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Geometry and time line for an L2 halo orbit. The L2 Lagrange point is on the Sun-Earth line of syzygy at about 0.01 AU (1.5 x 10 6 km) from the Earth. A halo orbit about this point is three dimensional, with coupled two-dimensional periodic motion in the ecliptic plane and independent periodic motion out of the ecliptic, thus describing a three-dimensional Lissajous figure. The amplitudes can be chosen such that the frequencies become equal and with appropriate phasing, the spacecraft will appear to be orbiting about the line of syzygy. The minimum in-plane amplitude must be of the order of 670,000 km, about 24° from the line of syzygy. The halo orbital period of 180 days is somewhat less than half the Earth's orbital period. Injection into a large-amplitude halo orbit requires a ∆V~50 m/s, far less than that needed for placement at L2 (~300 m/s). Orbital maintenance requires a ∆V~10 m/s/yr. Locations along the trajectory from Earth orbit are indicated in days.
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A point design for a mission to detect Earth-sized planets in the inner
orbits of solar-like stars is described. The observing technique is
based upon continuously and simultaneously monitoring 5000 solar-like
stars for brightness changes that would be caused by planets transiting
their star. Detection of periodic transits of the same amplitude and...
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Citations
... Suivra ensuite la mission Kepler (e.g. Borucki (2016) ou Borucki (2017)), imaginée dès 1996 par Borucki et al. (1996) et Koch et al. (1996), qui révolutionne le domaine avec 4600 candidats et plus de 1000 planètes confirmées. Une grande diversité, dépassant largement la taxonomie du système solaire, est mise à jour (Hatzes 2016;Lissauer et al. 2014a). ...
Les petites planètes, entre la taille de la Terre et celle de Neptune, présentent une grande diversité de compositions. Leur densité moyenne, obtenue en combinant la photométrie des transits avec la spectroscopie Doppler à haute précision, s'étend de mini-Neptunes peu denses aux super-Terres massives. À l'heure actuelle, on observe une transition continue entre les planètes rocheuses et gazeuses, et ces objets inconnus dans le système solaire défient les théories de formation planétaire. L'exploration de ces petites planètes est limitée actuellement par la précision atteinte sur leurs paramètres fondamentaux. Alors que plus d'une centaine de ces planètes ont été caractérisées à l'heure actuelle, il n'est possible de déterminer précisément la composition que d'une douzaine d'entre-elles. L'objectif de cette thèse est de contribuer à l'étude de la diversité des petits mondes autour d'étoiles solaires en combinant deux des plus puissants instruments pour la détection d'exoplanètes : le télescope spatial Kepler de la NASA dans le cadre de la mission K2 et le spectrographe HARPS de l'observatoire européen austral. Le premier objectif est l'exploitation et l'interprétation des données issues d'un large programme de deux ans sur HARPS, au sein d'un consortium européen, pour enrichir le nombre de petites planètes bien caractérisées, et faire le lien avec les scénarios de formation et d'évolution des corps planétaires. Cette thèse contribue aussi au suivi sol de la mission K2 avec le spectrographe SOPHIE à l'observatoire de Haute-Provence, et de la mission TESS avec HARPS. Au-delà de la précision des instruments, la limitation majeure dans l'identification des petits signaux planétaires est l'activité magnétique des étoiles. L'impact de ces bruits stellaires peut dans certains cas être dominant et il n'existe pour l'instant aucune méthode de correction parfaitement adaptée. Cette thèse s'intéresse modestement à ces aspects incontournables. En particulier, l'intérêt de contraintes additionnelles issues d'observations avec des techniques variées est explorée. C'est le cas notamment de la spectropolarimétrie qui permet un suivi de l'évolution du champ magnétique, responsable des modulations observées en vitesse radiale.
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Photometry with the transit method has arguably been the most successful exoplanet discovery method to date. A short overview about the rise of that method to its present status is given. The method's strength is the rich set of parameters that can be obtained from transiting planets, in particular in combination with radial velocity observations; the basic principles of these parameters are given. The method has however also drawbacks, which are the low probability that transits appear in randomly oriented planet systems, and the presence of astrophysical phenomena that may mimic transits and give rise to false detection positives. In the second part we outline the main factors that determine the design of transit surveys, such as the size of the survey sample, the temporal coverage, the detection precision, the sample brightness and the methods to extract transit events from observed light curves. Lastly, an overview over past, current and future transit surveys is given. For these surveys we indicate their basic instrument configuration and their planet catch, including the ranges of planet sizes and stellar magnitudes that were encountered. Current and future transit detection experiments concentrate primarily on bright or special targets, and we expect that the transit method remains a principal driver of exoplanet science, through new discoveries to be made and through the development of new generations of instruments.
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... A similar US space mission, Kepler (Borucki et al. 1997), which evolved from an earlier proposal FRESIP (Koch et al. 1996), was unsuccessful in its bid for selection as part of NASA's Discovery Program. With a 1-m aperture and 12 • field of view, Kepler would have continuously monitored some 80 000 main-sequence stars brighter than 14 mag in a specific sky area, at a photometric precision of 10 −5 . ...
The discovery of the first extra-solar planet surrounding a main-sequence star was announced in 1995, based on very precise radial velocity (Doppler) measurements. A total of 34 such planets were known by the end of March 2000, and their numbers are growing steadily. The newly discovered systems confirm some of the features predicted by standard theories of star and planet formation, but systems with massive planets, having very small orbital radii and large eccentricities, are common and were generally unexpected.
Other techniques being used to search for planetary signatures include accurate measurement of positional (astrometric) displacements, gravitational microlensing and pulsar timing, the latter resulting in the detection of the first planetary mass bodies beyond our solar system in 1992. The transit of a planet across the face of the host star provides significant physical diagnostics, and the first such detection was announced in 1999. Protoplanetary disks, which represent an important evolutionary stage for understanding planet formation, are being imaged from space. In contrast, direct imaging of extra-solar planets represents an enormous challenge. Long-term efforts are directed towards infrared space interferometry, the detection of Earth-mass planets, and measurement of their spectral characteristics.
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FRESIP (FRequency of Earth-Sized Inner Planets) is a mission designed to detect and characterize Earth-sizes planets around solar-like stars. The sizes of the planets are determined from the decrease in light from a star that occurs during planetary transits, while the orbital period is determined from the repeatability of the transits. Measurements of these parameters can be compared to theories that predict the spacing of planets, their distribution of size with orbital distance, and the variation of these quantities with stellar type and multiplicity. Because thousands of stars must be continually monitored to detect the transits, much information on the stars can be obtained on their rotation rates and activity cycles. Observations of p-mode oscillations also provide information on their age and composition. These goals are accomplished by continuously and simultaneously monitoring 500 solar-like stars for evidence of brightness changes caused by Earth-sized or larger planetary transits. To obtain the high precision needed to find planets as small as the Earth and Venus around solar-like stars, a wide field of view Schmidt telescope with an array of CCD detectors at its focal plane must be located outside of the Earth's at mosphere. SMM (Solar Maximum Mission) observations of the low-level variability of the Sun (1:100,000) on the time scales of a transit (4 to 16 hours), and our laboratory measurements of the photometric precision of charge-coupled devices (1:100,000) show that the detection of planets as small as the Earth is practical. The probability for detecting transits is quite favorable for planets in inner orbits. If other planetary systems are similar to our own, then approximately 1% of those systems will show transits resulting in the discovery of 50 planetary systems in or near the habitable zone of solar-like stars.
We compute the detection probability of satellites of extrasolar planets with the method of transits, under the assumption that the duration of the observations is at least as long as the planet orbital period. We separate the cases when the parent planet does and does not also transit over the star. The possible satellites are assumed to have orbital radii between the Roche limit and the Hill radius. We find that if a satellite is extended enough to produce a detectable drop in the stellar lightcurve, the probability to detect it when the planet also transits over the star is nearly unity. If the planet does not transit, the probability to detect a Jupiter-like or terrestrial satellite is modest, but it can be comparable to that of detecting a planet if the satellite orbital radius is large. If a satellite is not extended enough to produce a detectable drop in the stellar lightcurve during a transit, it might still be detected through the time shift of planetary transits resulting from the rotation of the planet around the barycenter of the planet-satellite system.
The Astrobiology Space Infrared Explorer (ASPIRE) is a Probe-class mission concept developed as part of NASA's Astrophysics Strategic Mission Concept studies. ASPIRE uses infrared spectroscopy to explore the identity, abundance, and distribution of molecules, particularly those of astrobiological importance throughout the Universe. ASPIRE's observational program is focused on investigating the evolution of ices and organics in all phases of the lifecycle of carbon in the universe, from stellar birth through stellar death while also addressing the role of silicates and gas-phase materials in interstellar organic chemistry. ASPIRE achieves these goals using a Spitzer-derived, cryogenically-cooled, 1-m-class telescope in an Earth drift-away heliocentric orbit, armed with a suite of infrared spectrometers operating in the 2.5-36 micron wavelength region supported by a Kepler-based spacecraft bus. This paper summarizes the results of the ASPIRE Origins Probe Mission Concept Study while focusing on its high heritage mission implementation.
The space mission COROT can be considered as a DARWIN/TPF precursor, since it will contribute to the pre-DARWIN/TPF effort with its dedicated exoplanet program. COROT will survey more than 50 thousands stars, each one during five months, in order to detect transits of planets. Despite of the modest size of the telescope, the photon-noise limited performances may lead to the detection of several tens of "hot jupiters" and, more important, of a few planets of the Earth-Uranus class, i.e. with a size of typically 1.5 to 4 Earth radius. In the basic mode of operation (characterization of a planet by at least 3 detected transits), only planets with a short orbital period, and thus rather "hot" ones (T = 600K), should be discovered. However, one of the COROTs features is its capability to provide a wavelength dependent information, thanks to a prism in the optical path.
With the detection of giant extrasolar planets and the quest for life on Mars, there is heightened interest in finding earth-class planets, those that are less than ten earth masses and might be life supporting. A space-based photometer has the ability to detect the periodic transits of earth-class planets for a wide variety of spectral types of stars. From the data and known type of host star, the orbital semi-major axis, size and characteristic temperature of each planet can be calculated. The frequency of planet formation with respect to spectral type and occurrence for both singular and multiple-stellar systems can be determined. A description is presented of a one-meter aperture photometer with a twelve-degree field of view and a focal plane of 21 CCDs. The photometer would continuously and simultaneously monitor 160,000 stars of visual magnitude <14. Its one-sigma system sensitivity for a transit of a twelfth magnitude solar-like star by a planet of one-earth radius would be one part in 50,000. It is anticipated that about 480 earth-class planets (0.5<M<10 M ⊕) would be detected along with 140 giant planets in transit and 1400 giant planets by reflected light. Densities could be derived for about seven cases where the planet is seen in transit and radial velocities are measurable.
