Characterization of directly imaged exoplanets at their youngest ages

Using ESO’s VLT adaptive optics instruments SPHERE and NaCo, we are conducting surveys to pursue the discovery and characterization of extrasolar planets through  direct imaging and direct spectroscopy at the youngest possible  ages, as the possible formation mechanisms core accretion and gravitational instability are only well distinguishable up to an age of about 10 Million years.

The Direct Imaging technique is complementary to the other search methods for extrasolar planets as it provides us with information on the mid to outer separation regions of very young planetary systems, as planets being still in their formation process are self-luminous because of their ongoing contraction as source of potential or gravitational energy. While currently only gas giant planets of more than 1 Jupiter mass can be directly imaged in other planetary systems, we know from the investigation of the Solar system that Jupiter plays an important role for the protection of Earth from a larger number of impacting bodies and recent direct imaging candidates are interesting themselves as they are found at partly much larger separations than previously expected.

In the last decade several dedicated direct imaging instruments, e.g. at VLT, Gemini, Subaru, LBT, … were built for the purpose of finding and characterizing planets in such young systems. About 5 years ago the observations of the Guaranteed Time Survey (GTO) program SHINE has begun on the VLT to search mainly for planets and disks around 5 — few hundred Myr old stars closer than 100 pc. We propose to continue our complementary search for very young planets, mostly younger than 5 Myr, whose host stars can almost solely be found at distances > 100 pc. We are thus able to cover the full theoretically predicted formation zone of gravitational instability formed planets. Comparing these two surveys, we want to learn about the dominant formation mechanism of planets as well as about dynamical interactions in the systems at very young ages, possibly even expelling planets within their evolution.

The proposed project is split into several parts. While we are surveying young associations for new planet candidates, we are also interested in characterization methods and all kinds of accretion signatures. Utilizing near-IR spectroscopy from SINFONI and SPHERE and the advantage of spatially resolving the photons of the host star and the planet, we can discern age-dependent properties, such as temperature, surface gravity, radius and mass as well as extinction, abundances, and atmospheric chemistry. Recent results in these disciplines suggest exoplanetary atmospheres to be even more diverse than previously expected.

Our analysis of known and yet unknown planetary candidates can thus further improve on three of the four core aspects of the SPP 1992, namely detection and formation of planetary systems, plus the understanding of exoplanet properties and diversity in terms of atmospheres.