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Artist's impression of 'Waterworld' Kepler 22b
Scientific discussion meeting organised by Professor Athena Coustenis, Professor Steve Miller, Professor Peter Read and Professor Jonathan Tennyson FRS
This meeting aims to set the agenda for the next decade in this rapidly expanding field of extra-solar planet science. Some 800 planets orbiting stars outside of our solar system have now been detected, with varying masses and orbital parameters. The challenge now is to move from detection to understanding these planets as bodies in their own right.
Biographies of speakers and their talk abstracts can be found below and you can download the programme. Recorded audio of the presentations will be available on this page after the event and papers will be published in a future issue of Philosophical Transactions A.
Enquiries: Contact the events team
Dr Athena Coustenis
Athena Coustenis is Director of Research with the National Centre for Scientific Research (CNRS) of France, working at Paris Observatory in Meudon. Her speciality is Planetology (exploration and study of the Solar System from ground-based and space observations). Her astronomy research is devoted to the investigation of planetary atmospheres and surfaces, with emphasis on Titan and Enceladus, Saturn’s satellites, and Jupiter’s Ganymede and Europe objects with high astrobiological potential. She also works on the characterisation of exoplanetary atmospheres. In the recent years she has been leading efforts towards future space missions.
Professor Steve Miller
BiographySteven Miller is Professor of Science Communication and Planetary Science at University College London, where he is head of the Science and Technology Studies (STS) Department. As a planetary scientist, Professor Miller’s main interests lie in understanding how the atmospheres of giant planets – like Jupiter and Saturn, and some of the hot, giant exoplanets – couple with the space environment around them. He is Co-Coordinator of Europlanet RI activities supporting ground-based observations to back up space missions, outreach and dissemination.A former political journalist, Professor Miller researches issues surrounding science and society at the European level. He is Director of the European Science Communication network, author of The Chemical Cosmos: a guided tour and co-author of Science in Public: communication, culture and credibility.
Steven Miller is Professor of Science Communication and Planetary Science at University College London, where he is head of the Science and Technology Studies (STS) Department. As a planetary scientist, Professor Miller’s main interests lie in understanding how the atmospheres of giant planets – like Jupiter and Saturn, and some of the hot, giant exoplanets – couple with the space environment around them. He is Co-Coordinator of Europlanet RI activities supporting ground-based observations to back up space missions, outreach and dissemination.A former political journalist, Professor Miller researches issues surrounding science and society at the European level. He is Director of the European Science Communication network, author of The Chemical Cosmos: a guided tour and co-author of Science in Public: communication, culture and credibility.
Professor Peter Read
Peter Read is currently Professor of Physics and Head of Atmospheric, Oceanic and Planetary Physics in the Department of Physics at the University of Oxford. He graduated in Physics at the University of Birmingham (UK) in 1975 and obtained a Ph.D. in Radioastronomy at the University of Cambridge in 1980. After completing his Ph.D., he became a Research Scientist in remote sensing and geophysical fluid dynamics at the Met. Office. He joined the academic staff of Oxford University in 1991, where he has been based until the present. His research interests cover a wide range of subjects, including aspects of fundamental fluid dynamics, planetary meteorology and climate, involving a mixture of laboratory experiments, numerical climate models and planetary observations. He has been a Co-Investigator or collaborator on NASA’s Mars Global Surveyor, Mars Reconnaissance Orbiter and Cassini Orbiter missions. He has published more than 140 refereed scientific papers and review articles, and a major research monograph on the Martian atmosphere and climate.
Professor Jonathan Tennyson FRS
Jonathan Tennyson gained a BA in Natural Sciences from King's College, Cambridge in 1977 and a PhD in Theoretical Chemistry from the University of Sussex in 1980. He spent a productive two years as Royal Society Western European Exchange Fellow at the University of Nijmegen in the Netherlands, In 1982 he joined the Theory Group at Daresbury Laboratory. He was appointed a “New Blood” lecturer at University College London in Theoretical Atomic Physics in 1985. He became Professor of Physics in 1994; was Head of Department in 2004-11 and became Massey Professor of Physics in 2005. He was elected an FRS in 2009. His research interests cover a range of topics on the theory of small molecules. In particular I compute spectra of these molecules (such as water) and collide electrons (and occasionally positrons) with them. He is interested in the astrophysical, atmospheric and other consequences of these processes.
Professor Bill BoruckiChair of Session 1
William Borucki is a space scientist at the NASA Ames Research Center in Mountain View, California. He received a MSc in physics from the University of Wisconsin in 1962 and then moved to NASA Ames where he first worked on the development of the heat shield for the Apollo Mission in the Hypersonic Free Flight Branch. After the successful Moon landings, he transferred to the Theoretical Studies Branch where he investigated lightning activity in planetary atmospheres and developed mathematical models to predict the effects of nitric oxides and chlorofluoromethanes on the Earth’s ozone layer. In 1984, he began advocating the development of a space mission that could detect Earth-size planets and determine the frequency of Earth-size planets in the habitable zone of Sun-like stars. In the succeeding years he developed the techniques required to find such small planets and showed that the technology and analysis techniques were sufficiently mature to proceed to flight status. Currently he is the Science Principal Investigator for the Kepler Mission that is designed to determine the frequency of terrestrial planets orbiting in and near the habitable zones of other stars. The Mission uses transit photometry to monitor over 170,000 stars, was launched on March 6, 2009, and is now in the science operations phase. Based on the first three years of observations, over 100 planets have been confirmed and an additional 2600 planetary candidates have been discovered.
Over 2700 planetary candidates have been found with an enormous range of sizes, temperatures, and types of stellar hosts. In particular, exoplanets near the size of Earth’s moon to those larger than Jupiter have been found orbiting stars much cooler and smaller than the Sun as well to stars hotter and often larger than the Sun. Orbital periods range from 0.84 days to over 1000 days and orbital distances range from 0.01 AU to many AU. Several planets have been discovered orbiting binary stars.Calculated radiative equilibrium temperatures (Teq) range from higher than molten lava (~1830K for Kepler-10b) for planets near the surface of their host star to temperatures to those as cold as -70C. The Kepler Mission has even found a planetary candidate in the HZ of a binary star. Masses of those planets with large masses and/or short orbital-periods can be are being determined by radial velocity and transit timing methods. By combining these results with the sizes obtained from transit photometry, densities of these planets are being calculated. These range from 0.2 gr/cc for Kepler-7b to 8.8 gr/cc for Kepler-10b. The results are indicative of planets that range from mostly gas, to water planets, and to iron-rich rocky planets. Surprisingly, a very wide range of densities has been found for closely-packed planets orbiting the same star (Kepler-11). This result implies that contrary to what is observed in our Solar System, the composition (whether rocky, water-rich, or gas) cannot be surmised from its semi-major axis or insolation.Because it is much more difficult to find small planets in the HZ compared to finding large planets in short period orbits, only a few dozen planetary candidates and confirmed planets have been found in the HZ. Unfortunately, no densities of planets in the HZ are available because the amplitudes of the RV and transit-timing signals they produce are too small for detection. A summary of the known characteristics of exoplanets, especially small planets and all those in the HZ will be presented.
Professor Didier QuelozOverview, limitations and prospects on exoplanet insights from HARPS and transiting planet perspective
Professor Didier Queloz is at the origin of the exoplanet revolution in astrophysics. Since 1995 where he discovered with Michel Mayor the first giant planet outside the solar system, he spent considerable effort improving the precision of the Doppler technique. More recently he is involved in the emerging area of planetary transit detection where he is collaborating with the WASP team. He was as well a key actor in the first transit detection of a rocky planet by Corot.
The discovery of first exoplanets sparked a real revolution in astronomy. Today, about 1000 such objects have been found and confirmed. We have learned that planets are quite common, and that their properties are much more diverse than originally predicted. The improvements and intensive efforts made during the last decade by teams carrying out surveys and dedicated space missions have lead to the identification of numerous planetary systems hosting Neptune-mass planets and super-Earths. While numerously found, we know little on the nature and origines of these planets. They remain a matter of fierce debate in the community.
In my talk I will discuss current limitations and describe a path towards improving this situation. More particularly I'll present New Generation Transit Survey (NGTS) ground facility and CHEOPS transit finder satelite as the two next facilites to play a important role by gaining insights about the true nature of small planetary systems.
Professor Christophe LovisThe low-mass exoplanet population discovered by HARPS
Christophe Lovis is a researcher within the exoplanet group at the University of Geneva. His research activities focus on the detection and characterization of planetary systems, with special emphasis on Neptunes and super-Earths around solar-type stars and M dwarfs. He has been working in particular with data from the HARPS spectrograph, which deliver the most precise radial velocities ever achieved and have unveiled a large population of low-mass planets on short-period orbits. His research interests also include the characterization of exoplanet atmospheres and the study of magnetic activity in solar-type stars.
I will discuss the recent progress made on the discovery and characterization of low-mass exoplanets in the solar neighbourhood. This involves in particular the results from the high-precision radial velocity surveys made with the HARPS spectrograph. The ultimate goals of these projects are twofold: an investigation into the statistical properties of planetary systems in general, and a search for nearby, bright transiting objects that will become the targets of choice for a detailed characterization of their internal structure and atmosphere. I will argue that radial velocities have significant advantages when it comes to improving our understanding of system architectures, in particular for studying the dichotomy between low-mass, compact systems and Solar-System-like architectures comprising giant planets orbiting at several AUs from the star. Finally, I will review the presently-known sample of transiting exoplanets that are sufficiently close to us to allow for atmospheric studies, and discuss how to expand this relatively small sample using new instrumentation, in particular HARPS-N and ESPRESSO, the high-precision velocimeter for ESO VLT.
Professor Hugh JonesRadial velocity studies of cool stars
Professor Hugh Jones is the Director of Bayfordbury Observatory at the University of Hertfordshire. His research is focused on the discovery and understanding of our stellar neighbourhood - this has led to the discovery of many of the coolest and closest brown dwarfs and extra-solar planets including the system most like our own, the one with the most eccentric orbit and the first in the Goldilock's zone.In 1988, he received his BSc in Physics from the University of Leeds. After working at Blackwell Scientific and setting up an educational electronics company he gained his PhD in astrophysics from the University of Edinburgh in 1995. Following appointments in Tokyo and Liverpool, Professor Jones moved to Hertfordshire in July 2004. He has a wide ranging commitment to astronomy through the promotion of dark skies, running public events and distance learning programmes completed by many thousands of students.
Over the last two decades, the field of exoplanets has made extraordinary progress. Rather than wondering if we are a lone or typical planetary system a series of independent experiments suggest that the architecture of Solar System is not so common but that stars do normally seem to have planets. One significant hole in our exoplanet knowledge are the exoplanets around the dominant stellar population by number so called low-mass stars or M dwarfs. The two traditional drawbacks of such investigation faintness and activity are addressed by investigating radial velocity signals as a function of wavelength and by a mini-survey at red-optical wavelengths where M dwarfs exhibit dramatically more flux. These experiments allow us to glimpse that M dwarf planetary systems appear to be scaled down versions of those found around more massive stars. One particularly interesting aspect of these new M dwarfs systems is the relative abundance of habitable zone exoplanets.
Dr Anne-Marie LagrangeDirect detection of exoplanets: results, consequences on planet formation theories, and future
Anne-Marie Lagrange is senior scientist at CNRS in France. She presently works at Institut de Planetologie et d'Astrophysique de Grenoble. She has been working since 25 years on extra solar planetary disks and then on the search for exoplanets using direct imaging or radial velocity techniques. Among results shared with colleagues: the indirect detection and study of "exo-comets", the studies of several debris disks, the direct detection of the first planetary mass objects around brown dwarfs or stars, the direct imaging of so far the closest planet detected in imaging, and predictions of the detection capabilities of Earth twins around Sun-like stars with future instruments. She has lead the Astronomy division at CNRS and Institut National des Sciences de l'Univers (2003-2006) and coordinated the Astronet EU-funded Eranet (2003-2006).
Most of the exoplanets known today have been discovered by indirect techniques, based on the study of the host star radial velocity or photometric temporal variations. These detections allowed the study of the planet content in the first 5-8 AU from the star. The numerous observations have provided precious information on the way planet form and evolve at such separations. One of the most interesting outcomes of these studies is that dynamical evolution (through e.g. disk-planet interaction, planet-planet interactions) plays an important role in the final architecture of the systems. In a few cases, spectroscopic observations of transiting planets allowed to make first exploration of the planet atmospheres. Direct imaging allows to detect giant planets at larger separations (currently typ. > 5-10 AU), complementing then the indirect techniques. Given the separations considered, most of them are expected to be formed by gravitational instability within a disk rather than by accretion of gas on to a solid core, which is the preferred scenario to explain solar system giant planets as well as most of radial velocity and transiting giant planets. Hence, direct imaging provides an opportunity to study this alternative mode of planet formation. Coupled to spectroscopy, it allows the exploration of the planets atmospheres. The surveys performed allowed to derive first statistics on the presence of giant planets at large separations. So far, only a few planets have been detected in direct imaging around young stars, but each of them provides an opportunity of very interesting individual studies of their orbital, physical and atmospheric properties and sometimes also on the interaction with "second generation", debris disks. I will present the direct imaging approach, the detections made so far, and what they already tell us about giant planet formation and evolution. I will also point out the limitations of this approach, as well as the needs for further work in terms of planet formation modelling. I will finally present the tremendous progress that are expected in this field thanks to forthcoming planet imagers on 8-meter class telescopes, on space telescopes (JWST) and later, on Extremely Large telescopes.
Dr James ChoChair of Session 2
After undergraduate degrees in Physics and Astronomy, James Cho received his PhD in Applied Mathematics from Columbia University in 1996. Afterwards, he was a Postdoctoral Scholar at the California Institute of Technology and a Research Scientist at the Carnegie Institution of Washington. He was also an Assistant Staff Scientist at MIT Lincoln Laboratory and a Senior Scientist at Spectral Sciences, Inc., in Boston. In 2005, he moved to Queen Mary, University of London, where he has been working on extrasolar planets and planetary physics, atmospheric dynamics and turbulence. His main interests are in astrophysical-geophysical fluid dynamics, mathematical physics and numerical methods.
Professor Richard NelsonThe role of migration in planetary system formation
Richard Nelson is currently the director of the Astronomy Unit at Queen Mary, University of London. He obtained his Ph.D. in Astrophysics from the School of Mathematical Sciences at QMUL, before taking up a postdoctoral fellowship at the Jet Propulsion Laboratory in Pasadena, U.S.A. His primary research interests are the theory of planet formation and the dynamics of astrophysical discs. More specifically, he is interested in how the interaction of forming planets with their protoplanetary discs leads to orbital migration, and how this combines with accretion processes to form the diversity of planetary systems we observe today.
Radial velocity and transit observations of extrasolar planet systems provide strong evidence that orbital migration, driven by interaction with their gaseous protoplanetary disc, plays an important role during planet formation. There has been significant development in our understanding of migration processes in recent years, and I will review this progress and the current state-of-the-art in my talk. Migration, planetary mass growth, and planet-planet mutual interactions are tightly coupled processes, and an improved understanding of planet formation requires models that incorporate this coupling explicitly. I will present the results of recent simulations that attempt to include these processes self-consistently, and compare them with the known population of extrasolar planets.
Dr Alessandro MorbidelliScenarios of giant planet formation and evolution and their impact on the formation of habitable terrestrial planets
Alessandro Morbidelli is CNRS researcher at Observatoire de la Cote d'Azur in Nice, France. He obtained his Ph.D. in mathematics in 1991 at the University of Namur (Belgium). He works on dynamical aspects of planetary science. He studied in detail the dynamics in the current solar system,in particular the transport of meteorites and near-Earth asteroids to the Earth. Since 2000, he has been active in investigating the formation and dynamical evolution of the solar system, with original studies on terrestrial planet formation, giant planet migration and the sculpting of the small bodies populations. He is now applying this experience on Solar System evolution to address the origin of the observed diversity of planetary systems.
The giant planets in our Solar System remained on orbits beyond the habitable zone. In addition, they remained on orbits with very small eccentricities and inclinations. These two dynamical features allowed the formation of terrestrial planets, one of which turned out to be habitable and inhabited. However, it is obvious from the orbital distribution of the extrasolar giant planets discovered to date that the evolution of the giant planets of our Solar System is not generic. Many giant planets migrated towards their parent star, crossing through or stopping near the habitable zone. In many cases, the giant planets also acquired eccentric orbits. I will discuss briefly the origin of the orbital diversity of giant planets and the effects that migration and eccentricity excitation can have on the formation and survival of terrestrial planets. I will also consider the case in which no giant planet forms, arguing that a number of icy super-Earths or Neptune-mass planets are likely to accrete beyond the snowline and migrate into the inner system, possibly jeopardizing the formation of rocky terrestrial planets.
Professor Olivier GrassetM-R relationships for highly compressed rocky cores – a possible new family of planets
Olivier Grasset is professor in Nantes University since 2004. His research activities are mostly focused on internal structure and dynamics of planets and moons. His studies combine experimental and numerical approaches. He is mostly interested in the exploration of the icy mantles of giant moons. He conducted several experimental projects to explore the stability domains and spectral signatures of icy materials and volatiles.
Since 5 years, he has also been involved in several research projects devoted to the characterisation of M-R relationships for solid exoplanets. He also co-chaired the Science Team of the JUICE project from 2008 to 2012, the first L-class mission of the Cosmic Vision programme.
Super-Earths are one of the most important target of space exploration for the next decade. With the discovery of potential candidates that suggests a high probability for having other Earths in our galaxy , it is important to ascertain how confident we can be that a planet with adequate mass and radius is indeed like our Earth’s planet.
It has already been shown in previous studies that similar mass and radius relationships can be found for Super-Earths and mini-Neptune. A third family can also be suggested. Since planetary migration is common process in stellar systems, it is highly possible that a few “planets“ discovered close to their stars are in fact the remnants of the inner core of gaseous exoplanets. In this paper, we investigate the M-R relationships of highly compressed rocky planets, similar to what could be the remants of Uranus-like planets. Characteristics of these bodies, as well as the probability of such occurrences, will be discussed.
Professor Lars StixrudeMaterial behavior in exoplanet interiors
Lars Stixrude is Professor of Geophysics and Mineral Physics in the Department of Earth Sciences, University College London. He has played a leading role in developing a new approach to the study of planetary interiors based on quantum mechanical simulation, which has led to important new insights into Earth’s molten origins. Professor Stixrude received his Ph.D. in geophysics from the University of California at Berkeley in 1991, and moved on to faculty positions at the Georgia Institute of Technology and the University of Michigan before moving to the UK four years ago. He is author or co-author of more than 100 peer-reviewed publications, which have been cited more than 3500 times. He serves as editor of Earth and Planetary Science Letters. Honors include the James B. MacElwane Medal of the American Geophysical Union in 1998, and membership in Academia Europaea in 2012.
What are exoplanet interiors made of? The answer matters because interiors comprise nearly all the planetary mass and therefore shape our ideas about formation, as well as controlling long-term evolution, the generation of planetary magnetic fields, and in the case of super-Earths the generation of surface environments, and the prospects for habitability. We examine possible connections between the interior and atmospheric composition, focusing on processes of differentiation, buoyant segregation, core erosion, and de-gassing. These processes highlight the importance of learning more about material behavior in the largely unexplored region of pressure-temperature space typical of most exoplanetary interiors discovered so far. We discuss two examples of progress in this area, focusing on ab initio quantum mechanical simulations of fluid helium and solid iron, and implications for the luminosity of giant planets and the generation of magnetic fields in super-Earths.
Professor Jonathan Tennyson FRSChair of Session 3
Dr Julianne MosesExoplanet kinetics: hot topic or out cold?
Julianne I. Moses received her undergraduate degree in physics from Cornell University in 1985 and her Ph.D. in planetary science and geophysics from the California Institute of Technology in 1991. She worked as an NRC Research Associate for two years at the NASA Ames Research Center before taking a staff scientist position in 1994 at the Lunar and Planetary Institute in Houston, Texas. She remained at the LPI for almost sixteen years before joining the Space Science Institute in 2010. Her diverse research interests revolve around theoretical investigations of physical and chemical processes in planetary and satellite atmospheres, with a particular emphasis on giant planet and extrasolar planet photochemistry, aerosol formation and dynamics, upper atmospheric structure and chemistry, and atmosphere-surface interactions.
Chemical kinetics plays an important role in controlling the atmospheric composition of all planetary atmospheres, including those of extrasolar planets. For the hottest exoplanets, the composition can closely follow thermochemical-equilibrium predictions, at least in the visible/infrared photosphere at dayside (eclipse) conditions. However, for atmospheric temperatures < ~2000 K, and in the uppermost atmosphere at any temperature, chemical kinetics matters. The two key mechanisms by which kinetic processes drive an exoplanet atmosphere out of equilibrium are photochemistry and transport-induced quenching. I will review these disequilibrium processes in detail, discuss observational consequences, and examine some of the current evidence for kinetic processes on extrasolar planets.
Professor Therese EncrenazInfrared spectroscopy of exoplanets: observational constraints
Therese Encrenaz is Senior Scientist at the Centre National de la Recherche Scientifique (CNRS). She works at the Paris Observatory in the LESIA Department (Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique). She is a specialist of the study of solar-system planetary and cometary atmospheres by remote sensing spectroscopy, especially in the infrared and millimetre ranges. She is or has been involved in several space missions (including Vega, Galileo, ISO, Mars Express and Venus Express) and in many ground-based observations (Mauna Kea Observatory, ESO). She has been recently involved in studies about the spectroscopic characterization of exoplanets. She is the author of over 250 articles in refereed journals and several textbooks and/or popularizing books. She has been the Director of the Space Research Department of Paris Observatory (1992-2002) and the Vice-President of Paris Observatory (2007-2011).
The exploration of transiting extrasolar planets is an exploding research area in astronomy. With more than 200 exoplanets identified so far, these discoveries have made possible the development of a new research field, the spectroscopic characterization of exoplanets’atmospheres, using both primary and secondary transits. However, these observations have been so far limited to a very small number of targets. In this paper, we will first review the advantages and limitations of both primary and secondary transit methods. Then we will analyse what kind of infrared spectra can be expected for different types of planets, and we will discuss how to optimize the spectral range and the resolving power of the observations. We will also try to identify the most promising targets for present and future ground‐based observations.
Professor Peter BernathMolecular opacities for exoplanets
Peter Bernath received his B.Sc. degree in Chemistry (Physics option) from the University of Waterloo (1976) and his Ph.D. degree in physical chemistry from MIT in 1981. After a post-doctoral stint at the National Research Council, he became a faculty member at the University of Arizona. In 1991 he took up a position as Professor of Chemistry at the University of Waterloo, followed by a move in 2006 to the University of York, UK, and is now Chair of the Department of Chemistry & Biochemistry at Old Dominion University, Norfolk, VA. His research interests are in laboratory spectroscopy, molecular astronomy and atmospheric science. Since 1998, he has been mission scientist for the Atmospheric Chemistry Experiment (ACE) satellite.
Spectroscopic observations of exoplanets are now possible by transit methods and direct emission. Spectroscopic requirements for exoplanets will be reviewed based on existing measurements and model predictions for hot Jupiters and super-Earths. Molecular opacities needed to simulate astronomical observations can be obtained from laboratory measurements, ab initio calculations or a combination of the two approaches. The talk will focus mainly on laboratory spectroscopy of hot molecules as needed for exoplanets.
Professor Isabelle BaraffeChair of Session 4
Professor Baraffe’s current fields of interest are in planetary and stellar physics. Her main research activities are devoted to the study of giant and terrestrial solar and extra-solar planets, of substellar objects (brown dwarfs) and of a wide variety of stars (from low mass to very massive stars). The aim is to understand and to model the physical processes characteristic of (i) the formation, (ii) the atmospheric and interior structure and (iii) the evolution of substellar (planets, brown dwarfs) and stellar objects. Her expertise covers a wide range of physical conditions, from Earth-like planets to very massive stars and supernovae. She have been awarded several prizes and distinctions including the Royal Society Wolfson Research Merit Award in 2010, Gauss-Professorship from Goettingen Academy of Sciences in 2005, Johann WEMPE prize of the Astrophysikalisches Institut Potsdam in 2004 and Bronze medal from the Centre National de la Recherche Scientifique (France) 1999.
Dr Leigh FletcherExploring the diversity of Jupiter-class planets
Dr Leigh Fletcher is a planetary scientist and Royal Society Research Fellow at the University of Oxford. Leigh specialises in exploring the formation, dynamics, meteorology and chemistry of planetary atmospheres, for both the gas and ice giants in our own solar system, and for giant planets around other stars. He gained his PhD from Oxford in 2007 and conducted his postdoctoral research at the Jet Propulsion Laboratory in California. His primary research involves the acquisition and analysis of images and spectra of the giant planets from the visible to the sub-millimetre from a variety of ground-based observatories, space-borne telescopes and planetary probes, notably the Cassini mission to Saturn and Titan. These data are used to understand the physical and chemical processes that shape planetary atmospheres at varying distances from their host stars.
Of the 860+ exoplanets discovered to date, 75% have masses larger than Saturn (0.3MJ), 55% are more massive than Jupiter, and 60% are within 1 AU of their host stars. And yet the term 'hot Jupiter' betrays the incredible diversity of this class of astrophysical object. This presentation will give an overview of our expectations for the temperatures, molecular composition and cloud properties of Jupiter-class objects under a variety of different conditions. We will review the taxonomy and classification schemes for these Jupiter-class planets proposed to date, including the implications for our own Solar System giant planets. We will attempt to show the potential categories of planetary types, accounting for: (i) thermochemical equilibrium expectations for cloud condensation and favoured chemical stability fields; (ii) the metallicity and formation mechanism for these giant planets; (iii) the importance of optical absorbers for energy partitioning and the generation of a temperature inversion; (iv) the favoured photochemical pathways and expectations for minor species (e.g., saturated hydrocarbons and nitriles); (v) molecular confusion arising from vertical mixing of species above their quench levels; and (vi) methods for energy redistribution throughout the atmosphere, from the radiative to the convective zones. Finally, we will discuss the benefits and pitfalls of retrieval techniques for establishing a family of atmospheric solutions that reproduce the available data without bias to a particular planetary model, and the requirements for future spectroscopic characterisation of a reference set of Jupiter-class objects to test our physical and chemical understanding of these planets.
Professor Caitlin GriffithInterpretation of transiting exoplanets measurements
Caitlin Griffith is a professor at the University of Arizona in the department of planetary sciences. With a background in mathematics and physics, she is interested in the structures of planetary atmospheres and the physical processes that govern them and conduct their evolutions. She investigates the chemical, dynamical and thermal structures of planetary atmospheres, using ground-based and spacecraft observations. Radiative transfer analyses of the spectra reveal the temperature, composition and dynamical signatures of planetary atmospheres. These results are interpreted with radiative, thermodynamical, and simple chemical models to address questions on atmospheric structure and evolution. Currently her work focuses on determining the composition and characteristics of extrasolar planets to understand the variety of planetary systems and how rare or common our solar system is. In addition, she spends half of her time investigating Titan's clouds, lakes, and rain made of natural gas. Titan's methane cycle is arguably the closest analogue to Earth's hydrological cycle, and yet we do not even understand this methane cycle came to be.
The atmospheres of transiting exoplanets are characterized by two distinct measurements. The primary transit provides transmission spectra of the exoplanet's limb as the planet passes in front of the star. The secondary eclipse, which inducates the star's emission alone, when compared to the star plus planet emission, recorded outside of eclipse, yields the planet's emission spectrum. Infrared transmission and emission spectroscopy have revealed over the past decade the primary carbon and oxygen molecular species (CH4, CO2, CO, and H2O) in a few exoplanets. However, efforts to constrain the molecular abundances to within several orders of magnitude are thwarted by the degenerate effectsthat the temperature and composition have on the emission spectra. Similarly, transmission spectra, while less sensitive to the atmospheric temperatures, provide a degenerate set of solutions, because the composition derived is highly dependent to the assumed radius. Problems in the interpretation of both spectra also arise from the potential variability of host stars. Apart from the challenges of deriving the basic properties of an exoplanet, the interpretation of the chemistry and possibly the evolution of an exoplanet requires knowledge of the starting composition of the planetary system. Here we discuss general methods for addressing these uncertainties, which include ground-based high resolution spectroscopy of host stars, optical photometry of exoplanet transmission, and the joint analysis of transit and secondary eclipse data of exoplanets. These methods will be explored with a discussion of recent and former measurements of the planet XO-2b, its host star (XO-2N) and stellar companion (XO-2S).
Dr Tommi KoskinenThermal escape from extrasolar giant planets
Originally from Finland, Tommi Koskinen obtained his MSci and PhD from University College London (UCL). Since 2009 he has been a Postdoctoral Research Associate at the Lunar and Planetary Laboratory of the University of Arizona in Tucson. He is a Fellow of the Royal Astronomical Society and a member of the American Astronomical Society. His research interests are centred on the dynamics and chemistry of planetary upper atmospheres, both in the solar system and beyond. His thesis work at UCL on the stability of close-in extrasolar planet atmospheres was awarded the Jon Darius Memorial Prize for Outstanding Postgraduate Research in Astronomy.
The detection of hot atomic hydrogen and heavy atoms and ions at high altitudes around some close-in extrasolar giant planets (EGPs) such as HD209458b imply that these planets have hot and rapidly escaping atmospheres that extend to several planetary radii. However, these characteristics cannot be generalized to all close-in EGPs. The thermal escape mechanism and mass loss rates from EGPs depend on a complex interplay between photochemistry and radiative transfer driven by the stellar UV radiation. In this work we explore how these processes change under different levels of irradiation on giant planets with different characteristics. We confirm that there are two distinct regimes of thermal escape from EGPs, and that the transition between these regimes is relatively sharp. Our results have significant implications on thermal mass loss rates from different EGPs that we discuss in the context of currently known planets and the detectability of their upper atmospheres.
Dr Francois ForgetClimates on terrestrial exoplanets
Francois Forget is a specialist of planetary atmosphere. He is CNRS senior scientist and head of the Solar System Department at Pierre-Simon Laplace Institute in Paris, France. He has also spent several years working for NASA in California, in 1992-1993 and 2004-2005. A large part of his research has been related to the exploration and the modeling of planet Mars. He is now also working on the numerical simulations of the possible climates on extrasolar planets in order to better understand the processes controlling habitability outside our solar system. Along with his post-doc Robin Wordsworth and other colleagues, they notably showed that exoplanet Gliese 581d was probably the first discovered planet which could potentially be suitable for liquid water and life.
The nature of the possible climates on extrasolar planets cannot yet be detected with telescopes. Nevertheless, key scientific questions motivates some investigations on the subject, for instance to prepare future observations, or to assess planetary habitability. For this purpose, we can use numerical climate models derived from the one used on the Earth to study climate changes, and which have been successfully tested on the terrestrial atmospheres of our solar system (Venus, Mars, Titan, Triton, Pluto). Such models can be considered as “planet simulators” that aims to simulate the complete environment on the basis of universal equations only. On the basis of our experience in the solar system, we have developed a new type of climate model flexible enough to simulate the wide range of conditions that may exist on terrestrial exoplanets, including any atmospheric cocktail of gases, clouds and aerosols for any planetary size, and around any star. Much can be learned from such models. Of course, to make further progress, we also have to learn about the possible composition of the atmospheres, which depends on their origin, escape, and long term chemical evolution.
Dr Daphne StamChair of Session 5
Daphne Stam received her PhD from the Physics Department of the Vrije Universiteit in Amsterdam. During her doctoral research, she worked on the transfer of polarized light through the Earth's atmosphere, modelling flux and especially polarization spectra of the Earth and interpreting remote-sensing data. As a post-doctoral fellow at Cornell University, Ithaca, NY, she analysed observations of Saturn and Neptune and derived properties of their hazes and clouds. Back in the Netherlands, she applied her expertise on polarized radiative transfer first on gaseous exoplanets and later on rocky, Earth-like exoplanets, at the University of Amsterdam, and subsequently at the Technical University of Delft. In parallel, she initiated the development of SPEX, a novel type of spectropolarimeter for remote-sensing of Solar System planets. A demonstration model of SPEX is currently being tested. Since 2008, she is the science lead of the Planetary Atmospheres group of SRON Netherlands Institute of Space Research.
Dr Ignas SnellenFinding extraterrestrial life using ground-based high-dispersion spectroscopy
Ignas Snellen is associate professor in astronomy at Leiden University in the Netherlands. After concluding his PhD research in Leiden in 1997, he worked for three years as a postdoctoral fellow at the Institute of Astronomy in Cambridge, after which he became an astronomy lecturer at the University of Edinburgh. He returned to Leiden University in 2004. His work is devoted to extrasolar planets. His science group develops ways to use ground-based telescopes to see and analyse exoplanets, using optical and near-infrared secondary eclipse photometry and transmission spectroscopy.
The cancellation of both the Terrestrial Planet Finder and Darwin missions means that it is unlikely that a dedicated space telescope to search for biomarker gases in exoplanet atmospheres will be launched within the next
25 years. In this talk I will advocate that ground-based telescopes provide a strong alternative for finding biomarkers in exoplanet atmospheres through high-resolution transit observations. I will review some of the exciting result we have recently obtained on hot-Jupiter atmospheres, and will show what can be done with the planned E-ELT.
Ultimately, large arrays of dedicated flux collector telescopes equipped with high-dispersion spectrographs can provide the large collecting area needed to perform a statistical study of life-bearing planets in the solar neighborhood.
Dr Giovanna TinettiSpectroscopy of planetary atmospheres in our galaxy
Dr Giovanna Tinetti is a Royal Society URF and Reader at the University College London, where she leads a team on exoplanets since 2007. Dr Tinetti received her PhD in theoretical physics from the University of Turin (Italy) in 2003 and then moved to Caltech in the US and Paris in France to work on exoplanetary atmospheres supported by NASA and ESA fellowships. She received the 2011 Institute of Physics Moseley Medal for her pioneering work on the use of infrared, primary transit spectroscopy to characterise the molecular composition of extra solar planets.Dr Tinetti has led the successful proposal for the mission candidate EChO (Exoplanet Characterisation Observatory), a space telescope dedicated to the study of exoplanetary atmospheres, currently under study by the European Space Agency. She is an editor for Icarus, the planetary journal of the American Astronomical Society. She has authored more than eighty refereed publications.
About 20 years after the discovery of the first extrasolar planet, the number of planets known has grown by three orders of magnitude, and continues to increase at breakneck pace. For most of these planets we have little information, except for the fact that they exist and possess an address in our Galaxy. For about one third of them, we know how much they weigh, their size and their orbital parameters. For less than twenty, we start to have some clues about their atmospheric temperature and composition. How do we progress from here? We are still far from the completion of a hypothetical Hertzsprung–Russell diagram for planets comparable to what we have for stars, and today we do not even know whether such classification will ever be meaningful for planetary objects. But one thing is clear: planetary parameters such as mass, radius and temperature alone will not explain the diversity revealed by current observations. The chemical composition of these planets is needed to trace back their formation history and evolution, as it happened for the planets in our Solar System. As in situ measurements are and will remain off-limits for exoplanets to study their chemical composition, we will have to rely on remote sensing spectroscopic observations of their gaseous envelopes.
Little more than 10 years ago, the detection of a signal from an exoplanet atmosphere was still in the realm of science fiction. Pioneering results were then obtained through transit spectroscopy with Hubble, Spitzer and ground-based facilities, making possible the detection of ionic, atomic and molecular species and of the planet’s thermal structure. The few available transit spectra of hot exoplanets are comparable in quality with the Solar System planetary spectra known in the 1970s, before the Voyager era. With the arrival of improved or dedicated instruments in the coming decade, planetary science will expand beyond the narrow boundaries of our Solar System to encompass our whole Galaxy.
Professor Charles CockellHabitable worlds with no signs of life
Charles Cockell is Professor of Astrobiology at the University of Edinburgh and Director of the UK Centre for Astrobiology. His academic interests encompass life in extreme environments, the interactions of microbes with minerals and the implications for earth system processes and the habitability of extraterrestrial environments. He received his first degree in biochemistry and molecular biology at the University of Bristol and his PhD (DPhil) from the University of Oxford in molecular biology. He then undertook a National Research Council Associateship at the NASA Ames Research Centre in California before working at the British Antarctic Survey in Cambridge. He moved to the Open University to take up a Chair in Geomicrobiology in 2005. He sits on ESA’s Planetary Protection and Life Sciences Working Groups. He is a Senior Editor of the journal, Astrobiology. Popular science books include ‘Impossible Extinction’ (CUP), which explores the tenacity of microbes on the Earth, and ‘Space on Earth’ (Macmillan) which looks at the links between environmentalism and space exploration. He is Chair of the Earth and Space Foundation, a non-profit organisation he established in 1994 and was first Chair of the Astrobiology Society of Britain.
Habitable planets may turn out to be abundant in the Universe. However, the search of life on them could yield many negative results. Habitable worlds with no signs of life could include: 1) planets that are habitable, but have no biosphere (uninhabited habitable worlds); 2) planets with life, but where biologically-derived atmospheric gases out of equilibrium with abiotic processes are within the thermodynamic uncertainty in the atmospheric constituents. The uncertainties in the sources and sinks of the atmospheric trace gases, CO and H2 on Mars, illustrate the problem, even in our own Solar System; and 3) planets that have abundant life, but lack surface signatures of that life. This can be demonstrated in the laboratory. Accepting obvious limitations in instrument resolving power, these scenarios can be examined with the experimentally testable hypothesis that the universe contains many habitable worlds with no signs of life. If the hypothesis is rejected and most or all habitable planets have signatures of life, then we could conclude that: life is inevitable on any planet with habitable conditions, it always rapaciously colonizes a planet wherever it emerges, giving rise to detectable gaseous and surface signatures, and it always ‘discovers’ oxygenic photosynthesis that is then produced in high abundance. The acceptance of the hypothesis would suggest the possible rarity of the origin of life or the lack of inevitability of the ‘discovery’ of oxygenic photosynthesis by biological evolution.
Panel discussion 25 May
Public lecture 29 May
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