A Punctured Pufferfish: Atmospheric Escape from a Neptune-mass Planet Inflated to the Size of Jupiter

Version 1 just to be sure we have something in. -1423685945 Assigned ID: 6295 ----- Attempting Submission 1 (Wed Apr 09 22:01:28 GMT 2025) ----- STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME ORBIT PLANNER SERVER INTERNAL ERROR STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME Submission #1: only warnings are regarding heavy data volume for each visit, and the bright object protection tool which assumes an O-type star instead of K-type like the target. This makes use of settings drawn from the previous G230L observation of the target so I believe it should be fine? Submission #2: Changed the actual duration of Exposure 2 in Visit 5 from 1719 seconds to 1650 seconds to ease scheduling. Changed the aperture for all exposures from 52x0.2 to 52x2 to minimize systematic errors from slit losses, a change discussed with Program Coordinator and Contact Scientist. Ran all tools and it looks like a new warning was introduced for all visits where the last 3 orbits of each visit now have 25 seconds of Orbital Visibility Overrun. I am leaving the exposure times unchanged for now unless advised to alter them. Submission #3: Updated ETC calculation to use new 52x2 aperture, lowered BUFFERTIME to 200 sec as per new ETC calculation, and redid all exposure times to prevent orbital visibility overrruns. Now there is an unexplained error for Visit 1 that seems related to some parameter for the PHASE constraint being NIL, but I cannot identify what field is throwing this error since the PHASE requirements for the first 2 exposures of visit 1 is populated similarly to all the other visits. The warnings for too many buffer dumps remain unchanged. Submission #4: Corrected target's category from EXT-STAR to STAR G V-IV -1371861218 ----- Attempting Submission 1 (Wed Jul 30 20:08:32 GMT 2025) ----- ----- Attempting Submission 2 (Fri Dec 05 20:28:31 GMT 2025) ----- ----- Attempting Submission 3 (Mon Feb 16 22:57:36 GMT 2026) ----- HST Phase II Proposal 18121 successfully submitted. Receipt: # 18121-3 ----- Attempting Submission 4 (Tue Feb 17 02:17:11 GMT 2026) ----- I have adjusted the BUFFERTIME to 200 sec, changed exposure times to avoid visibility overruns, and have justified the buffer dumps to the Contact Scientist. A Punctured Pufferfish: Atmospheric Escape from a Neptune-mass Planet Inflated to the Size of Jupiter We propose to observe 5 transits of HIP 67522 b, a Neptune-mass planet inflated to Jupiter's size orbiting a 17 Myr old solar analog, in the near ultraviolet to measure its mass loss rate, outflow velocity, and exospheric structure. HIP 67522 b is a planet where we can precisely measure transit depths with both Hubble and JWST and study a planet's atmosphere as a structure in its entirety instead of piecemeal. In fact, JWST has already measured this planet's infrared transmission spectrum. The goal is to use the metallicity constraint from JWST in tandem with HST near-ultraviolet transits to measure the rate of Fe+ and Mg+ mass-loss for HIP 67522 b, construct the most complete map of a young planet's escaping atmosphere thus far, and thereby anchor the initial stages of sub-Jovian-mass planet evolution. We will observe five transits of HIP 67522 b using the STIS/G230L instrument/grating centered at 2376 Angstroms. This near ultraviolet wavelength range will span transitions of Fe I, Fe II, and Mg II, enabling us to search for atsmopheric escape in these metal lines. We will observe the five transits with five visits of five orbits each, spaced out in phase to encompass a potentially extended ingress/egress and to account for the 20 minute transit timing variation amplitude induced by the outer planet HIP 67522 c. Each visit will start with a target acquisition exposure using the F28X50OII filter for 1 second, a setting which was previously successful for this target. The remainder of the first orbit and the entirety of the next four orbits in each visit will filled with an exposure of STIS/G230L centered at 2376 Angstroms with a buffer time of 350s (as done for the previous out-of-transit G230L observation). The phase windows for the first exposure of each orbit are 0.011 phase units wide (6614 seconds / 1.837 hours), and defined such that the individual visit windows are spaced apart in phase relative to mid-transit as follows: 0.956 -- 0.967, 0.967 -- 0.978, 0.978 -- 0.989, 0.989 -- 1.0, and 0 -- 0.011. This means that the very first exposure of the earliest visit will be slightly greater than 1.5 transit durations before mid-transit, while the end of the last exposure will be slightly less than 2 transit durations after mid-transit. PI Duvvuri has scientific and technical expertise in the time-series spectroscopy of cool dwarfs observed at X-ray + ultraviolet + optical wavelengths to characterize the variability of stellar activity and in modeling stellar X-ray and extreme ultraviolet radiation. Co-I France is the PI of the HST MUSCLES Treasury Survey (GO13650) and MEATS (GO16166) Survey to study the UV and X-ray spectral and temporal properties of exoplanet host stars. Co-I Schneider has extensive experience with HST UV observations, magnetic activity of low-mass stars, and the impact of the stellar high-energy emission on exoplanetary atmospheres. Co-I Brown has extensive experience observing and studying the UV and X-ray spectra of young, low-mass stars in local regions of recent star formation and young associations using current (HST, CXO, XMM-Newton) and earlier (FUSE, EUVE, ROSAT, IUE) space observatories. Co-I Garcia Munoz has significant experience in the investigation of exoplanet atmospheres, in particular in modelling of upper atmospheres and the connection between the lower and upper atmospheres. Co-I Feinstein has expertise in ground- and space-based observations of young planets and identification and identification and characterization of stellar flares. Co-I Mann is an expert on young stars and planets, including transmission spectroscopy from HST, JWST, and the ground. Co-I Youngblood has extensive experience with HST UV observations and Lyman alpha reconstructions and airglow subtractions and is the PI of GO-16701, which obtained the STIS data of HIP 67522 referenced in this proposal. Co-I Thorngren is an expert in planetary interior structures with particular focus on matching observed exoplanet parameters with interior models using Bayesian statistics. Co-I Newton is an expert in stellar astrophysics and exoplanets and is co-PI of the THYME survey, which synthesizes characterization of young stars and stellar associations with exoplanet detections. Co-I Rockcliffe is an expert in observationally characterizing atmospheric escape in young exoplanet systems. A number of other Co-Is are included due to their expertise in a subset of: UV spectroscopy, transmission spectroscopy, planet atmosphere models, and prior analysis of HIP 67522 b (the main target of this proposal). Exoplanets and Exoplanet Formation 6 false true false false false false false SUPPORTED STAR G V-IV 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 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/NUV-MAMA Spectroscopic No No G230L 2376 1771281606902 The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18121 :visit-id "01" :proposal-version -1 :trans-version "20250929" :date "16-Feb-2026 16:40:06.0" :trans-errors '(:WARNINGS 1 :ERRORS 1 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 4331936 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18121 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 18121 :visit-id "01" :obset-id "A1" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18121 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2596 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "01" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "01" :orbit-number 4 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "01" :orbit-number 5 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 603 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) true 5 0 1771281824102 The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18121 :visit-id "02" :proposal-version -1 :trans-version "20250929" :date "16-Feb-2026 16:43:43.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 4331936 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18121 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 18121 :visit-id "02" :obset-id "A2" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18121 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2601 :al-overhead-at-end 0 :internal-dur-at-end 178 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "02" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "02" :orbit-number 4 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18121 :visit-id "02" :orbit-number 5 :pcs-time 380 :si-vis-utilization 2621 :al-overhead-at-end 0 :internal-dur-at-end 603 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3001 :pcs-gap 0 ) true 5 0 1771281825384 The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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