johnson_iya_review

johnson_iya_review - Draft version A Preprint typeset using...

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arXiv:0903.3059v1 [astro-ph.EP] 17 Mar 2009 Draft version August 20, 2009 Preprint typeset using L A T E X style emulateapj v. 10/09/06 INTERNATIONAL YEAR OF ASTRONOMY INVITED REVIEW ON EXOPLANETS John Asher Johnson 1 Draft version August 20, 2009 ABSTRACT Just fourteen years ago the Solar System represented the only known planetary system in the Galaxy, and conceptions of planet formation were shaped by this sample of one. Since then, 320 planets have been discovered orbiting 276 individual stars. This large and growing ensemble of exoplanets has informed theories of planet formation, placed the Solar System in a broader context, and revealed many surprises along the way. In this review I provide an overview of what has been learned from studies of the occurrence, orbits and physical structures of planets. After taking a look back at how far the field has advanced, I will discuss some of the future directions of exoplanetary science, with an eye toward the detection and characterization of Earth-like planets around other stars. Subject headings: 1. INTRODUCTION The state of knowledge on planetary systems has un- dergone a major revolution over the past 14 years. Start- ing with the discovery of the first exoplanet orbiting a normal, hydrogen-burning star in 1995 (Mayor & Queloz 1995), the sample of known exoplanets has rapidly ex- panded from a sample of one to 320 individual planets residing in 276 planetary systems 2 . The majority of these planets were detected by either Doppler techniques or by photometric transit surveys, and therefore have well- characterized orbits with system parameters amenable to uniform statistical analyses (Butler et al. 2006b; Torres et al. 2008). Additional planets have been dis- covered using gravitational microlensing and a handful of planets have even been directly imaged (Beaulieu et al. 2006; Gaudi et al. 2008; Kalas et al. 2008; Marois et al. 2008). The occurrence rates, orbital properties, and physical characteristics of these worlds inform our under- standing of the formation and orbital evolution of planets in general, and the origin of our Solar System in partic- ular. 2. PLANET OCCURRENCE The search for exoplanets began with a humble and ancient question: do planets exist around other stars. Hints initially emerged with the detection of Kuiper Belt- like dust disks around young stars such as Vega and β Pic (Aumann et al. 1984; Smith & Terrile 1984), the ra- dial velocity (RV) detection of progressively smaller sub- stellar companions (Latham et al. 1989), and the discov- ery of “pulsar planets” (Wolszczan & Frail 1992). Since then, the study of planet occurrence has evolved from a question of existence to a full-fledged statistical study of hundreds of systems. Where planets are found and their relative frequencies around stars of various types provide valuable insights into the planet formation process and guide future planet search efforts.
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