A Headwind-like Helium Outflow from TOI-3884b

Joe P. Ninan; Jessica Libby-Roberts; Suvrath Mahadevan; Oleg Kochukhov; Daniel M. Krolikowski; Gudmundur Stefansson; Shubham Kanodia; Jaume Orell-Miquel; Caroline V. Morley; Kevin France; Girish Duvvuri; Chad F. Bender; William D. Cochran; Megan Delamer; Scott A. Diddams; Samuel Halverson; Fred Hearty; Leslie Hebb; Andrew Monson; Paul Robertson; Arpita Roy; Christian Schwab

arXiv · 2610.31492

A Headwind-like Helium Outflow from TOI-3884b

View original source ↗Read source document ↗Export metadata ↓

Abstract

Constraining atmospheric loss is crucial for understanding the evolution of planetary atmospheres. We report the detection of an evaporating exosphere from TOI-3884b, a super-Neptune in a polar orbit around an M4 dwarf star. We infer this evaporation from a 6.8$\pm$0.27\% excess transit depth in the He I 10830 Å\, line, observed during five transits of TOI-3884b with the Habitable Zone Planet Finder spectrometer. While we observe outflow signatures starting as early as 5 hours before the onset of the planet's optical transit, no significant post-transit tail is detected. Hitherto, such a pre-transit headwind without a significant post-transit tail has only been detected from HAT-P-67b, a hot Saturn orbiting an F-type star. This asymmetric outflow morphology supports irradiation-driven mass loss over core-heated mass loss, and we explore whether this could be caused by sub-Alfvén star-planet interaction. The detection of such complex outflow morphologies is now opening a new window, enabling us to test theories of star-planet interactions and planetary magnetic fields with observations.

Explore related subjects

astro-ph.EP

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Joe P. Ninan, Jessica Libby-Roberts, Suvrath Mahadevan, Oleg Kochukhov, Daniel M. Krolikowski, Gudmundur Stefansson, Shubham Kanodia, Jaume Orell-Miquel, Caroline V. Morley, Kevin France, Girish Duvvuri, Chad F. Bender, William D. Cochran, Megan Delamer, Scott A. Diddams, Samuel Halverson, Fred Hearty, Leslie Hebb, Andrew Monson, Paul Robertson, Arpita Roy, Christian Schwab. 2026-10-22. A Headwind-like Helium Outflow from TOI-3884b. https://arxiv.org/abs/2610.31492

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

A 36.34-day Sub-Neptune Candidate Transiting the Nearby K Dwarf TIC 402710280

Transiting sub-Neptunes on orbits longer than a month are rare around bright stars. We report a candidate with a 36.34-day period around TIC 402710280, a $V = 10.0$ K dwarf at 66.8 pc that the Transiting Exoplanet Survey Satellite (TESS) has observed only in full-frame images. Four transits from 2021 to 2026, reduced by three independent pipelines, have consistent depths (mean $2092 \pm 47$ ppm) and a duration of $5.27 \pm 0.05$ h. Two are 36.36 days apart. The light curves exclude every shorter period consistent with both down to one day, and the duration disfavors still shorter ones, leaving $P = 36.33986 \pm 0.00051$ d. The candidate's radius is $3.75 \pm 0.22\,R_\oplus$ and its equilibrium temperature $498 \pm 21$ K. Difference-image centroids place the signal $1.5'' \pm 1.3''$ from the target, and eclipse models of the only nearby Gaia source, $3.5''$ away, fit worse than a planet by $Δχ^2 \geq 142$ for every main-sequence pair. TRICERATOPS gives a false-positive probability of $0.003 \pm 0.004$; without high-resolution imaging, the object remains a candidate. The transit times scatter about a linear ephemeris by 21.8 min (rms), and an independent reduction reproduces the largest departure. Four transits cannot separate timing systematics from transit-timing variations. A second signal, of $407 \pm 26$ ppm at 3.78 days, may come from the target, an unresolved companion, or the background star. We predict a transit in TESS Sector 114 on 2027 February 19.

astro-ph.EP↗

arXiv2026

A sub-Earth-sized TESS planet candidate in the nearby M-dwarf binary GJ 774, most likely orbiting GJ 774 A (TIC 351339274)

Small planets transiting the nearest M dwarfs are the terrestrial planets most accessible to detailed characterisation. We report a sub-Earth-sized transiting planet candidate in the wide (17.6") M-dwarf binary GJ 774 at 12.86 pc, most likely orbiting the M2.5 primary GJ 774 A (TIC 351339274). The signal was a SPOC multi-sector threshold-crossing event (MES = 7.95) and is not a TESS Object of Interest. In eight TESS sectors (2019-2026) a 1.28-h transit recurs every 4.225138 +/- 0.000010 d with a box-mean depth of 365 +/- 32 ppm in A's light. The 2026 data, which entered neither the SPOC search nor our selection, show it at the ephemeris predicted from 2019-2023 data (304 +/- 43 ppm; none of 10^5 phase-scrambled versions of the 2026 data is as deep). The per-target false-alarm probability is < 0.03 at 95%. Odd/even, secondary-eclipse, archival-plate and Gaia radial-velocity tests exclude unrelated blended eclipsing binaries and eclipsing companions on 4.2-d orbits, and hierarchical eclipsing binaries are improbable. The stars are 0.85 TESS pixel apart, so the TRICERATOPS false-positive probability (0.26) is set by a planet on GJ 774 B. B is disfavoured because its own light does not dim enough: PRF-deblended photometry gives 109 +/- 115 ppm in B's light, against 1089 ppm required if B were the host. Conditional on a point source at A or at B, the joint host model gives P(A)=0.59-0.97 (0.97 for the native target-pixel baseline). Over all sectors the PRF photometry is consistent with A, but in the out-of-sample 2026 data 40% of the deficit appears at B's position, an unexplained 2-3 sigma (PSF-model and depth dependent) tension with host A. On A the planet has R_p=0.70 +/- 0.06 R_Earth, S=15.0 +/- 1.8 S_Earth and T_eq=548 +/- 16 K. It is not validated; resolved ground-based photometry of the pair would test host B directly.

astro-ph.EP↗

arXiv2026

Uncertainty estimation of incoming comet trajectories with a thermophysical non-gravitational force model for Comet Interceptor encounter planning

The European Space Agency Comet Interceptor mission is designed to fly-by an as-yet undetermined incoming long-period or dynamically-new comet, which will require an accurate prediction of its trajectory. Cometary orbits are perturbed from purely gravitational trajectories by non-gravitational accelerations (NGAs) stemming from their outgassing, however, and these must be taken into account in the navigation. We here test the ability of ground-based astrometry and standard NGA-fitting techniques to predict the position and velocity of incoming comets perturbed by a Monte Carlo sampled thermophysical acceleration model. We find that, due to the difficulties of predicting NGA evolution as well as the limitations of reasonably simulated astrometry, predicted accuracies are unlikely to meet the mission goals of 1000 km and 1 m s$^{-1}$ in position and velocity, sixty days before intercept. We instead recommend expanded uncertainties of $10,000$ km and several m s$^{-1}$. Our NGA fits struggle to reproduce the reference accelerations and trajectories when outgassing is rising steeply at a few AU-incoming, but with more observations up until perihelion, do eventually converge, leading to good estimates of many of the underlying acceleration parameters even for half an orbital arc.

astro-ph.EP↗