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PLATO: A New ESA Planet Hunter Concept

Looking through the list of candidate missions selected by the European Space Agency recently, my attention was immediately drawn to PLATO, a planet-finder spacecraft designed to study transiting exoplanets and to measure the seismic oscillations of the stars they orbit. Although at first reminiscent of COROT, PLATO (Planetary Transits and Oscillations of Stars) is really more like an enhanced version of NASA’s upcoming Kepler mission, as I’m reminded by Centauri Dreams regular Vincenzo Liguori, who passed along helpful background information.

One immediate difference turns out to be field-of-view, which in PLATO is wide indeed due to the observation strategy involved. Unlike COROT or Kepler, PLATO would put photometric techniques to work in the study of relatively bright stars — 100,000 of these, with another 400,000 studied down to 14th magnitude. The earlier mission concepts are aimed at surveying fainter and more distant stars in a smaller field.

Note the significance of this: If COROT or Kepler identifies interesting planets around much fainter stars, follow-up studies — in particular direct imaging and spectroscopic investigation — become much more difficult than they would be with PLATO’s brighter targets. This mission description from LESIA (Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique) further explains the difference:

Moreover, for this sample of 100,000 stars, similar in size as that of Kepler, PLATO will reach a noise level at least three times lower than the average level of noise of Kepler, and will therefore allow us to detect smaller planets in front of cool dwarf stars, or terrestrial planets in front of hotter and larger stars, thus significantly extending our knowledge of the statistics of exoplanetary systems.

In addition, PLATO is designed to detect terrestrial planets in the habitable zone down to about mV = 14, a performance very similar to that of Kepler. Due to the larger size of the surveyed field, PLATO will monitor about 400,000 stars down to this magnitude, extending by approximately a factor of four the sample of detected planetary systems over Kepler.

Staring concept for PLATO

And two concepts for the satellite are in play. The first involves 100 small, wide-field telescopes mounted on a single platform, all of these looking at the same field with its own set of 24 CCDs. This so-called ‘staring’ concept involves a first phase in which the same field is studied continuously for several years. The second, the ‘spinning’ concept, uses three identical instruments pointing 120 degrees from one another, in the words of LESIA ‘sweeping out a great circle on the sky perpendicular to the spin axis.’ Both designs assume insertion into an L2 orbit by a Soyuz-Fregat launcher.

Images: Above: One configuration for PLATO, the so-called ‘staring’ concept. Below: The ‘spinning’ concept. Credit: LESIA.

It will be interesting to see how this mission evolves, especially since PLATO should be able to observe smaller exoplanets than could be detected by the two earlier missions. Moreover, since the stars it studies will be three magnitudes brighter, spectroscopy and astroseismology follow-up studies as well should be correspondingly more precise. Tying in PLATO’s findings with subsequent James Webb Space Telescope data could help pin down exoplanet atmosphere information.

Spinning concept for PLATO

You’ll find the complete PLATO proposal here. ESA’s other proposed missions give us much else to think about, including two proposals for a dark energy mission, the Marco Polo asteroid return mission, and new mission concepts for Jupiter and Saturn. The candidates undergo an assessment period that should end with two missions emerging as the winners, their proposed launches in 2017 and 2018 respectively. Need I point out how much depends upon budgetary considerations in making these choices and deciding if and when they fly?

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  • ljk November 28, 2007, 1:17

    Observational Window Functions in Planet Transit Searches

    Authors: Kaspar von Braun, David R. Ciardi (Caltech)

    (Submitted on 27 Nov 2007)

    Abstract: Window functions describe, as a function of orbital period, the probability that an existing planetary transit is detectable in one’s data for a given observing strategy. We show the dependence of this probability upon several strategy and astrophysical parameters, such as length of observing run, observing cadence, length of night, and transit duration. The ability to detect a transit is directly related to the intrinsic noise of the observations.

    In our simulations of the window function, we explicitly address non-correlated (gaussian or white) noise and correlated (red) noise and discuss how these two different noise components affect window functions in different manners.

    Comments: 8 pages, 6 figures; to appear in the Proceedings of the 249th IAU Meeting: “Exoplanets: Detection, Formation and Dynamics” (Suzhou, China)

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0711.4256v1 [astro-ph]

    Submission history

    From: Kaspar von Braun [view email]

    [v1] Tue, 27 Nov 2007 01:58:23 GMT (163kb)


  • ljk December 19, 2007, 12:49

    Adaptive Scheduling Algorithms for Planet Searches

    Authors: Eric B. Ford (U Florida)

    (Submitted on 30 Dec 2004 (v1), last revised 17 Dec 2007 (this version, v2))

    Abstract: High-precision radial velocity planet searches have surveyed over ~2000 nearby stars and detected over ~200 planets. While these same stars likely harbor many additional planets, they will become increasingly challenging to detect, as they tend to have relatively small masses and/or relatively long orbital periods. Therefore, observers are increasing the precision of their observations, continuing to monitor stars over decade timescales, and also preparing to survey thousands more stars. Given the considerable amounts of telescope time required for such observing programs, it is important use the available resources as efficiently as possible.

    Previous studies have found that a wide range of predetermined scheduling algorithms result in planet searches with similar sensitivities. We have developed adaptive scheduling algorithms which have a solid basis in Bayesian inference and information theory and also are computationally feasible for modern planet searches. We have performed Monte Carlo simulations of plausible planet searches to test the power of adaptive scheduling algorithms.

    Our simulations demonstrate that planet searches performed with adaptive scheduling algorithms can simultaneously detect more planets, detect less massive planets, and measure orbital parameters more accurately than comparable surveys using a non-adaptive scheduling algorithm. We expect that these techniques will be particularly valuable for the N2K radial velocity planet search for short-period planets as well as future astrometric planet searches with the Space Interferometry Mission which aim to detect terrestrial mass planets.

    Comments: 20 pages, 6 figures, accepted to AJ

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:astro-ph/0412703v2

    Submission history

    From: Eric B. Ford [view email]

    [v1] Thu, 30 Dec 2004 22:48:15 GMT (38kb)

    [v2] Mon, 17 Dec 2007 21:07:55 GMT (43kb)


  • ljk January 16, 2008, 1:46

    ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) – A possible expert-system based cooperative effort to hunt for planets of Earth mass and below

    Authors: M. Dominik, K. Horne, A. Allan, N.J. Rattenbury, Y. Tsapras, C. Snodgrass, M.F. Bode, M.J. Burgdorf, S.N. Fraser, E. Kerins, C.J. Mottram, I.A. Steele, R.A. Street, P.J. Wheatley, L. Wyrzykowski

    (Submitted on 14 Jan 2008)

    Abstract: (abridged) The technique of gravitational microlensing is currently unique in its ability to provide a sample of terrestrial exoplanets around both Galactic disk and bulge stars, allowing to measure their abundance and determine their distribution with respect to mass and orbital separation. In order to achieve these goals in reasonable time, a well-coordinated effort involving a network of either 2m or 4 x 1m telescopes at each site is required. It could lead to the first detection of an Earth-mass planet outside the Solar system, and even planets less massive than Earth could be discovered.

    From April 2008, ARTEMiS (Automated Robotic Terrestrial Exoplanet Microlensing Search) is planned to provide a platform for a three-step strategy of survey, follow-up, and anomaly monitoring. As an expert system embedded in eSTAR (e-Science Telescopes for Astronomical Research), ARTEMiS will give advice on the optimal targets to be observed at any given time, and will also alert on deviations from ordinary microlensing light curves by means of the SIGNALMEN anomaly detector. While the use of the VOEvent (Virtual Observatory Event) protocol allows a direct interaction with the telescopes that are part of the HTN (Heterogeneous Telescope Networks) consortium, additional interfaces provide means of communication with all existing microlensing campaigns that rely on human observers.

    The success of discovering a planet by microlensing critically depends on the availability of a telescope in a suitable location at the right time, which can mean within 10 min. Real-time modelling offers the opportunity of live discovery of extra-solar planets, thereby providing ”Science live to your home”.

    Comments: 4 pages with 2 eps figures embedded. Accepted for publication in Astronomische Nachrichten as part of the Proceedings of the Joint VOEvent & HTN Workshop “Hot-wiring the Transient Universe” held in Tucson, Arizona (US), June 4-7 2007

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0801.2162v1 [astro-ph]

    Submission history

    From: Martin Dominik [view email]

    [v1] Mon, 14 Jan 2008 23:54:58 GMT (340kb)


  • ljk January 18, 2008, 12:47

    Characterizing the Orbital Eccentricities of Transiting Extrasolar Planets with Photometric Observations

    Authors: Eric B. Ford, Samuel N. Quinn, Dimitri Veras

    (Submitted on 17 Jan 2008)

    Abstract: The discovery of over 200 extrasolar planets with the radial velocity (RV) technique has revealed that many giant planets have large eccentricities, in striking contrast with most of the planets in the solar system and prior theories of planet formation.

    The realization that many giant planets have large eccentricities raises a fundamental question: “Do terrestrial-size planets of other stars typically have significantly eccentric orbits or nearly circular orbits like the Earth?”

    Here, we demonstrate that photometric observations of transiting planets could be used to characterize the orbital eccentricities for individual transiting planets, as well the eccentricity distribution for various populations of transiting planets (e.g., those with a certain range of orbital periods or physical sizes). Such characterizations can provide valuable constraints on theories for the excitation of eccentricities and tidal dissipation. We outline the future prospects of the technique given the exciting prospects for future transit searches, such as those to be carried out by the CoRoT and Kepler missions.

    Comments: 29 pages, 9 figures, submitted to ApJ

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0801.2591v1 [astro-ph]

    Submission history

    From: Eric B. Ford [view email]

    [v1] Thu, 17 Jan 2008 17:06:16 GMT (209kb)


  • ljk February 4, 2008, 9:36




    Dear colleagues,

    here two wonderful initiatives!

    1) I have the pleasure of mailing You here enclosed the statement edit by Angelo Angeletti, about XO-2b transit happened on 24th January last where You can find light curves obtained in Italy using different instrumentations, from an 80mm apochromatic refractor to a 500mm RC reflecting telescope equipped both with classic CCD and with simple digital CMOS camera. We beg You to look over this very interesting document!

    We sincerely wish this report can induce a great number of astronomy lovers – also from other European Countries – to attemp shooting XO-2b transit on 6th, 14th and 27th February next!
    LET’S TRY!!



    FROM 10:00 p.m. TO 02:00 a.m.

    While preparing the great event that will happen on 27th February 2008,
    on 6th February next, the Centro Astronomico di Libbiano –

    “AAAV – Associazione Astrofili Alta Valdera di Peccioli” (http://www.astrofilialtavaldera.com/obs/Osservatorio.html) will broadcast XO-2b transit live from the web site: http://www.coelum.com.

    During this night, all procedures indispensable to get images of the star field where XO-2b planetary system is located will be applied.

    This observation will also have a didactic purpose: anyone having doubts or problems about using software TRel, about images calibration procedures or about correct exposure time, will be possible to ask relative questions to the qualified member of “Centro Astronomico di Libbiano”, by live – chat (also available in English language for foreign users).


    Rodolfo Calanca, Angelo Angeletti, Fabiano Barabucci, Francesco Barabucci, Gianclaudio Ciampechini, Alberto Villa, Paolo Bacci, Enzo Rossi and all the italian Team members wish you a nice observation!



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