Strict Limits on Helium Absorption from LHS 1140 b from Four JWST NIRISS Transits
- 1University of Chicago
Abstract
Orbiting in the habitable zone of its host star, the 1.7 R ⊕ , 5.6 M ⊕ planet LHS 1140 b is a target of great interest. Recently C. Cherubim et al. published a detection of metastable He escaping from the atmosphere of LHS 1140 b, simultaneously providing the first inference of an atmosphere on this planet and indicating that the atmosphere is He-rich and H-poor, as would be expected due to Gyr of fractionated mass loss. In this work, we analyze four archival transits of LHS 1140 b, spanning 2023 December to 2026 July, taken with the NIRISS instrument on JWST, for evidence of He absorption. Each of the four visits disfavors the presence of He absorption compared to a flat continuum with odds ratios ranging from 3.9 to 11.6:1. He absorption with an amplitude and width equivalent to that observed by C. Cherubim et al. is strongly ruled out by the data, with odds ratios from 300 to 8.6 × 10 ⁴ :1 compared to a flat continuum—though it should be noted that none of the JWST transits are contemporaneous with the C. Cherubim et al. detection. We also fit the absolute out-of-transit stellar spectra from these four visits, as well as an additional JWST NIRISS transit of planet c, to search for evidence of stellar variability. The stellar properties inferred from the first visit are discrepant with the other four, potentially indicating evidence for variability. Further monitoring is necessary to confirm this. In all, our work provides a set of strict limits on He escape from LHS 1140 b that will be valuable to future studies into the nature and evolution of this intriguing world.
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BibTeX
@article{radica2026strict,
title = {{Strict Limits on Helium Absorption from LHS 1140 b from Four JWST NIRISS Transits}},
author = {Michael Radica},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = oct,
doi = {10.3847/2041-8213/aeaa39},
url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeaa39},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Strict Limits on Helium Absorption from LHS 1140 b from Four JWST NIRISS Transits
AU - Michael Radica
PY - 2026
DA - 2026/10/05
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/aeaa39
UR - https://iopscience.iop.org/article/10.3847/2041-8213/aeaa39
AB - Orbiting in the habitable zone of its host star, the 1.7 R ⊕ , 5.6 M ⊕ planet LHS 1140 b is a target of great interest. Recently C. Cherubim et al. published a detection of metastable He escaping from the atmosphere of LHS 1140 b, simultaneously providing the first inference of an atmosphere on this planet and indicating that the atmosphere is He-rich and H-poor, as would be expected due to Gyr of fractionated mass loss. In this work, we analyze four archival transits of LHS 1140 b, spanning 2023 December to 2026 July, taken with the NIRISS instrument on JWST, for evidence of He absorption. Each of the four visits disfavors the presence of He absorption compared to a flat continuum with odds ratios ranging from 3.9 to 11.6:1. He absorption with an amplitude and width equivalent to that observed by C. Cherubim et al. is strongly ruled out by the data, with odds ratios from 300 to 8.6 × 10 ⁴ :1 compared to a flat continuum—though it should be noted that none of the JWST transits are contemporaneous with the C. Cherubim et al. detection. We also fit the absolute out-of-transit stellar spectra from these four visits, as well as an additional JWST NIRISS transit of planet c, to search for evidence of stellar variability. The stellar properties inferred from the first visit are discrepant with the other four, potentially indicating evidence for variability. Further monitoring is necessary to confirm this. In all, our work provides a set of strict limits on He escape from LHS 1140 b that will be valuable to future studies into the nature and evolution of this intriguing world.
SN - 2041-8205
SN - 2041-8213
ER -