Division F - Abstracts
Initial Results from the Transiting Exoplanet Survey Satellite (TESS)
Ricker, George
The Transiting Exoplanet Survey Satellite (TESS)--a NASA Astrophysics Explorer-- is expected to discover thousands of exoplanets in orbit around the brightest stars in the sky. The launch is to take place in March 2018 from Cape Canaveral on a SpaceX Falcon 9 rocket. In a two-year survey, TESS will monitor ~200,000 pre-selected bright stars for planetary transits in the solar neighborhood at a 2-minute cadence. This survey will identify planets ranging from Earth-sized to gas giants, around a wide range of stellar types and orbital distances. TESS will also provide full frame images (FFI) at a cadence of 30 minutes or less. These FFI will provide precise photometric information for every object within the 2300 square degree instantaneous field of view of the TESS cameras. In total, more than 30 million stars and galaxies brighter than magnitude I=16 will be precisely photometered during the two-year prime mission. In principle, the lunar-resonant TESS orbit will provide opportunities for an extended mission lasting more than a decade, with data rates of ~100 Mbits/s. An extended survey by TESS of regions surrounding the North and South Ecliptic Poles will provide prime exoplanet targets for characterization with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes of the future. The TESS legacy will be a catalog of the nearest and brightest main-sequence stars hosting transiting exoplanets, which should endure as the most favorable targets for detailed future investigations. Initial results from the first few months of the TESS mission will be presented.
The Asteroid Impact & Deflection Assessment (AIDA) mission: current status of both the US and European components of the first asteroid deflection test
Michel, Patrick
The main objectives of the joint ESA-NASA Asteroid Impact & Deflection Assessment (AIDA) mission are twofold: (1) to perform an asteroid deflection test by means of a kinetic impactor under detailed study at NASA called DART; and (2) to investigate the changes in geophysical and dynamical properties of the target after the DART impact with the European (ESA) component of the mission, called Hera, has been redesigned from the original version called AIM. The baseline target is the binary near-Earth asteroid (NEA) (65803) Didymos. In particular, its secondary component, called hereafter Didymoon (163 ± 18 m diameter), is the target of the DART mission and will be fully investigated by Hera, providing precious data for science, mining and planetary defense purposes on the smallest investigated asteroid. This joint mission will allow extrapolating the results of the kinetic impact to other asteroids and therefore fully validate such asteroid deflection techniques. As such, AIDA will be the first documented deflection experiment and binary asteroid investigation. In particular, it will be the first mission to investigate a binary asteroid, and return new scientific knowledge with important implications for our understanding of asteroid formation and solar system history. Finally, a mission like AIDA will certainly fire the imagination of young people and adults, as the science is accessible and understandable to those audiences and is associated with fascinating challenges and goals of planetary defense. The status of the study and payloads of both mission components will be presented.
Discovering Circumbinary Planets with TESS
Kostov, Veselin
One of Kepler's most exciting breakthroughs was the discovery of circumbinary planets. Only about a dozen were found, however, leaving a vast gap in our understanding — similar to the state of exoplanet science when only hot Jupiters were known. TESS, and only TESS, will allow us to detect an order of magnitude more circumbinary planets using a new technique we have developed and tested: "the 1-2 punch". In addition to enchanting individual-case discoveries and their intriguing dynamics, our sample will enable statistical studies of occurrence rates, formation, and habitability (an astonishing ~30% of Kepler circumbinary planets are in the habitable zone).
Shallow Transits - Deep Learning: using deep learning to detect habitable planets
Zucker, Shay
Deep learning is currently taking the world of Artificial Intelligence by storm. Deep learning techniques already have proven success in varied fields, such as image processing, speech recognition and even drug discovery. Specifically, deep learning can provide new hope in needle-in-a-haystack problems, such as the detection of very faint signals in the presence of many kinds of noise. Detection of transiting terrestrial planets in the presence of stellar-activity red noise is one such problem. The non-linear nature of deep learning renders it completely different from traditional techniques (such as those based on the BLS). Such innovative approaches will be crucial in order to fully exploit the potential of future planet-detection space missions (TESS, PLATO). We hereby present an extremely short tutorial of what deep learning is, and how it can be applied to detect and analyze transiting terrestrial planets. We also introduce preliminary results of a feasibility study we have performed which demonstrate the immense capability of this novel and exciting approach.
Titan’s Global Geology from Cassini
Lopes, Rosaly
We investigate the geologic history of Titan through mapping and analyzing the distribution of observed geomorphologic features using a combination of Cassini data collected by RADAR,VIMS (Visual and Infrared Mapping Spectrometer), and ISS (Imaging Science Subsystem). Determining the spatial and superposition relations between geomorphologic units on Titan leads to an understanding of the likely time evolution of the landscape and gives insight into the process interactions that drove its geologic history. We have used all available datasets to extend the mapping initially done by Lopes et al. (2010, Icarus, 205) and Birch et al. (2017, Icarus, 282) to a global map at 1:800,000 scale in all areas covered by the RADAR Synthetic Aperture Radar (SAR). We show how we are extending the map to regions not covered by SAR, to produce a 1:1,500,000 scale map compatible with USGS standards. We use the map to infer the stratigraphic relations among Titan’s different terrain types, which in turn allows us to establish the sequence of geologic processes that have shaped the satellite’s surface.
Revisiting the Oort cloud in the age of large sky surveys
Fernández, Julio A.
Our knowledge about the Oort cloud rests on the so-called new comets, namely comets whose original orbital energies are very close to zero (i.e. near-parabolic orbits), suggesting that they are coming to the inner planetary region for the first time. We have analyzed the sample of observed new comets that reached the planetary region in the last 20 years (1998-2017), which corresponds to the period when large sky surveys have come into operation with the consequence of a dramatic increase in the discovery rate of minor bodies. From the analysis of the sample of new comets and using a debias technique based on the ``excess magnitude'' (Everhart 1967, Astron. J. 72, 716), we find that the influx rate of comets with original energies in the range 0 < x < 30 (in units of 10-6 au-1) has remained more or less constant in time and uniform in perihelion distances at a rate of 0.4 comets yr-1 au-1 brighter than absolute total magnitude H=9. These are essentially comets coming from the outer Oort cloud (semimajor axes a > ~3.3 x 104 au) where perturbations by external perturbers (galactic tides and passing stars) are able to inject comets with perihelion distances outside the planetary region (q > 30 au) in the inner planetary region in a single revolution. By constrast, the influx rate of comets coming from the inner portions of the Oort cloud (energies 30 < x < 100) is found to increase with the perihelion distance. This suggests a dynamical process of kreeping into the inner planetary region after several passages by the outer planetary region, and where some comets can finally leak through the Jupiter-Saturn barrier into the cis-Jovian region. These results are of fundamental importance to set more stringent constraints on the population and space distribution of comets in the Oort cloud, and from this on mass transport processes and scattering of bodies in the early solar system.
The Dawn Mission: Latest Results
Russell, Christopher
The Dawn mission is currently in its third successful year of exploration of the dwarf planet Ceres. Very little was known about Ceres prior to Dawn’s arrival, but much has been learned in the last three years. Perhaps most importantly, Ceres is a wet body. It has ice close to the surface and shows evidence of cryovolcanism and the delivery of brines to the surface. Some ice is exposed and appears to undergo changes with time. A temporary atmosphere has been observed stimulated by energetic solar proton events and recently a “reactive” campaign to observe such an atmosphere was held using the VLT. The bright spots in the Occator crater are composed of sodium carbonate. This is estimated to be the largest deposit of sodium carbonate outside of Earth. The crater Ernutet has ample deposits of prebiotic organic material that appears to have been produced in Ceres. The lumpy surface, including the 4-mile high mountain Ahuna Mons, is indicative of active cryovolcanism. Tectonically rich terrain, such as in the region of Nar Sulcus, tells of an active planet. The rich geological and geophysical potential of Ceres and its large inventory of water suggests that Ceres will be a major focus of future planetary exploration.
Exploration of the binary asteroid 65803 Didymos by the payload of the Asteroid Impact Deflection Assessment (AIDA) mission
Küppers, Michael
The AIDA mission consists of three components: 1) NASA's Double Asteroid Redirection Test (DART) kinetic impactor that will hit the minor component of the double asteroid 65803 Didymos (Didymoon), to demonstrate the technology of asteroid deflection 2) A cubesat provided by ASI that will separate from DART hours before impact and take images of the Didymos system. It is based on the Argomoon cubesat that will be carried to the moon by NASA's exploration mission 1.3) ESA's Hera rendezvous mission that will investigate the Didymos system over several months, calibrating the impact experiment by an accurate characterization of Didymoon.We will present the investigations foreseen by the different payload elements: The DRACO imager on DART, based on the LORRI camera from the New Horizons mission, will take images of Didymoon just before impact, providing local context of the impact. The imager on the 6U ASI cubesat will capture Didymoon after the impact, potentially observing the impact crater. Hera will monitor the binary asteroid for several months, accurately measuring its dynamical state and completely mapping the surface with the Asteroid Framing Cameras (the flight spares of the Framing Cameras of the Dawn mission) and the European Lidar payload. Those instruments will also measure the mass of Didymoon, from the "wobble" motion of Didymos due to the gravity of Didymoon. Hera will additionally carry a cubesat, with the ASPECT visible and near-IR imaging spectrometer as the baseline payload. It will allow the spectral characterisation of the targets, testing hypotheses of the origin of the binary. Observations of fresh, unweathered material in the DART impact crater will uniquely determine the meteorite analogue of Didymos.Technological advances in recent years make planetary defence possible. The AIDA mission provides, for the first time, the opportunity to demonstrate our capability to deflect a hazardous asteroid.
The Habitability of Exomoons
Tylor, Christopher
In recent years, astrobiologists have begun to seriously consider the possibility that suitable conditions for life to develop might be found on planetary satellites, as well as on planets themselves. For this reason, the moons of planets around other stars (exomoons) provide a fascinating route by which astrobiological studies can move beyond the search for habitable-zone planets. Habitability fundamentally depends on the reliability of the energy supply (astrophysical, geophysical or geochemical) for life, and the local environment. The icy moons of the outer Solar System already provide targets for the search for subsurface oceanic life. Given that such satellites rely on tidal heating to provide a stable environment for life, a key factor in Exo-Moon habitability would be the long-term orbital stability of a given moon around the host exoplanet. In this project, the long-term orbital stability of the Jovian moons is explored using numerical modelling with the REBOUND N-body integrator code to assess the potential for significant orbital changes on timescales of tens to hundreds of millions of years. The results to date indicate that the Jovian satellite system is characterised by an extremely stable orbital configuration, and hence provides a thermally stable environment to within one part in 100,000 in energy input into any subsurface oceans present over timescales of at least tens of millions of years. As a result, those moons could provide a stable environment for life to develop and survive. These results can be used to speculate that a range of stable Exo-Moon orbital configuration and environments could exist that expand the potential number of habitable worlds well beyond the estimates made on the basis of classical habitable-zone exoplanets alone.
Mixing of Condensible Constituents with H/He During Formation of Giant Planets
Lissauer, Jack
We present the results of simulations of the early stages of growth of giant planets that incorporate the mixing of light gases with denser material that enters the planet as solids. We find that silicates and gas begin to intimately mix when the planet becomes roughly as massive as Earth because incoming silicates can then fully vaporize if they arrive in the form of planetesimals or smaller. Most of the rocky material accreted by a giant planet becomes part of its extensive envelope, although the vast majority of silicates remain within the lower portions of the envelope that contains < 1% H/He by mass when the growing planet is several times as massive as Earth. The inner zone of primarily supercritical fluid silicates and the outer layers dominated by H/He are separated by a narrow region with a steep composition gradient that inhibits convection. Nonetheless, this lower envelope substantially affects the planet's growth and structure because it retains accretion energy as heat and thus is far larger than a cold, solid core of the same mass. The simulations are ongoing and more extensive and detailed results will be presented in Vienna.
The CHEWIE survey of exoplanet transmission spectra
Lendl, Monika
During planetary transit, stellar light is filtered through an exoplanet's atmosphere, revealing the planet's atmospheric properties as wavelength-dependent absorption features. Transmission spectra obtained though spectroscopic observations of transits are today providing key information on the composition and structure of planetary atmospheres. Further, as observations become more numerous, they allow us to investigate the diversity of exoplanetary atmospheres.While transmission spectra have long been dominated by space-based observations, recent improvements in instrumentation and analysis techniques have placed ground-based observatories at the forefront of exoplanet characterization.I will present CHEWIE (Clouds, Hazes and Elements vieWed on gIant Exoplanets), a survey of exoplanet transmission spectra with 8m-class ground-based telescopes. I will give an overview on the survey and present recent results. The latter include the first transmission spectrum of WASP-103b, one of the most massive (1.5 M_J) and hottest (2500 K) planets characterized so far using transmission spectroscopy, and the transmission spectra of several planets in the Neptune to Saturn mass range.
Getting to Know Sub-Saturns and Super-Earths: High-Resolution Spectroscopy of Transiting Exoplanets
Jayawardhana, Ray
Characterizing exoplanet atmospheres presents a formidable challenge, primarily due to the extreme brightness contrast between the planet and the host star. However, spectroscopy during transits, when stellar light passes through a planet’s atmosphere, offers a rare opportunity to identify the presence of atomic and molecular species and other atmospheric features. To date, for the most part, transit spectroscopy has targeted hot Jupiter planets, mainly at low spectral resolution. High-resolution spectroscopy, on the other hand, could be used to not only make robust detections but also to probe the temperature-pressure profile and dynamics (i.e., wind speeds) in the planets’ upper atmospheres. Recently we have extended such studies to exoplanets in the sub-Saturn and super-Earth mass regimes, using high-resolution spectroscopy with 8-meter-class telescopes and cross-correlation techniques, to search for alkali metal lines as well as water vapor. Here we report on our latest findings, including new detections, and discuss prospects for the near future.
Realistic modeling of collisional water delivery during the late stages of planet formation
Burger, Christoph
Even most state-of-the-art N-body simulations of late-stage planet formation still assume perfectly inelastic merging once two bodies collide. This strong simplification of the actual collision physics falsifies results in general, and particularly for volatile constituents like water, which are in addition found preferentially at or close to the surface. Our aim is to investigate how the outcome of individual collisions can influence the overall picture of water transfer and loss during (terrestrial) planet formation, believed to be one of the most important factors for planetary habitability. High resolution Smooth Particle Hydrodynamics (SPH) simulations of self-gravitating, differentiated planetary embryos enable us to study the principal outcome as well as the detailed fate of different materials in collisions, covering all outcome regimes from low-velocity, almost perfect merging, to fast and highly erosive, as well as hit-and-run encounters. The latter are characterized by two instead of one large surviving fragment which makes them complicated to describe, but also interesting and important for studying volatile delivery. While combined (projectile & target) water losses in a single collision can amount to 50% and more – provided large enough impact velocities – more moderate encounters often leave the larger of the colliding bodies relatively intact, while the smaller one is still stripped of a majority of its volatile inventory. Yet higher water losses can be expected once high enough impact energies result in a significant fraction of vaporized volatiles, then potentially subject to atmospheric loss processes. Understanding the behavior of water inventories in collisions is a major prerequisite for including realistic modeling of collisions in the upcoming next generation of N-body planet formation simulations.
The structure and strength of meteorite producing meteoroids
Borovicka, Jiri
Meteorites are the best studied macroscopic samples of interplanetary material. They represent, however, only the strongest parts of the meteoroids they are delivering them. Almost all meteoroids fragment to some extent during their passage through the Earth’s atmosphere. The strength of the fragmenting body can be roughly estimated as the dynamic pressure acting at its front side at the moment of fragmentation: p = ρv2, where ρ is atmospheric density and v is velocity. Previous investigations showed that the strengths are much lower than tensile strengths of meteorites (which are typically 5-50 MPa). The low strengths are probably caused by internal cracks acquired during collisions in interplanetary space. We analyzed seven falls of ordinary chondrite meteorites with good data on atmospheric trajectories, velocities and light curves from the cameras of the European Fireball Network. A fragmentation model was applied to the data in order to reveal fragmentation points and to estimate the fragmented mass. The sample was supplemented with several other meteorite producing fireballs where the meteorites were not recovered. This way, stony meteoroids ranging in size from ~10 cm to about two meters were analyzed. It was found that meteoroid strengths are not random and cumulate in two regions, 0.04 -0.12 MPa and 1-3 MPa in most cases. There are therefore two types of cracks, which we call weak ones and common ones. Weak cracks are not always present, the common ones are only rarely absent (e.g. in the Carancas crater-forming meteoroid). For comparison, we analyzed also the carbonaceous meteorite fall Maribo. Though the data are restricted it is obvious that that meteoroid behaved differently and fragmented all the way along the trajectory. We found no evidences for rubble pile meteoroids. Even bodies that re-accumulated from different meteorite types (e.g. Benešov) have bulk strengths similar to that of weak cracks.
Relationship between stellar and solar system organics
Kwok, Sun
From laboratory measurements, insoluble organic matter (IOM) in carbonaceous chondrites is known to consist of islands of aromatic rings linked by aliphatic chains. Similar structures are also seen in interplanetary dust particles and cometary dust. Stellar organics synthesized during the late stages of stellar evolution show strong emission bands and broad emission plateaus but the exact chemical structure of the carrier is not known. We report results of quantum chemical calculations of different classes of organic compounds and compare their theoretical spectra with astronomical spectra. We suggest that the chemical structure of circumstellar synthesized organics show similarities with solar system organics. The possibility of stellar origin of solar system organics will be discussed.
The New and Unexpected Venus from Akatsuki
Peralta, Javier
Akatsuki (originally Venus Climate Orbiter) is a mission from the Japan Aerospace Exploration Agency (JAXA) aimed to study the meteorology of the planet Venus. It was launched on 21th May, 2010 and successfully inserted into orbit on 7th December, 2015. At present, it performs an equatorial orbit towards the west of Venus, with an apoapsis and periapsis height of ~360,000 km and 1,000–8,000 km respectively, and a rotation period of 10 days. Akatsuki has an onboard ultra-stable oscillator (USO) to perform radio occultation measurements and 5 cameras to sense different levels of the atmosphere: UVI (filters 283 and 365 nm) permits to study the absorption of the sunlight at ~70 km due to SO2 and a mysterious absorber; IR1 (0.90−1.01 µm) allows to study the clouds at ~60 km, H2O and the thermal emission from the surface; IR2 (1.74−2.32 µm) enables studying CO and other aerosols, the opacity of deepest clouds and the altitude of dayside cloud tops; LIR (10 µm) retrieves the temperature at the cloud tops; finally, LAC cannot retrieve global images but is sensitive enough to detect fluorescence phenomena and lightning. The first two years of Akatsuki observations have unveiled a completely new Venus. The full set of cameras allowed to visualize an impressive variety of new cloud morphologies and atmospheric phenomena (Limaye, 2018), LIR has enabled the discovery of the biggest stationary wave in our solar system (Fukuhara, 2017; Kouyama, 2018), IR2 nightside images permitted to discover an unexpected powerful jet which periodically appears at the equatorial deep clouds (Horinouchi 2017), UVI images have provided valuable hints about the true nature of the unknown absorber (Lee, 2017) and new behaviour in cloud tops’ winds (Horinouchi, 2018), while radio occultation using USO is retrieving localtime-dependent structures at deeper levels than ever before.
Secular Dynamics on TNOs and Planet Nine Interactions
Li, Gongjie
The existence of Planet Nine has been suggested to explain the pericenter alignment of extreme trans-Neptunian objects. However, the underlying dynamics involving Planet Nine, test particles and Neptune is rich, including secular interactions, mean motion resonances and close encounters between the objects and Neptune/Planet Nine. It remains unclear which dynamical processes dominate the alignment of orbits, and the detailed dependence of the alignment on the orbital parameters of the outer planet is poorly characterized. We investigate the secular interactions between an eccentric outer perturber and objects starting in a near-coplanar configuration. We find that secular dynamics leads to clustering in the longitude of pericenter relative to planet Nine ($\Delta \varpi \sim 0^\circ$ and $180^\circ$) for large semi-major axis, small pericenter distance objects ($a\gtrsim 250$ AU, $30<r_p<80$ au).="" for="" the="" low="" inclination="" particles,="" initial="" orbital="" orientations="" of="" anti-aligned="" ($\delta\varpi\sim="" 180^\circ$)="" population="" is="" primarily="" also="" ($\delta\varpi_0="" \sim="" with="" respect="" to="" planet="" nine's="" orbit.="" on="" other="" hand,="" $\delta="" \varpi="" 0^\circ$="" more="" likely="" be="" ejected="" through="" non-secular="" processes="" (close="" encounters="" and="" chaos="" due="" overlap="" mean="" motion="" resonances).="" high="" objects="" ($60^\circ<i<120^\circ$),="" secular="" interactions="" leads="" clustering="" in="" \varpi$="" around="" $90^\circ$="" $270^\circ$,="" as="" well="" longitude="" ascending="" node="" argument="" pericenter="" ($\delta\omega="" 90^\circ~\&~270^\circ$="" $\delta\omega="" 0^\circ~\&~180^\circ$).="" contrast,="" we="" see="" no="" $\omega$="" population:="" this="" inconsistent="" current="" observations="" tnos,="" therefore="" excluding="" possibility="" a="" massive="" nine="" ($\sim="" 10{\rm="" m_{\oplus}}$,="" $\sim="" 500$="" au="" eccentricity="" 0.6$)="" close="" plane="" ecliptic.<="" p="">
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Hydrodynamics and Thermodynamics of Embedded Planets’ First Atmospheres
Kuiper, Rolf
Context: In the core accretion paradigm of planet formation, gas giants form a massive atmosphere in a run-away gas accretion phase once their progenitors exceed a threshold mass: the critical core mass. On the one hand, the majority of observed exo-planets, being smaller and rock/ice-dominated, never crossed this line. On the other hand, these exo-planets have accreted substantial amounts of gas from the circumstellar disk during their embedded formation epoch. Methods: We investigate the hydrodynamical and thermodynamical properties of proto-planetary atmospheres by direct numerical modeling of their formation epoch. Our studies cover one-dimensional (1D) spherically symmetric, two-dimensional (2D) axially symmetric, and three-dimensional (3D) hydrodynamical simulations with and without radiation transport. We check the feasibility of different numerical grid geometries (Cartesian vs. spherical), perform convergence studies, and scan the physical parameter space with respect to planet mass and optical depth of the surrounding. Results: In terms of hydrodynamic evolution, no clear boundary demarcates bound atmospheric gas from disk material in a 3D scenario in contrast to 1D and 2D computations. The atmospheres denote open systems where gas enters and leaves the Bondi sphere in both directions. In terms of thermodynamics, we compare the gravitational contraction of the forming atmospheres with its radiative cooling and advection of thermal energy, as well as the interplay of these processes. The coaction of radiative cooling of atmospheric gas and advection of atmospheric-disk gas prevents the proto-planets to undergo run-away gas accretion. Hence, this scenario provides a natural explanation for the preponderance of super-Earth like planets.
How do external giant planets influence the evolution of compact multi-planet systems?
Lai, Dong
The Kepler mission has detected hundreds of compact multi-planet systems containing super-Earths and mini-Neptunes with orbital periods shorter than 200 days. These ``Systems of Tightly Packed Inner Planets'' (STIPs) bear little resemblance to our Solar System. Many STIPs have recently been found to have external giant planet or binary star companions. How are the architectures of the inner multi-planet systems influenced by the outer companions? What happens to the inner system when surrounded by an unstable system of outer giant planet companions? How common are misaligned (with respect to the spins of host stars) STIPs (like Kepler 56) produced? We will discuss our recent works in these areas, including both semi-analytic theory and numerical simulations. We will present relevant semi-analytic expressions or scaling relations that can be applied to a wide variety of systems, and we will confront theoretical/numerical results to observations to constrain the evolutionary history of compact multi-planet systems.
Exploration of the Jupiter Trojans with the Lucy Mission
Noll, Keith
The Lucy Mission is being planned for launch in 2021 and will begin a series of encounters with Trojans starting in 2027. Six Trojan objects will be explored including objects in both the L4 and L5 clouds. The targets that Lucy will fly by include members of all three spectral classes that occur in the Trojans, C-type, P-type, and D-type. Infrared albedos span the full range of variation seen in the Trojans. Lucy is equipped with a three science instruments that will obtain color and panchromatic imaging, high resolution imaging, near-infrared spectral imaging, and thermal mapping. Radio science will utilize the spacecraft telecommunications system. Knowledge of the target properties is essential for planning and ongoing observations include determinations of lightcurves, searches for satellites, and spectroscopy. Photometric observations of mutual events of the Patroclus -Menoietius binary are continuing in order to further refine knowledge of the binary mutual orbit. The goal of the Lucy mission is to understand the Trojans in the context of a bigger picture understanding of planetesimals in the outer protoplanetary disk and their redistribution by giant planet migration. Continued constraints both observational and theoretical can be expected to enhance the return from the Lucy mission.
Long-Term Asteroid Orbit Deflection Optimization
Eggl, Siegfried
Current technology would in principle allow humankind to avert catastrophic collisions between asteroids and our planet. Asteroids that could impact near a population center may be diverted using so-called kinetic impactor spacecraft. The latter would transfer momentum to the asteroid through a high-velocity collision. Differences in asteroid shape and composition, however, cause the magnitude and direction of the delivered momentum to be uncertain. Without accurate information on where an asteroid is “parked” after a deflection attempt, the same object may become a concern for planetary defense at a later date. In the worst case, the target asteroid enters a so-called “gravitational keyhole,” retaining a high probability to collide with our planet. In this contribution we demonstrate how to best target an asteroid during a kinetic deflection maneuver so as to minimize the chances of an Earth impact in the foreseeable future.
The Pan-STARRS search for Near-Earth Objects
Wainscoat, Richard
Pan-STARRS consists of two 1.8-meter wide-field telescopes located near the summit of Haleakala, Maui, Hawaii. Each is equipped with a very large (1.4 Gigapixel) CCD camera that imnages an area of 7 square degrees on the sky. The first telescope, Pan-STARRS1, initially conducted a multi-pupose multi-color survey of the sky north of declination -30 degrees, and since then has been conducting a search for near-Earth objects. The second telescope, Pan-STARRS2, is presently being commissioned, and will double the survey power when it comes into regular operation during 2018. Pan-STARRS1 is the leading discovery telescope for near-Earth objects, and is also a prolific comet discovery telescope. It has recently been responsible for the discovery of approximately 50% of all new comets.In October 2017, Pan-STARRS1 discovered the first interstellar object, `Oumuamua. Interstellar objects were expected to be cometary in nature. Instead, `Oumuamua is asteroidal in appearance, and has other unusual properties. This important discovery has opened an entriely new field of research. Its discovery underscores the need to find additional similar objects so that we can study them in more detail in order to better understand their origin. In fact, large surveys may have seen multiple interstaller objects in the past, but they escaped discovery due to their fast motion.The Pan-STARRS survey for near-Earth objects will be described in detail, and compared to other surveys. Pan-STARRS is efficient at discovery of larger, more distant near-Earth objects, but is inefficient at discovery of smaller faster moving objects due to the characteristics of the CCD detectors.The inventory of even the largest near-Earth objects (diameter > 1 km) is still incomplete, and surveys such as Pan-STARRS will need to continue for many years in order for us to start to complete our inventory of large (and potentially dangerous) near-Earth objects.
The Origins Space Telescope and Solar System Science
Bauer, James
The Origins Space Telescope (OST) is the mission concept for the Far Infrared Surveyor, a study in development by NASA in preparation for the 2020’s Astronomy and Astrophysics Decadal Survey. With approximately three orders of magnitude gain in sensitivity over previous far-infrared missions, the telescope also provides high angular resolution to overcome spatial confusion in deep surveys, and new spectroscopic capabilities to detect water and other volatiles in planet forming disks as well as solar system objects. OST’s spectroscopic capabilities will facilitate an unprecedentedly large statistical study of volatile isotopes. With more than 100 comets from multiple reservoirs of diverse origin, including the Oort Cloud, Halley Type, and Jupiter Family comets, the mission will provide a better understanding of the delivery of volatiles to terrestrial planets, and their evolution across varying environments and histories of insolation. By expanding the measurements of D/H in comets to statistically meaningful numbers, OST will be able to map this ratio in much fainter and less active comets than current facilities can reach, and provide insight into the possible origins of Earth’s oceans.OST will also characterize the most distant bodies in the solar system. OST will discover thousands of new TNOs while and measuring their sizes down to ~10km, thus providing size distributions that will test theories of their formation and origin. The high spatial resolution will detect activity in the most distant of comets, as well, and allow thermal imaging of extended structures of dark material or low-albedo binary companions that may accompany these distant bodies. We will introduce the vast array of solar system science that this survey mission offers.
Exploration of icy moons as habitats
Coustenis, Athena
When looking for habitable conditions in the solar system, recent studies focus on the natural satellites of gas giants. Indeed, liquid water may be present underneath the surfaces of the natural satellites around Jupiter and Saturn [1]. And several of these satellites show in addition evidence for harboring organic chemistry in their atmospheres or exospheres, as well as energy sources. Measurements from the ground but also by the Voyager, Galileo and the Cassini spacecraft revealed the potential of these satellites in this context, and our understanding of habitability in the solar system and beyond can be greatly enhanced by investigating several of these bodies.Indeed, several of the moons show promising conditions for habitability and the development and/or maintenance of life. Europa, Callisto and Ganymede are hiding, under their icy crust, undersurface liquid water oceans which, in the case of Europa, may be in direct contact with a silicate mantle floor and kept warm by tidally generated heat.Titan and Enceladus, Saturn’s satellites, were found by the Cassini-Huygens mission to possess active organic chemistry with seasonal variations, unique geological features and possibly internal liquid water oceans. As revealed by Cassini, the liquid hydrocarbon lakes currently distributed mainly at polar latitudes on Titan are ideal isolated environments to look for biomarkers.The simultaneous presence of water, geodynamic interactions, chemical energy sources and a diversity of key chemical elements on some of these satellites as on Earth, may fulfil the basic conditions for habitability. These would be investigated with future space missions.Such potential habitats can only be investigated with appropriate designed space missions, like ESA’s L1 JUICE and NASA’s Europa Clipper mission.[1] Coustenis and Encrenaz, 2013, In “Life Beyond Earth”, CUP
The origin of meteorites and near-Earth asteroids
Dermott, Stanley
A century ago Hirayama discovered the clustering of asteroid orbital elements, revealing that some asteroids are in families originating from the disruption of a few large primordial bodies. However, the asteroids now classified as family members constitute a minority of the asteroids in the main belt. Here we show that the non-family asteroids in the inner belt have orbital inclinations that increase and orbital eccentricities that decrease with increasing asteroid size. These correlations can be accounted for if both the non-family and the family asteroids originate from the disruption of a small number of large asteroids. Separating the non-family asteroids into halo and non-halo asteroids allows us to estimate that 85% of all the asteroids in the inner main belt originate from the Flora, Vesta, Nysa, Polana and Eulalia families with the remaining 15% originating from either the same families or, more likely, a few ghost families. These new results imply that we must seek explanations for the differing characteristics of the various meteorite groups and the near-Earth asteroids in the evolutionary histories of a few, large, precursor bodies. These results also support the model that asteroids formed big through the gravitational collapse of material in a protoplanetary disk.
Modelling the rotation of icy satellites with application to exoplanets
Boue, Gwenael
The rotation dynamics of terrestrial exoplanets plays an important role in their physical evolution. It affects not only the climate at their surface, but also the amount of energy produced by tides. Indeed, most of the known rocky exoplanets orbit close to their parent star and are thus subject to strong tidal dissipation. Moreover, many of them are in multiplanetary systems where non vanishing eccentricities and inclinations perturb their rotation. Until recently, studies of exoplanet deformation relied on oversimple models of tides. In the last years, physically motivated rheologies have been introduced but exoplanets are still mostly described as homogeneous bodies. We may nonetheless expect some of them to be composed of a solid crust floating on a viscous mantle with a solid core, as in the case of the Earth for instance. This type of internal structure enriches the dynamics but it also requires an efficient mathematical formalism allowing to explore large parameter spaces.In our solar system, several icy satellites hold an underneath ocean making them composed of three layers as described above. Furthermore, these bodies have been accurately analysed thanks to spacial missions. This enables to test complex internal models against observations. In the case of Titan, for example, an obliquity of 0.3 degree---which cannot be explained if this satellite were entirely rigid---as been measured by the Cassini mission. In this talk, we will present our fully analytical three-layer model based on a Hamiltonian formalism. The agreement with the observations and with an hydrodynamic code will be shown. And finally, the application to the exoplanet field will be discussed.
Novel approaches to exoplanet life detection: Disequilibrium biosignatures and their detectability with the James Webb Space Telescope
Krissansen-Totton, Joshua
Upcoming ground- and space-based telescopes will characterize habitable exoplanets and look for atmospheric gases produced by life. Oxygen is a promising biosignature gas, but several hypothetical scenarios have been proposed for producing abiotic oxygen or its surrogate, ozone. Furthermore, even if these scenarios can be ruled out by other observations, there is no guarantee that oxygenic photosynthesis is a common metabolism. Oxygen biosignatures may be rare. Atmospheric chemical disequilibrium is potentially a more general biosignature. We have developed a quantitative metric for atmospheric disequilibrium and applied it to the Solar System planets. The biogenic disequilibrium in the modern Earth's atmosphere, which is mostly attributable to the coexistence of O2, N2, and liquid water, far exceeds the photochemically-produced disequilibria of the other Solar System atmospheres. We also applied our disequilibrium metric to the Earth through time, and found that on the anoxic Archean Earth (4-2.5 billion years ago), life maintained a predominant disequilibrium between CO2, CH4, N2, and liquid water. Such a combination of gases would not persist without significant replenishment of CH4 from the surface, which we have shown to be difficult to explain without life. This leads us to propose that the coexistence of CO2 and CH4 in the atmosphere of an ostensibly habitable exoplanet as a potential biosignature. The inference to life would be strengthened by the absence of atmospheric CO, which would be present if abiotic CH4 were outgassed and if no life were consuming CO. Finally, we evaluate the detectability of this new biosignature with the James Webb Space Telescope for nearby transiting planets such as the TRAPPIST-1 system.
Analysis of the historic meteorite falls
Tancredi, Gonzalo
The worldwide accepted clearing-house of meteorites is the Meteoritical Society, which maintains the Meteoritical Bulletin Database (hereafter MBD), a collection of information about recovered meteorites from all over the world. Up to end 2017, there are 57108 registered meteorite names with their respective taxonomic classification.Meteorites recovered following observed passage through the atmosphere are called falls; while those which are serendipitously found or they cannot definitely be associated with a passage are called finds. In the MBD there are 1161 registered meteorites falls with official names. We combine the information of the MBD and other databases to analyze the time distribution of meteorite falls. The database includes information of falls extended for several centuries, but with a uniform coverage over the last century. We compute the frequency of falls as a function of the day of the year and the Sun's longitude. The frequency is compared with a Poisson process to look for dates with a frequency larger than expected; which it could be a signal of a meteorite stream.A subset of the falls that generate a lot of concern are those meteorites that directly impact human beings or their belongings, we call them “damaging falls”. From an analysis of the registered meteorite falls and the damaging subset in the last century, we calculate an average rate of 7.25 falls and 1.25 damaging falls over the urban land per year registered in the database. We then estimate ~5600 falls per year over the entire Earth and ~1600 over the land.
Existence, Frequency and Detectability of Inclined and Non-Transiting Circumbinary Planets
Haghighipour, Nader
The success of the Kepler space telescope in detecting planets in circumbinary orbits strongly indicates that planet formation around binary stars is robust and planets of a variety of sizes and orbital configurations may exist in such dynamically complex environments. A survey of the currently known circumbinary planets (CBPs) indicates that the orbits of many of these objects are slightly inclined and they precess with rates that place them out of transit for the majority of time. The latter strongly suggests that inclined and non-transiting CBPs are very common and the reason that not many of them have been detected is that they did not transit during the primary mission of the Kepler telescope. This has raised several fundamental questions on the formation, orbital evolution, long-term stability, and ultimately, the detectability of inclined and non-transiting CBPs. We have addressed these questions by carrying out a comprehensive 3D study of the post-formation evolution of CBPs and a detailed analysis of the orbital dynamics of these objects for a large range of their orbital inclinations. We have determined the frequency of transiting and non-transiting CBPs for different values of the binary orbital parameters and mass-ratios as well as the orbital inclination of the planet. Results indicate that, consistent with observational results, majority of CBPs are on inclined, and even non-transiting orbits, and that these orbits are the natural consequence of the post-formation evolution of these objects. We have derived, for the first time, empirical formulae for calculating the locations of (3D) boundaries of stability for inclined CBPs, and examined the possibility of the pile up of CBPs near these (3D) stability boundaries. We have found that no such preference exists. We present results of our study and discuss their implications for the probability of detection of inclined and non-transiting CBPs in terms of their orbital inclinations.
Kepler Exoplanet Radius Demographics in the Gaia Era
Huber, Daniel
The Kepler space telescope has revolutionized our understanding of exoplanet demographics. However, for nearly all of Kepler's discoveries our knowledge of planet radii is limited by the uncertainties in the radii of the host stars. Additionally, large radius uncertainties for the full sample of 150,000 Kepler exoplanet program targets are still a dominant source of systematic errors for measuring occurrence rates of small planets. The release of Gaia DR2 parallaxes in April 2018 will spectacularly solve this bottleneck by allowing the determination of <~5% radii for nearly every Kepler target. In this talk I will present the latest results on Kepler exoplanet radius demographics based on combining Gaia DR2 parallaxes with the Kepler stellar properties catalog, including an investigation of the intriguing "radius gap" for close-in super-Earths shaped by photoevaporation and a revised catalog of small, habitable-zone exoplanets based on updated stellar parameters. I will also discuss the prospects of using Gaia to investigate age demographics of exoplanets discovered by Kepler/K2.
The effects of non-equilibrium chemistry on atmospheric spectra of exoplanets
Molaverdikhani, Karan
The number of detected exoplanets has increased drastically in the recent years and has revealed a surprising diversity. Current instruments are being pushed to their limits to study their atmospheres and upcoming instruments, such as the James Webb Space Telescope, will only provide the community with very limited resources; demanding wide yet in-detail simulations of these planets to select the most promising candidates.Planetary atmospheres have been studied mostly by assuming thermochemical equilibrium. However, many recent studies suggest this assumption is most likely to be not valid at all-pressures. In particular, it breaks down at mid/low-pressure levels where diffusion and photochemistry dominate. These pressures are also where we have access to the atmosphere (aka planetary photosphere) through emission and transmission spectroscopy, and hence our interpretation of observations is susceptible to the effect of non-equilibrium chemistry on atmospheric spectra of exoplanets.We developed a fast 1D chemical kinetic model to study these effects over a wide range of planets. We employed our in-house radiative self-consistent model (petitCODE) to calculate temperature structure of these planets and we used our kinetic model to investigate how effective temperature [400k to 2500k], surface gravity [logg: 2.0 to 5.0], metallicity [Fe/H: -1.0 to 2.0], C/O [0.25 to 1.25], stellar type [M to F] and eddy diffusion coefficient [kzz: 106 to 1012 cm2/s] affect species abundances. We then calculated how transmission and emission spectra of exoplanets are affected by diffusion. Altogether we studied spectra of more than 100,000 models.We highlight the spectral regions where signatures of non-equilibrium chemistry are more prominent. We present sensitivity of the spectra to the diffusion strength, what planets are the best candidates for the JWST to observe the spectral signatures due to the non-equilibrium chemistry, and where its effect is negligible.
Gravitational Microlensing Results Challenge the Core Accretion Theory
Bennett, David
The gravitational microlensing planet detection method is currently the only method sensitive to low-mass exoplanets orbiting beyond the snow line, where the core accretion theory predicts that planet formation should be most efficient. I present a comparison between the mass ratio distribution of exoplanets from microlensing found by Suzuki et al. (2016) to theoretical population synthesis calculations by two different groups. The Suzuki et al. (2016) mass ratio distribution conforms to core accretion expectations that Neptune mass planets are much more common than Jupiters. However, both population synthesis simulations of core accretion predict a deficit of planets at intermediate masses (between Neptune and Saturn) that is not seen in the microlensing data. This mass gap in the core accretion prediction is due to the runaway gas accretion that is thought to occur once giant planet cores reach a critical mass threshold. The microlensing observations suggest that this gap may not exist. Perhaps, the formation of gas giant planets is more complicated than previously thought, or it might be that the variations in the planet formation process in different systems are so large that the gap is washed out in a statistial sample, like that of Suzuki et al. (2016). Finally, I discuss how the microlensing test of the core accretion theory will be improved with a mass measurements of microlens planets and their host stars, as well as a larger sample of planetary microlensing events.
OSIRIS-REX: MAPPING THE DENSITY OF PARTICLES OVER THE SURFACE OF ITS TARGET
Winter, Othon
Asteroids and comets are thought to be critical for understanding the origin and evolution of the Solar system and possibly the origin of life on Earth. Several countries and space agencies have launched missions to these small bodies. The most recent one is the OSIRIS-REX mission to Asteroid (101955) Bennu. One of its main goals is to bring back to Earth a sample of pristine carbonaceous regolith from Bennu. The analysis of such material will be important to understand the role that primitive asteroids may have played in the formation of planets and the origin of life. In the present work we study the motion of particles near the surface of Bennu. An application of the results is to give assistance for the selection of the sample site. Considering the gravitational potential given by the polyhedral model of Bennu (1348 vertices, 2692 faces), we numerically simulated many samples of 10,000 test particles initially located randomly in a cloud around the asteroid. We have investigated eccentric and inclined orbits, and we also adopted different particle sizes, from fine dust grains up to small particles. It is already know that Bennu has eight equilibrium points around it, and according to the adopted density, a couple of them might be stable. The influence of the equilibrium points is very strong on the orbital evolution of the particles. In the long term dynamics most of the particles collided with the asteroid surface. From our results we generated map diagrams indicating the amount of particles distributed over the surface of Bennu. They show the spots of very high collision rates, where are expected to be fully covered of particles, and also those where it is expected to be cleaner (sites of very low collision rates). These diagrams are made for a range of dffierent particle sizes and also, with and without taking into account the solar radiation pressure in the dynamics of the orbital evolution. In order to make the selection for the sample site.
Characterizing Free Floating Planet Candidates in the K2 Campaign 9 Microlensing Survey
Shan, Yutong
Properties of the free-floating planet (FFP) population across the galaxy shed critical insights to planet formation and dynamical evolution models. The occurrence rate and mass function of FFPs may help to constrain the importance of dynamical instabilities in these systems and ejection probability of planets, as well as any environmental dependence of these processes. Gravitational microlensing represents perhaps the only way to detect small planets without hosts across the galaxy. However, in general it is difficult to fully characterize individual microlensing systems, especially FFPs, from the ground alone. As a simultaneous and continuous second line of sight from space, K2 Campaign 9 (K2C9) provides the first opportunity to probe the properties of distant and isolated low-mass field objects. Jointly modelling data from ground-based surveys and K2C9, we characterize FFP candidates by measuring their microlensing parallaxes. Such a sample is the first step to constraining the mass function of this nearly invisible planet population, which could help refine our understanding of the physical processes associated with the formation and evolution of planets and planetary systems.
New Planets from K2
Livingston, John
The NASA K2 mission has continued to yield large numbers of new planet discoveries in its second year. We have carried out a systematic program of transit detection and ground-based follow-up, resulting in a sample of well-vetted planet candidates. The K2 photometry along with constraints from follow-up spectroscopy and high resolution imaging have enabled us to statistically validate a large fraction of these systems. Of particular interest are a number of planets with bright host stars which are amenable to detailed characterization via radial velocity mass measurement and transmission spectroscopy, multiplanet systems, and small planets receiving Earth-like insolation. By conducting follow-up transit photometry with Spitzer, we have also refined the ephemerides of many interesting systems, which helps to ensure the feasibility of future atmospheric studies (i.e. with JWST).
Characterising ExOPlanet Satellite (CHEOPS): ESA's first s-class science mission
Isaak, Kate
Kate Isaak on behalf of the ESA CHEOPS Project Team and the CHEOPS ConsortiumCHEOPS (CHaracterising ExOPlanet Satellite) is the first exoplanet mission dedicated to the search for transits of exoplanets by means of ultrahigh precision photometry of bright stars already known to host planets. It is the first S-class mission in ESA’s Cosmic Vision 2015- 2025. The mission is a partnership between Switzerland and ESA’s science programme, with important contributions from 10 other member states.Foreseen to be ready to launch at the very end of this year, CHEOPS will provide the unique capability of determining radii of planets in the super-Earth to Neptune mass range to 10% precision. It will also provide accurate radii for new planets discovered by the next generation of ground-based or space transit surveys (from super-Earth to Neptune-size). The high photometric precision of CHEOPS will be achieved using a photometer covering the 0.33 - 1.1um waveband, designed around a single frame-transfer CCD which is mounted in the focal plane of a 30 cm equivalent aperture diameter, f/5 on-axis Ritchey-Chretien telescope.20% of the observing time in the 3.5 year nominal mission will be available to the Community through the Guest Observers Programme that will be run by ESA. The call for proposals for the first year of observing will come out in Summer 2018.In this presentation I will give an overview of CHEOPS mission, the science, the mission status and the Community opportunities to observe with CHEOPS.
Modelling the Formation of Extrasolar Comet Clouds
Loibnegger, Birgit
In the last years observations of absorption lines varying on short time scales in spectra of stars accumulate. Scientists refer to these findings as features caused by objects evaporating material on their orbit when they come close to the star and thus call them comets in exoplanetary systems -- exocomets. This theory is based on the knowledge about the Solar System. The aim of our dynamical investigation is to find a statistical model for the scattering of small bodies which shows the most probable whereabouts of these objects after the gravitational interaction with the planets. The setup includes a star, a Jupiter-like planet and a disk of planetesimals (testparticles). As a consequence of the migration of the gas giant planetesimals are scattered either inward or outward. The outward scattered objects will form analogues to the Kuiper belt respectively the Oort Cloud in our Solar System. The created reservoirs are different depending on the initial conditions of the planetesimal disk and the migration of the Jupiter-like planet. Semi-major axis, eccentricity, perihel, aphel, inclination and orbital period after 4byr of integration of each testparticle are measured and statistics are made by comparing the outcomes of the computations with different acting forces applied -- as there are gravitational influence of the galactic tide and passing stars. Additionally the influence of the migration of the gas giant on the outcome of the scattering process is examined. In order to apply the described method to extrasolar planetary systems we start with different masses of the central star and different initial conditions for the planet (mass, orbit...) as given from observations. The gained knowledge can be used to generate a general model for the formation of cometary reservoirs in extrasolar systems with respect to the system architecture which can be used to predict the location of cometary reservoirs in extrasolar systems.
Stability and Habitability of Multi-Planetary Systems hosted by Binary Stars
Pilat-Lohinger, Elke
Even though we have evidence of about 3000 planets outside the solar system, our Earth is still the only habitable planet we know so far. Therefore, the question arises whether we have to detect solar system like configurations to discover an exo-Earth. Since a large fraction of stars in the solar neighborhood form binary or multiple star systems we consider Jupiter-Saturn like configurations orbiting one stellar component in a binary star system. In this study, we address the stability of various Jupiter-Saturn configurations in tight binary stars where we vary the distance and the eccentricity of the two stars. For all stable configurations, we determine the gravitational perturbations in the HZ using either numerical simulations or a semi-analytical method which has been developed recently. We therefore, get information whether Jupiter-Saturn configurations in binary stars could provide similar conditions for habitable terrestrial planets as in the solar system.
INPOP planetary ephemerides: updates about P9 localization
fienga, agnes
In this talk proposed for the planets days workshop, we will present recent progress in the INPOP planetary ephemerides. We will describe how in using Cassini and Juno radio science data, new constraints about P9 localization have been found, compatible with dynamical studies such as (Mulholland and Laughlin 2017) or (Batygin and Brown 2016). We will also discuss the role of other possible perturbations in our constraints on P9 localization.
Debiased estimates for near-Earth-object orbit and absolute-magnitude distributions
Granvik, Mikael
The debiased absolute-magnitude and orbit distributions as well as entrance routes or regions (ER) for near-Earth objects (NEOs) provide a fundamental frame of reference for studies of individual NEOs and more complex population-level questions. We present a new four-dimensional model of the NEO population that describes debiased steady-state distributions of semimajor axis, eccentricity, inclination, and absolute magnitude H in the range 17<H<25. The modeling approach improves upon the methodology originally developed by Bottke et al. (2000, Science 288) in that it is, for example, based on more realistic orbit distributions and uses source-specific H distributions that allow for a power-law slope that varies with H. We divide the main asteroid belt into six different ERs: the ?6, 3:1J, 5:2J and 2:1J resonance complexes as well as Hungarias and Phocaeas. In addition we include the Jupiter-family comets as the primary cometary source of NEOs. We calibrate the model against NEO detections by Catalina Sky Surveys' stations 703 and G96 during 2005–2012 and use their complementary nature to quantify systematic effects. We find that the (fitted) H distributions have significant differences, although most of them show a minimum power-law slope at H~20. As a consequence of the differences between the ER-specific H distributions we find significant variations in, for example, the NEO orbit distribution, average lifetime, and the relative contribution of different ERs as a function of H. The most important ERs are the ?6 and 3:1J resonance complexes with JFCs contributing a few percent of NEOs on average. A significant contribution from the Hungaria group leads to notable changes compared to the predictions by Bottke et al. in, for example, the orbit distribution and average lifetime of NEOs. We predict that there are 962+52-56 (802+48-42 x 103) NEOs with H<17.75 (H<25) and these numbers are in agreement with the most recent estimates found in the literature.
25 years of adaptive optics in planetary astronomy, from the direct imaging of asteroids to Earth-Like exoplanets
Marchis, Franck
Adaptive Optics (AO), a technology that compensates in real time for the atmospheric turbulences on ground-based telescopes has been used in planetary astronomy for 25 years. Saint-Pe et al (1993) is the first article reporteing the direct imaging of the asteroid Ceres. Since then AO has flourished and has been installed on 4m-class and in 2000+ on 8m class telescopes allowing astronomers to conduct studies in our solar system, such as the monitoring the volcanic activity of Io (Marchis al., 2000), study Titan's atmosphere of haze and clouds (de Pater et al. 2006), identification of new storms on Neptune (Max et al., 2003), and the measure of the density of asteroids from newly discovered moons (Marchis et al., 2005).Over the last decade, adaptive optics technology has matured and has been used for studies outside our solar system. Thank to a high contrast achieved with coronagraph the close environment of stars can be directly imaged. Using the Gemini Planet Imager, Macintosh et al (2015) discovered a young self-luminous exo-Jupiter planet orbiting the star 51 Eridani. Structures like gaps in young circumstellar disks (e.g. HD97048, Ginski et al. 2016) have been reported and interpreted as the presence of nascent exoplanets. Instruments that can reach the diffraction limit of 8m-class telescopes in visible light (e.g. Zimpol) provide images sufficient to study craters on the surface of main belt asteroid (Vernazza et al. 2017).The future of AO systems in planetary science is bright. AO systems are key to image Earth-like exoplanets around nearby stars and are part of future telescopes like ELTs, LUVOIR & HABEX. Several near-term privately funded projects are competing to image Earth-like exoplanets in the Alpha Centauri system. The 30-cm space telescope Project Blue (Morse et al., 2018) or the TIKI AO-equipped mid-infrared camera (Blain et al. 2018) could one day give us the image of another pale blue dot around one of these stars.