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Register a new userAstrometry and Exoplanet Characterization: Gaia and Its Pandoras Box
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Added by
Alessandro Sozzetti
Publication date
2012
fields
Physics
and research's language is
English
Authors
A. Sozzetti
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In its all-sky survey, Gaia will monitor astrometrically hundreds of thousands of main-sequence stars within $approx200$ pc, looking for the presence of giant planetary companions within a few AUs from their host stars. Indeed, Gaia observations will have great impact is the astrophysics of planetary systems (e.g., Casertano et al. 2008), in particular when seen as a complement to other techniques for planet detection and characterization (e.g., Sozzetti 2011). In this paper, I briefly address some of the relevant technical issues associated with the precise and accurate determination of astrometric orbits of planetary systems using Gaia data. I then highlight some of the important synergies between Gaia high-precision astrometry and other ongoing and planned, indirect and direct planet-finding and characterization programs, both from the ground and in space, and over a broad range of wavelengths, providing preliminary results related to one specific example of such synergies.
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The wealth of information in the Gaia catalogue of exoplanets will constitute a fundamental contribution to several hot topics of the astrophysics of planetary systems. I briefly review the potential impact of Gaia micro-arsec astrometry in several areas of exoplanet science, discuss what key follow-up observations might be required as a complement to Gaia data, and shed some light on the role of next generation astrometric facilities in the arena of planetary systems.
The power of micro-arcsecond ($mu$as) astrometry is about to be unleashed. ESAs Gaia mission, now headed towards the end of the first year of routine science operations, will soon fulfil its promise for revolutionary science in countless aspects of Galactic astronomy and astrophysics. The potential of Gaia position measurements for important contributions to the astrophysics of planetary systems is huge. We focus here on the expectations for detection and improved characterization of young planetary systems in the neighborhood of the Sun using a combination of Gaia $mu$as astrometry and direct imaging techniques.
Over 300 extrasolar planets (exoplanets) have been detected orbiting nearby stars. We now hope to conduct a census of all planets around nearby stars and to characterize their atmospheres and surfaces with spectroscopy. Rocky planets within their stars habitable zones have the highest priority, as these have the potential to harbor life. Our science goal is to find and characterize all nearby exoplanets; this requires that we measure the mass, orbit, and spectroscopic signature of each one at visible and infrared wavelengths. The techniques for doing this are at hand today. Within the decade we could answer long-standing questions about the evolution and nature of other planetary systems, and we could search for clues as to whether life exists elsewhere in our galactic neighborhood.
Gaia is an astrometric mission that will be launched in spring 2013. There are many scientific outcomes from this mission and as far as our Solar System is concerned, the satellite will be able to map thousands of main belt asteroids (MBAs) and near-Earth objects (NEOs) down to magnitude < 20. The high precision astrometry (0.3-5 mas of accuracy) will allow orbital improvement, mass determination, and a better accuracy in the prediction and ephemerides of potentially hazardous asteroids (PHAs). We give in this paper some simulation tests to analyse the impact of Gaia data on known asteroids orbit, and their value for the analysis of NEOs through the example of asteroid (99942) Apophis. We then present the need for a follow-up network for newly discovered asteroids by Gaia, insisting on the synergy of ground and space data for the orbital improvement.
The Pandoras Box Problem, originally formalized by Weitzman in 1979, models selection from set of random, alternative options, when evaluation is costly. This includes, for example, the problem of hiring a skilled worker, where only one hire can be made, but the evaluation of each candidate is an expensive procedure. Weitzman showed that the Pandoras Box Problem admits an elegant, simple solution, where the options are considered in decreasing order of reservation value,i.e., the value that reduces to zero the expected marginal gain for opening the box. We study for the first time this problem when order - or precedence - constraints are imposed between the boxes. We show that, despite the difficulty of defining reservation values for the boxes which take into account both in-depth and in-breath exploration of the various options, greedy optimal strategies exist and can be efficiently computed for tree-like order constraints. We also prove that finding approximately optimal adaptive search strategies is NP-hard when certain matroid constraints are used to further restrict the set of boxes which may be opened, or when the order constraints are given as reachability constraints on a DAG. We complement the above result by giving approximate adaptive search strategies based on a connection between optimal adaptive strategies and non-adaptive strategies with bounded adaptivity gap for a carefully relaxed version of the problem.
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