arXiv subjects

Erik Meier Valdés

Publications and source records attributed to Erik Meier Valdés.

6 recordsLinked to original sources

arXiv2026

Hot Rocks Survey VI: An anomalously hot dayside for the rocky planet GJ 357 b

As part of the JWST Hot Rocks Survey, we analyzed a JWST/MIRI F1500W secondary-eclipse observation of GJ 357 b, a rocky exoplanet orbiting a nearby M dwarf. We also performed a new global analysis of the GJ 357 system, combining TESS photometry, a JWST/NIRSpec transit observation, the MIRI secondary eclipse, radial velocities, and Gaia parallax measurements to obtain a self-consistent set of stellar and planetary parameters. We measure an occultation depth of $200.5 \pm 12.7,\mathrm{ppm}$, corresponding to a dayside brightness temperature at $15,μ\mathrm{m}$ of $T_{\mathrm{b},15,μ\mathrm{m}}=923^{+39}_{-38},\mathrm{K}$. The inferred brightness temperature substantially exceeds the zero-Bond-albedo, no-redistribution, disk-integrated bolometric dayside reference temperature of $686 \pm 14,\mathrm{K}$. The measured eclipse depth differs from the tested zero-albedo, grey airless-surface model by $5.2σ$ and is also inconsistent with the high-mean-molecular-weight atmospheric models considered here, including pure CO$_2$, pure H$_2$O, and N$_2$ with 100 ppm CO$_2$. Possible explanations for the excess emission in the MIRI/F1500W band include wavelength-dependent surface emissivity, localized hot regions, or atmospheric temperature structures and opacity sources not included in the tested models. Follow-up mid-infrared eclipse spectroscopy would constrain the shape of the dayside emission spectrum and help test the proposed surface and atmospheric explanations.

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arXiv2026

Hot Rocks Survey V: Secondary Eclipse Photometry of GJ 3473 b with JWST/MIRI

JWST is transforming our ability to characterise small exoplanets, from sub-Neptunes to rocky worlds. A key open question is whether highly irradiated rocky planets can retain atmospheres or are stripped bare by stellar irradiation -- a boundary that remains to be mapped observationally. Here we present the first JWST secondary eclipse observations of the rocky exoplanet GJ 3473 b, obtained with MIRI F1500W photometry. Using four visits, we confidently detect the eclipse at an average depth of 186$\pm$45 ppm, somewhat lower than expected for a blackbody. We test a wide range of data reduction and analysis assumptions and provide new insights into MIRI detector settling behaviour that will benefit future observations. We model a suite of airless surfaces with varied compositions, textures, and degrees of space weathering, as well as idealised atmospheric scenarios including the possibility of atmospheric collapse. Both atmospheric and bare-rock interpretations remain consistent with the data, but we exclude thick CO$_2$ atmospheres, placing a 95 % credible upper limit of 1.2-6.5 bar on the surface pressure. We also find tentative evidence for visit-to-visit variability in eclipse depth (33-371 ppm), though additional data are required to confirm this. Our results highlight the challenges and intrinsic degeneracies in interpreting MIRI F1500W eclipse measurements of rocky exoplanets, indicating that such observations alone may not uniquely distinguish between bare-rock and atmospheric scenarios. Future spectroscopic or phase-curve observations will be required to determine whether or not GJ 3473 b hosts a substantial atmosphere

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arXiv2026

Mantle Convection and Nightside Volcanism on Lava World K2-141 b

Ultra-short period lava worlds offer a unique window into the coupled evolution of planetary interior and atmospheres under extreme irradiation. In this study, we investigate the mantle dynamics, nightside volcanism, and volatile outgassing on lava world K2-141 b ($1.54 R_{\oplus}$, $5.31 M_{\oplus}$) using two-dimensional convection models with tracer-based volatile tracking. Our simulations explore a range of interior configurations, including models with and without plastic yielding, basal versus mixed heating, core cooling, and melt intrusion. In models without plastic yielding (i.e. with a strong lithosphere), we find that mantle upwellings form at the substellar and antistellar points, while downwellings form near the day-night terminators at the boundary between the magma ocean and cold, solid nightside. These downwellings facilitate the recycling of crustal material, representing a form of asymmetric, single-lid tectonics. The resulting magma ocean thickness varies from 200 to 300 km depending on the model parameters, corresponding to about 2-3% of the planet's radius. Continuous nightside volcanism produces a basaltic crust and gradually depletes the mantle of volatiles. We find that over a billion years, volcanic eruptions can outgas tens of bars of CO$_{2}$ and H$_{2}$O. We show that even relatively large volcanic eruptions on the nightside produce thermal emission signals of no more than 1 ppm, remaining below the current detectability threshold in thermal phase curves. However, for most models, outgassing rates are increased near the day-night terminators and future studies should assess whether such localised outgassing could lead to atmospheric signatures in transmission spectroscopy.

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arXiv2025

Hot Rocks Survey IV: Emission from LTT 3780 b is consistent with a bare rock

It is an open question whether small planets around M dwarfs are able to maintain atmospheres. The Hot Rocks Survey aims to address this question by observing 9 rocky exoplanets orbiting M dwarfs with MIRI emission photometry to constrain the onset of atmospheres. In this paper, we present two MIRI F1500W (15$μ$m) eclipses of LTT 3780 b, an ultra-short period super-Earth ($P=0.768$ d, $R=1.325 \,R_\oplus$, $M = 2.46\,M_\oplus$) that receives 111x Earth's instellation, the highest in the survey. We find a combined eclipse depth of $312\pm38$ ppm, which is consistent between different data reduction and analysis assumptions, bolstering our confidence in the eclipse detection. This eclipse depth is consistent with the thermal emission from a bare rock surface, with a dayside temperature of $T_d=1143^{+104}_{-99}$ K, $98\pm9$ % of the maximum temperature predicted for a zero albedo, zero heat redistribution blackbody. We are able to confidently rule out CO$_2$-based atmospheres down to 0.01 bar surface pressure to greater than 3$σ$ (ruling out an approximately Mars-like atmosphere). We are unable to rule out a pure H$_2$O 1 bar atmosphere, though we argue that this composition is unlikely on such a highly irradiated planet, nor O$_2$ atmospheres due to the lack of features in the bandpass, though we can put constraints on CO$_2$-mixture atmospheres. As a potential bare rock, we consider a variety of surface composition models, but are unable to distinguish between them. However, LTT 3780 b is an excellent target for follow-up JWST observations to determine its surface composition and rule out additional atmospheric compositions.

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arXiv2025

Hot Rocks Survey III: A deep eclipse for LHS 1140c and a new Gaussian process method to account for correlated noise in individual pixels

Time-series photometry at mid-infrared wavelengths is becoming a common technique to search for atmospheres around rocky exoplanets. This method constrains the brightness temperature of the planet to determine whether heat redistribution is taking place - indicative of an atmosphere - or whether the heat is reradiated from a low albedo bare rock. By observing at 15$μ$m we are also highly sensitive to CO$_2$ absorption. We observed three eclipses of the rocky super-Earth LHS 1140c using MIRI/Imaging with the F1500W filter. We found significant variation in the initial settling ramp for these observations and identify a potential trend between detector settling and the previous filter used by MIRI. We analysed our data using aperture photometry but also developed a novel approach which joint-fits pixel light curves directly using a shared eclipse model and a flexible multi-dimensional Gaussian process which models changes in the PSF over time. We demonstrate using simulated data that our method has the ability to weight away from particular pixels which show increased systematics, allowing for the recovery of eclipse depths in a more robust and precise way. Both methods and an independent analysis detect the eclipse at $>5σ$ and are highly consistent with a low albedo bare rock. We recover a dayside brightness temperature of $T_\mathrm{day} = 561\pm44$ K, close to the theoretical maximum of $T_\text{day; max} = 537\pm9$ K. We rule out a wide range of atmospheric forward models to $>3σ$ including pure CO$_2$ atmospheres with surface pressure $\ge10$ mbar and pure H$_2$O atmospheres with surface pressure $\ge1$ bar. Our strict constraints on potential atmospheric composition, in combination with future observations of the exciting outer planet LHS 1140b, could provide a powerful benchmark to understand atmospheric escape around M dwarfs.

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arXiv2025

A Disintegrating Rocky World Shrouded in Dust and Gas: Mid-IR Observations of K2-22b using JWST

The disintegrating ultra-short period rocky exoplanet K2-22b periodically emits dusty clouds in a dynamically chaotic process resulting in a variable transit depth from 0-1.3%. The effluents that sublimate off the surface and condense out in space are probably representative of the formerly interior layers convectively transported to the molten surface. Transmission spectroscopy of these transiting clouds reveal spectral fingerprints of the interior composition of this rocky world. We used JWST's Mid-Infrared Instrument (MIRI) as a low-resolution slitless spectrograph to observe four predicted transit windows for K2-22b. For each observation, we extracted a transmission spectrum over the spectral range of 4.4-11.8 $μ$m. Over the spectral range of 4.4-8 $μ$m, where the spectral precision is highest, we detect one transit at high significance and two at low significance. While the S/N of the spectrum limits our ability to draw firm conclusions, we find that the data: 1) disfavor featureless, iron-dominated core material, 2) are consistent with some form of magnesium silicate minerals, likely from mantle material, and 3) show a distinct and unexpected feature at $\sim$5 $μ$m. The unexpected feature, also seen weakly in the low-significance transits, is consistent with an unknown gaseous absorber, possibly NO and/or CO$_2$. These findings warrant further study to improve the constraints on the composition of this disintegrating rocky world.

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