Imaging Extrasolar Giant Planets

High-contrast adaptive optics (AO) imaging is a powerful technique to probe the architectures of planetary systems from the outside-in and survey the atmospheres of self-luminous giant planets. Direct imaging has rapidly matured over the past decade and especially the last few years with the advent of high-order AO systems, dedicated planet-finding instruments with specialized coronagraphs, and innovative observing and post-processing strategies to suppress speckle noise. This review summarizes recent progress in high-contrast imaging with particular emphasis on observational results, discoveries near and below the deuterium-burning limit, and a practical overview of large-scale surveys and dedicated instruments. I conclude with a statistical meta-analysis of deep imaging surveys in the literature. Based on observations of 384 unique and single young (approximate to 5-300 Myr) stars spanning stellar masses between 0.1 and 3.0 M-circle dot, the overall occurrence rate of 5-13 M-Jup companions at orbital distances of 30-300 au is 0.6(-0.5)(+0.7)% assuming hot-start evolutionary models. The most massive giant planets regularly accessible to direct imaging are about as rare as hot Jupiters are around Sun-like stars. Dividing this sample into individual stellar mass bins does not reveal any statistically significant trend in planet frequency with host mass: giant planets are found around 2.8(-2.3)(+3.7)% of BA stars, < 4.1% of FGK stars, and < 3.9% of M dwarfs. Looking forward, extreme AO systems and the next generation of ground-and space-based telescopes with smaller inner working angles and deeper detection limits will increase the pace of discovery to ultimately map the demographics, composition, evolution, and origin of planets spanning a broad range of masses and ages.