Category: 7. Science

Surveys for exoplanets indicate that the occurrence rate of gas giant planets orbiting late-type stars in orbits with periods shorter than 1000 days is lower than in the case of Sun-like stars.

This is in agreement with planet formation models based on the core or pebble accretion paradigm. The CARMENES exoplanet survey has been conducting radial-velocity observations of several targets that show long-period trends or modulations that are consistent with the presence of giant planets at large orbital separations.

We present an analysis of five such systems that were monitored with the CARMENES spectrograph, as well as with the IRD spectrograph. In addition, we used archival data to improve the orbital parameters of the planetary systems. We improve the parameters of three previously known planets orbiting the M dwarfs GJ 317, GJ 463, and GJ 3512.

We also determine the orbital parameters and minimum mass of the planet GJ 3512 c, for which only lower limits had been given previously. Furthermore, we present the discovery of two new giant planets orbiting the stars GJ 9733 and GJ 508.2, although for the second one only lower limits to the orbital properties can be determined.

The new planet discoveries add to the short list of known giant planets orbiting M-dwarf stars with subsolar metallicity at long orbital periods above 2000 days. These results reveal that giant planets appear to form more frequently in wide orbits than in close-in orbits around low-mass and lower metallicity stars.

J. C. Morales, I. Ribas, S. Reffert, M. Perger, S. Dreizler, G. Anglada-Escudé, V. J. S. Béjar, E. Herrero, J. Kemmer, M. Kuzuhara, M. Lafarga, J. H. Livingston, F. Murgas, B. B. Ogunwale, L. Tal-Or, T. Trifonov, S. Vanaverbeke, P. J. Amado, A. Quirrenbach, A. Reiners, J. A. Caballero, J. F. Agüí Fernández, J. Banegas, P. Chaturvedi, S. Dufoer, A. P. Hatzes, Th. Henning, C. Rodríguez-López, A. Schweitzer, E. Solano, M. Zechmeister, H. Harakawa, T. Kotani, M. Omiya, B. Sato, M. Tamura

Comments: 32 pages (including appendix with radial velocity time series), 16 figures, 14 tables. Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.15516 [astro-ph.EP] (or arXiv:2507.15516v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.15516
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From: Juan Carlos Morales
[v1] Mon, 21 Jul 2025 11:34:40 UTC (9,156 KB)
https://arxiv.org/abs/2507.15516
Astrobiology,

This work describes new dynamical simulations of terrestrial planet formation. The simulations started at the protoplanetary disk stage, when planetesimals formed and accreted into protoplanets, and continued past the late stage of giant impacts.

We explored the effect of different parameters, such as the initial radial distribution of planetesimals and Type-I migration of protoplanets, on the final results. In each case, a thousand simulations were completed to characterize the stochastic nature of the accretion process.

In the model best able to satisfy various constraints, Mercury, Venus, and Earth accreted from planetesimals that formed early near the silicate sublimation line near 0.5 au and migrated by disk torques.

For Venus and Earth to end up at 0.7-1 au, Type-I migration had to be directed outward, for example as the magnetically driven winds reduced the surface gas density in the inner part of the disk. Mercury was left behind near the original ring location. We suggest that Mars and multiple Mars-sized protoplanets grew from a distinct outer source of planetesimals at 1.5-2 au.

While many migrated inwards to accrete onto the proto-Earth, our Mars was the lone survivor. This model explains: (1) the masses and orbits of the terrestrial planets, (2) the chemical composition of the Earth, where ~70% and ~30% come from reduced inner-ring and more-oxidized outer-ring materials, and (3) the isotopic differences of the Earth and Mars.

It suggests that the Moon-forming impactor Theia plausibly shared a similar isotopic composition and accretion history with that of the proto-Earth.

David Nesvorny, Alessandro Morbidelli, William F. Bottke, Rogerio Deienno, Max Goldberg

Comments: in press in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.14814 [astro-ph.EP] (or arXiv:2507.14814v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.14814
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From: David Nesvorny
[v1] Sun, 20 Jul 2025 04:09:06 UTC (982 KB)
https://arxiv.org/abs/2507.14814
Astrobiology,

While wandering along the cliffs of the Mediterranean Sea — particularly in southern Italy and Sicily — one might come across outcrops composed entirely of thick layers of salt and gypsum.

Thanks to geophysical surveys and an extensive drilling campaign conducted during the Glomar Challenger expedition, we now know that these salt layers extend beneath the Mediterranean Sea and, in some regions, reach thicknesses of up to 2.5 kilometers. Such deposits can only form by evaporating large amounts of seawater. For almost 200 years scientists wondered how this was possible, and one unique salt lake — the Dead Sea in Israel — may provide an answer.

“These large deposits in the earth’s crust can be many, many kilometers horizontally, and they can be more than a kilometer thick in the vertical direction,” says UC Santa Barbara mechanical engineering professor Eckart Meiburg, lead author of a new study. “How were they generated? The Dead Sea is really the only place in the world where we can study the mechanism of these things today.”

Salinity levels in the Dead Sea are famously so high that only few organisms can survive in its waters, giving it its name.

Indeed, while there are other bodies of water in the world with high salinity levels, only in the Dead Sea they form massive salt deposits, which allows researchers to tackle the physical processes behind their evolution, and in particular, the spatial and temporal variations in their thickness.

In their study, Meiburg and fellow author Nadav Lensky of the Geological Survey of Israel cover the fluid dynamics and associated sediment transport processes currently governing the Dead Sea.

In 2019, the researchers observed a rather unique process occurring in the lake during the summer. While evaporation was increasing the salinity of the water on the surface, salts washed into the lake were nonetheless continuing to dissolve due to its warmer temperature. When the dense, salt-rich water sinks to the ground, it mixes with cooler water rising upwards. At the interface between the two layers, halite (common salt) crystals start to grow. The heavy crystals fall to the bottom, forming a sort of “salt snow” covering the bottom of the Dead Sea basin.

In contrast to shallower hypersaline bodies in which precipitation and deposition occur during the dry season, in the Dead Sea salt formation occurs during the entire year.

In addition to other factors including internal currents and surface waves, this process is highly effective in creating salt deposits of various shapes and sizes, the authors conclude.

About 5.96 to 5.33 million years ago tectonic forces closed off the Strait of Gibraltar, reducing the inflow from the Atlantic into the Mediterranean basin and creating conditions similar to the Dead Sea basin — but on a vastly larger scale.

“The sea level dropped 3 to 5 kilometers (2-3 miles) due to evaporation, creating the same conditions currently found in the Dead Sea and leaving behind the thickest of this salt crust that can still be found buried below the deep sections of the Mediterranean,” Meiburg explains.

“But then a few million years later the Strait of Gibraltar opened up again, and so you had inflow coming in from the North Atlantic and the Mediterranean filled up again.”

The full study, “Fluid Mechanics of the Dead Sea,” was published in the journal Annual Review of Fluid Mechanics and can be found online here.

Additional material and interviews provided by University of California – Santa Barbara.

Sub-Neptune exoplanets are the most abundant type of planet known today. As they do not have a Solar System counterpart, many open questions exist about their composition and formation.

Previous spectroscopic studies rule out aerosol-free hydrogen-helium-dominated atmospheres for many characterized sub-Neptunes but are inconclusive about their exact atmospheric compositions.

Here we characterize the hot (T_eq=1311K) sub-Neptune HD 86226 c, which orbits its G-type host star. Its high equilibrium temperature prohibits methane-based haze formation, increasing the chances for a clear atmosphere on this planet. We use HST data taken with WFC3 and STIS from the Sub-neptune Planetary Atmosphere Characterization Experiment (SPACE) Program to perform near-infrared 1.1-1.7micrometer transmission spectroscopy and UV characterization of the host star.

We report a featureless transmission spectrum that is consistent within 0.4 sigma with a constant transit depth of 418+-14ppm. The amplitude of this spectrum is only 0.01 scale heights for a H/He-dominated atmosphere, excluding a cloud-free solar-metallicity atmosphere on HD 86226 c with a confidence of 6.5 sigma.

Based on an atmospheric retrieval analysis and forward models of cloud and haze formation, we find that the featureless spectrum could be due to a metal enrichment [M/H] above 2.3 (3 sigma confidence lower limit) of a cloudless atmosphere, or silicate (MgSiO₃), iron (Fe), or manganese sulfide (MnS) clouds. For these species, we perform an investigation of cloud formation in high-metallicity, high-temperature atmospheres.

Our results highlight that HD 86226c does not follow the aerosol trend of sub-Neptunes found by previous studies. Follow-up observations with the JWST could determine whether this planet aligns with the recent detections of metal-enriched atmospheres or if it harbors a cloud species otherwise atypical for sub-Neptunes.

K. Angelique Kahle (1 and 2), Jasmina Blecic (3 and 4), Reza Ashtari (5), Laura Kreidberg (1), Yui Kawashima (6), Patricio E. Cubillos (7 and 8), Drake Deming (9), James S. Jenkins (10 and 11), Paul Mollière (1), Seth Redfield (12), Qiushi Chris Tian (12 and 13), Jose I. Vines (14), David J. Wilson (15), Lorena Acuña (1), Bertram Bitsch (16), Jonathan Brande (17), Kevin France (15), Kevin B. Stevenson (5), Ian J.M. Crossfield (17 and 1), Tansu Daylan (18 and 19), Ian Dobbs-Dixon (3 and 4), Thomas M. Evans-Soma (20), Cyril Gapp (1 and 2), Antonio García Muñoz (21), Kevin Heng (22 and 23 and 24), Renyu Hu (25 and 26), Evgenya L. Shkolnik (27), Keivan G. Stassun (28), Johanna Teske (29 and 30) ((1) Max Planck Institute for Astronomy, (2) Department of Physics and Astronomy, Heidelberg University, (3) Department of Physics, New York University Abu Dhabi, (4) Center for Astrophysics and Space Science (CASS), New York University Abu Dhabi, (5) JHU Applied Physics Laboratory, (6) Department of Astronomy, Graduate School of Science, Kyoto University, (7) Space Research Institute, Austrian Academy of Sciences, (8) INAF, Osservatorio Astrofisico di Torino, (9) University of Maryland: College Park, (10) Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, (11) Centro de Astrofísica y Tecnologías Afines (CATA), (12) Astronomy Department and Van Vleck Observatory, Wesleyan University, (13) Department of Physics and Astronomy, The Johns Hopkins University, (14) Instituto de Astronomía, Universidad Católica del Norte, (15) Laboratory for Atmospheric and Space Physics, University of Colorado, (16) Department of Physics, University College Cork, (17) Department of Physics and Astronomy, University of Kansas, (18) Department of Physics, Washington University, (19) McDonnell Center for the Space Sciences, Washington University, (20) School of Information and Physical Sciences, University of Newcastle, (21) Université Paris-Saclay, Université Paris Cité, (22) Faculty of Physics, Ludwig Maximilian University, (23) Department of Physics & Astronomy, University College London, (24) Department of Physics, University of Warwick, (25) Jet Propulsion Laboratory, California Institute of Technology, (26) Division of Geological and Planetary Sciences, California Institute of Technology, (27) School of Earth and Space Exploration, Arizona State University, (28) Department of Physics & Astronomy, Vanderbilt University, (29) Earth and Planets Laboratory, Carnegie Institution for Science, (30) Observatories, Carnegie Institution for Science)

Comments: Accepted for publication in Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.13439 [astro-ph.EP] (or arXiv:2507.13439v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.13439
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From: Kim Angelique Kahle
[v1] Thu, 17 Jul 2025 18:00:01 UTC (7,291 KB)
https://arxiv.org/abs/2507.13439
Astrobiology,

The case of Ross 176 is a late K-type star that hosts a promising water-world candidate planet. The star has a radius of R_∗=0.569±0.020R_⊙ and a mass of M_⋆ = 0.577 ± 0.024 M_⊙.

We constrained the planetary mass using spectroscopic data from CARMENES, an instrument that has already played a major role in confirming the planetary nature of the transit signal detected by TESS.

We used Gaussian Processes (GP) to improve the analysis because the host star has a relatively strong activity that affects the radial velocity dataset. In addition, we applied a GP to the TESS light curves to reduce the correlated noise in the detrended dataset. The stellar activity indicators show a strong signal that is related to the stellar rotation period of ∼ 32 days.

This stellar activity signal was also confirmed on the TESS light curves. Ross 176b is an inner hot transiting planet with a low-eccentricity orbit of e=0.25±0.04, an orbital period of P∼5 days, and an equilibrium temperature of T_eq∼682K.

With a radius of R_p=1.84±0.08R_⊕ (4% precision), a mass of M_p=4.57+0.89−0.93M_⊕ (20% precision), and a mean density of ρp=4.03+0.49−0.81gcm⁻³, the composition of Ross 176b might be consistent with a water-world scenario. Moreover, Ross 176b is a promising target for atmospheric characterization, which might lead to more information on the existence, formation and composition of water worlds.

This detection increases the sample of planets orbiting K-type stars. This sample is valuable for investigating the valley of planets with small radii around this type of star. This study also shows that the dual detection of space- and ground-based telescopes is efficient for confirm new planets.

S. Geraldía-González, J. Orell-Miquel, E. Pallé, F. Murgas, G. Lacedelli, V. J. S. Béjar, J. A. Caballero, C. Duque-Arribas, J. Lillo-Box, D. Montes, G. Morello, E. Nagel, A. Schweitzer, H. M. Tabernero, Y. Calatayud-Borras, C. Cifuentes, G. Fernández-Rodríguez, A. Fukui, J. de Leon, N. Lodieu, R. Luque, M. Mori, N. Narita, H. Parviainen, E. Poultourtzidis, A. Reiners, I. Ribas, M. Schlecker, S. Seager, K. G. Stassun, T. Trifonov, S. Vanaverbeke, J. N. Winn

Comments: Accepted for publication in A&A. 16 pages. 13 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.15763 [astro-ph.EP] (or arXiv:2507.15763v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.15763
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Related DOI:
https://doi.org/10.1051/0004-6361/202553719
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From: Samuel Geraldía González
[v1] Mon, 21 Jul 2025 16:20:12 UTC (2,559 KB)
https://arxiv.org/abs/2507.15763
Astrobiology,

The search for habitable, Earth-like exoplanets faces major observational challenges due to their small size and faint signals.

M-dwarf stars offer a promising avenue to detect and study smaller planets, especially sub-Neptunes-among the most common exoplanet types. K2-18 b, a temperate sub-Neptune in an M-dwarf habitable zone, has been observed with HST and JWST, revealing an H₂-rich atmosphere with CH₄ and possible CO₂.

Conflicting interpretations highlight the importance of non-equilibrium chemistry, which is critical for constraining atmospheric parameters like metallicity, C/O ratio, and vertical mixing (K_zz). This study explores the parameter space of metallicity, C/O ratio, and K_zz for K2-18 b using the non-equilibrium chemistry model FRECKLL and JWST data. We generated spectra from a 3D grid of models and compared them to observations to refine atmospheric constraints.

A fixed pressure-temperature profile was used to capture first-order chemical trends, acknowledging some uncertainties. Our best-fit model favors high metallicity (266^{+291}{-104} at 2 sigma) and high C/O ratio (C/O > 2.1 at 2 sigma). CH4 is robustly detected (log₁₀[CH₄] = -0.3^{+0.1}{-1.7} at 1 mbar), while CO₂ remains uncertain due to spectral noise. Kzz has no clear impact on the fit and remains unconstrained.

Non-equilibrium models outperform flat spectra at > 4 sigma confidence, confirming atmospheric features. Minor species, such as H₂O and NH₃, may be present but are likely masked by dominant absorbers. Our results highlight the limits of constant-abundance retrievals.

The atmosphere has a high C/O ratio suggesting possible aerosol formation. Better constraints require higher-precision data. Future JWST NIRSpec G395H and ELT/ANDES observations will be critical for probing habitability and refining models.

A. Y. Jaziri, O. Sohier, O. Venot, N. Carrasco

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.14983 [astro-ph.EP] (or arXiv:2507.14983v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.14983
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From: Adam Yassin Jaziri
[v1] Sun, 20 Jul 2025 14:39:00 UTC (748 KB)
https://arxiv.org/abs/2507.14983
Astrobiology,

Searching for signs of life is a primary goal of the Habitable Worlds Observatory (HWO). However, merely detecting oxygen, methane, or other widely discussed biosignatures is insufficient evidence for a biosphere.

In parallel with biosignature detection, exoplanet life detection additionally requires characterization of the broader physicochemical context to evaluate planetary habitability and the plausibility that life could produce a particular biosignature in a given environment.

Life detection further requires that we can confidently rule out photochemical or geological phenomena that can mimic life (i.e. “false positives”). Evaluating false positive scenarios may require different observatory specifications than biosignature detection surveys.

Here, we explore the coronagraph requirements for assessing habitability and ruling out known false positive (and false negative) scenarios for oxygen and methane, the two most widely discussed biosignatures for Earth-like exoplanets.

We find that broad wavelength coverage ranging from the near UV (0.26 μm) and extending into the near infrared (1.7 μm), is necessary for contextualizing biosignatures with HWO. The short wavelength cutoff is driven by the need to identify Proterozoic-like biospheres via O₃, whereas the long wavelength cutoff is driven by the need to contextualize O₂ and CH₄ biosignatures via constraints on C-bearing atmospheric species.

The ability to obtain spectra with signal-to-noise ratios of 20-40 across this 0.26-1.7 μm range (assuming R=7 UV, R=140 VIS, and R=70 NIR) is also required. Without sufficiently broad wavelength coverage, we risk being unprepared to interpret biosignature detections and may ultimately be ill-equipped to confirm the detection of an Earth-like biosphere, which is a driving motivation of HWO.

Known biosignature false positive scenarios and their contextual clues for rocky planets
around F/G/K stars. Only bolded scenarios with shaded backgrounds are considered in this study. — astro-ph.EP

Joshua Krissansen-Totton, Anna Grace Ulses, Maxwell Frissell, Samantha Gilbert-Janizek, Amber Young, Jacob Lustig-Yaeger, Tyler Robinson, Stephanie Olson, Eleonora Alei, Giada Arney, Celeste Hagee, Chester Harman, Natalie Hinkel, Emilie Lafleche, Natasha Latouf, Avi Mandell, Mark M. Moussa, Niki Parenteau, Sukrit Ranjan, Blair Russell, Edward W. Schwieterman, Clara Sousa-Silva, Armen Tokadjian, Nicholas Wogan

Comments: In review at Astrobiology. Comments welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.14771 [astro-ph.EP] (or arXiv:2507.14771v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.14771
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From: Joshua Krissansen-Totton
[v1] Sat, 19 Jul 2025 23:58:29 UTC (2,000 KB)
https://arxiv.org/abs/2507.14771
Astrobiology, Astronomy,