0 Assigned ID: 4895 ----- Attempting Submission 1 (Wed Sep 27 18:21:39 GMT 2023) ----- Version 3: Added a bunch of zeroes to POSTARG 802574658 ----- Attempting Submission 1 (Mon Oct 16 21:02:22 GMT 2023) ----- HST Phase II Proposal 17585 successfully submitted. Receipt: # 17585-1 ----- Attempting Submission 2 (Mon Oct 16 21:36:23 GMT 2023) ----- ----- Attempting Submission 3 (Wed Oct 18 01:01:26 GMT 2023) ----- Everything ran successfully The Discovery of a Fourth Low-Mass Planet in an Unusual Super-Puff System The Kepler-51 system consists of three known "super-puff" exoplanets - ultra-low density objects that challenge current theories of planet formation and evolution, with masses measured exclusively from transit timing variations (TTVs). The transmission spectra of Kepler-51b and d were observed with JWST to investigate their atmospheric composition and to search for high altitude hazes and/or planetary rings that may be responsible for their large observed radii. However, the JWST mid-transit time of Kepler-51d was discrepant from TTV predictions by 2 hours, compared to the prediction uncertainty of 2.7 minutes. In order to match the new observations, a fourth planet must be included in the TTV models, with the uncertainty in its mass and period greatly increasing the uncertainty on the masses of the three known planets and their future transit times. As a result, not only is it more difficult to interpret the JWST spectra, but we now run the risk of missing future transits of the Kepler-51 planets altogether. We therefore propose to observe the next transits of Kepler-51c and d in late Oct/early Nov 2023 with HST. Observing these two planets would provide the tightest constraints possible on the mass and period of the fourth planet and reduce the uncertainties on the masses and future transit times of the other three planets. These transits cannot be observed from the ground due to the faintness of the host star and the availability of large telescopes, nor can we wait for subsequent transits due to the increasing uncertainty of the transit time with time. With HST being the ideal space telescope for this observation and the timing of these transits, we request DD time. There are two transits observations, one each of Kepler-51c and Kepler-51d. PI Dr. Peter Gao is an atmospheric modeling expert who is the PI of the JWST Cycle 1 proposal to observe Kepler-51b. Co-PI Dr. Jessica Libby-Roberts has extensive experience with the Kepler-51 system and led the previous HST/WFC3 reduction and analysis of the Kepler-51 observations. She is also the PI of the JWST Cycle 1 proposal to observe Kepler-51d. Co-Is Dr. Kento Masuda and Dr. Shreyas Vissapragada are experts on transit timing variations. Dr. Masuda has extensive expertise specifically modeling the Kepler-51 system. Co-Is Dr. Zach Berta-Thompson, Dr. Guangwei Fu, Dr. Kevin Stevenson, and Dr. Aaron Bello-Arufe are experts on data reduction and analysis of HST and JWST observations. Co-Is Dr. Xi Zhang, Dr. Luis Welbanks, Dr. Renyu Hu and Dr. Yui Kawashima are experts in atmospheric modeling especially in regards to low-gravity exoplanets. Co-I Dr. Richard Freedman also specializes in gas opacities in exoplanet atmospheres. Co-I Dr. Leslie Hebb is an expert at modeling stellar activity and star spot crossing events. All Co-Is are members of either the JWST Cycle 1 proposal to observe Kepler-51b or Kepler-51d. Exoplanets and Exoplanet Formation 0 false SUPPORTED STAR EXTRA-SOLAR PLANETARY SYSTEM This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 J = 13.562, H = 13.291, K=13.197 WFC3/IR Spectroscopic No No G141 WFC3/IR Spectroscopic No No G141 /private/var/folders/5h/0btnb98970jgr8npn_k3ycjh0000gp/T/OPVisit7129329854225708386.xml The scheduling data was generated by CASM 31.1. CASM was run in Phase II mode. 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