The Feasibility of Directly Imaging Nearby Cold Jovian Planets with MIRI/JWST

TL;DR

This study evaluates the potential of JWST's MIRI instrument to directly image nearby cold Jovian exoplanets around M-dwarfs, demonstrating feasible detection strategies and identifying optimal filters and targets.

Contribution

It provides the first detailed simulation-based assessment of JWST/MIRI's capability to detect cold Jovian planets around nearby M-dwarfs, highlighting optimal observational parameters.

Findings

Jupiter-like planets are detectable at 15.5μm around 14 stars in the sample.

Saturn-like planets are detectable at 10.65μm and 11.4μm within 3 parsecs.

Surveying 27 stars requires less than 170 hours of JWST time.

Abstract

The upcoming launch of the James Webb Space Telescope (JWST) will dramatically increase our understanding of exoplanets, particularly through direct imaging. Microlensing and radial velocity surveys indicate that some M-dwarfs host long period giant planets. Some of these planets will likely be just a few parsecs away and a few AU from their host stars, a parameter space that cannot be probed by existing high-contrast imagers. We studied whether the coronagraphs on the Mid-Infrared Instrument on JWST can detect Jovian-type planets around nearby M-dwarfs. For a sample of 27 very nearby M-dwarfs, we simulated a sample of Saturn--Jupiter-mass planets with three atmospheric configurations, three orbital separations, observed in three different filters. We found that the f1550c $15.5\mu$m filter is best suited for detecting Jupiter-like planets. Jupiter-like planets with patchy cloud cover, 2 AU from their star, are detectable at $15.5\mu$m around 14 stars in our sample, while Jupiters with clearer atmospheres are detectable around all stars in the sample. Saturns were most detectable at 10.65 and $11.4\mu$m (f1065c and f1140c filters), but only with cloud-free atmospheres and within 3 pc (6 stars). Surveying all 27 stars would take $<170$ hours of JWST integration time, or just a few hours for a shorter survey of the most favorable targets. There is one potentially detectable known planet in our sample -- GJ~832~b. Observations aimed at detecting this planet should occur in 2024--2026, when the planet is maximally separated from the star.