Constraining Composition, Clouds, and Hazes in a Long-Period Giant Planet

0 Assigned ID: 6003 ----- Attempting Submission 1 (Fri Nov 08 00:55:49 GMT 2024) ----- HST Phase I Proposal 6003 successfully submitted. Receipt: # 6003-1 ----- Attempting Submission 2 (Fri Nov 08 00:59:16 GMT 2024) ----- HST Phase I Proposal 6003 successfully submitted. Receipt: # 6003-2 ----- Attempting Submission 3 (Fri Nov 08 00:59:33 GMT 2024) ----- HST Phase I Proposal 6003 successfully submitted. Receipt: # 6003-3 Unschedulable Visit 0 ----- Attempting Submission 1 (Fri Jan 31 22:36:03 GMT 2025) ----- HST Phase II Proposal 17920 successfully submitted. Receipt: # 17920-1 ----- Attempting Submission 2 (Fri Feb 07 02:50:39 GMT 2025) ----- As requested by our PC, we are resubmitting the Phase II with an 8-orbit strategy rather than a 6-orbit strategy for STScI to schedule using external tools. Constraining Composition, Clouds, and Hazes in a Long-Period Giant Planet With TSM = 243, TOI-2134 c is by far the best known temperate (Teq < 400 K) planet for transmission spectroscopy with a precise mass constraint, largely because the host star is exceptionally bright (Ks = 6.1). We propose to measure the transmission spectrum of this uniquely important planet between 1.1-1.7 micron with WFC3/G141, where all available JWST observation modes would otherwise saturate. We expect that a WFC3/G141 spectrum of this planet will constrain the planet's NH3 abundance to a precision of 0.6 dex, providing unprecedented constraints on planet formation and evolution models. If the atmosphere of this temperate planet is cloudy, our data would instead provide the first constraints on water clouds in a planet or brown dwarf outside the Solar System. Finally, if the planetary atmosphere is hazy, this would be the coldest exoplanet for which hazes have been detected, allowing us an opportunity to bridge Solar System haze studies (e.g. in Titan) with the hazes detected in warmer exoplanets. Only WFC3/G141 can enable these exciting advances in exoplanet atmosphere studies, and it can do so in only 8 orbits. We will observe the transit of TOI-2134c, which lasts roughly 3.5 orbits. We require a full transit duration's worth of baseline, plus an extra orbit at the start of the visit to cover ramp effects, totaling 8 consecutive HST orbits to enable transmission spectroscopy of the target. We will use WFC3/G141 with a similar setup to dozens of exoplanet transit observations in the infrared with HST. We use the spatial scanning mode to extend exposure times, opting for the 512 subarray for improved observational efficiency on this bright source. Using PandExo, we identified the optimal sampling sequence and scan rate, choosing round-trip scans to improve efficiency. The resultant observtions are expected to hit the ~35 ppm noise floor (determined by Stevenson & Fowler) for WFC3/IR spectroscopic observations given the brightness of the host. We start each orbit sequence with a direct image for wavecal as is standard for WFC3/IR scan spectroscopy, and buffer with additional wavecal reads to ensure that there is a buffer dump exactly at the end of each orbit, maximizing observing efficiency. The remainder of the exposures in the orbit are science exposures. This strategy was adopted previously in GO 13501, which was a WFC3 spatial scan observation of another very bright source HD 97658. We adopt POS TARG X of -16.5 to roughly center the spectral trace on the detector (same setup as GO 15333 and GO 15255, both of which spatially scan for GRISM512 on similarly (very) bright sources), and POS TARG Y of -24 to capture the full spatially scanned trace on the detector in every image. Dr. Shreyas Vissapragada is an expert in the characterization of planetary dynamical and atmospheric evolution, and currently leads multiple large ground- and space-based (with HST) programs aimed at constraining planetary evolution. Dr. Nicole Wallack is an expert in transmission and emission spectroscopy, with wide-ranging expertise from Spitzer secondary eclipses to high-resolution ground-based brown dwarf work to JWST transmission spectroscopy of sub-Neptunes. Michael Greklek-McKeon has extensive experience in the characterization of transiting exoplanets with photometry and spectroscopy from ground and space-based telescopes, and expertise in modeling exoplanet orbital dynamics and tidal dissipation through numerical simulations. Julie Inglis is an expert in atmospheric characterization of giant planets, especially with JWST and groundbased high resolution spectroscopy, and led the spectroscopic detection of a cloud feature in HD 189733b's atmosphere using JWST/MIRI. Dr. Armen Tokadjian is a postdoc at the Jet Propulsion Laboratory and works on atmospheric modeling and retrievals of transmission and reflection spectra. He works on analyzing observed transmission data to constrain the chemical makeup and cloud/haze structures with Bayesian inverse retrieval methods, including applications to current HST and JWST data. He also has experience generating forward models of exoplanet atmospheres to simulate data and distinguish between different atmospheric scenarios and the key characteristics one can potentially observe in spectra. Dr. Renyu Hu is a scientist at the Jet Propulsion Laboratory and his research strives to identify and characterize habitable environments in the solar system and beyond. He has studied exoplanet atmospheres with the Hubble and JWST as PI and provided data and science analyses of many Hubble, Spitzer, and JWST programs. Complementary to his experience in observations, Dr. Hu is also an expert in atmospheric chemistry and radiative transfer modeling for exoplanets. Exoplanets and Exoplanet Formation 6 false false false false false false SUPPORTED STAR EXTRA-SOLAR PLANET EXTRA-SOLAR PLANETARY SYSTEM K III-I K V-IV NO This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. J2000 J2000 WFC3/IR Spectroscopic No No G141 1741297358900 /private/var/folders/q5/pgd2_mqs78b2rc6c4f68fd900005mw/T/OPVisit14601379662571125963.xml The scheduling data was generated by CASM 33.0. CASM was run in Phase II mode. WFC3 IR transit of TOI-2134c. We would like the transit to be scheduled with 8 continuous orbits, which is longer than the typical WFC3 IR spatial scan transit observation because of the unique nature of the target (an exceptionally long-period gas giant with a correspondingly long transit duration). 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