IAU has observer status, and formally expressed since 1999. This led in 2014 to the formation of two international coordinating bodies for NEO detection and NEO impact mitigation: the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG).In support of these developments, the IAU 28th General Assembly, Session II, held in Beijing on 30 August 2012, adopted a Resolution (3B) recommending the establishment of an International NEO EarlyWarning System, as proposed by the IAU Division III (now Division F) Working Group on Near-Earth Objects. The GA recommended “… that the IAU National Members work with the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS) and the International Council for Science (ICSU), to coordinate and collaborate on the establishment of an International NEO Early Warning System, relying on the scientific and technical advice of the relevant astronomical community, whose main purpose is the reliable identification of potential NEO collisions with the Earth, and the communication of the relevant parameters to suitable decision makers of the nation(s) involved. ….”The NEO hazard issue received world-wide attention on 13 February 2013 when a NEA with an estimated size of 17 to 20 meters and an estimated mass of 11,000 tons exploded over Chelyabinsk (Russia), releasing 440 kT TNT of energy at an altitude of ∼23 km.Subsequently, on 5 December 2014, the United Nations General Assembly adopted a Resolution (69/85, 9–10), noting “… the importance of information-sharing in discovering, monitoring and physically characterizing potentially hazardous near-Earth objects to ensure that all countries, in particular developing countries with limited capacity in predicting and mitigating a near-Earth object impact, are aware of potential threats, emphasizes the need for capacitybuilding for effective emergency response and disaster management in the event of a near-Earth object impact, .…”In spite of all dedicated NEO surveys operational to date, the present inventory and thus our assessment of the level of threat of NEOs is severely limited by their huge number and by the available observational capabilities. E.g., while the estimated number of all NEOs larger than 40 meters in diameter is ∼700, 000, only ∼2% have been detected to date. For NEOs with sizes between 40 and 140 meters, the detection percentage amounts to less than 1% of the estimated number. Only dedicated space-based surveys, preferably in the infrared, will be able to provide the much needed orders of magnitude improvement in the detection, tracking and characterizing of NEOs. One promising project is the NASA-JPL NEOCam mission, studied since 2005 but not yet approved: a dedicated infrared observatory aiming to detect, track and characterize NEO’s from the Sun-Earth Lagrange point L1.As Yeomans puts it: we better find them before they find us (Yeomans 2013). Traditionally, astronomers are looking back into the past, if only because of the limited speed of light. But we should realize that the clear and present danger posed by hazardous Near Earth Objects to mankind and all other life forms obliges us to look also forward, into the future. Provided with the proper means, we astronomers can do that, as a small service to society, including ourselves. The astronomical community at large should give high priority to NEO survey projects, in particular space-based surveys.

Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System

Abstract 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. Our simulations show a range of surface temperatures, most of which are not habitable, although an aqua planet TRAPPIST-1 e could maintain a temperate surface given Earth-like geological outgassing and CO2. We find that a desiccated TRAPPIST-1 h may produce habitable surface temperatures beyond the maximum greenhouse distance. Potential observational discriminants for these atmospheres in transmission and emission spectra are influenced by photochemical processes and aerosol formation and include collision-induced oxygen absorption (O2–O2), and O3, CO, SO2, H2O, and CH4 absorption features, with transit signals of up to 200 ppm. Our simulated transmission spectra are consistent with K2, Hubble Space Telescope, and Spitzer observations of the TRAPPIST-1 planets. For several terrestrial atmospheric compositions, we find that TRAPPIST-1 b is unlikely to produce aerosols. These results can inform JWST observation planning and data interpretation for the TRAPPIST-1 system and other M dwarf terrestrial planets.

The Near-infrared Transmission Spectra of TRAPPIST-1 Planets b, c, d, e, f, and g and Stellar Contamination in Multi-epoch Transit Spectra

Abstract The seven approximately Earth-sized transiting planets in the TRAPPIST-1 system provide a unique opportunity to explore habitable- and nonhabitable-zone small planets within the same system. Its habitable-zone exoplanets—due to their favorable transit depths—are also worlds for which atmospheric transmission spectroscopy is within reach with the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). We present here an independent reduction and analysis of two HST Wide Field Camera 3 (WFC3) near-infrared transit spectroscopy data sets for six planets (b through g). Utilizing our physically motivated detector charge-trap correction and a custom cosmic-ray correction routine, we confirm the general shape of the transmission spectra presented by de Wit et al. Our data reduction approach leads to a 25% increase in the usable data and reduces the risk of confusing astrophysical brightness variations (e.g., flares) with instrumental systematics. No prominent absorption features are detected in any individual planet’s transmission spectra; by contrast, the combined spectrum of the planets shows a suggestive decrease around 1.4 μm similar to an inverted water absorption feature. Including transit depths from K2, the SPECULOOS-South Observatory, and Spitzer, we find that the complete transmission spectrum is fully consistent with stellar contamination owing to the transit light source effect. These spectra demonstrate how stellar contamination can overwhelm planetary absorption features in low-resolution exoplanet transit spectra obtained by HST and JWST and also highlight the challenges in combining multi-epoch observations for planets around rapidly rotating spotted stars.

A study of Babylonian planetary theory I. The outer planets

In this study I attempt to provide an answer to the question how the Babylonian scholars arrived at their mathematical theory of planetary motion. Although no texts are preserved in which the Babylonians tell us how they did it, from the surviving Astronomical Diaries we have a fairly complete picture of the nature of the observational material on which the scholars must have based their theory and from which they must have derived the values of the defining parameters. Limiting the discussion to system A theory of the outer planets Saturn, Jupiter and Mars, I will argue that the development of Babylonian planetary theory was a gradual process of more than a century, starting sometime in the fifth century BC and finally resulting in the appearance of the first full-fledged astronomical ephemeris around 300 BC. The process of theory formation involved the derivation of long “exact” periods by linear combination of “Goal–Year” periods, the invention of a 360° zodiac, the discovery of the variable motion of the planets and the development of the numerical method to model this as a step function. Longitudes of the planets in the Babylonian zodiac could be determined by the scholars with an accuracy of 1° to 2° from observations of angular distances to Normal Stars with known positions. However, since the sky is too bright at first and last appearances of the planets and at acronychal rising for nearby stars to be visible, accurate longitudes as input for theoretical work could only be determined when the planets were near the stationary points in their orbits. In this study I show that the Babylonian scholars indeed based their system A modeling of the outer planets on planetary longitudes near stations, that their system A models of Saturn and Jupiter provided satisfactory results for all synodic phenomena, that they realized that their system A model of Mars did not produce satisfactory results for the second station so that separate numerical schemes were constructed to predict the positions of Mars at second station from the model at first station, and finally that their system A model for Mars provided quite poor predictions of the longitude of Mars at first and last appearances over large stretches of the zodiac. I further discuss ways in which the parameters of the system A models may have been derived from observations of the outer planets. By analyzing contemporaneous ephemerides from Uruk of four synodic phenomena of Jupiter from the second century BC, I finally illustrate how the Babylonian scholars may have used observations of Normal Star passages of planets to choose the initial conditions for their ephemerides.

Application of an evolution strategy in planetary ephemeris modeling

Classical planetary ephemeris construction comprises three major steps which are to be performed iteratively: numerical integration of coupled equations of motion of a multi-body system (propagator step), reduction of observations (reduction step), and optimization of model parameters (adjustment step). In future, this approach may become challenged by further refinements in force modeling (e.g. inclusion of much more significant minor bodies than in the past), an ever-growing number of planetary observations (e.g. the vast amount of spacecraft tracking data), and big data issues in general. In order to circumvent the need for both the inversion of normal equation matrices and the determination of partial derivatives, and to prepare the ephemeris for applications apart from stand-alone solar-system planetary orbit calculations, here we propose an alternative ephemeris construction method. The main idea is to solve it as an optimization problem by straightforward direct evaluation of the whole set of mathematical formulas, rather than to solve it as an inverse problem with all its tacit mathematical assumptions and potential numerical difficulties. The usual gradient search is replaced by a stochastic search, namely an evolution strategy, the latter of which is perfect for the exploitation of parallel computing capabilities. Furthermore, this new approach allows for multi-criteria optimization and time-varying optima. These issues will become important in future once ephemeris construction is just one part of even larger optimization problems, e.g. the combined and consistent determination of a generalized physical state (orbit, size, shape, rotation, gravity, …) of celestial bodies (planets, satellites, asteroids, or comets), and/or if one seeks near real-time solutions. Here, we outline the general idea and exemplarily optimize high-correlated asteroidal ring model parameters (total mass and heliocentric radius), and individual asteroid masses, based on simulated observations.

Characterization of the HD 219134 multiplanet system I. Observations of stellar magnetism, wind, and high-energy flux★

HD 219134 hosts several planets, with seven candidates reported, and the two shortest period planets are rocky (4-5 $M_{\oplus}$) and transit the star. Here we present contemporaneous multi-wavelength observations of the star HD 219134. We observed HD 219134 with the Narval spectropolarimeter at the Observatoire du Pic du Midi, and used Zeeman Doppler Imaging to characterise its large-scale stellar magnetic field. We found a weak poloidal magnetic field with an average unsigned strength of 2.5 G. From these data we confidently confirm the rotation period of 42 days, measure a stellar inclination of 77$\pm$8 degrees, and find evidence for differential rotation. The projected obliquity of the two transiting super-Earths is therefore between 0 and 20 degrees. We employed HST STIS observations of the Ly$\alpha$ line to derive a stellar wind mass-loss rate of half the solar value ($10^{-14} M_{\odot} {\rm yr}^{-1}$). We further collected photometric transit observations of the closest planet at near-UV wavelengths centred on the Mg II h&k lines with AstroSat. We found no detectable absorption, setting an upper limit on the transit depth of about 3%, which rules out the presence of a giant magnesium cloud larger than 9 planet radii. Finally, we estimated the high-energy flux distribution of HD 219134 as seen by planets b and c. These results present a detailed contemporaneous characterisation of HD 219134, and provide the ingredients necessary for accurately modelling the high-energy stellar flux, the stellar wind, and their impact on the two shortest-period planets, which will be presented in the second paper of this series.

Large regional shortwave forcing by anthropogenic methane informed by Jovian observations.

Recently, it was recognized that widely used calculations of methane radiative forcing systematically underestimated its global value by 15% by omitting its shortwave effects. We show that shortwave forcing by methane can be accurately calculated despite considerable uncertainty and large gaps in its shortwave spectroscopy. We demonstrate that the forcing is insensitive, even when confronted with much more complete methane absorption spectra extending to violet light wavelengths derived from observations of methane-rich Jovian planets. We undertake the first spatially resolved global calculations of this forcing and find that it is dependent on bright surface features and clouds. Localized annual mean forcing from preindustrial to present-day methane increases approaches +0.25 W/m2, 10 times the global annualized shortwave forcing and 43% of the total direct CH4 forcing. Shortwave forcing by anthropogenic methane is sufficiently large and accurate to warrant its inclusion in historical analyses, projections, and mitigation strategies for climate change.

Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk

Context. The observation of planets in their formation stage is a crucial but very challenging step in understanding when, how, and where planets form. PDS 70 is a young pre-main sequence star surrounded by a transition disk, in the gap of which a planetary-mass companion has recently been discovered. This discovery represents the first robust direct detection of such a young planet, possibly still at the stage of formation. Aims. We aim to characterize the orbital and atmospheric properties of PDS 70 b, which was first identified on May 2015 in the course of the SHINE survey with SPHERE, the extreme adaptive-optics instrument at the VLT. Methods. We obtained new deep SPHERE/IRDIS imaging and SPHERE/IFS spectroscopic observations of PDS 70 b. The astrometric baseline now covers 6 yr, which allowed us to perform an orbital analysis. For the first time, we present spectrophotometry of the young planet which covers almost the entire near-infrared range (0.96–3.8 μm). We use different atmospheric models covering a large parameter space in temperature, log g, chemical composition, and cloud properties to characterize the properties of the atmosphere of PDS 70 b. Results. PDS 70 b is most likely orbiting the star on a circular and disk coplanar orbit at ~22 au inside the gap of the disk. We find a range of models that can describe the spectrophotometric data reasonably well in the temperature range 1000–1600 K and log g no larger than 3.5 dex. The planet radius covers a relatively large range between 1.4 and 3.7 RJ with the larger radii being higher than expected from planet evolution models for the age of the planet of 5.4 Myr. Conclusions. This study provides a comprehensive data set on the orbital motion of PDS 70 b, indicating a circular orbit and a motion coplanar with the disk. The first detailed spectral energy distribution of PDS 70 b indicates a temperature typical of young giant planets. The detailed atmospheric analysis indicates that a circumplanetary disk may contribute to the total planetflux.

PYMIEDAP: a Python–Fortran tool for computing fluxes and polarization signals of (exo)planets

PYMIEDAP (the Python Mie Doubling-Adding Programme) is a Python-based tool for computing the total linearly and circularly polarized fluxes of incident unpolarized sunlight or starlight that is reflected by solar system planets or moons, respectively, or by exoplanets at a range of wavelengths. The radiative transfer computations are based on an doubling-adding Fortran algorithm and fully include polarization for all orders of scattering. The model (exo)planets are described by a model atmosphere composed of a stack of homogeneous layers containing gas and/or aerosol and/or cloud particles bounded below by an isotropically depolarizing surface (that is optionally black). The reflected light can be computed spatially resolved and/or disk-integrated. Spatially resolved signals are mostly representative for observations of solar system planets (or moons), while disk-integrated signals are mostly representative for exoplanet observations. PYMIEDAP is modular and flexible, and allows users to adapt and optimize the code according to their needs. PYMIEDAP keeps options open for connections with external programs and for future additions and extensions. In this paper, we describe the radiative transfer algorithm that PYMIEDAP is based on and the principal functionalities of the code. We also provide benchmark results of PYMIEDAP that can be used for testing its installation and for comparison with other codes.

Masses of the Main Asteroid Belt and the Kuiper Belt from the Motions of Planets and Spacecraft

Dynamical mass estimates for the main asteroid belt and the trans-Neptunian Kuiper belt have been found from their gravitational influence on the motion of planets. Discrete rotating models consisting of moving material points have been used to model the total attraction from small or as yet undetected bodies of the belts. The masses of the model belts have been included in the set of parameters being refined and determined and have been obtained by processing more than 800 thousand modern positional observations of planets and spacecraft. We have processed the observations and determined the parameters based on the new EPM2017 version of the IAA RAS planetary ephemerides. The large observed radial extent of the belts (more than 1.2 au for the main belt and more than 8 au for the Kuiper belt) and the concentration of bodies in the Kuiper belt at a distance of about 44 au found from observations have been taken into account in the discrete models. We have also used individual mass estimates for large bodies of the belts as well as for objects that spacecraft have approached and for bodies with satellites. Our mass estimate for the main asteroid belt is $(4.008 \pm 0.029)\cdot 10^{-4} \ m_{\oplus}$ (3$\sigma$). The bulk of the Kuiper belt objects are in the ring zone from 39.4 to 47.8 AU. The estimate of its total mass together with the mass of the 31 largest trans-Neptunian Kuiper belt objects is $(1.97 \pm 0.030)\cdot 10^{-2} \ m_{\oplus}$ (3$\sigma$), which exceeds the mass of the main asteroid belt almost by a factor of 50. The mass of the 31 largest trans-Neptunian objects (TNOs) is only about 40% of the total one.

A Study of Evaluation Criteria Setting about Ability to Move the Viewpoint of Planetary Observation

A Study of Evaluation Criteria Setting about Ability to Move the Viewpoint of Planetary Observation

Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment.

We describe how environmental context can help determine whether oxygen (O2) detected in extrasolar planetary observations is more likely to have a biological source. Here we provide an in-depth, interdisciplinary example of O2 biosignature identification and observation, which serves as the prototype for the development of a general framework for biosignature assessment. Photosynthetically generated O2 is a potentially strong biosignature, and at high abundance, it was originally thought to be an unambiguous indicator for life. However, as a biosignature, O2 faces two major challenges: (1) it was only present at high abundance for a relatively short period of Earth's history and (2) we now know of several potential planetary mechanisms that can generate abundant O2 without life being present. Consequently, our ability to interpret both the presence and absence of O2 in an exoplanetary spectrum relies on understanding the environmental context. Here we examine the coevolution of life with the early Earth's environment to identify how the interplay of sources and sinks may have suppressed O2 release into the atmosphere for several billion years, producing a false negative for biologically generated O2. These studies suggest that planetary characteristics that may enhance false negatives should be considered when selecting targets for biosignature searches. We review the most recent knowledge of false positives for O2, planetary processes that may generate abundant atmospheric O2 without a biosphere. We provide examples of how future photometric, spectroscopic, and time-dependent observations of O2 and other aspects of the planetary environment can be used to rule out false positives and thereby increase our confidence that any observed O2 is indeed a biosignature. These insights will guide and inform the development of future exoplanet characterization missions. Key Words: Biosignatures—Oxygenic photosynthesis—Exoplanets—Planetary atmospheres. Astrobiology 18, 630–662.

Exoplanet Biosignatures: At the Dawn of a New Era of Planetary Observations.

The rapid rate of discoveries of exoplanets has expanded the scope of the science possible for the remote detection of life beyond Earth. The Exoplanet Biosignatures Workshop Without Walls (EBWWW) held in 2016 engaged the international scientific community across diverse scientific disciplines, to assess the state of the science and technology in the search for life on exoplanets, and to identify paths for progress. The workshop activities resulted in five major review papers, which provide (1) an encyclopedic review of known and proposed biosignatures and models used to ascertain them (Schwieterman et al., 2018 in this issue); (2) an in-depth review of O2 as a biosignature, rigorously examining the nuances of false positives and false negatives for evidence of life (Meadows et al., 2018 in this issue); (3) a Bayesian framework to comprehensively organize current understanding to quantify confidence in biosignature assessments (Catling et al., 2018 in this issue); (4) an extension of that Bayesian framework in anticipation of increasing planetary data and novel concepts of biosignatures (Walker et al., 2018 in this issue); and (5) a review of the upcoming telescope capabilities to characterize exoplanets and their environment (Fujii et al., 2018 in this issue). Because of the immense content of these review papers, this summary provides a guide to their complementary scope and highlights salient features. Strong themes that emerged from the workshop were that biosignatures must be interpreted in the context of their environment, and that frameworks must be developed to link diverse forms of scientific understanding of that context to quantify the likelihood that a biosignature has been observed. Models are needed to explore the parameter space where measurements will be widespread but sparse in detail. Given the technological prospects for large ground-based telescopes and space-based observatories, the detection of atmospheric signatures of a few potentially habitable planets may come before 2030. Key Words: Exoplanets—Biosignatures—Remote observation—Spectral imaging—Bayesian analysis. Astrobiology 18, 619–626.

Temperature and para hydrogen gradients on Jupiter observed from the FORCAST camera on SOFIA

Jupiter was observed on December 8, 2010 with SOFIA using the FORCAST mid-infrared camera with selected spectral channels in the 5–40 µm region. Although the channels were not optimized for planetary observations, we demonstrate that useful information on latitude gradients of upper tropospheric temperature and the para hydrogen fraction ƒp can be retrieved. Calibration of the data is refined using simultaneous measurements of Callisto, along with a simplified model of Callisto's thermal behavior. In this preliminary study, an inversion algorithm is applied to measurements in three channels to obtain temperature and ƒp as functions of latitude in an atmospheric layer centered near 300 mbar. The results are compared with those previously obtained from Voyager IRIS, Cassini CIRS, and ground-based measurements. The low-latitude minimum in ƒp is found to be significantly displaced northward from the equatorial minimum in temperature, unlike the gradients found in the earlier Voyager and ground-based measurements. Possible explanations for this behavior are explored.