Direct Imaging of Extrasolar Planets – Bruce Macintosh, UCSC – 10/05/2022

This is a high-level research talk designed for professional astronomers. It is part of the Caltech Astronomy Colloquium Series, hour-long presentations given weekly by top scientists from around the world to the members of our department. All are welcome to watch these colloquium presentations; however, for talks specifically designed for the general public, please see our Caltech Astro Outreach channel: https://youtube.com/c/caltechastro. Timestamps and abstract are included below.

Date: 10/05/22
Speaker: Bruce Macintosh, UCO director, UCSC
Title: Direct Imaging of Extrasolar Planets

Abstract : Direct detection of extrasolar planets – spatially resolving a planet from its host star while blocking, moving, or post-processing the starlight – is a powerful complement to transit, RV, and microlensing approaches. Direct detection is sensitive to planets in wider orbit, and allows spectroscopic characterization of planetary atmosheres. One of the most effective instruments in this regime has been the Gemini Planet Imager (GPI). GPI was a facility instrument combining advanced adaptive optics, a diffraction-controlling coronagraph, and an infrared integral field spectrograph on the Gemini South Telescope. From 2014-2019 we carried out the Gemini Planet Imager Exoplanet Survey (GPIES), which observed 532 young (10-200 Myr) nearby stars. I will summarize the key results of the GPIES program, including constraints on giant-planet distributions and atmospheric properties. We have also extensively characterized GPI’s performance, leading to insights into next-generation systems. With current technology, direct imaging with GPI or other instruments is sensitive primarily to planets that are significantly younger than, more massive than, and in wider orbits than Jupiter, and such planets are rare. Moving beyond this will require new capabilities. The GPI 2.0 project upgrades the existing instrument with faster adaptive optics, better coronagraph designs, and new spectrograph modes.When deployed on Gemini North, GPI 2.0 will be able to search younger stars in the Taurus and Ophiucus star-forming regions, and be sensitive to Jupiter-like « cold start » planets. I will summarize the science drivers that guided the GPI 2.0 upgrade and the project’s status.

In the even longer run, direct imaging is the best path to characterizing true Earth analogs – planets orbiting in the habitable zone of sunlike stars, beyond the reach of practical transit spectroscopy. Such detection will require a dedicated space mission incorporating an advanced coronagraph. The recent Astro2020 Decadal Survey laid out a vision leading such a mission over the next decades. Finally, I will summarize the path forward for direct imaging leading to that possible Earth.

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