Habitable Worlds Across Time and Space Poster Presentations
Listing of Poster Abstracts
Superflares on Sun-Like Stars: Bane of Habitability?
Thomas Ayres (University of Colorado)
A key aspect of planetary habitability is the existence of rare, but catastrophic events. One Earthly example is the attribution of several geological mass extinctions to asteroid collisions. Indeed, the Late Heavy Bombardment, during which the 600 Myr old Earth was pummeled persistently by impactors over a period of perhaps a hundred Myr, likely significantly delayed the permanent foothold of life on our planet. Another, less well known, example is the proposed existence of "superflares" on Sun-like stars. Although the quantity of energy in a superflare is negligible compared with the time-integrated X-ray dose from the quiescent multi-MK corona, the quality of the radiation (i.e., composition dominated by gamma rays) released from the transient, but extreme, outburst is what could be of concern to the survival of primitive lifeforms struggling for existence on a semi-habitable world. However, existing reports of superflares mainly involve interpretations of historical materials, such as long-term astronomical plate collections; there are very few concrete examples of such events observed by modern techniques at the most relevant wavelengths, namely ultraviolet or X-rays. The lack of good examples is mostly because these rare events are, well, rare. However, a recent HST Cosmic Origins Spectrograph program to record the ultraviolet spectrum of young (~50 Myr) solar analog EK Draconis, fortuitously captured a giant, hour-long FUV transient, in hot lines like the C IV 155 nm doublet (T~100,000 K), and very toasty Fe XXI 124 nm coronal forbidden line (~10 MK). If translated into the equivalent GOES 0.1-0.8 nm X-ray fluence, the event would correspond to an X25000-class flare (most extreme observed on the Sun might reach as high as a mere X50). The EK Dra giant flare, as viewed with the excellent wavelength resolution, broad coverage, and high sensitivity of COS, provides the opportunity to deduce properties of such events to help inform possible impacts on planetary habitability, especially in the context of the early development of life on Earth-like planets orbiting young Sun-like stars.
Young Debris Disks With Newly Discovered Emission Features
Nick Ballering (University of Arizona)
We analyzed the Spitzer/IRS spectra of young A and F stars that host debris disks with previously unidentified silicate emission features. Such features probe small, warm dust grains in the inner regions of these young systems where terrestrial planet formation may be proceeding (Lisse et al. 2009). For most systems, these regions are too near their host star to be directly seen with high-contrast imaging and too warm to be imaged with submillimeter interferometers. Mid-infrared excess spectra—originating from the thermal emission of the debris disk dust—remain the best data to constrain the properties of the debris in these regions. For each target, we fit physically-motivated model spectra to the data. Typical spectra of unresolved debris disks are featureless and suffer severe degeneracies between the dust location and the grain properties; however, spectra with solid-state emission features provide significantly more information, allowing for a more accurate determination of the dust size, composition, and location (e.g. Chen et al. 2006; Olofsson et al. 2012). Our results shed light on the dynamic properties occurring in the terrestrial regions of these systems. For instance, the sizes of the smallest grains and the nature of the grain size distribution reveal whether the dust originates from steady-state collisional cascades or from stochastic collisions. The properties of the dust grains—such as their crystalline or amorphous structure—can inform us of grain processing mechanisms in the disk. The location of this debris illuminates where terrestrial planet forming activity is occurring. We used results from the Beta Pictoris—which has a well-resolved debris disk with emission features (Li et al. 2012)—to place our results in context.
Chen et al. 2006, ApJS, 166, 351
Li et al. 2012, ApJ, 759, 81
Lisse et al. 2009, ApJ, 701, 2019
Olofsson et al. 2012, A&A, 542, A90
Molecules for (Earth-Like) Habitability in the Planet-Formation Region of Young Protoplanetary Disks
Andrea Banzatti (STScI)
In this poster, I will summarize my results from studies of the rich infrared molecular emission observed in the planet formation region of young protoplanetary disks. The emission from water, OH, and organic molecules gives the exceptional opportunity to study the environments where planets are being formed, and possibly a fundamental key to understand planet diversity and put our Earth into a broader context. I will review in particular my results on: 1) the effects of accretion flares in shaping the molecular conditions in the planet formation region, and 2) some tools to distinguish large water abundances as due to evaporation of icy bodies migrating inward of the snow line. Both results brings us closer to unveil elusive processes linked to planet formation and our own history, and help focus better the goals for upcoming planet characterization missions.
Do Massive Stars Have Planets?
Sara Barber (University of Oklahoma)
A number of issues, such as high brightness contrast and large discrepancies in size and mass, make detection of main-sequence era exoplanets difficult. These challenges are all compounded with increasing stellar mass. One can more easily search for planets by looking at these systems in post-main sequence. Circumstellar dust around a white dwarf star is thought to originate from the tidal disruption of asteroid-like bodies and is thus used as a tracer for planetary systems. For Cycle 9 of the Spitzer mission we were awarded 15 hours to search 100 massive white dwarfs from the SDSS in the 4.5 micron IRAC band for excess emission in order to constrain the frequency of disks at massive WDs, and the frequency of planets at their massive progenitors, for the first time. Our sample is selected to have mass greater than 0.8 M (~3.5Msol progenitor mass) and Teff = 9500 - 22,500K. In Cycle 10, we are currently following up on 23 of these targets found to exhibit excess emission in the 4.5 micron IRAC band to allow for robust characterization of the excess. The most up-to-date results from this project will be presented.
High Precision Pointing Stability and Control for Exoplanet Missions
Arnold Barnes (Ball Aerospace)
Exoplanet imaging and characterization space observatories require high precision pointing stability and stability. We have developed a toolbox of sensors, actuators and algorithms along with a systems approach to meet the demanding needs of these missions. Grown from developments and experience gained from high precision Earth remote sensing missions such as the WorldView satellites, as well as high performance astrophysics missions such as Kepler and JWST, these capabilities are enabling for a wide range of future missions. The approaches take advantage of highly flexible software architectures; Enhanced ground simulation capabilities for system tuning and verification and validation; Testing capabilities to verify our modelling; High precision sensors including sub-arc-second star trackers and fine guidance sensors; High bandwidth fast steering mirrors for optical path control; and high precision reaction wheels and control moment gyros for overall observatory control. Many of these capabilities coupled with innovative thinking have been applied to the recent Kepler mission to enable the K2 extended mission concept.
The MEarth Project: Finding the Best Targets for Atmospheric Characterization with JWST
Zach Berta-Thompson (MIT)
If we want to directly observe the radius, orbit, mass, and atmosphere of a small, cool, habitable exoplanet, our best opportunity is to find such a planet transiting a small, cool, nearby M dwarf star. The MEarth Project is an ongoing all-sky survey for Earth-like planets transiting the closest, smallest M dwarfs in the Galaxy. MEarth aims to find good targets for atmospheric characterization with JWST and the next generation of enormous ground-based telescopes. This poster provides a status update on the MEarth Project, including the progress we’ve made over the past five years with 8 telescopes in the Northern hemisphere and promising early results from our new installation of 8 more telescopes in the Southern hemisphere.
Coronagraph Architecture Selection for the WFIRST-AFTA Mission
Gary Blackwood (NASA JPL)
This talk describes the selection process and results of the WFIRST-AFTA Coronagraph architectures designed to detect and characterize exoplanets orbiting nearby stars. Multiple coronagraph mask technologies are available for high contrast imaging, and the WFIRST-AFTA project required a prioritization in order to focus design and technology investments. A community working group of all stakeholders met over six months to develop a scientific- and technically-motivated evaluation process to determine the strongest options based on science yield, technical readiness, accommodation of telescope interfaces, cost and schedule. Risks and opportunities were considered. The paper describes the evaluation of the architectures against these technical metrics and expected exoplanet science yield and describes the selection of the Occulting Mask Coronagraph and the Phase-Induced Apodized Aperture Complex Mask Coronagraph as the respective primary and backup coronagraph architectures. A description of the group trade process leading to consensus is described.
Snow Line Localization in Classical Protoplanetary Disks
Sandra Blevins (CUA/STScI)
Protoplanetary disks are volatile-rich environments capable of producing the essential conditions that make planet formation viable. Establishing a molecular inventory of dominant volatile species, such as water, in the planet-forming zones surrounding young, solar-type stars elevates our understanding of the chemistry involved with planet formation, composition and disk evolution. For this study we measure the water vapor content and determine the location of the condensation front, or snow line, for four classical disks selected for the strong water emission present in their mid-infrared spectra. To accomplish this we combine deep Herschel PACS observations with high resolution Spitzer IRS spectra to create molecular maps comprised of water lines with excitation temperatures that trace the disks' surfaces from ~ 1-100 AU. We use two-dimensional, axisymmetric radiative transfer modeling to retrieve the disks' dust structures and the RADLite raytracer to render model spectra for each disk. A simple step function is used to define the abundance structure and the model spectra are fit to the observed water lines. Preliminary results will be discussed, including the inner disk chemical content, snow line radius and fractional water vapor abundances for the classical disk RNO 90.
Finding Habitable Zone Planets: Transit or RV?
Christopher Burke (SETI / NASA Ames)
Transit and radial velocity searches are two techniques for identifying the nearest extrasolar planets that transit bright stars. Identifying a robust sample of these exoplanets around bright stars for detailed atmospheric characterization using HST and JWST is a major observational undertaking. In this study we describe a framework that answers the question of whether a transit or radial velocity survey is more efficient at finding transiting exoplanets given the same amount of observing time. Within the framework we show that a transit survey's window function can be approximated using the hypergeometric probability distribution which simplifies the design and analysis of a transit survey.
Searching for Terrestrial Planetary Companions to White Dwarfs
Matthew Burleigh (University of Leicester)
We present an update to our on-going search for eclipsing and transiting terrestrial planets around white dwarf stars in the SuperWASP survey. Over 300 white dwarfs have now been monitored across baselines of several years, and the resultant statistics place some constraints on the existence of planets in close, stable orbits. We also present a search for planetary companions to a single, rapidly rotating magnetic white dwarf, and look forward to the prospect of hunting for transits of white dwarfs in the forthcoming Next Generation Transit Survey.
How the Sausage is Made: Kepler's False Alarms, False Positives, and Planet Candidates
Jeffrey Coughlin (SETI Institute)
The Kepler mission has now designated over 7,000 Kepler objects of interest (KOIs), or transit-like signatures, utilizing up to four years of data. The number of potentially habitable planet candidates (PCs) among this sample has risen significantly over time. However, starting with Kepler threshold crossing events (TCEs), there are initially about as many false alarms (FAs) detected as there are KOIs. Furthermore, due to its design, contamination from eclipsing binaries, variable stars, and other transiting planets result in a significant number of KOIs being designated as false positives (FPs). Many of these FAs and FPs occur at long orbital periods, where habitable planets are typically found. I will review the process of how an initial TCE becomes a KOI, and then is ultimately classified as a FA, FP, or PC, along with the various vetting tools employed. The understanding of this process is crucial to performing accurate statistical analyses on populations of habitable planet candidates discovered by Kepler.
Detailed Follow-Up of Transiting Habitable WD Planets with the Hubble Space Telescope
John Debes (STScI)
Transit signals from habitable planets in orbit around white dwarfs (WDs) suffer from much different technological challenges compared to planets around other host stars--while the transit depth of such a planet is orders of magnitude deeper for WD hosts compared to main sequence stars, the transit duration is on the order of 60s. In this poster we assess the feasability of detecting atmospheric signatures from WD planets. In the UV and optical one can leverage the existing capabilities of the Hubble Space Telescope, such as the time-tag capability of COS and the WFC3 spatial scanning mode, to take high cadence observations of terrestrial planets that transit their WD hosts. We demonstrate the current capabilities of COS in particular with a selection of lightcurves derived from archival COS WD spectra.
Water Transport in the Early Planetary System
Rudolf Dvorak (University of Vienna)
For an estimate of water transport in the early planetary system we investigate the degree of possible water delivery by means of asteroid collisions. Here we present a study of the distribution of impact velocities and angles of small bodies with a certain water content and initial mass of a tenth lunar mass. They are distributed on orbits with semimajor axes a=1.5 ... 1.7 AU, small eccentricities e <= 0.15 and small inclinations. The bodies' initial water (ice) content increases with their distance from the Sun. By simulating mutual collisions via n-body calculations we trace how the masses and water contents of those bodies evolve depending on the presence of a perturbing Jupiter-like planet in different distances. We find that within 1 Myr the masses of the bodies increase up to one lunar mass and the inclination-distribution is widened while the water content closer to the Sun tends to increase from inward scattered objects. We also present means of verification of our present perfect merging assumption via simulating the collision processes using SPH.
MUSCLES: Measurements of the Ultraviolet Spectral Characteristics of Low-Mass Exoplanetary Systems
Kevin France (University of Colorado)
The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. Ultraviolet photons influence the atmospheric temperature profiles and production of potential biomarkers on Earth-like planets around these stars. In this talk, I will present results from a recent study of the UV radiation fields around nearby M dwarf planet hosts that covers both FUV and NUV wavelengths. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No “UV quiet” M dwarfs are observed. The bright stellar Lyman-alpha emission lines are reconstructed, and we find that the Lyman-alpha line fluxes comprise ~37 – 75% of the total 1150 – 3100 A flux from most M dwarfs; > 1000 times the solar value. The F(FUV)/F(NUV) flux ratio, a driver for possible abiotic production of the suggested biomarkers O2 and O3, is shown to be ~ 0.5 – 3 for all M dwarfs in our sample, > 1000 times the solar ratio. For the four stars with moderate signal-to-noise COS time-resolved spectra, we find UV emission line variability with amplitudes of 50 – 500% on 100 – 1000 second timescales. Finally, we observe relatively bright H2 fluorescent emission from four of the M dwarf exoplanetary systems (GJ 581, GJ 876, GJ 436, and GJ 832). I will describe the possible origins of the hot (T (H2) ~ 2000 – 4000 K) molecular gas observed in these systems.
What Can The Habitable Zone Gallery Do For You?
Dawn Gelino (NASA Exoplanet Science Institute)
The Habitable Zone Gallery (www.hzgallery.org) came online in
August 2011 as a service to the exoplanet community that provides Habitable Zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table, a plot with the period and eccentricity of each of the planets with respect to their time spent in the HZ, a gallery of known systems which plot the orbits and the location of the HZ with respect to those orbits, and orbital movies. Recently, we have added new features including: implementation of both conservative and optimistic HZs, more user-friendly table and movies, movies for circumbinary planets, and a count of planets whose orbits lie entirely within the system’s HZ. Here we discuss various educational and scientific applications of the site such as target selection, exploring planets with eccentric or circumbinary orbits, and investigating habitability.
The Contribution of Pointing Instability and Detector Intra-Pixelsensitivity to NIRSpec Noise Budget
Giovanna Giardino (ESA - ESTEC)
The JWST near-infrared spectrometer NIRSpec has the capability to
observe the atmospheric features of a super-Earth/sub-Neptune planet,
transiting a nearby star, with unprecedented sensitivity. In terms of
shot- and read-noise only, a spectrum with S/N better than 2000 (per
spectral element) can be obtained for a star with J-band magnitude
brighter than 12, in one hour of integration (at a resolution of
1000). However, one source of additional systematic noise will be due
to the interplay of the telescope pointing instability and the
intra-pixel sensitivity of NIRSpec detectors. Here we present a
preliminary analysis showing that for a predicted long-term telescope
pointing instability smaller than 7 mas (1-sigma), typical intra-pixel
sensitivity variations would result in a systematic noise component of
about 0.04% of the signal level. This is a significant component but not one that undermines NIRSpec's potential to deliver ground-breaking
observations of exoplanets.
Direct Imaging and Interferometric Followup of Our Closest Low-Mass Stellar Neighbors
Julien Girard (European Southern Observatory)
Luhman 16 AB is a L/T brown dwarf binary system at only 2 pc from us. Discovered a year ago thanks to WISE (Luhman 2013), it has already been extensively studied (spectral types, variability, cloud map, etc. a total of 8 refereed publications). In this contribution I tackle the possibility of following up such target with the state of the art high contrast imaging and interferometric techniques. Though the system isn't young, it is so close and its components have mild effective temperature that we can probe for planetary-mass companions down to solar system scales. I will present results from our deep NACO L'-band search and expose our strategy and attempt with VLTI/PIONIER H-band (four 8m telescopes) to reach the habitable zone (~0.005 AU) and provide direct upper limits on the diameter of both Luhman A and B. Finally I will discuss the possibility of tackling such objects with the coming generation of high contrast imagers.
Flare Rates for L Dwarf Stars
John Gizis (University of Delaware)
Flares have long been recognized as an important factor for planets in the "habitable zone" around low luminosity M dwarfs. White light flares in an L-type dwarf star have been detected for the first time. The flare rate is measured using Kepler short-cadence photometry, with Gemini spectroscopy providing confirmation and additional flare constraints. I discuss the consequences for planets in close orbits.
How Should We Value a Planet?
Jacob Haqq-Misra (Blue Marble Space Institute of Science)
The idea that a planet or its biota may be intrinsically valuable, apart from its usefulness to humans, is contentious among ethicists, while difficulties abound in attempting to decide what is objectively better or worse for a planet or life. As a way of dissecting the issue of value and life, I present a two-axis comparative tool for ethical frameworks that considers the intrinsic or instrumental value placed upon organisms, environments, planetary systems, and space. I discuss ethical considerations relevant to contemporary space exploration, near-future human exploration of Solar System bodies, and long-term possibilities of interplanetary colonization. This allows for more transparent discussions of value with regard to future space exploration or the discovery of extraterrestrial life.
Habitability of Extrasolar Moons
René Heller (McMaster University)
Most of the roughly one hundred Kepler planets and candidates in
the stellar habitable zones are much larger than Earth. Though
some of them may have their bulk mass in the form of rock, many
of these super-Earths are reminiscent of Uranus, Neptune, or even
Saturn, and they cannot have liquid surface water. Yet, their
moons may be habitable. With the first detection of an extrasolar
moon on the horizon, parameterization of the effects that
constrain their habitability has become a new subdiscipline of
planetary research. I here summarize our recent work on the
effects of planetary illumination, planet-moon eclipses, tidal
heating, gas giants' magnetic environments, and orbital stability
on the potential of moons to maintain liquid surface water. I
also present our new targeted Search for Exomoons Escorting
Kepler Exoplanets (SEEKE), which favors detection of moons
orbiting planets in the stellar habitable zones of M and K stars.
Insights into Terrestrial Planet Formation from Observations of a Circumbinary Ring in the KH 15D System: A New Mechanism for Chondrule Formation
William Herbst (Wesleyan University)
A thin, settled layer of solids has formed within the terrestrial planet formation zone (roughly 1-4 AU) around the 3 Myr old T Tauri binary system KH 15D, The stars are of K1 and K7 spectral class, with a total mass of about 1.3 solar masses, have an eccentric orbit (e=0.6), and a period of 48.37 days. Precession of its slightly misaligned ring has alternately revealed one, and then the other, of the stars. The system is undoubtedly representative of others of the same mass and age, since its ring is only detectable by stellar occultations, which require an extremely privileged location in spacetime from which to view the phenomenon. Among the insights into terrestrial planet formation processes that this system provides, is a novel suggestion for the formation of chondrules. The poster will update observations of KH 15D and propose a mechanism for heating chondrules that has not previously been considered.
Constraints on Terrestrial Planet Formation in Close Binaries
Hannah Jang-Condell (University of Wyoming)
Several exoplanets have been discovered in close binaries (a<100 AU)
to date, including gamma Cephei, HD 41004, and GL 86, to name a few.
The fact that planets can form in these dynamically challenging
environments says that planet formation must be a robust process.
Disks in these systems should be tidally truncated to within a few AU,
so if they form in situ, the efficiency of planet formation must be
high. I examine the truncation of protoplanetary disks in close
binary stars, studying how the disk mass is affected as it evolves
from higher accretion rates to lower rates. The formation of
terrestrial mass planets is limited by the amount of solid materials
available for their formation. I present an analysis of the
feasibility of terrestrial planet formation in disks truncated by
close binary companions based on binary orbital parameters such as
stellar mass, companion mass, eccentricity and semi-major axis. Using
this measure, we can quantify the robustness of planet formation in
close binaries and better understand the overall efficiency of planet
formation in general.
Radial Velocity Studies of M Dwarfs
Hugh Jones (University of Hertfordshire)
Our current view of exoplanets is one derived primarily from Solar-like stars with a strong focus on understanding our Solar System. Our knowledge about the properties of exoplanets around the dominant stellar population by number, the so called low-mass stars or M dwarfs is much more cursory. Based on combining radial velocities of nearby M dwarfs obtained with UVES and HARPS we find 8 new M dwarf planets and 2 previous known from a sample of 41 stars. By computing the estimated detection probability function the occurrence rate of planets less than 10 Earth masses around nearby M dwarfs is found to be of the order of one planet per star and that of habitable zone planets between 3 and 10 Earth masses around 20 percent. The mass of radial velocity M dwarf planets is relatively much lower than the expected mass dependency based on stellar mass and thus it is inferred that planet formation efficiency around low mass stars is relatively impaired. Techniques to overcome the practical issue of obtaining good quality radial velocity data for M dwarfs are considered: (1) the wavelength sensitivity of radial velocity signals, (2) the combination of radial velocity data from different experiments for robust detection of small amplitude signals and (3) optimum selection of targets.
An Inconvenient Truth: Do We Really Know Where the Habitable Zone Is?
Stephen Kane (San Francisco State University)
An important property of exoplanetary systems is the extent
of the Habitable Zone (HZ), defined as that region where water can
exist in a liquid state on the surface of a planet with sufficient
atmospheric pressure. Both ground and space-based observations have
revealed a plethora of confirmed exoplanets and exoplanetary
candidates, most notably from the Kepler mission using the transit
detection technique. Many of these detected planets lie within the
predicted HZ of their host star. However, as is the case with the
derived properties of the planets themselves, the HZ boundaries depend
on how well we understand the host star. Here I will address an
inconvenient truth: the location of the HZ has (sometimes substantial)
error bars. I will demonstrate the uncertainty in the location of the
HZ based on the stellar parameter uncertainties, both for the Kepler
candidates and the confirmed exoplanets. I will show applications of
this HZ uncertainty to several known systems with a supposed HZ planet
to determine the uncertainty in their HZ status.
Habitable Zone Limits as a Guide to Count, Identify and Characterize Potential Habitable Planets
Ravi Kopparapu (Pennsylvania State University)
Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing exoplanet surveys and proposed space-based flagship missions. I will present our recent results on the new estimates of HZs around Main-sequence stars with Earth and super-Earth planets. According to our new model, a conservative estimate of the inner (moist greenhouse) and outer (maximum greenhouse) HZ limits for our Solar System are at 0.99 AU and 1.67 AU, respectively, and more massive planets (superEarths) have wider HZs. I will also discuss HZ limits from 3D climate models, which point to a sharp shift in the width of the HZs from F to M stars. Applying the new HZ limits to extrasolar planetary systems in NASA's "Kepler" data, we find that potentially habitable planets around M-dwarfs are more common than previously reported, and the frequency of Earth-size planets around G & K stars may be lower (~ 10-15%) than recent estimates (~22%).
FINESSE 2.0 – Providing Context for the Study of Habitable Worlds
Michael Line (UCSC)
FINESSE (Fast INfrared Spectroscopic Survey Explorer) is a survey mission dedicated to the study of exoplanet atmospheres. By performing spectroscopic measurements of ~1000 transiting planets, FINESSE will explore how the atmospheric conditions are influenced by factors such as of the parent star, planet bulk properties, planet formation and atmospheric evolution, and the atmospheric dynamic response. Additionally, the FINESSE survey will complement JWST by identifying the most spectroscopically interesting targets for detailed JWST observations. The FINESSE mission's survey of exoplanet atmospheres will provide a unique data set that will reveal how our solar system fits into the larger exoplanet family and will help make these other worlds tangible places.
Silica Debris Disk Evidence for Giant Planet Forming Impacts
Carey Lisse (Johns Hopkins University Applied Physics Lab)
Giant impacts are major formation events in the history of our solar system. The final assembly of the planets, as we understand it, had to include massive fast collision events as the planets grew to objects with large escape velocities or in regions of high Keplerian velocities (Chambers 2004; Kenyon & Bromley 2004a,b, 2006; Fegley & Schaefer 2005).
These massive impact events should create large amounts of glassy silica material derived from the rapid melting, vaporization, and refreezing of normal silicate rich primitive rocky material. We report here the detection of 4 bright silica-rich debris disks in the Spitzer IRS spectral archive, and the possible identification of 7 others. The stellar types of the system primaries span from A5V to G0V, their ages are 10 – 100 Myr, and the dust is warm, 280 – 480 K, and is located between 1.5 and 6 AU, well inside the systems’ terrestrial planet regions. The minimum amount of detected 0.1 - 20 dust mass ranges from 10^21 – 10^23 kg; assuming < 10% dust formation efficiency (Benz 2009, 2011) this implies collisions involving impactors massing at least 10^22 – 10^24 kg, i.e. from Moon to Earth mass. We find possible trends in the mineralogy of the silica, with predominantly amorphous silica found in the 2 younger systems, and crystalline silica in the older systems. We speculate this is due higher velocity impacts found in younger, hotter systems, coupled with the effects of energetic photon annealing of small amorphous silica grains. All of these measures are consistent with the creation of silica rich rubble, or construction debris, during the terrestrial planet formation era of giant impacts.
Detailed Abundances of a Planet-Hosting Wide Binary System: Did Planet Formation Imprint Chemical Signatures in the Atmospheres of HD20782/81?
Claude Mack (Vanderbilt University)
We present a detailed chemical abundance analysis of a planet-hosting wide binary system (HD20782 + HD20781), where both stars are G-dwarfs, and each of them hosts giant planets on eccentric orbits with pericenters ~< 0.2 AU. We investigate if giant planets on such orbits could scatter inner rocky planets into the atmospheres of their host stars, and thereby imprint a detectable chemical signature in the stellar photospheric abundances. Using high-resolution, high signal-to-noise echelle spectra, we derive the abundances of 15 elements. In addition, the refractory elements (Tc > 900 K) in both stars show a positive correlation between the elemental abundances and condensation temperatures (Tc), with similar slopes of ~1x10^(-4) dex K^(-1). In each star, the measured positive correlations are imperfect, with a scatter of ~5x10^(-5) dex K^(-1) about the mean trend; also, certain elements (Na, Al, Sc) are similarly deviant in both stars. We interpret these results in the context of simulations of giant planet migration that predict the accretion of H-depleted rocky material by the host star. We demonstrate that a simple model for a solar-type star accreting material with Earth-like composition predicts a positive -- but imperfect -- correlation between [X/H] and Tc. According to this model, our measured slopes are consistent with the ingestion of 10-20 Earths by both HD20782 and HD20781.
'Characterizing Exoplanet Atmospheres with HST/WFC3'
Avi Mandell (NASA)
The Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) provides the potential for spectroscopic characterization of molecular features in exoplanet atmospheres, a capability that has not existed in space since the demise of NICMOS on HST and the IRS on Spitzer. We present analysis of transit and eclipse spectroscopy for a number of Jupiter-mass planets observed during the HST Cycles 18 and 19; measurement of molecular absorption in the atmospheres of these planets offers the chance to explore several outstanding questions regarding the atmospheric structure and composition of these highly irradiated massive planets. The observations cover either the primary transit or secondary eclipse for each planet, and we analyze the data using a strategy that allows us to correct for channel- or wavelength-dependent instrumental effects by utilizing the band-integrated time series and measurements of the drift of the spectrum on the detector over time. We achieve almost photon-limited results for individual spectral bins, but the uncertainties in the depth of each event for the the band-integrated data are exacerbated by instrument systematics as well as the orbital phasing of HST’s observations. Our transit spectra show evidence for the presence of a broad absorption feature at 1.4 microns most likely due to water, but the amplitude of the absorption is less than that expected possibly due to hazes absorbing in the NIR or non-solar compositions. Our eclipse spectra all appear to be consistent with a featureless spectrum, which is unexpected and may also require non-solar compositions. Future observations with WFC3 to improve the S/N and/or a comprehensive multi-wavelength analysis combined with a robust systematic retrieval effort will allow us to better distinguish between different models
Architecture and Stability of Planetary Systems Based on Kepler Data
Jean-Luc Margot (University of California, Los Angeles)
We used a sample of Kepler candidate planets with orbital periods less
than 200 days and radii between 1.5 and 30 Earth radii to determine
the typical dynamical spacing of neighboring planets (Fang and Margot,
ApJ 767, 2013). To derive the intrinsic (i.e., free of observational
bias) dynamical spacing of neighboring planets, we generated
populations of planetary systems following various dynamical spacing
distributions, subjected them to synthetic observations by the Kepler
spacecraft, and compared the properties of observed planets in our
simulations with actual Kepler detections. We found that, on average,
neighboring planets are spaced 21.7 mutual Hill radii apart with a
standard deviation of 9.5. This dynamical spacing distribution is
consistent with that of adjacent planets in the Solar System. To test
the packed planetary systems (PPS) hypothesis, the idea that all
planetary systems are filled to capacity, we determined the fraction
of systems that are dynamically packed by performing long-term (10e8
years) numerical integrations. In each simulation, we integrated a
system with planets spaced according to our best-fit dynamical spacing
distribution but containing an additional planet on an intermediate
orbit. We chose the least disruptive initial conditions for the
additional planet, and chose its mass to be equal to that of the
smallest planet in the system. The fraction of simulations exhibiting
signs of instability (ejections or collisions) provides an approximate
lower bound on the fraction of systems that are dynamically packed.
We found that over 31%, 35%, and 45% of 2-planet, 3-planet, and
4-planet systems are dynamically packed, respectively. Such sizeable
fractions suggest that many planetary systems are indeed filled to
capacity. This feature of planetary systems is a fundamental
constraint that formation and evolution models must satisfy.
High-Accuracy Spitzer/IRAC Subarray Photometry of Potential Warm Debris Disk Sources Uncovered by WISE
Raquel Martinez (NASA Goddard Space Flight Center)
All-sky mapping performed by the Wide-Field Infrared Survey Explorer (WISE) at wavelengths of 3.4, 4.6, 12, and 22 microns has identified 346 nearby Hipparcos stars as warm debris disk candidate sources with [3.4]- colors indicative of excess 22 micron emission above that expected of the stellar photosphere at a better than 4-sigma level. A considerable number of additional nearby Hipparcos stars show 22 micron color excess but at lower significance due to saturation of the W1 (3.4 micron) images. Here, we present Spitzer/Infrared Array Camera (IRAC) Channel 1 (3.6 micron) subarray mode observations of 421 Hipparcos stars within 120 pc ranging in spectral type from B3 to M9 and assess their potential as warm debris disk candidates. We confirm 169 of these low-significance color excesses by performing aperture photometry on the new, unsaturated Spitzer/IRAC Ch 1 images. We also detail our Spectral Energy Distribution (SED) fitting strategy that enabled accurate subtraction of the stellar photosphere to improve confidence of one-hundred and four 22 micron excess detections to better than 4-sigma significance. After careful scrutiny of the images in our sample to exclude sources plagued by contamination or confusion, 79 stars have excess 22 micron emission attributable to debris disks. The spectral type breakdown of these infrared excess objects are as follows; 11 B stars, 39 A stars, 25 F stars, and 4 G stars. Of these 79 infrared excess stars, 55 are newly identified.
Corrections in the Application of the Habitable Zone to Planets in Elliptical Orbits
Abel Mendez (University of Puerto Rico at Arecibo)
Estimates on the occurrence of exoplanets orbiting within the habitable zone of their star, including those potentially habitable, require the correct application of formal definitions of the habitable zone. About 74% of all known confirmed planets have eccentricities larger than Earth. It is then often assumed that the mean equilibrium temperature of a planet in an elliptical orbit can be simply calculated from its mean orbital distance or stellar flux. Here we calculated analytic solutions for both the spatial and temporal averages of orbital distance, stellar flux, and equilibrium temperature. Our solutions demonstrate that while elliptical orbits do cause an increase of the mean stellar flux as compared to a circular orbit, the mean equilibrium temperature of a planet decreases with eccentricity until a converging value. Therefore, the mean surface temperature of a planet in an elliptical orbit might decrease or increase depending on the greenhouse effect as compared to a circular orbit. This result is important to correctly assess whether planets in elliptical orbits are within the habitable zone or not. This analysis was incorporated for all known confirmed planets in the PHL’s Exoplanet Orbit Catalog where many were duly reclassified. About 12% of all known confirmed planets are in the habitable zone, but only 4% of the Kepler candidates. Additional suggestions will be presented on how to classify planets and their potential habitability.
Disk Evolution in the Solar Neighborhood
Bruno Merín (ESA)
We study the evolution of circumstellar disks in 22 young (1 to 100 Myr) nearby (within 500 pc) associations over the entire mass spectrum using photometry covering from the optical to the mid-infrared.
We compiled a catalog of 2,340 spectroscopically-confirmed members of these nearby associations. We analyzed their spectral energy distributions and searched for excess related to the presence of protoplanetary and/or debris disks. The dataset has been analyzed in a homogeneous and consistent way.
We derive disk fractions as probed by mid-infrared excess in the 22 regions. The unprecedented size of our sample allows us to confirm the timescale of disk decay reported in the literature and to find new trends. The fraction of excess sources increases systematically if measured at longer wavelengths. The dust probed at 22–24 micron evolves slower than that probed at shorter wavelengths (3.4–12 micron). Assuming an exponential decay, we derive a longer timescale at 22–24 micron for primordial disks, compared to 2∼3 Myr at shorter wavelength (3.4–12 micron). Primordial disks disappear around 10∼20 Myr.
The increase in timescale of excess decay at longer wavelength is compatible with inside-out disk clearing scenarios. The increased timescale of decay and larger dispersion in the distribution of disk fractions at 22–24 micron suggest that the inner (terrestrial-planet forming) and outer (giant-planet forming) zones evolve differently, the latter potentially following a variety of evolutionary paths.
This large disk database allows the analysis of evolutionary paths for different types of disks and it can be used to connect the known input disk populations with the output exoplanet populations, once the observational biases at both ends have been considered.
The Search for Planets Around Solar Twins: the Anomalous Chemical Abundance Pattern of the Oldest Solar Twin
TalaWanda Monroe (Universidade de São Paulo)
High precision chemical abundance studies reveal that the Sun appears deficient in refractory elements relative to volatile species, in comparison to solar twin stars. Planetesimal and terrestrial planet formation may have imprinted such a signature in the solar composition by using up refractory elements in the surrounding disk, and leaving behind material low in refractory elements to accrete onto the Sun. In an effort to identify other stars that may host rocky planets, we present the results of a high precision (0.004 - 0.01 dex) abundance study of the oldest solar twin HIP 102152, with a derived age of 8.2 Gyr, and the younger 2.9 Gyr solar twin 18 Sco, using high-resolution (R = 110,000), high S/N (500-1000) VLT-UVES spectra. Elemental abundance ratios examined as a function of dust condensation temperature reveal a solar abundance pattern for this star, in contrast to most solar twins, such as 18 Sco. The solar chemical pattern of HIP 102152 thus makes it a potential candidate to host terrestrial planets, which is reinforced by the lack of giant planets in its terrestrial planet region. These results are considered in the context of our ongoing solar twin radial velocity planet search, which combines our high level of precision in abundances along with the sensitivity of the ESO HARPS spectrograph to probe the chemical abundance-planet connection at an increased level of detail.
The Stability of Multiplanet Systems on the Main Sequence and Post-Main Sequence
Alexander Mustill (Lund Observatory, Lunds Universitet)
When stars leave the main sequence they lose a significant fraction of their mass: around 50% for a Solar-mass star, and greater fractions for more massive stars. This mass loss has significant effects on the orbits of planets: in particular, in multi-planet systems, dynamical interactions become stronger, and previously stable systems can be destabilised. We study the stability of multi-planet systems through the lifetimes of their host stars, from the zero-age main sequence to an old white dwarf, with numerical integrations incorporating the changes to the star's mass and radius as it evolves. We show that orbital instability occurs following mass loss in many systems, both those that already experienced instability on the main sequence and those that were stable. We discuss implications for the orbits and detectability of giant planets orbiting WDs, the prospects for the delivery of terrestrial planets to the WD "habitable zone", and the efficiency of WD atmospheric pollution by destabilised planetesimals.
Modeling the Infrared Spectra of Earth-Analog Exoplanets
Conor Nixon (NASA GSFC)
As a preparation for future observations with the James Webb Space Telescope (JWST) and other facilities, we have undertaken to model the infrared spectra of Earth-like exoplanets. Two atmospheric models were used: the modern (low CO2) and archean (high CO2) predictive models of the Kasting group at Penn state. Several model parameters such as distance to star, and stellar type (visible-UV spectrum spectrum) were adjusted, and the models reconverged. Subsequently, the final model atmospheres were input to a radiative transfer code (NEMESIS) and the results intercompared to search for the most significant spectral changes. Implications for exoplanet spectrum detectivity will be discussed.
Detecting Exoplanets with the George Mason University Telescope
Peter Panka (George Mason University)
The George Mason Exoplanet Team has become an official follow up team for the KELT Survey. Research areas for the team include: Transit Timing Variations, High-altitude spectroscopy, and characterization of extrasolar planets. Detections were performed using the STX 16803 and filter wheel STX-FW7 at the George Mason 0.8m Telescope. We will present observed transit characteristics of Kelt-1b, HD189733b, WASP-33b, as well as others - discussing the transit depths, timing variations, and data reduction methods.
A Prototype Integral Field Spectrograph for High Contrast Visible-Light Imaging Spectroscopy of Jovian and Terrestrial Worlds
Marshall Perrin (STScI)
We present the design and status of PISCES, a visible light (0.4-1 micron) integral field spectrograph (IFS) being developed for NASA’s High Contrast Imaging Testbed at the Jet Propulsion Laboratory. PISCES, the Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies, is a lenslet-based IFS with diffraction limited spatial sampling and a spectral resolution of ~70. It will be a laboratory prototype for future space instruments intended for exoplanet characterization via high contrast imaging, for instance imaging of Jovian and Neptunian class planets with the AFTA Coronagraph and eventually terrestrial planets with a future TPF/ATLAST/NWO type mission. PISCES will demonstrate visible light imaging spectroscopy at the challenging contrast levels required for direct detection and characterization of habitable exoplanets, and is compatible with both coronagraph and starshade mission concepts.
Origin of Al26 in the Solar System
Giovanni Privitera (University of Geneva - IRSOL)
Short-lived radionuclides (SLRs) are radioactive elements with mean lifetimes under 100 Myr that were incorporated into meteorites’ primitive components such as calcium- and aluminum-rich inclusions (CAIs) or chondrules during the earliest evolution phases of our solar system. These SLRs may be sources of energy during the first millions years in small planetesimals allowing their differentiation and the loss of part of their water. We present here new grids of stellar rotating models with predictions for the ejections by stellar winds of Al26 and other isotopes. We discuss the differences with previous works and discuss the consequences when incorporated in the model proposed by Gounelle and Meynet (2012) to explain the past presence of SLRs in the nascent solar system.
Can Increased CO2 Levels Trigger a Runaway Greenhouse on the Earth?
Ramses Ramirez (Pennsylvania State University)
Recent one-dimensional (globally averaged) climate model calculations suggest that increased atmospheric CO2 could conceivably trigger a runaway greenhouse if CO2 concentrations were approximately 100 times higher than today. The new prediction runs contrary to previous calculations, which indicated that CO2 increases could not trigger a runaway, even at Venus-like CO2 concentrations. Goldblatt et al. argue that this different behavior is a consequence of updated absorption coefficients for H2O that make a runaway more likely. Here, we use a 1-D cloud-free climate model with similar, up-to-date absorption coefficients, but with a self-consistent methodology, to demonstrate that CO2 increases cannot induce a runaway greenhouse on the modern Earth. However, these initial calculations do not include cloud feedback, which may be positive at higher temperatures, destabilizing Earth’s climate. We then show new calculations demonstrating that cirrus clouds cannot trigger a runaway, even in the complete absence of low clouds. Thus, the habitability of an Earth-like planet at Earth’s distance appears to be ensured, irrespective of the sign of cloud feedback. Our results are of importance to Earth-like planets that receive similar insolation levels as does the Earth and to the ongoing question about cloud response at higher temperatures.
Detecting Exoplanets with the George Mason University Telescope
Joe Renaud (George Mason University)
The George Mason Exoplanet Team has become an official follow up team for the KELT Survey. Research areas for the team include: Transit Timing Variations, High-altitude spectroscopy, and characterization of extrasolar planets. Detections were performed using the STX 16803 and filter wheel STX-FW7 at the George Mason 0.8m Telescope. We will present observed transit characteristics of Kelt-1b, HD189733b, WASP-33b, as well as others - discussing the transit depths, timing variations, and data reduction methods.
*(Presenting a poster with Alex Panka, who also submitted the above abstract)
An Estimate of Mass Transfer on Tidally Locked Heated Super-Earths
Prabal Saxena (George Mason University )
We estimate mass transport rates towards the night side on tidally locked heated Super-Earths due to surface sublimation on the sub-stellar side. These estimates build upon previous work exploring the atmospheres of Io and selected heated Super-Earths. Atmospheric abundances are estimated based on vapor pressure equilibrium for a variety of proposed compositions. We explore these mass transport rates for a range of Super-Earth temperatures, masses and volumes and discuss the implications of resurfacing.
Modeling Atmospheres and Spectra of Earth-like Exoplanets
Jeremy Schnittman (NASA/GSFC)
We couple publicly-available 1-D radiative-convective and
photochemistry models to a post-processor radiative transfer code to
efficiently generate spectra for a wide range of exoplanet parameter
The atmospheric composition changes due to the photochemistry
module as the radiative-convective module converges toward
We study a range of stellar types from M-dwarfs to
Sun-like stars and focus on terrestrial and "Super-Earth" exoplanets
in or near the habitable zone.
We then pass these synthetic
spectra through the expected response function of the James Webb Space
Telescope (JWST) in order to determine the sensitivity of that
observatory to measuring various atmospheric properties.
show what might be learned from direct imaging observations with a
next-generation space telescope.
Exo-C: A Probe-Scale Space Mission to Directly Image and Spectroscopically Characterize Exoplanetary Systems Using an Internal Coronagraph
Karl Stapelfeldt (NASA/Goddard)
"Exo-C" is NASA's first community study of a modest aperture space telescope designed for high contrast observations of exoplanetary systems. The mission will be capable of taking optical spectra of nearby exoplanets in reflected light, searching for previously undetected planets, and imaging structure in a large sample of circumstellar disks. We present the mission/payload design and highlight steps to reduce mission cost and risk relative to previous mission concepts. At the study's conclusion in 2015, NASA will evaluate it for potential development at the end of this decade.
Maximizing the ExoEarth Yield For a Future Direct Imaging Mission
Christopher Stark (NASA GSFC)
The number of potentially habitable extrasolar Earth-like planets (exoEarths) detected and spectroscopically characterized is a key scientific metric for future missions that aim to directly image extrasolar planets. The predicted exoEarth yield will inform telescope design, mission lifetime, and may ultimately help select a technology for high-contrast imaging. A number of previous studies have estimated exoEarth yield via Monte Carlo simulations, but few have sought to optimize observations such that the overall mission yield is maximized. I will introduce Altruistic Yield Optimization (AYO), a novel approach to target prioritization and exposure time allotment that has the single goal of maximizing the number of detected exoEarths. I will compare this method with previous methods and show that AYO can potentially double the number of detected exoEarths. I will use the AYO method to illustrate how the yield of a mission responds to fundamental parameters, including telescope aperture size, inner working angle, and exozodi level.
Increasing the Sensitivity of the Kepler Legacy Archive to Habitable Zone Planets and Earth Analogs
Martin Still (NASA Ames Research Center)
All legacy light curves archived by the Kepler project are available to the community. They are based upon simple aperture extractions from time-tagged pixel data. We demonstrate that this photometry method works well for the bright end of the Kepler target sample yet there is enormous scope for further gains in sensitivity to planet transits of faint stars in the sample. To this end, all pixel data have been made available in the archive. Methods for the user community to optimize aperture photometry and exploit point spread function modeling are being developed. Exploiting existing Kepler planet candidates, we showcase the signal-to-noise to be gained by these methods. We argue that at the faintest end of the candidate distribution, optimization provides a factor two improvement in sensitivity to transits, reaching beyond the signal-to-noise promised by the eight year mission, curtailed by reaction wheel failure after four years. These methods can provide potentially significant improvement to a number of facets of the Kepler mission: 1. Sensitivity to new planet candidates residing currently below the signal-to-noise detection threshold; 2. Characterizing known transit profiles to higher precision; 3. Identifying contamination from nearby sources and removing contamination bias from transit depths; 4. Mitigating focus and pointing systematics within the Kepler data, and 5. Allowing the direct characterization of time-dependent physical and detector biases within the image background. With exisiting focal plane calibrations, the number of targets that currently benefit from optimized photometry is relatively small, limited to sources of magnitude Kp > 16. However, with additional refinement of the focal plane calibration, improvement in light curve quality for objects 14 < Kp < 16 can be anticipated, impacting 50% of the Kepler target sample. These methods are equally applicable to data from the upcoming TESS mission and are potentially a critical component to the exploitation of the two-wheel K2 mission currently being developed and tendered.
3D Simulations of the Convective Zone in Accreting White Dwarfs.
Pier-Emmanuel Tremblay (STScI)
A significant fraction of white dwarfs are accreting metals from disrupted bodies that could be the remnants of former planets. The majority of these polluted white dwarfs have a convective atmosphere, and the derived abundances of accreted metals are sensitive to the model of convection. In particular, the size of the convective zone, where the metals are mixed and slowly diffuse at the bottom, is very sensitive to the current 1D parametrization of convection. We have developed 3D radiation-hydrodynamical simulations that provide a more robust model of the atmospheres and envelopes of hydrogen- and helium-atmosphere white dwarfs. These structures can be employed to predict
3D spectra in order to determine the raw photospheric abundances, and then to improve the diffusion timescales at the bottom of the convective zone to recover the initial abundances of the accreted material.
The Effect of High-Pressure Ice Layer on Ice-Covered Terrestrial Planets
Shoji Ueta (Tokyo Institute of Technology)
A lot of extrasolar terrestrial planets have been discovered. Whether terrestrial planets with liquid H2O exist is an important question to consider, especially in terms of the planets' habitability. Even in a globally ice-covered state, liquid water could exist beneath the surface ice shell because sufficient geothermal heat flow from the planetary interior could melt the interior ice, so that an internal ocean under the surface ice shell could appear. In this study, we argue the conditions under which ice-covered terrestrial planets have an internal ocean on the timescale of planetary evolution (Ueta & Sasaki 2013). Geothermal heat flow calculated by a parameterized convection model is considered as the heat source at the origin of the internal ocean. We also examine how the amount of radiogenic heat and H2O mass affect these conditions. Moreover, we investigate the structures of surface H2O layers of ice-covered planets by considering the effects of ice under high pressure (high-pressure ice). At 1 AU from the central star, a 1M_Earth planet with 0.6-25 times H2O mass of the Earth could have an internal ocean. When the planet has an H2O mass over 25 times that of the Earth, high-pressure ice layers may appear between the internal ocean and the rock-part of the planet. The results indicate that planetary size and surface H2O mass strongly ristrict the conditions required for an extrasolar terrestrial planet to have an internal ocean without high-pressure ice existing under the internal ocean. The habitability of a planet might be influenced by the existence of such high-pressure ice layers.
Finding the Needle in the Haystack: A High-Fidelity Model of the Solar System for Exoplanet Observations
Ashlee Wilkins (University of Maryland)
As the possibility of discovering habitable, Earth-like planets around Sun-like stars improves, the need for both accurate model representations of such systems and advanced, dedicated high-contrast instrumentation in order to characterize and understand such systems becomes ever more pressing. We present a model and an instrument to address this need.
The signals of habitability will be buried within spectral information like needles in haystacks, so we present a complete model of the Solar System we call “Hackstacks” that can be readily placed at various distances and inclinations to simulate an exoplanetary system with a known habitable planet. The Haystacks data product is a three-dimensional spectral cube. The spatial x-y plane spans 150 AU in both directions, centered on the Sun. The spectral z-dimension is divided into four hundred slices ranging from 0.3 μm to 2.5 μm, evenly spaced in wavelength, yielding R ~ 200 in the V-band. In the model, we include the Solar System planets, inner (exo)zodiacal dust, outer Kuiper Belt dust, and extragalactic background, all sourced from a combination of observations and models. This makes the Haystacks model the most comprehensive, robust, and detailed model available for prediction of noise levels, confusion, and the ability to measure biomarkers in a directly observed system. The final data cubes are available for download by the public. Any user who accesses our NASA-hosted webpage simply inputs a desire wavelength range, a distance, and an inclination, and they are provided with the corresponding spectral cube. We demonstrate the power of such data cubes with several simulations of observations with various telescopes and instruments using the PROPER suite of algorithms, and present preliminary results on detectability and necessary instrument/telescope capabilities.