0Assigned ID: 7563
----- Attempting Submission 1 (Thu Apr 16 19:21:37 GMT 2026) -----Could not connect to APT Status ServerFirst submission, using LP7157364807----- Attempting Submission 1 (Fri Aug 14 15:05:03 GMT 2026) -----Unsure why this warning is appearing, as I do have an internet connection.Hydrodynamic escape in a young sub-Neptune progenitorDuring their early lives (< 100 Myr), planets experience hydrodynamic escape, a process in which their H+He envelopes evaporate vigorously to space and entrain metallic species (such as C, N, O and Mg) in their outflows. This is thought to be the their main evolutionary channel of young (< 100 Myr) sub-Jovian worlds and is used as a convincing explanation for demographic features in the exoplanet population. Although predicted by theory, including for our own early Solar System rocky planets, to this day we lack decisive observational evidence for hydrodynamic escape occurring in a sub-Jovian exoplanet younger than 100 Myr. Thus, this key hypothesis that is foundational for our understanding of planetary evolution remains to be tested against observations. In this program, we propose to observe escaping metals in the young (45 Myr) Neptune-sized exoplanet DS Tuc Ab, which is predicted to be a progenitor to a sub-Neptune, the most common type of exoplanet in the solar neighborhood. We used a leading-edge modeling framework to simulate the transmission spectrum of DS Tuc Ab and a well-tested experimental design to predict observable escape signals; we estimate that, within two transits, we can securely detect escaping carbon and tentatively other species in the upper atmosphere of the planet. The results of this observational campaign will allow us to accurately measure the mass-loss rate of DS Tuc Ab, which has challenging to obtain with previous observations of this planet using escaping H and He. This measurement will enable us to perform the first empirical test to hypotheses involving the role of hydrodynamic escape in exoplanet evolution.We shall observe two transits of the young exoplanet DS Tuc Ab using COS/FUV. The objective is to detect metals escaping from the planet, and producing in-transit absorption in emission lines between 1100 and 1400 angstrom. DS Tuc is a binary system where the A component is brighter, so it is automatically acquired instead of the companion DS Tuc B. The angular separation between the components is 5 arcsec, so DS Tuc B will be outside of the COS aperture.
This program is time sensitive because it can only be executed when the planet transits. Thus, we setup this 14-orbit program in the following structure:
- Visit 1, pre-transit 1 baseline: 2 consecutive orbits happening ~12 hours before the transit 1 midpoint to establish the out-of-transit spectrum temporally far from the transit center.
- Visit 2, transit 1: 5 consecutive orbits starting a few hours before transit center
- Visit 3, pre-transit 2 baseline: 2 consecutive orbits happening ~11.25 hours before the transit 2 midpoint (the offset from 12 h is necessary to cover the Earth occultation gaps from transit 1)
- Visit 4, transit 2: 5 consecutive orbits starting a few hours before transit center
The program is broken into 4 visits instead of 2 because UV visits are limited to a maximum of 5 consecutive orbits. So, we establish pre-transit exposures with enough offset from the transits visits to avoid the SAA passages. To achieve this observing setup, we set phase constraints on the pre-transit visits and set an "After Visit" constraint for the transit visits with enough flexibility in the after range to facilitate scheduling.
We will use the G130M grating centered at 1291 angstrom with the PSA aperture and both SEGMENTs on aiming for the best wavelength coverage, including z=0 Lyman-alpha. We will use the TIME-TAG mode to allow us to break down each exposure into sub-exposures, which in turn is necessary to obtain a precise time series of fluxes. As described in the Phase 2 instructions, we shall use LP7 and FP-POS=3, 4.Data analysis effort:
The Principal Investigator L. dos Santos has previously led six HST programs to pin down the high-energy environment and atmospheric escape rates of exoplanets and specializes in transmission spectroscopy techniques for transiting exoplanets, as well as modeling of planetary outflows. Dos Santos is the main developer of the p-winds code, and will oversee the entire program, including the observational, archival and theoretical efforts. Dos Santos will also develop the adaptions to the modeling codes necessary to achieve the goals of this program. K. France and D. Ehrenreich have an extensive experience on UV data analysis of planet-hosting stars, space- and ground-based transmission spectra, and will contribute to the many aspects involved in the observational effort of this program.
Theoretical analysis effort:
V. Bourrier developed empirical and analytical tools to analyze and interpret observations of atmospheric escape from exoplanets, including the 3D upper atmosphere particle dynamics code EVE (Bourrier & Lecavelier des Etangs 2013; Bourrier et al. 2016; Allart et al. 2018). A. Vidotto and A. Presa specialize in simulating the space weather and stellar wind interactions of exoplanet upper atmospheres using hydrodynamical models, whose work has extensively been used to interpret HST observations. J. Lothringer is an expert in both observing exoplanet atmospheres with HST, as well as atmosphere modeling with PHOENIX with extensive experience studying ultra-hot Jupiters. M. Broome is the leading developer of the Wind-AE code, and will lead the intepretation of the observation using this model.Exoplanets and Exoplanet FormationStellar Physics and Stellar Types6falsetruefalsefalsefalsefalsefalseSUPPORTEDEXT-STAREXTRA-SOLAR PLANETARY SYSTEMG V-IVNOThis object was generated by the targetselector and retrieved from the SIMBAD database.
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