New Worlds Observer Mission Design

Glassman, Tiffany; Lo, Amy; Lillie, Chuck; Kroening, Keith

doi:10.2514/6.2007-6221

Cited by 5 publications

(6 citation statements)

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“…A starshade spacecraft that could accommodate ∼70 retargets with an average of 40 • between targets may only have ∼50 retargeting maneuvers if the average distance between targets was 90 • . It would take the starshade > 3 weeks on average (Glassman et al 2007) to move between targets. With the Sun-exclusion constraint, only 18% of the sky is observable at any given time, so the issue of target availability will greatly increase the difficulty of follow-up measurements.…”

Section: Assumptions For the Jwst Plus Starshade External Occulter MImentioning

confidence: 99%

“…In §7 we investigate how effectively the JWST plus starshade external occulter can measure the orbits of the planets it detects. A minimum of four detections are needed to determine an orbit (Shao et al 2010;Glassman et al 2007). After detecting the planet once, the instrument is required to detect the planet at three additional positions in its orbit, to confirm that the planet is in the habitable zone.…”

Section: Introductionmentioning

confidence: 99%

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Exo-Earth/Super-Earth Yield of JWST Plus a Starshade External Occulter

Catanzarite

Shao

2011

Publications of the Astronomical Society of the Pacific

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ABSTRACT. We estimate the exo-Earth/super-Earth yield of an imaging mission that combines the James Webb Space Telescope (JWST) with a starshade external occulter under a realistic set of astrophysical assumptions. For the purpose of this study, we define "exo-Earth" and "super-Earth" as a planet of mass 1 to 2 M ⊕ and 2 to 10 M ⊕ , respectively, orbiting within the habitable zone (HZ) of a solar-type star. We show that for a survey strategy that relies on a single image as the basis for detection, roughly half of all exo-Earth/super-Earth detections will be false alarms for η ⊕ of 0.1, 0.2, and 0.3. Here, a false alarm is a mistaken identification of a planet as an exo-Earth/superEarth, and we define η ⊕ as the frequency of exo-Earth/super-Earths orbiting sunlike stars. We then consider two different survey strategies designed to mitigate the false alarm problem. The first is to require that for each candidate exo-Earth/super-Earth, a sufficient number of detections are made to measure the orbit. When the orbit is known we can determine if the planet is in the habitable zone. With this strategy, we find that the number of exo-Earth/superEarths found is, on average, 0.9, 1.9, and 2.7 for η ⊕ ¼ 0:1, 0.2, and 0.3. There is a ∼40% probability of finding zero exo-Earth/super-Earths for η ⊕ ¼ 0:1. A second strategy can be employed if a space-based astrometry mission capable of submicroarcsecond precision has identified and measured the orbits and masses of the planets orbiting nearby stars. In this case, the occulter mission is much more efficient, because it surveys only the stars known to have exo-Earth/super-Earths. We find that with prior knowledge from a space-based astrometric survey of 60 nearby stars, JWST plus an external occulter can obtain spectra, as well as orbital solutions, for the majority (70% to 80%) of the exo-Earth/super-Earths orbiting these 60 stars. The yield of exo-Earth/super-Earths is approximately five times higher than the yield for the JWST plus occulter mission without prior astrometric information. With prior space-based astrometry, the probability that an imaging mission will find zero exo-Earth/super-Earths is reduced to <1% for the case of η ⊕ ¼ 0:1.

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Section: Assumptions For the Jwst Plus Starshade External Occulter MImentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exo-Earth/Super-Earth Yield of JWST Plus a Starshade External Occulter

Catanzarite

Shao

2011

Publications of the Astronomical Society of the Pacific

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“…External occulters use a large (∼50 m) star shade at a long distance (tens of thousands of km) in front of a telescope to block the starlight. The preliminary designs of occulter missions allow 120-130 observations over five years (Glassman et al 2007;Lindler 2007). The limited number of visits is not sufficient, without a prior astrometric mission, to obtain orbits of more than a few candidate exoEarths (Savransky et al 2010).…”

Section: Planetary Orbit Determination From Imaging Alonementioning

confidence: 99%

“…In principle, three images of one planet at 3 different epochs are sufficient to determine an orbit. But since we can't use photometry to assign a dot in an image to a specific planet, a fourth detection of the planet is needed to ensure that all 4 observations were of the same planet (Glassman et al 2007). If the planet is observable only over 20% of the orbit, getting an orbit re-quires, on average, 20 images.…”

Section: Planetary Orbit Determination From Imaging Alonementioning

confidence: 99%

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The Synergy of Direct Imaging and Astrometry for Orbit Determination of Exo-Earths

Shao

Catanzarite

Pan

2010

ApJ

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The holy grail of exoplanet searches is an exo-Earth, an Earth mass planet in the habitable zone (HZ) around a nearby star. Mass is one of the most important characteristics of a planet and can only be measured by observing the motion of the star around the planet-star center of gravity. The planet's orbit can be measured either by imaging the planet at multiple epochs or by measuring the position of the star at multiple epochs by space-based astrometry. The measurement of an exoplanet's orbit by direct imaging is complicated by a number of factors. One is the inner working angle (IWA). A space coronagraph or interferometer imaging an exo-Earth can separate the light from the planet from the light from the star only when the star-planet separation is larger than the IWA. Second, the apparent brightness of a planet depends on the orbital phase. A single image of a planet cannot tell us whether the planet is in the HZ or distinguish whether it is an exo-Earth or a Neptune-mass planet. Third is the confusion that may arise from the presence of multiple planets. With two images of a multiple planet system, it is not possible to assign a dot to a planet based only on the photometry and color of the planet. Finally, the planet-star contrast must exceed a certain minimum value in order for the planet to be detected. The planet may be unobservable even when it is outside the IWA, such as when the bright side of the planet is facing away from us in a "crescent" phase. In this paper we address the question: "Can a prior astrometric mission that can identify which stars have Earth-like planets significantly improve the science yield of a mission to image exoEarths?" In the case of the Occulting Ozone Observatory, a small external occulter mission that cannot measure spectra, we find that the occulter mission could confirm the orbits of ∼4 to ∼5 times as many exo-Earths if an astrometric mission preceded it to identify which stars had such planets. In the case of an internal coronagraph we find that a survey of the nearest ∼60 stars could be done with a telescope half the size if an astrometric mission had first identified the presence of Earth-like planets in the HZ and measured their orbital parameters.

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