Review Report on the WFIRST

An independent review board for NASA’s next flagship astronomy mission concluded in its final report that the project is “not executable” without additional funding or adjustments to the spacecraft.

NASA released the report, a 65-page document in the form of a PowerPoint presentation, Nov. 22, a month after the agency published its response calling for a reduction in the proposed cost of the Wide-Field Infrared Survey Telescope (WFIRST) and changes to its management.

The report, prepared by an outside committee established by NASA called the WFIRST Independent External Technical/Management/Cost Review (WIETR), found that various changes made to WFIRST since it was proposed as the top-ranking large, or flagship, mission in the 2010 astrophysics decadal survey created cost and technical difficulties.

“After multiple discussions that set the boundary conditions, NASA HQ made a series of decisions that set the stage for an approach and mission system concept that is more complex than probably anticipated from the point of view of scope, complexity, and the concomitant risks of implementation,” the report stated.

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The Demographics of Rocky Free-floating Planets and their Detectability by WFIRST

The Demographics of Rocky Free-floating Planets and their Detectability by WFIRST

Authors:

Barclay et al

Abstract:

Planets are thought to form via accretion from a remnant disk of gas and solids around a newly formed star. During this process, material in the disk either remains bound to the star as part of either a planet, a smaller celestial body, or makes up part of the the interplanetary medium; falls into the star; or is ejected from the system. Herein we use dynamical models to probe the abundance and properties of ejected material during late-stage planet formation and estimate their contribution to the free-floating planet population. We present 300 N-body simulations of terrestrial planet formation around a solar-type star, with and without giant planets present, using a model that accounts for collisional fragmentation. In simulations with Jupiter and Saturn analogs, about one-third of the initial (~5 M ⊕) disk mass is ejected, about half in planets more massive than Mercury but with a mass lower than 0.3 M ⊕, and the remainder in smaller bodies. Most ejections occur within 25 Myr, which is shorter than the timescale typically required for Earth-mass planets to grow (30–100 Myr). When giant planets are omitted from our simulations, almost no material is ejected within 200 Myr and only about 1% of the initial disk is ejected by 2 Gyr. We show that about 2.5 terrestrial-mass planets are ejected per star in the Galaxy. We predict that the space-borne microlensing search for free-floating planets from the Wide-Field Infra-Red Space Telescope will discover up to 15 Mars-mass planets, but few free-floating Earth-mass planets.

Planetary Society on WFIRST's Planned Coronograph

I have previously written about WFIRST (Summer 2015 Planetary Report). This NASA mission, planned to launch into space in the mid-2020s will have a coronagraph at least 1,000 times more powerful than any existing coronagraph. The power of a coronagraph is measured by the 'contrast ratio'—the ratio of the brightness of the central star to the brightness of the planet being studied. Current coronagraphs have a contrast ratio of about 100,000-1 million, which means that astronomers can see objects that are 100,000-1 million times dimmer (less bright) than the central star. WFIRST is being designed to achieve a contrast ratio of one billion to one! The primary difficulty in designing any coronagraph is in blocking all of the starlight. Once light has entered the telescope, it is extremely difficult to block it all with a coronagraph, partly due to a process called 'diffraction.' This is a process in which light is bent around corners or is scattered at the edges of objects. An analogy would be when you close the curtains, but there is a little gap and the light spreads as it passes through the small gap. In a telescope, this scattered light sometimes finds its way to the camera recording the telescope observations. So, achieving a contrast ratio of one billion to one requires us to keep that scattered light level very, very low.

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There are Concerns About WFIRST's Cost Growing

The estimated cost of NASA’s next major astrophysics mission after the James Webb Space Telescope has increased by up to 25 percent, growth that a new report warns could hurt other priorities for NASA astronomy missions in the coming years.

The potential cost increase in the Wide Field Infrared Survey Telescope (WFIRST) mission was noted in a report issued by the National Academies Aug. 15 that reviewed the progress by NASA and other agencies in implementing the most recent astrophysics decadal survey, published in 2010.

WFIRST, which became a formal project in February, had an estimated cost of $2.0 to 2.3 billion, based on an independent cost and technical estimate performed by the Aerospace Corp. in 2015. However, the National Academies report said that between the completion of that assessment and the decision to make WFIRST a formal project, known as Key Decision Point A, the cost of the mission had increased by $550 million.

Part of that increase, according to the report, is linked to the decision to fly WFIRST at the Earth-sun L-2 Lagrange point, about 1.5 million kilometers from the Earth, rather than in geostationary orbit as originally planned. Increased prices for the baseline launch vehicle, a United Launch Alliance Delta 4 Heavy, also contributed to the cost growth by an unknown amount. “Some of it may simply reflect more accurate assessment as the mission design matures,” the report added.

NASA spokeswoman Felicia Chou said Aug. 15 that of that $550 million increase, only $100 million was linked to design changes to the WFIRST spacecraft. The rest, she said, was caused by factors that included a change in the estimated launch vehicle price and a delayed launch date.

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WFIRST's Evolution

Many NASA missions and projects have become household names – Apollo, Hubble, and, more recently, Curiosity. These names are chosen with care, and the names themselves can change over the course of a project, from inception to completion. Tracking the changing names of a project can reveal the story of a mission's development. NASA’s next big “flagship” astronomy mission, following the ambitious James Webb Space Telescope due to be launched in 2018, is currently known as the Wide Field Infrared Survey Telescope (WFIRST). When NASA formally committed to flying WFIRST in February 2016, news stories stated that NASA had then "begun" work on WFIRST. This amused me because I, along with many of my colleagues, had already put hundreds of collective work-years into the development of WFIRST, under a slew of different names.

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Detecting Micro Lensing of Free Floating Planets

Microlensing by Kuiper, Oort, and Free-Floating Planets

Author:

Gould

Abstract:

Microlensing is generally thought to probe planetary systems only out to a few Einstein radii. Microlensing events generated by bound planets beyond about 10 Einstein radii generally do not yield any trace of their hosts, and so would be classified as free floating planets (FFPs). I show that it is already possible, using adaptive optics (AO), to constrain the presence of potential hosts to FFP candidates at separations comparable to the Oort Cloud. With next-generation telescopes, planets at Kuiper-Belt separations can be probed. Next generation telescopes will also permit routine vetting for all FFP candidates, simply by obtaining second epochs 4-8 years after the event. At present, the search for such hosts is restricted to within the "confusion limit" of theta_confus ~ 250 mas, but future WFIRST observations will allow one to probe beyond this confusion limit as well.

Augmenting WFIRST Microlensing Detections with a Ground-based Optical Telescope Network

Augmenting WFIRST Microlensing with a Ground-based Optical Telescope Network

Authors:

Zhu et al

Abstract:

Augmenting the WFIRST microlensing campaigns with intensive observations from a ground-based network of wide-field survey telescopes would have several major advantages. First, it would enable one-dimensional (1-D) microlens parallax measurements over the entire mass range M≳M⊕. For luminous lenses, such 1-D parallax measurements can be promoted to complete solutions (mass, distance, transverse velocity) by high-resolution imaging a few years after the observations. This would provide crucial information not only about the hosts of planets and other lenses, but also enable a much more precise Galactic model. The addition of such a ground-based survey would also yield full 2-D vector parallax measurements, with largest sensitivity to low-mass lenses, which (being non-luminous) are not subject to followup imaging. These 2-D parallax measurements will directly yield mass and distance measurements for most planetary and binary events. It would also yield additional complete solutions for single-lens events, especially those with low-mass lenses. Other benefits of such a survey include improved understanding of binaries (particularly with low mass primaries), and sensitivity to distant ice-giant and gas-giant companions of WFIRST lenses that cannot be detected by WFIRST itself due to its restricted observing windows. Such a ground-based survey can only be conducted in the optical and therefore requires that WFIRST be pointed at lower-extinction fields than is currently envisaged. This would come at some cost to the event rate. Therefore the benefits of improved characterization of lenses must be weighed against these costs.

WFIRST Gets Profiled

NASA said Thursday that it's getting down to business building a new telescope that could get us a step closer to finding E.T. and perhaps reveal other mysteries of the universe along the way.

The Wide-Field Infrared Survey Telescope (WFIRST) will have capabilities that make it similar to taking Hubble's telescope and putting a panoramic lens on it. It will carry a wide-field instrument allowing it to capture images with the same depth and quality as Hubble, but covering 100 times its field of view.

In addition to having such a wide view of parts of space, WFIRST will also sport a coronagraph that can block the glare from individual stars to better characterize not only planets orbiting those, but the atmospheres of planets as well.

"It will also develop technology that will pave the way for finding and characterizing Earth-like planets in the future," said Nikole Lewis of the Space Telescope Science Institute in a statement.

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WFIRST Gets an Early Start

In a clean room at the Goddard Space Flight Center in Maryland, the light-collecting heart of NASA’s next great space telescope is finally coming together. For the last several weeks, technicians, aided by a robotic arm, have been putting hexagonal mirror segments into a structure for the James Webb Space Telescope (JWST). As of last week, 13 of the 18 mirror segments were in place, with all 18 expected to be in position by the end of February.

The assembly of JWST’s primary mirror is just one aspect of the telescope’s construction. Elsewhere, the telescope’s instruments are being tested while the spacecraft bus and its deployable sunshade, the size of a tennis court, are put together. Several years after a critical “replan” of the observatory, years behind its original schedule and billions of dollars over its original budget, NASA says JWST remains on track for launch on an Ariane 5 in October 2018.

That means that spending on JWST—$620 million for the 2016 fiscal year—will soon ramp down. For several years, NASA had been anticipating the “wedge” in the budget this would create and started planning for the next large space observatory beyond JWST that wedge of funding would enable. The leading candidate for that mission has been a concept called the Wide Field Infrared Survey Telescope (WFIRST), one endorsed by astronomers as their top priority large mission in their latest decadal survey in 2010.

WFIRST, as it turns out, will start even sooner that NASA expected. At the 227th Meeting of the American Astronomical Society (AAS) held last week in Florida, agency officials announced that WFIRST will “enter formulation” in February. That milestone, also known in NASA’s project management terminology as “Key Decision Point A,” sets WFIRST on course for a launch in the mid-2020s.

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Determing Radial Velocity Detected Exoplanets' Masses may NOT be Possible With EXO & WFIRST

TRUE MASSES OF RADIAL-VELOCITY EXOPLANETS

Author:

Brown

Abstract:

We study the task of estimating the true masses of known radial-velocity (RV) exoplanets by means of direct astrometry on coronagraphic images to measure the apparent separation between exoplanet and host star. Initially, we assume perfect knowledge of the RV orbital parameters and that all errors are due to photon statistics. We construct design reference missions for four missions currently under study at NASA: EXO-S and WFIRST-S, with external star shades for starlight suppression, EXO-C and WFIRST-C, with internal coronagraphs. These DRMs reveal extreme scheduling constraints due to the combination of solar and anti-solar pointing restrictions, photometric and obscurational completeness, image blurring due to orbital motion, and the "nodal effect," which is the independence of apparent separation and inclination when the planet crosses the plane of the sky through the host star. Next, we address the issue of nonzero uncertainties in RV orbital parameters by investigating their impact on the observations of 21 single-planet systems. Except for two—GJ 676 A b and 16 Cyg B b, which are observable only by the star-shade missions—we find that current uncertainties in orbital parameters generally prevent accurate, unbiased estimation of true planetary mass. For the coronagraphs, WFIRST-C and EXO-C, the most likely number of good estimators of true mass is currently zero. For the star shades, EXO-S and WFIRST-S, the most likely numbers of good estimators are three and four, respectively, including GJ 676 A b and 16 Cyg B b. We expect that uncertain orbital elements currently undermine all potential programs of direct imaging and spectroscopy of RV exoplanets.

Can WFIRST With an Optical Coronagraph Directly Image Jupiter Analogs?

The Direct Detectability of Giant Exoplanets in the Optical

Authors:

Greco et al

Abstract:

Motivated by the possibility that an optical coronagraph will be put on WFIRST/AFTA, we present an exploration of the general character of the direct detectability of extrasolar giant planets (EGPs) in the optical. We quantify a planet's direct detectability by the fraction of its orbit for which it is in an observable configuration--defined to be its observability fraction (fobs). Using a suite of Monte Carlo experiments, we study the dependence of fobs upon various technological and astrophysical parameters, including the inner working angle (IWA) and minimum achievable contrast (Cmin) of the direct-imaging observatory; the planet's scattering phase function, geometric albedo, single-scattering albedo, radius, and distance from Earth; and the semi-major axis distribution of EGPs. We assume cloud-free, homogeneous atmospheres and calculate phase functions for a given geometric or single-scattering albedo, assuming various scattering mechanisms. We find that the often-assumed Lambertian phase function can predict significantly larger fobs values with respect to the more physically motivated Rayleigh phase function. For observations made with WFIRST/AFTA's baseline coronagraphic capabilities (Cmin∼10−9, IWA∼0.2″), Jupiter-like planets orbiting stars within 10, 30, and 50 pc from Earth have volume-averaged (assuming a uniform distribution of stars) observability fractions of ∼12%, 3%, and 0.5%, respectively. Using a plausible estimate for the occurrence rate of EGPs, we find that, in all but the most optimistic configurations, the probability a blind search will lead to a detection is low (less than 5%). However, with orbital parameter constraints from long-term radial-velocity campaigns and Gaia astrometry, the tools we develop in this work can be used to determine both the most promising systems to target and when to observe them.

The Effectiveness of EXO & WFIRST's Star Shades & Coronagraph

True Masses of Radial-Velocity Exoplanets

Author:

Brown

Abstract:

We explore the science power of space telescopes used to estimate the true masses of known radial-velocity exoplanets by means of astrometry on direct images. We translate a desired mass accuracy (+/10% in our example) into a minimum goal for the signal-to-noise ratio, which implies a minimum exposure time. When the planet is near a node, the mass measurement becomes difficult if not impossible, because the apparent separation becomes decoupled from the inclination angle of the orbit. The combination of this nodal effect with considerations of solar and anti-solar pointing restrictions, photometric and obscurational completeness, and image blurring due to orbital motion, severely limits the observing opportunities, often to only brief intervals in a five-year mission. We compare the science power of four missions, two with external star shades, EXO-S and WFIRST-S, and two with internal coronagraphs, EXO-C and WFIRST-C. The star shades out-perform the coronagraph in this science program by about a factor of three. For both coronagraphs, the input catalog includes 16 RV planets, of which EXO-C could possibly observe 10, of which 6 would have a 90% guarantee of success. Of the same 16 planets, WFIRST-C could possibly observe 12, of which 9 are guaranteed. For both star-shade missions, the input catalog includes 55 planets, of which EXO-S could possibly observe 37, of which 20 are guaranteed. Of the same 55, WFIRST-S could possibly observe 45, of which 30 are guaranteed. The longer spectroscopic exposure times should be easily accommodated for the RV planets with guaranteed success.

Future NASA/NSF Exoplanet Hunting Missions

The last several years have made it clear we are living in a golden era of extrasolar planet studies. Less than 20 years ago, astronomers discovered the first planets orbiting Sun-like stars. Now, the number of exoplanets is in the thousands, including a growing number of “Earth-like” planets, a designation based on some combination of the planets’ mass, radius, and orbit around their stars. Just this past Friday, for example, astronomers reported detecting three planets between 1.5 and 2.4 times the radius of the Earth orbiting a single star, one of which lies in the star’s habitable zone, where liquid water could exist on its surface.

We don’t know, however, if these or other Earth-like planets are really like the Earth in the characteristics that really count: whether they have atmospheres like the Earth, oceans of liquid water like the Earth, and life like the Earth. Those determinations are largely beyond the capabilities of ground- and space-based observatories in operation today. A new generation—arguably, generations—of instruments and telescopes will be needed to determine just how Earth-like these Earth-like worlds really are. And the ability to develop those instruments will depend, at least in part, on the ability of exoplanet scientists to come into agreement on what’s needed to enable that next round of discoveries.

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Coronagraphic Exoplanet Imaging and Spectroscopy Using WFIRST

Scientific Return of Coronagraphic Exoplanet Imaging and Spectroscopy Using WFIRST

Author:

Burrows

Abstract:

In this study, we explore and review the scientific potential for exoplanet characterization by a high-contrast optical coronagraph on WFIRST/AFTA. We suggest that the heterogeneity in albedo spectra and planet/star flux ratios as a function of orbital distance, planet mass, and composition expected for the giant exoplanets at separations from their primaries accessible to WFIRST will provide unique constraints on giant planet atmospheres, evolution, aerosol and cloud properties, and general theory. Such exoplanets are not merely extrapolations of Jupiter and Saturn, but are likely to occupy a rich continuum of varied behaviors. Each in themselves and jointly, optical spectra, photometry, and polarization measurements of a diverse population of giant exoplanets in the solar neighborhood has the potential to reveal a multitude of fundamental features of their gas-giant chemistry, atmospheres, and formation. Such a campaign will enrich our understanding of this class of planets beyond what is possible with even a detailed exploration of the giants in our own solar system, and will compliment ongoing studies of exoplanets in the infrared and on close-in orbits inaccessible to coronagraphy.

Preparing for the WFIRST Microlensing Survey

NASA ExoPAG Study Analysis Group 11: Preparing for the WFIRST Microlensing Survey

Authors:

Yee et al

Abstract:

NASA's proposed WFIRST-AFTA mission will discover thousands of exoplanets with separations from the habitable zone out to unbound planets, using the technique of gravitational microlensing. The Study Analysis Group 11 of the NASA Exoplanet Program Analysis Group was convened to explore scientific programs that can be undertaken now, and in the years leading up to WFIRST's launch, in order to maximize the mission's scientific return and to reduce technical and scientific risk. This report presents those findings, which include suggested precursor Hubble Space Telescope observations, a ground-based, NIR microlensing survey, and other programs to develop and deepen community scientific expertise prior to the mission.

A new EMCCD for Space-based High Contrast Imaging Spectroscopy for WFIRST

Characterization of a photon counting EMCCD for space-based high contrast imaging spectroscopy of extrasolar planets

Authors:

Wilkins et al

Abstract:

We present the progress of characterization of a low-noise, photon counting Electron Multiplying Charged Coupled Device (EMCCD) operating in optical wavelengths and demonstrate possible solutions to the problems of Clock-Induced Charge (CIC) and other trapped charge through sub-bandgap illumination. Such a detector will be vital to the feasibility of future space-based direct imaging and spectroscopy missions for exoplanet characterization, and is scheduled to fly on-board the AFTA-WFIRST mission. The 512×512 EMCCD is an e2v detector housed and clocked by a N\"uv\"u Cameras controller. Through a multiplication gain register, this detector produces as many as 5000 electrons for a single, incident-photon-induced photoelectron produced in the detector, enabling single photon counting operation with read noise and dark current orders of magnitude below that of standard CCDs. With the extremely high contrasts (Earth-to-Sun flux ratio is ∼ 10−10) and extremely faint targets (an Earth analog would measure 28th - 30th magnitude or fainter), a photon-counting EMCCD is absolutely necessary to measure the signatures of habitability on an Earth-like exoplanet within the timescale of a mission's lifetime, and we discuss the concept of operations for an EMCCD making such measurements.