J/AJ/170/49 TOI-1685b transit spectra from JWST (Luque+, 2025)
A dark, bare rock for TOI-1685 b from a JWST NIRSpec G395H phase curve.
Luque R., Coy B.P., Xue Q., Feinstein A.D., Ahrer E.-M., Changeat Q.,
Zhang M., Moran S.E., Bean J.L., Kite E., Mansfield M.W., Palle E.
<Astron. J., 170, 49 (2025)>
=2025AJ....170...49L 2025AJ....170...49L
ADC_Keywords: Exoplanets; Spectra, infrared
Keywords: Exoplanets ; James Webb Space Telescope ; Exoplanet atmospheres ;
Extrasolar rocky planets
Abstract:
We report JWST NIRSpec/G395H observations of TOI-1685 b, a hot rocky
super-Earth orbiting an M2.5V star, during a full orbit. We obtain
transmission and emission spectra of the planet and characterize the
properties of the phase curve, including its amplitude and offset. The
transmission spectrum rules out clear H2-dominated atmospheres, while
secondary atmospheres (made of water, methane, sulfur dioxide, or
carbon dioxide) cannot be statistically distinguished from a flat
line. The emission spectrum is featureless and consistent with a dark
surface, ruling out carbon dioxide-, sulfur dioxide-, or
methane-dominated atmospheres thicker than 100 mbar. Collecting all
evidence, the properties of TOI-1685 b are consistent with a blackbody
with no heat redistribution and a low albedo, with a dayside
brightness temperature 0.99±0.07 times that of a perfect
blackbody in the NIRSpec NRS2 wavelength range (3.823-5.172um).
Our results add to the growing number of seemingly airless M-star
rocky planets, thus constraining the location of the "Cosmic
Shoreline." Three independent data reductions have been carried out,
all showing a high-amplitude correlated noise component in the white
and spectroscopic light curves. The correlated noise properties are
different between the NRS1 and NRS2 detectors-importantly, the
timescales of the strongest components (4.5 hr and 2.5 hr,
respectively)-suggesting the noise is from instrumental rather than
astrophysical origins. We encourage the community to look into the
systematics of NIRSpec for long time series observations.
Description:
We observed TOI-1685 b with the NIRSpec instrument on JWST on 2024 February
14-15 between 23:37 and 18:36 UTC as part of program GO-3263 (PI:
Luque). The observations can be accessed via
doi: 10.17909/jhgr-hc58. We used the Bright Object Time Series mode
with the G395H grating. The observations were designed similarly to
most phase curves: starting 1hr before the ingress of a secondary
eclipse up until the end of the following eclipse. The uninterrupted
observation lasted 18.97hr and consisted of 4450 integrations using
16 groups per integration.
To ensure the robustness and accuracy of our results, we perform
multiple independent data reductions using three different well-tested
and widely used open-source pipelines, namely, Eureka!
(Bell+, 2022JOSS....7.4503B 2022JOSS....7.4503B), Tiberius (Kirk+2017, J/MNRAS/468/3907;
+2021, 2021AJ....162...34K 2021AJ....162...34K), and ExoTIC-JEDI
(Alderson+2022, 2022MNRAS.512.4185A 2022MNRAS.512.4185A; +2023, 2023Natur.614..664A 2023Natur.614..664A).
Objects:
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RA (2000) DE Designation(s)
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04 34 22.49 +43 02 14.6 TOI-1685 b = TOI-1685.01
04 34 22.49 +43 02 14.6 TOI-1685 = Gaia DR3 252366608956186240
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table7.dat 61 26 NIRSpec/G395H NRS1 Transmission Spectrum
table8.dat 69 40 NIRSpec/G395H NRS2 Transmission Spectrum
table9.dat 141 10 NIRSpec/G395H Emission Spectrum
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See also:
J/MNRAS/459/3890 : ExoMol line lists for SO2 (Underwood+, 2016)
J/MNRAS/468/3907 : HAT-P-18b wavelength binned light curves (Kirk+, 2017)
J/A+A/605/A95 : CH4 & hot methane continuum hybrid line list (Yurchenko+, 2017)
J/other/Sci/377.1211 : RV and LC of 8 M dwarf stars with planets (Luque+, 2022)
J/A+A/698/A68 : Hot Rocks Survey II. TOI-1468 b fluxes (Meier Valdes+, 2025)
J/AJ/169/38 : HD 189733b NIRCam transmission & emission spectra (Zhang+, 2025)
J/A+A/696/A28 : TOI-238 and TOI-1685 light curves (Egger+, 2025)
http://doi.org/10.17909/jhgr-hc58 : MAST data
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.4 um wave [2.8/3.7] Wavelength
8- 13 F6.4 um e_wave [0.01/0.02] Uncertainty in wave
15- 19 F5.1 ppm Depth-Eu [703.9/864.7] Transit depth, Eureka!
21- 24 F4.1 ppm e_Depth-Eu [38/45.9] Lower uncertainty in Eureka
26- 29 F4.1 ppm E_Depth-Eu [36.7/45.1] Upper uncertainty in Eureka
31- 35 F5.1 ppm Depth-Ti [702.5/889.7] Transit depth, Tiberius
37- 40 F4.1 ppm e_Depth-Ti [41.7/50.8] Lower uncertainty in Tiberius
42- 45 F4.1 ppm E_Depth-Ti [41.3/51.7] Upper uncertainty in Tiberius
47- 51 F5.1 ppm Depth-Ex [718.3/898.9] Transit depth, ExoTIC-JEDI
53- 56 F4.1 ppm e_Depth-Ex [32.7/64.7] Lower uncertainty in ExoTIC-JEDI
58- 61 F4.1 ppm E_Depth-Ex [31/60.2] Upper uncertainty in ExoTIC-JEDI
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Byte-by-byte Description of file: table8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.4 um wave [3.8/5.2] Wavelength
8- 13 F6.4 um e_wave [0.01/0.02] Uncertainty in wave
15- 19 F5.1 ppm Depth-Eu [597.2/916.5] Transit depth, Eureka!
21- 25 F5.1 ppm e_Depth-Eu [44.4/102] Lower uncertainty in Eureka
27- 31 F5.1 ppm E_Depth-Eu [43.9/100] Upper uncertainty in Eureka
33- 37 F5.1 ppm Depth-Ti [430.1/959.7] Transit depth, Tiberius
39- 43 F5.1 ppm e_Depth-Ti [52.2/125] Lower uncertainty in Tiberius
45- 49 F5.1 ppm E_Depth-Ti [52.3/127] Upper uncertainty in Tiberius
51- 56 F6.1 ppm Depth-Ex [535.7/1008] Transit depth, ExoTIC-JEDI
58- 62 F5.1 ppm e_Depth-Ex [50.5/229] Lower uncertainty in ExoTIC-JEDI
64- 69 F6.1 ppm E_Depth-Ex [46.8/195] Upper uncertainty in ExoTIC-JEDI
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Byte-by-byte Description of file: table9.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.4 um wave [2.9/5.02] Wavelength
8- 12 F5.3 um e_wave [0.08/0.14] Uncertainty in wave
14- 18 F5.1 ppm Depth-Eu-1 [59.8/139.1] Eclipse depth, Eureka!, First
eclipse
20- 23 F4.1 ppm e_Depth-Eu-1 [17.7/28.3] Lower uncertainty in Eureka-1
25- 28 F4.1 ppm E_Depth-Eu-1 [17.4/29.5] Upper uncertainty in Eureka-1
30- 34 F5.1 ppm Depth-Eu-2 [63.9/148] Eclipse depth, Eureka!, Second
eclipse
36- 39 F4.1 ppm e_Depth-Eu-2 [19.2/31.1] Lower uncertainty in Eureka-2
41- 44 F4.1 ppm E_Depth-Eu-2 [20.8/30.9] Upper uncertainty in Eureka-2
46- 50 F5.1 ppm Depth-Eu-C [58.7/138.2] Eclipse depth, Eureka!,
Combined
52- 55 F4.1 ppm e_Depth-Eu-C [13.6/24.3] Lower uncertainty in Eureka-C
57- 60 F4.1 ppm E_Depth-Eu-C [13.5/23.8] Upper uncertainty in Eureka-C
62- 66 F5.1 ppm Depth-Eu-F [91.5/178.3] Eclipse depth, Eureka!, Full
phase curve
68- 71 F4.1 ppm e_Depth-Eu-F [9.5/18.5] Lower uncertainty in Eureka-F
73- 76 F4.1 ppm E_Depth-Eu-F [9.6/19.1] Upper uncertainty in Eureka-F
78- 82 F5.1 ppm Depth-Ti-C [54.7/137.6] Eclipse depth, Tiberius,
Combined
84- 87 F4.1 ppm e_Depth-Ti-C [15/29.2] Lower uncertainty in Tiberius-C
89- 92 F4.1 ppm E_Depth-Ti-C [14.9/29] Upper uncertainty in Tiberius-C
94- 98 F5.1 ppm Depth-Ti-F [93.5/183.1] Eclipse depth, Tiberius, Full
phase curve
100- 103 F4.1 ppm e_Depth-Ti-F [10/24.6] Lower uncertainty in Tiberius-F
105- 108 F4.1 ppm E_Depth-Ti-F [10.1/24.9] Upper uncertainty in Tiberius-F
110- 114 F5.1 ppm Depth-Ex-1 [77.9/124.4] Eclipse depth, ExoTIC-JEDI,
First eclipse
116- 119 F4.1 ppm e_Depth-Ex-1 [18.6/27.7] Uncertainty in ExoTIC-JEDI-1
121- 125 F5.1 ppm Depth-Ex-2 [43.5/152.2] Eclipse depth, ExoTIC-JEDI,
Second eclipse
127- 130 F4.1 ppm e_Depth-Ex-2 [13.9/33.5] Uncertainty in ExoTIC-JEDI-2
132- 136 F5.1 ppm Depth-Ex-C [73.1/118.7] Eclipse depth, ExoTIC-JEDI,
Combined
138- 141 F4.1 ppm e_Depth-Ex-C [16.9/26.5] Uncertainty in ExoTIC-JEDI-C
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History:
From electronic version of the journal
(End) Preapred by [AAS], Robin Leichtnam [CDS] 17-Apr-2026