TY - JOUR
T1 - Double trouble
T2 - two transits of the super-Earth GJ 1132 b observed with JWST NIRSpec G395H
AU - May, E. M.
AU - MacDonald, Ryan J.
AU - Bennett, Katherine A.
AU - Moran, Sarah E.
AU - Wakeford, Hannah R.
AU - Peacock, Sarah
AU - Lustig-Yaeger, Jacob
AU - Highland, Alicia N.
AU - Stevenson, Kevin B.
AU - Sing, David K.
AU - Mayorga, L. C.
AU - Batalha, Natasha E.
AU - Kirk, James
AU - Lopez-Morales, Mercedes
AU - Valenti, Jeff A.
AU - Alam, Munazza K.
AU - Alderson, Lili
AU - Fu, Guangwei
AU - Gonzalez-Quiles, Junellie
AU - Lothringer, Joshua D.
AU - Rustamkulov, Zafar
AU - Sotzen, Kristin S.
N1 - Funding: R.J.M. is supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51513.001, also awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. The work by S.P. is supported by NASA under award number 80GSFC21M0002. J.K. acknowledges financial support from Imperial College London through an Imperial College Research Fellowship grant. This material is based upon work performed as part of NASA's CHAMPs team, supported by the National Aeronautics and Space Administration (NASA) under grant No. 80NSSC21K0905 issued through the Interdisciplinary Consortia for Astrobiology Research (ICAR) program.
PY - 2023/12/11
Y1 - 2023/12/11
N2 - The search for rocky planet atmospheres with JWST has focused on planets transiting M dwarfs. Such planets have favorable planet-to-star size ratios, enhancing the amplitude of atmospheric features. Since the expected signal strength of atmospheric features is similar to the single-transit performance of JWST, multiple observations are required to confirm any detection. Here, we present two transit observations of the rocky planet GJ 1132 b with JWST NIRSpec G395H, covering 2.8-5.2 μm. Previous HST WFC3 observations of GJ 1132 b were inconclusive, with evidence reported for either an atmosphere or a featureless spectrum based on analyses of the same dataset. Our JWST data exhibit substantial differences between the two visits. One transit is consistent with either a H2O-dominated atmosphere containing ~1% CH4 and trace N2O (χν2 = 1.13) or stellar contamination from unocculted starspots (χν2 = 1.36). However, the second transit is consistent with a featureless spectrum. Neither visit is consistent with a previous report of HCN. Atmospheric variability is unlikely to explain the scale of the observed differences between the visits. Similarly, our out-of-transit stellar spectra show no evidence of changing stellar inhomogeneity between the two visits - observed 8 days apart, only 6.5% of the stellar rotation rate. We further find no evidence of differing instrumental systematic effects between visits. The most plausible explanation is an unlucky random noise draw leading to two significantly discrepant transmission spectra. Our results highlight the importance of multi-visit repeatability with JWST prior to claiming atmospheric detections for these small, enigmatic planets.
AB - The search for rocky planet atmospheres with JWST has focused on planets transiting M dwarfs. Such planets have favorable planet-to-star size ratios, enhancing the amplitude of atmospheric features. Since the expected signal strength of atmospheric features is similar to the single-transit performance of JWST, multiple observations are required to confirm any detection. Here, we present two transit observations of the rocky planet GJ 1132 b with JWST NIRSpec G395H, covering 2.8-5.2 μm. Previous HST WFC3 observations of GJ 1132 b were inconclusive, with evidence reported for either an atmosphere or a featureless spectrum based on analyses of the same dataset. Our JWST data exhibit substantial differences between the two visits. One transit is consistent with either a H2O-dominated atmosphere containing ~1% CH4 and trace N2O (χν2 = 1.13) or stellar contamination from unocculted starspots (χν2 = 1.36). However, the second transit is consistent with a featureless spectrum. Neither visit is consistent with a previous report of HCN. Atmospheric variability is unlikely to explain the scale of the observed differences between the visits. Similarly, our out-of-transit stellar spectra show no evidence of changing stellar inhomogeneity between the two visits - observed 8 days apart, only 6.5% of the stellar rotation rate. We further find no evidence of differing instrumental systematic effects between visits. The most plausible explanation is an unlucky random noise draw leading to two significantly discrepant transmission spectra. Our results highlight the importance of multi-visit repeatability with JWST prior to claiming atmospheric detections for these small, enigmatic planets.
U2 - 10.3847/2041-8213/ad054f
DO - 10.3847/2041-8213/ad054f
M3 - Letter
SN - 2041-8213
VL - 959
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1
M1 - L9
ER -